Karps Cell and Molecular Biology 8th Edition by Karp - Test Bank Instant Download - Complete Test Bank With Answers Sample Questions Are Posted Below Package Title: Test Bank Course Title: Karp7e Chapter Number: 5 Question Type: Multiple Choice 1) Which of the following is not found …
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Karps Cell and Molecular Biology 8th Edition by Karp – Test Bank
Instant Download – Complete Test Bank With Answers
Sample Questions Are Posted Below
Package Title: Test Bank
Course Title: Karp7e
Chapter Number: 5
Question Type: Multiple Choice
1) Which of the following is not found in a reducing atmosphere?
Answer: c
Difficulty: Medium
Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.
Section Reference: Section 5.1 Mitochondrial Structure and Function
2) What advantage do the cristae confer on the mitochondria?
Answer: b
Difficulty: Easy
Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.
Section Reference: Section 5.1 Mitochondrial Structure and Function
3) The balance between fusion and fission is likely a major determinant of __________.
Answer: e
Difficulty: Medium
Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.
Section Reference: Section 5.1 Mitochondrial Structure and Function
4) When fusion of mitochondria becomes more frequent than fission, the mitochondria tend to become __________.
Answer: e
Difficulty: Medium
Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.
Section Reference: Section 5.1 Mitochondrial Structure and Function
5) When fission of mitochondria becomes more frequent than fusion, the mitochondria tend to become __________.
Answer: e
Difficulty: Medium
Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.
Section Reference: Section 5.1 Mitochondrial Structure and Function
6) The presence of Ca2+ ion transport molecules in the inner mitochondrial membrane is consistent with the mitochondrion’s role in _______.
Answer: b
Difficulty: Easy
Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.
Section Reference: Section 5.1 Mitochondrial Structure and Function
7) Mitochondria are sites of the __________.
Answer: e
Difficulty: Medium
Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.
Section Reference: Section 5.1 Mitochondrial Structure and Function
8) Which of the following is(are) regulated by mitochondria?
1) intracellular levels of Ca2+ ions
2) intracellular levels of K+ ions
3) process of cell death
4) process of closure
Answer: e
Difficulty: Medium
Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.
Section Reference: Section 5.1 Mitochondrial Structure and Function
9) Which of the following regulate intracellular levels of Ca2+ ions?
Answer: e
Difficulty: Medium
Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.
Section Reference: Section 5.1 Mitochondrial Structure and Function
10) What are the two interconnected domains of the inner mitochondrial membrane?
Answer: a
Difficulty: Medium
Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.
Section Reference: Section 5.1 Mitochondrial Structure and Function
11) What is defined as a domain of the inner mitochondrial membrane that is present within the interior of the mitochondrion as a series of invaginated membranous sheets?
Answer: c
Difficulty: Easy
Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.
Section Reference: Section 5.1 Mitochondrial Structure and Function
12) The inner boundary membrane is particularly rich in which of the following?
Answer: b
Difficulty: Medium
Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.
Section Reference: Section 5.1 Mitochondrial Structure and Function
13) Which lipid is known for playing an important role in facilitating the activity of proteins involved in ATP synthesis?
Answer: e
Difficulty: Medium
Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.
Section Reference: Section 5.1 Mitochondrial Structure and Function
14) What evidence suggests that the inner mitochondrial membrane has evolved from a bacterial plasma membrane?
1) the presence of porins in both membranes
2) the virtual absence of cholesterol from both membranes
3) both membranes being rich in cardiolipin
4) both membranes being rich in diphosphatidylglycerol
Answer: e
Difficulty: Medium
Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.
Section Reference: Section 5.1 Mitochondrial Structure and Function
15) What evidence suggests that the outer mitochondrial membrane has evolved from the outer membrane that is present as part of the cell wall of certain bacteria?
1) the presence of porins in both membranes
2) the virtual absence of cholesterol from both membranes
3) both membranes being rich in cardiolipin
4 both membranes being rich in diphosphatidylglycerol
Answer: a
Difficulty: Medium
Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.
Section Reference: Section 5.1 Mitochondrial Structure and Function
16) From what does the mitochondrial RNA polymerase appear to have evolved?
1) the multisubunit RNA polymerase found in prokaryotic cells
2) the multisubunit RNA polymerase found in eukaryotic cells
3) the multisubunit RNA polymerase found in bacterial viruses (bacteriophage)
4) the single subunit RNA polymerase found in bacterial viruses (bacteriophage)
Answer: d
Difficulty: Medium
Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.
Section Reference: Section 5.1 Mitochondrial Structure and Function
17) In what ways can pyruvate and NADH be metabolized?
Answer: c
Difficulty: Hard
Learning Objective: LO 5.2 Discuss the mechanism by which NADH produced in cytosol by glycolysis is able to feed electrons into the TCA cycle.
Section Reference: Section 5.2 Oxidative Metabolism in the Mitochrondrion
18) How many carbons from 13 original glucose molecules enter the Krebs cycle in the presence of oxygen?
Answer: d
Difficulty: Medium
Learning Objective: LO 5.2 Discuss the mechanism by which NADH produced in cytosol by glycolysis is able to feed electrons into the TCA cycle.
Section Reference: Section 5.2 Oxidative Metabolism in the Mitochrondrion
19) How many carbons from 13 original glucose molecules enter the Krebs cycle in the absence of oxygen?
Answer: a
Difficulty: Medium
Learning Objective: LO 5.2 Discuss the mechanism by which NADH produced in cytosol by glycolysis is able to feed electrons into the TCA cycle.
Section Reference: Section 5.2 Oxidative Metabolism in the Mitochrondrion
20) What happens to the carbons of pyruvate that do not enter the Krebs cycle?
Answer: b
Difficulty: Medium
Learning Objective: LO 5.2 Discuss the mechanism by which NADH produced in cytosol by glycolysis is able to feed electrons into the TCA cycle.
Section Reference: Section 5.2 Oxidative Metabolism in the Mitochrondrion
21) What molecule is responsible for conveying 2 carbons from pyruvate to the Krebs cycle?
Answer: b
Difficulty: Easy
Learning Objective: LO 5.2 Discuss the mechanism by which NADH produced in cytosol by glycolysis is able to feed electrons into the TCA cycle.
Section Reference: Section 5.2 Oxidative Metabolism in the Mitochrondrion
22) Which component involved in the Krebs (TCA) cycle is bound to the inner mitochondrial membrane?
Answer: c
Difficulty: Easy
Learning Objective: LO 5.2 Discuss the mechanism by which NADH produced in cytosol by glycolysis is able to feed electrons into the TCA cycle.
Section Reference: Section 5.2 Oxidative Metabolism in the Mitochrondrion
23) Where are most of the enzymes of the Krebs cycle located?
Answer: d
Difficulty: Easy
Learning Objective: LO 5.2 Discuss the mechanism by which NADH produced in cytosol by glycolysis is able to feed electrons into the TCA cycle.
Section Reference: Section 5.2 Oxidative Metabolism in the Mitochrondrion
24) To what is the 2-carbon fragment of acetyl CoA added to make citric acid at the start of the Krebs cycle?
Answer: a
Difficulty: Easy
Learning Objective: LO 5.2 Discuss the mechanism by which NADH produced in cytosol by glycolysis is able to feed electrons into the TCA cycle.
Section Reference: Section 5.2 Oxidative Metabolism in the Mitochrondrion
25) What is the terminal electron acceptor of the electron transport chain?
Answer: b
Difficulty: Easy
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
26) How is the energy used to make ATP via the electron transport chain generated?
Answer: e
Difficulty: Medium
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
27) What is the name of the process by which the electron transport chain generates the electrochemical gradient that drives ATP production in the mitochondrion?
Answer: d
Difficulty: Medium
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
28) On average, how many ATPs would be made if 4 NADH and 6 FADH2 molecules donated their high-energy electrons to the mitochondrial electron transport chain?
Answer: b
Difficulty: Medium
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
29) How do mitochondria generate and store the energy used to produce most of the ATP made during aerobic respiration?
Answer: c
Difficulty: Medium
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
30) ___________ exhibit lower electron affinity.
Answer: c
Difficulty: Hard
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
31) Spontaneous oxidation-reduction (redox) reactions are accompanied by ________.
Answer: b
Difficulty: Medium
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
32) The direct formation of ATP by the transfer of a phosphate group from a donor molecule to ADP is called ________.
Answer: a
Difficulty: Easy
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
33) Which enzyme of the Krebs (TCA) cycle is different from the others with respect to its location and where is it located?
Answer: c
Difficulty: Medium
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
34) What type of electron carrier has a prosthetic group derived from vitamin B2?
Answer: a
Difficulty: Easy
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
35) What type of electron carrier has a prosthetic group derived from riboflavin?
Answer: a
Difficulty: Easy
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
36) What is another name from for partially reduced ubiquinone?
Answer: b
Difficulty: Medium
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
37) What is the final electron acceptor in the electron transport chain?
Answer: e
Difficulty: Easy
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
38) What is formed when electrons reach the bottom of the mitochondrial electron transport chain and bind to the final electron acceptor?
Answer: a
Difficulty: Medium
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
39) How do many potent respiratory poisons exert their effect?
Answer: c
Difficulty: Medium
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
40) You are trying to figure out an electron transport pathway including the following electron transport molecules: B, K, T, Q and X. You do so by employing inhibitors for various steps in the process. When you do, you get the following results:
Inhibitor Electron Transport Molecules Trapped in Reduced Form
Ticin Q & K
Digitin K
Estin T, K, Q & B
Lucin Q, K & T
What is the order of the molecules (the pathway) in the electron transport chain suggested by the above data from the most reduced to the least reduced molecule?
Answer: c
Difficulty: Hard
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
41) Why must the process by which cytochrome oxidase works be efficient?
Answer: c
Difficulty: Medium
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
42) What is unusual about the way that H+ ions are transported across the inner mitochondrial membrane as compared to the movement of other ions like Na+ and Cl– ions?
Answer: b
Difficulty: Hard
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
43) Pathways in which H+ ions can “hop” through a channel by exchanging themselves with other protons present along the pathway are called ___________.
Answer: e
Difficulty: Hard
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
44) Electrochemical gradients have both a(n) _________ and a(n) __________ component.
Answer: d
Difficulty: Easy
Learning Objective: LO 5.4 Elaborate on the two components of the proton-motive force and how their relative contribution vary from one cell to another.
Section Reference: Section 5.4 Translocation of Protons and the Establishment of a Proton-Motive Force
45) Electrochemical gradients have both a(n) _________ and a(n) _________ component.
Answer: d
Difficulty: Easy
Learning Objective: LO 5.4 Elaborate on the two components of the proton-motive force and how their relative contribution vary from one cell to another.
Section Reference: Section 5.4 Translocation of Protons and the Establishment of a Proton-Motive Force
46) Why did DNP kill patients who took the drug to help them lose weight?
Answer: a
Difficulty: Easy
Learning Objective: LO 5.4 Elaborate on the two components of the proton-motive force and how their relative contribution vary from one cell to another.
Section Reference: Section 5.4 Translocation of Protons and the Establishment of a Proton-Motive Force
47) What is the purpose of uncoupling proteins in mammalian brown adipose tissue?
Answer: c
Difficulty: Medium
Learning Objective: LO 5.4 Elaborate on the two components of the proton-motive force and how their relative contribution vary from one cell to another.
Section Reference: Section 5.4 Translocation of Protons and the Establishment of a Proton-Motive Force
48) The F0 base of ATP synthase serves as a(n) ______.
Answer: c
Difficulty: Medium
Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.
Section Reference: Section 5.5 The Machinery for ATP Formation
49) The energy released by proton movement through ATP synthase ___________.
Answer: d
Difficulty: Medium
Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.
Section Reference: Section 5.5 The Machinery for ATP Formation
50) The energy expended during the formation of ATP by ATP synthase is required to _______.
Answer: c
Difficulty: Medium
Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.
Section Reference: Section 5.5 The Machinery for ATP Formation
51) How many catalytic sites does ATP synthase possess?
Answer: c
Difficulty: Medium
Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.
Section Reference: Section 5.5 The Machinery for ATP Formation
52) The three catalytic sites of ATP synthase ___________.
Answer: e
Difficulty: Medium
Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.
Section Reference: Section 5.5 The Machinery for ATP Formation
53) The L conformation of ATP synthase catalytic sites ________.
Answer: e
Difficulty: Medium
Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.
Section Reference: Section 5.5 The Machinery for ATP Formation
54) It has been shown that one part of ATP synthase rotates relative to another part of the enzyme. This phenomenon is referred to as ________.
Answer: c
Difficulty: Easy
Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.
Section Reference: Section 5.5 The Machinery for ATP Formation
55) What drives the rotation of the F1 head of ATP synthase?
Answer: a
Difficulty: Easy
Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.
Section Reference: Section 5.5 The Machinery for ATP Formation
56) Which of the statements below served as evidence that rotational catalysis occurs in ATP synthase?
Answer: b
Difficulty: Medium
Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.
Section Reference: Section 5.5 The Machinery for ATP Formation
57) In the experiment that demonstrated that rotational catalysis occurs, a fluorescently labeled actin filament attached to the ATP synthase enzyme’s subunit was seen to rotate when ATP was added to the enzyme, which was fixed to a cover slip. With each step in the rotational catalysis, how much could the actin filament be seen to rotate?
Answer: c
Difficulty: Hard
Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.
Section Reference: Section 5.5 The Machinery for ATP Formation
58) What energy source other than ATP hydrolysis do mitochondria, unlike most other organelles, routinely use to power their activities?
Answer: b
Difficulty: Easy
Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.
Section Reference: Section 5.5 The Machinery for ATP Formation
59) Which activity below is not thought to be driven by the proton-motive force?
Answer: a
Difficulty: Easy
Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.
Section Reference: Section 5.5 The Machinery for ATP Formation
60) Which molecule below plays a key role in regulating the rate of glycolysis and Krebs cycle by regulating the activity of key enzymes?
Answer: c
Difficulty: Easy
Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.
Section Reference: Section 5.5 The Machinery for ATP Formation
61) Which molecule below plays a key role in regulating respiratory rate in the mitochondrion?
Answer: a
Difficulty: Easy
Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.
Section Reference: Section 5.5 The Machinery for ATP Formation
62) An unusual type of phospholipid is found in the myelin sheath that insulates brain axons; abnormalities in the synthesis of this phospholipid can lead to severe neurological dysfunction. What are these phospholipids called?
Answer: c
Difficulty: Easy
Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.
Section Reference: Section 5.6 Peroxisomes
63) Which of the following is true of peroxisomes?
Answer: e
Difficulty: Medium
Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.
Section Reference: Section 5.6 Peroxisomes
64) What properties do mitochondria share with peroxisomes?
Answer: e
Difficulty: Medium
Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.
Section Reference: Section 5.6 Peroxisomes
65) Peroxisomal enzymes __________.
1) produce hydrogen peroxide
2) break down hydrogen peroxide
3) include catalase
Answer: e
Difficulty: Medium
Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.
Section Reference: Section 5.6 Peroxisomes
66) Which organelle below is not found in both plants and animals?
Answer: d
Difficulty: Medium
Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.
Section Reference: Section 5.6 Peroxisomes
Question Type: Essay
67) How can biologists be sure that the appearance of photosynthetic organisms preceded that of aerobic organisms in the Earth’s evolutionary history?
Answer:
Difficulty: Easy
Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.
Section Reference: Section 5.1 Mitochondrial Structure and Function
Solution: Since aerobic organisms require the presence of oxygen in the atmosphere to serve as the final electron acceptor in the electron transport chain, photosynthetic organisms must have appeared first. The earliest atmospheres on Earth (during the first 2 billion years) were highly reduced and contained no free oxygen, but did contain hydrogen gas (H2), ammonia (NH3) and water (H2O). Aerobic respiration could not have occurred in such an atmosphere. When photosynthetic organisms, the cyanobaccteria, appeared about 2.7 billion years ago, they started producing oxygen as a byproduct and thus produced an atmosphere that contained significant amounts of free molecular oxygen within a few hundred million years. Only then could aerobic organisms have evolved.
68) Observations of two different cell types indicate a couple of differences in their mitochondria. Cell type 1 has 2-3 times the mitochondria of Cell Type 2. The mitochondria in Cell Type 1 are also larger, contain more cristae and the cristae extend farther across the mitochondria than in Cell Type 2. Which cell type is likely to have more extensive energy requirements?
Answer:
Difficulty: Medium
Learning Objective: LO 5.1 Compare the properties and evolutionary history of the inner and outer mitochondrial membranes and the intermembrane space and the matrix.
Section Reference: Section 5.1 Mitochondrial Structure and Function
Solution: Since ATP synthase is located on the cristae, cells that have more cristae with a larger surface area will be able to make more ATP to satisfy those energy requirements. The number of cristae and their surface area in the cell can be increased by any combination of the following strategies: increasing the number of mitochondria, increasing the number of cristae packed into each mitochondrion, increasing the size of cristae so that they extend all the way across the mitochondrion and increasing the size of each mitochondrion. Consequently, Cell Type 1 probably has the largest energy requirements.
69) How many carbons from an original glucose molecule get into the TCA cycle? What happens to the carbons that do not enter the cycle?
Answer:
Difficulty: Medium
Learning Objective: LO 5.2 Discuss the mechanism by which NADH produced in cytosol by glycolysis is able to feed electrons into the TCA cycle.
Section Reference: Section 5.2 Oxidative Metabolism in the Mitochrondrion
Solution: Four (4) carbons from an original 6-C glucose get into the TCA cycle, 2 from each of two 3-C pyruvates. The other two carbons are removed from the chain and released as carbon dioxide.
70) Given the overall equation for respiration: C6H12O6 + 6O2 <—> 6CO2 + 6H2O, at what point in respiration are the reactants used up and the products made?
Answer:
Difficulty: Hard
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
Solution: Glucose is used up at the first step in glycolysis when a phosphate group is transferred to it. Oxygen (O2) is used up when it acts as the final electron acceptor at the end of the electron transport chain, thus producing water. Carbon dioxide is produced as a carbon atom is removed from pyruvate before the entry of two of its carbon atoms into the TCA cycle and at various points in the cycle as carbons are removed from some of the TCA metabolites.
71) You are studying the enzyme kinetics of enzymes in the TCA cycle. You add a molecule to the mixture that appears to act as a competitive inhibitor of one of the enzymes. At first, you cannot tell which enzyme is inhibited, but you can tell that it is bound to the inner mitochondrial membrane. Can you guess which TCA enzyme you have inhibited and how do you know?
Answer: The enzyme is succinate dehydrogenase since it is the only enzyme of the TCA cycle that is bound to the inner mitochondrial membrane. The other TCA enzymes are located in the mitochondrial matrix.
Difficulty: Hard
Learning Objective: LO 5.2 Discuss the mechanism by which NADH produced in cytosol by glycolysis is able to feed electrons into the TCA cycle.
Section Reference: Section 5.2 Oxidative Metabolism in the MitochrondrionSolution: The enzyme is succinate dehydrogenase since it is the only enzyme of the TCA cycle that is bound to the inner mitochondrial membrane. The other TCA enzymes are located in the mitochondrial matrix.
72) Why are molecules that block oxidative phosphorylation and the electron transfer chain such dangerous and potentially deadly poisons?
Answer:
Difficulty: Medium
Learning Objective: LO 5.2 Discuss the mechanism by which NADH produced in cytosol by glycolysis is able to feed electrons into the TCA cycle.
Section Reference: Section 5.2 Oxidative Metabolism in the MitochrondrionSolution: By blocking the electron transport chain, the electron transport chain backs up. This will eventually prevent the recycling of NADH and FADH2. Since these molecules are present in finite amounts, a lack of recycling will place most of them in the reduced state. Since the oxidized forms of NADH (NAD+) and FAD are needed for the TCA cycle and glycolysis to occur, it will be unavailable in the presence of electron transport inhibitors and little or no ATP will be made. Consequently, the organism will die.
73) There are four large complexes of electron transport molecules in the inner mitochondrial membrane. There are also two smaller proteins that carry electrons between the complexes. What is a possible reason for the much smaller size of these shuttle proteins, cytochrome c and ubiquinone?
Answer:
Difficulty: Medium
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
Solution: Cytochrome c and ubiquinone are smaller because they must shuttle electrons between the complexes. They would be unable to diffuse through the membrane efficiently if they were extremely large like the complexes.
74) A doctor in a hospital emergency room sees an obese patient who has come into the emergency room. He has been losing weight rapidly but complains that he has lost energy and is tired most of the time. During his interview with the patient, the doctor thinks he has discovered what is causing the man’s condition. What do you think he has found?
Answer:
Difficulty: Hard
Learning Objective: LO 5.4 Elaborate on the two components of the proton-motive force and how their relative contribution vary from one cell to another.
Section Reference: Section 5.4 Translocation of Protons and the Establishment of a Proton-Motive Force
Solution: He probably discovers that the patient has taken a self-prescribed diet pill called 2, 4 – dinitrophenol (DNP), a chemical that was used in the 1920s for this very purpose. It was found to be dangerous, since a number of people using it died. It is dangerous because it uncouples the production of ATP from the process of glucose oxidation. While glucose is broken down, no ATP is made and it becomes difficult to keep vital processes going.
75) A preparation of submitochondrial particles is made. The particles are able to oxidize substrates, generate a proton gradient and make ATP. If the particles are treated with urea, what happens? If DNP is added, what happens? How does DNP make the inner mitochondrial membrane permeable to protons?
Answer:
Difficulty: Hard
Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.
Section Reference: Section 5.5 The Machinery for ATP Formation
Solution: Urea treatment removes the F1 spheres from ATP synthase. As a result, the membrane is no longer able to maintain the proton gradient. Protons leak out of the F0 base piece in an uncontrolled fashion when the headpiece is removed and ATP cannot be made because the headpiece that makes it is gone. DNP also uncouples ATP production from electron transport. It causes the membrane to become permeable to protons and thus dissipates the proton gradient, making ATP production by ATP synthase impossible. DNP combines with protons and, because of its lipid solubility, carries the protons across the inner mitochondrial membrane down their electrochemical gradient.
76) You treat some cells with DNP and discover that ATP production ceases. Upon closer examination, you also note that the number of calcium ions sequestered in the mitochondrion decreases. Please explain.
Answer:
Difficulty: Medium
Learning Objective: LO 5.4 Elaborate on the two components of the proton-motive force and how their relative contribution vary from one cell to another.
Section Reference: Section 5.4 Translocation of Protons and the Establishment of a Proton-Motive Force
Solution: DNP dissipates the proton gradient generated by electron transport, and this prevents ATP production. The gradient also appears to play a role in moving calcium ions into the mitochondrion. If the gradient is dissipated, the mitochondrion will be unable to move calcium ions into it, and thus it will not be able to maintain calcium ion sequestration.
77) You are a world-wide expert in mitochondria. If an investigator tells you that he wishes to study mitochondrial uncoupling proteins, what kind of organism would you suggest he use as a source of the protein? What is the function of brown adipose tissue? Humans lose brown fat deposits as they age. How does that happen and how do humans maintain body temperature when the brown fat is gone? Uncoupling protein (UCP) isoforms are found in cells of the nervous system. While their roles are debated, what is the most prominent hypothesis that may explain their function?
Answer:
Difficulty: Medium
Learning Objective: LO 5.4 Elaborate on the two components of the proton-motive force and how their relative contribution vary from one cell to another.
Section Reference: Section 5.4 Translocation of Protons and the Establishment of a Proton-Motive Force
Solution: Uncoupling protein is most plentiful in brown fat. Such tissue is found in newborn mammals, hibernating animals or animals acclimated to cold environments. Brown adipose tissue functions as a source of heat production during exposure to cold temperatures. Human infants also rely on brown fat deposits to maintain body temperature. Brown fat cells are largely lost as we grow up. When humans are older they are dependent on muscle contractions (shivering) to generate body heat. It has been suggested that UCPs in the inner mitochondrial membrane may prevent the build-up of an excessively large proton-motive force. If such a high-energy state were to form, it could block the passage of electrons through the respiratory complexes, leading to the leakage of electrons and the production of reactive oxygen radicals.
78) Rat liver mitochondria are isolated and placed in an assay medium. What happens to the pH of the medium when the medium is kept anaerobic? What happens when O2-saturated saline is added to the mixture?
Answer:
Difficulty: Hard
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
Solution: When the medium is kept anaerobic, the pH of the medium stays constant. When O2 is injected into the mixture, the mitochondria start doing aerobic respiration. Protons are pumped out of the matrix and the medium becomes acidified, decreasing the pH.
79) You prepare red blood cell ghosts with a very high internal potassium ion concentration and a very high external sodium ion concentration, higher than normally exists in the body. The red blood cell ghost also contains ADP and inorganic phosphate ions in the interior and the Na+-K+ pump in the membrane. What happens?
Answer:
Difficulty: Hard
Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.
Section Reference: Section 5.5 The Machinery for ATP Formation
Solution: Potassium ions move out of the ghost and sodium ions move into the ghost down their gradients, rather than up as would normally occur in a living cell. The movement of the ions causes ATP to be synthesized rather than hydrolyzed.
80) In addition to driving the synthesis of ATP, what other processes in the mitochondria are driven by the proton-motive force?
Answer:
Difficulty: Medium
Learning Objective: LO 5.5 Show the basic structure of the ATP synthase, describing the process where proton diffusion drives the phosphorylation of ADP.
Section Reference: Section 5.5 The Machinery for ATP Formation
Solution: The proton-motive force drives the uptake of ADP and Pi into the mitochondria in exchange for ATP and H+, respectively. It may also be used as the source of energy to “pull” calcium ions into the mitochondrion; it may be used to drive the events of mitochondrial fusion and to cause specifically targeted polypeptides to enter the mitochondrion from the matrix.
81) What are some of the diverse activities in which the enzymes found in peroxisomes are involved?
Answer:
Difficulty: Medium
Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.
Section Reference: Section 5.6 Peroxisomes
Solution: These enzymes are involved in the oxidation of very-long-chain fatty acids (VLCFAs, ones whose chain typically contains 24 to 26 carbons) and the synthesis of plasmalogens, an unusual class of phospholipids in which one of the fatty acids is linked to glycerol by an ether linkage rather than an ester linkage. Plasmalogens are very abundant in the myelin sheaths that insulate axons in the brain. Abnormalities in the synthesis of these molecules can lead to severe neurological dysfunction. The enzyme luciferase, which generates the light emitted by fireflies, is also a peroxisomal enzyme.
82) What properties do mitochondria and peroxisomes have in common?
Answer:
Difficulty: Medium
Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.
Section Reference: Section 5.6 Peroxisomes
Solution: They both form by splitting from preexisting organelles, using some of the same proteins to accomplish the feat. Both types of organelles import preformed proteins from the cytosol, and both engage in similar types of oxidative metabolism. In fact, at least one enzyme, alanine/glyoxylate aminotransferase is found in the mitochondria of some mammals (like cats and dogs) and the peroxisomes of other mammals (like rabbits and humans).
83) Where did peroxisomes get their name? How is the toxic hydrogen peroxide generated by these organelles disposed of? What is the specialized type of peroxisome found in plant seedlings and what specialized function do these organelles perform?
Answer:
Difficulty: Medium
Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.
Section Reference: Section 5.6 Peroxisomes
Solution: Their name is derived from the fact that they are the site of the synthesis and degradation of hydrogen peroxide, a highly reactive and toxic oxidizing agent. Hydrogen peroxide is produced by a number of peroxisomal enzymes, including urate oxidase, glycolate oxidase and amino acid oxidases, which utilize molecular oxygen to oxidize their respective substrates. The hydrogen peroxide generated in these reactions is rapidly broken down by the enzyme catalase, which is present in high concentrations in these organelles. The specialized peroxisome is called a glyoxysome. Plant seedlings rely on stored fatty acids to provide the energy and material to form a new plant. One of the primary metabolic activities in germinating seedlings is the conversion of stored fatty acids to carbohydrate. When stored fatty acids are disassembled, acetyl CoA is generated. The acetyl CoA condenses with oxaloacetate to form citrate. Citrate is then converted to glucose by a series of enzymes of the glyoxylate cycle localized in the glyoxysome.
84) Which reaction releases more free energy – the removal of a phosphate group from creatine phosphate or the removal of a phosphate group from ATP?
Answer:
Difficulty: Hard
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
Solution: The removal of a phosphate group from creatine phosphate releases more free energy than the removal of a phosphate group from ATP. In fact, creatine phosphate gives off enough free energy to drive the production of ATP, a reaction that actually happens. ATP’s conversion to ADP, however, does not give off enough free energy to phosphorylate creatine.
85) You have isolated some muscle cells in a tissue culture system. You are able to get them to contract in culture. If you add an inhibitor of the electron transport system to these cells, they do not contract quite as much, but they still contract noticeably. What kind of muscle fiber type are you employing?
Answer:
Difficulty: Medium
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
Solution: These muscle fibers are most likely to be fast twitch fibers, since they are able to operate in the presence of an electron transport inhibitor. Fast twitch fibers run anaerobically for the most part and do not carry out much aerobic respiration. Nor do they have many mitochondria with which to perform aerobic respiration.
86) If fatty acids are a more efficient storehouse of energy than glucose or glycogen, why aren’t they used immediately to drive muscle contraction?
Answer:
Difficulty: Medium
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
Solution: While fatty acids store more energy per unit of mass, the lipids are more difficult to transport to the muscle than the glycogen, which is already there. In addition, it takes longer to mobilize energy from fatty acids than from glycogen.
87) Which person would tend to have a higher proportion of slow-twitch than fast-twitch muscles: a weight lifter, a sprinter, or a long distance runner?
Answer:
Difficulty: Easy
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
Solution: The long distance runner will tend to have a higher proportion of slow twitch muscles.
88) Why do your muscles hurt for some time after a large amount of anaerobic exercise?
Answer:
Difficulty: Medium
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
Solution: If your muscles have been running anaerobically, they will produce lactic acid as a byproduct of fermentation. The buildup of lactic acid can lower the pH of muscle tissue from 7.0 to 6.35. This may lead to the pain and cramps that can accompany vigorous exercise.
89) What is meant by aerobic exercise?
Answer:
Difficulty: Medium
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
Solution: Aerobic exercises are designed to allow your muscles to continue to perform aerobically so that they can continue to make the necessary ATP by electron transport. Such exercises depend largely upon the contraction of the slow-twitch fibers of the skeletal muscles. They generate less force overall, but can continue to function for long periods of time due to their continuing aerobic production of ATP without the production of lactic acid.
90) Why is aerobic exercise one of the best ways to lose weight by decreasing the body’s fat content?
Answer:
Difficulty: Medium
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
Solution: Aerobic exercise is initially fueled by the glucose stored as glycogen in the muscles. After a short time, however, the muscles depend increasingly on free fatty acids released into the bloodstream from adipose tissue. As the exercise period increases in length, the dependency on fatty acids grows. Within 20 minutes of vigorous aerobic exercise, it is estimated that about 50% of the calories consumed by muscles is derived from fat. Thus, aerobic exercise is best at depleting the body’s fat stores.
91) Which muscles would contain more fast-twitch fibers, arm muscles or the postural muscles of the back?
Answer:
Difficulty: Easy
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
Solution: Arm muscles that are used to throw or lift an object, activities that require the generation of more force and thus a larger number of fast-twitch fibers, would have a higher proportion of fast-twitch fibers.
92) A muscle cell is obtained and studied with electron microscopy. The study reveals that it has very few mitochondria. What kind of muscle fiber is it?
Answer:
Difficulty: Hard
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
Solution: It is a fast-twitch fiber, since these fibers do relatively little aerobic respiration and thus have little need for many mitochondria.
93) Explain why fast-twitch fibers “prefer” to use anaerobic respiration rather than aerobic respiration even though aerobic respiration is about 20 times more efficient in terms of ATP produced per glucose molecule?
Answer:
Difficulty: Medium
Learning Objective: LO 5.3 Describe the steps by which the transport of electrons down the respiratory chain leads to the formation of a proton gradient.
Section Reference: Section 5.3 The Role of Mitochondria in the Formation of ATP
Solution: Glycolytic reactions occur much more rapidly than the reactions of the TCA cycle and electron transport. Thus, while the yield of ATP is less efficient, the ATP that can be produced is produced at a higher rate. The higher rate of ATP production is better suited to the function and more forceful contractions of fast-twitch fibers.
94) Why does the DNA in mitochondria exhibit about 10 times the mutation rate seen in nuclear DNA and what is the possible effect of this on disease processes?
Answer:
Difficulty: Medium
Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.
Section Reference: Section 5.6 Peroxisomes
Solution: Because of its proximity to electron-transport processes, which lead to the release of mutagenic oxygen radicals, mtDNA is thought to come under a much greater level of attack than nuclear DNA. In addition, nuclear DNA is better protected from persistent damage by the presence of a greater variety of DNA repair systems. Thus, damage inflicted upon nuclear DNA can be repaired, while damage to mitochondrial DNA cannot be repaired as effectively. These factors explain the greater than 10-fold higher mutation rate of mtDNA. Thus, mutations are particularly likely to accumulate in the mitochondria of cells that remain in the body for long periods of time (nerves and muscle tissue). The degenerative changes in mitochondrial functions are thought to contribute to a number of common neurological diseases with adult-onset, most notably Parkinson’s disease (PD).
95) Which mitochondrial genes when mutated or experiencing deletions cause the most serious disorders?
Answer:
Difficulty: Medium
Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.
Section Reference: Section 5.6 Peroxisomes
Solution: Mutations or deletions in the genes encoding the mitochondrial tRNAs tend to cause the most serious disorders. Mitochondrial tRNAs are required for the synthesis of all 13 polypeptides produced in human mitochondria.
96) What is unique about the inheritance of mitochondrial disorders? What word describes the mixture of wild-type and mutant mitochondrial DNA found in the mitochondria of a cell?
Answer:
Difficulty: Hard
Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.
Section Reference: Section 5.6 Peroxisomes
Solution: They are not inherited in a Mendelian fashion, but exhibit maternal inheritance. The mitochondria present in the cells of a human embryo are derived exclusively from mitochondria that were present in the egg at the time of conception without any contribution from the fertilizing sperm and thus they all come from the mother. In addition, the mitochondria of a cell can contain a mixture of both normal (i.e., wild-type) and mutant mtDNA. The level of mutant mtDNA can vary from one organ to another within a single individual, and it is only when a preponderance of the mitochondria in a particular tissue contains defective genetic information that clinical symptoms usually appear. Because of this variability, members of a family carrying the same mtDNA mutation can exhibit significantly different symptoms. Heteroplasmy describes the mixture of wild-type and mutant mitochondrial DNA found in the mitochondria of a cell.
97) A patient who has abnormal mitochondria has the following symptoms: long-term fatigue and muscle weakness, elevated metabolic rate and body temperature. Studies indicate that the mitochondria have been released from their normal respiratory control. How does this explain the elevated temperature? Why are most disorders that have been traced to mitochondrial dysfunction characterized by degeneration of muscle or brain tissue? What are the characteristics of some of the conditions that result from dysfunctional mitochondria?
Answer:
Difficulty: Medium
Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.
Section Reference: Section 5.6 Peroxisomes
Solution: If the cells run at an abnormally high metabolic rate for a long time, energy given off that is not harnessed to do mechanical work will result in heat production instead, which will build up to higher levels than usual and thus increase body temperature. Both of these tissues utilize exceptionally large amounts of ATP and thus degenerate because of the shortage of ATP that results from dysfunctional mitochondria. These conditions range in severity from diseases that lead to death during infancy; to disorders that produce seizures, blindness, deafness, and/or stroke-like episodes; to mild conditions characterized by intolerance to exercise or nonmotile sperm. Patients with serious conditions generally have abnormal skeletal muscle fibers, which contain large peripheral aggregates of mitochondria. When examined, these mitochondria are seen to have large numbers of abnormal inclusions.
98) In the early 1980s, a number of young drug addicts showed up in hospitals with the sudden onset of severe muscular tremors that are characteristic of advanced Parkinson’s disease (PD) in elderly adults. What caused these PD-like symptoms in such young people? How were the cells of the substantia nigra in PD patients similar to those in the substantia nigra of MPTP patients? What are some possible environmental causes of PD?
Answer:
Difficulty: Medium
Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.
Section Reference: Section 5.6 Peroxisomes
Solution: They had intravenously injected themselves with a synthetic heroin that was contaminated with a compound called MPTP. It was eventually discovered that MPTP caused damage to complex I of the mitochondrial respiratory chain, leading to the death of nerve cells in the same region of the brain (the substantia nigra) that is affected in PD patients. Cells from the substantia nigra of PD patients were found to have a marked and selective decrease in complex I activity, just like the MPTP patients. It appears that this complex I deficiency is probably due to a documented increase in the mutation rate in the DNA of these cells compared to other cells. Exposure to certain pesticides, particularly rotenone, has been implicated as an environmental risk factor for PD development. Rotenone is a known complex I inhibitor. Administration of rotenone to rats causes the destruction of dopamine-producing neurons, which is characteristic of the human disease.
99) What happens to the mtDNA of mice that are homozygous for the mutant gene called Polg? How do the “mutator” mice differ from their normal littermates? How do mice that are heterozygous for the Polg mutation differ from those that are homozygous for the Polg mutation? What should have happened to the life span of mice heterozygous for the Polg gene, if mtDNA mutations were a major contributor to the normal aging process? What do the above results of studies of the Polg mutation suggest about the relationship between mtDNA mutations and premature aging in animals?
Answer:
Difficulty: Hard
Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.
Section Reference: Section 5.6 Peroxisomes
Solution: The Polg gene encodes the enzyme that replicates mtDNA. The mtDNA of these mutant mice (called “mutator” mice) accumulates a much higher level of mutations than that of their normal littermates. The “mutator” mice appear normal for the first 6 to 9 months of age, but then rapidly develop signs of premature aging, such as hearing loss, graying hair and osteoporosis. The control mice have a lifespan of more than two years, however, members of the experimental group live, on average, only about one year. Mice heterozygous for the Polg mutation have an elevated mtDNA mutation rate (although far less than in the homozygotes). They, however, do not exhibit a shortened life span. If this were the case, the heterozygotes should have a significantly shorter life. The results suggest mutations in mtDNA may be sufficient to cause an animal to age prematurely, but they are not necessarily required as part of the normal aging process.
100) What causes Zellweger’s syndrome? What do the peroxisomes of ZS patients look like?
Answer:
Difficulty: Medium
Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.
Section Reference: Section 5.6 Peroxisomes
Solution: Peroxisomes in Zellweger’s syndrome patients lack the peroxisomal enzymes that are normally found inside of them. These enzymes are located in the cytoplasm instead. It is caused by deficiencies in genes coding for receptor proteins that recognize peroxisomal enzymes or proteins that participate in the transport of peroxisomal enzymes across peroxisome membranes. Genetic studies of cells from ZS patients showed that the disorder can arise from mutations in at least 12 different genes, all encoding proteins involved in the uptake of peroxisomal enzymes from the cytosol. Initially, investigators thought that the peroxisomes were missing from the cells of these patients. It was later found that peroxisomes were not entirely absent from the cells of these individuals. Instead, they were present as empty membranous “ghosts”. The organelles were present but the enzymes usually located within them were in the cytoplasm.
101) What is the basis of adrenoleukodystrophy (ALD) and other similar diseases?
Answer:
Difficulty: Medium
Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.
Section Reference: Section 5.6 Peroxisomes
Solution: ALD and other similar diseases are caused by single enzyme/protein deficiencies in peroxisomes. The missing enzyme/protein cannot oxidize its normal substrate, which then builds up to higher than normal levels. These higher levels become toxic and damage tissues, eventually leading to debilitation or death. In ALD, the defect is in a membrane protein that transports very-long-chain fatty acids (VLCFAs) into peroxisomes, where they are normally metabolized. Without this protein, VLCFAs accumulate in the brain and destroy the myelin sheaths that insulate nerve cells. Boys with this disease are usually unaffected until mid-childhood, when they begin to exhibit symptoms of adrenal insufficiency and neurological dysfunction.
102) What treatments have been tried to help ALD patients?
Answer:
Difficulty: Medium
Learning Objective: LO 5.6 Discuss the major activities of peroxisomes and how they are linked to the mitochondria.
Section Reference: Section 5.6 Peroxisomes
Solution: The movie Lorenzo’s Oil dealt with the parents of an ALD patient who discovered that a diet rich in certain fatty acids was able to retard the progress of the disease. Subsequent studies have generated contradictory results regarding the value of this diet. Some ALD patients have been helped by bone marrow transplantation, which provides normal cells capable of metabolizing VLCFAs and by administration of drugs (e.g., lovastatin) that may lower VLCFA levels. Clinical studies employing gene therapy are also planned.
Original price was: $30.00.$20.00Current price is: $20.00.
Original price was: $30.00.$20.00Current price is: $20.00.
Original price was: $30.00.$20.00Current price is: $20.00.
Original price was: $30.00.$20.00Current price is: $20.00.
Original price was: $30.00.$20.00Current price is: $20.00.
Original price was: $30.00.$20.00Current price is: $20.00.
