Question 1

How do the cytosolic and mitochondrial isozymes of glycerol 3-phosphate dehydrogenase differ from each other?

Accepted Answer

Glycerol 3-phosphate dehydrogenase (GPDH) is an enzyme that catalyzes the reversible redox conversion of dihydroxyacetone phosphate (DHAP) to glycerol 3-phosphate (G3P). There are two distinct isozymes of GPDH: one located in the cytosol (cGPDH) and the other in the mitochondria (mGPDH). These isozymes differ in several key aspects:

1. **Location and Function in Cellular Metabolism**:
   - **Cytosolic GPDH (cGPDH)**: This isozyme is involved in the glycolytic pathway, where it facilitates the conversion of DHAP to G3P, which can then be used for triglyceride synthesis or further glycolysis. It plays a role in the shuttle mechanism for transferring reducing equivalents from NADH produced in the cytosol into the mitochondria.
   - **Mitochondrial GPDH (mGPDH)**: This isozyme is part of the glycerol phosphate shuttle, which transfers reducing equivalents from cytosolic NADH into the electron transport chain within the mitochondria. mGPDH oxidizes G3P back to DHAP while reducing FAD to FADH2, which then donates electrons to the respiratory chain.

2. **Enzymatic Mechanism and Electron Carriers**:
   - **cGPDH** uses NAD+/NADH as its electron acceptors and donors.
   - **mGPDH** uses FAD/FADH2 as its electron acceptors and donors.

3. **Genetic Origin and Regulation**:
   - **cGPDH** and **mGPDH** are encoded by different genes and are subject to different regulatory mechanisms. cGPDH is typically regulated by the availability of substrates and by the energy needs of the cell, while mGPDH is regulated in part by the redox state of the mitochondrial matrix and the demand for ATP production.

4. **Physiological Role**:
   - **cGPDH** is primarily involved in lipid metabolism and the regulation of glycolysis.
   - **mGPDH** is crucial for the efficient transfer of electrons from cytosolic NADH into the mitochondrial electron transport chain, which is essential for ATP production during oxidative phosphorylation.

5. **Tissue Distribution**:
   - The expression of **cGPDH** and **mGPDH** can vary between tissues, depending on the metabolic requirements of the cells. For example, tissues with high rates of fatty acid synthesis (like liver and adipose tissue) have higher levels of cGPDH.

6. **Kinetic Properties**:
   - The kinetic properties of cGPDH and mGPDH, such as their affinity for substrates and sensitivity to inhibitors, can differ, reflecting their adaptation to specific cellular roles and conditions.

In summary, the cytosolic and mitochondrial isozymes of glycerol 3-phosphate dehydrogenase differ in their cellular location, function, enzymatic mechanisms, genetic regulation, physiological roles, tissue distribution, and kinetic properties. These differences allow them to fulfill distinct roles in cellular metabolism, particularly in the context of lipid metabolism and energy production.

Question 2

Upon the addition of 2,4-dinitrophenol (DNP) to a suspension of mitochondria carrying out oxidative phosphorylation linked to the oxidation of malate, what does NOT occur?

Accepted Answer

A)  Oxygen consumption decreases. 
B)  Oxygen consumption increases. 
C)  The P/O ratio drops from a value of approximately 2.5 to 0. 
D)  The proton gradient dissipates. 
E)  The rate of transport of electrons from NADH to O2 becomes maximal. 
A)  Oxygen consumption decreases. 
B)  Oxygen consumption increases. 
C)  The P/O ratio drops from a value of approximately 2.5 to 0. 
D)  The proton gradient dissipates. 
E)  The rate of transport of electrons from NADH to O2 becomes maximal. A

Question 3

Which statement is NOT a feature of Complex IV?

Accepted Answer

A)  Cytochrome c is a one-electron donor. 
B)  Oxygen is a substrate. 
C)  Copper is an essential metal for the reaction. 
D)  For every electron passed to Complex IV, two protons are consumed from the matrix (N) side. 
E)  In order to generate two water molecules, Complex IV must go through the catalytic cycle two times. 
A)  Cytochrome c is a one-electron donor. 
B)  Oxygen is a substrate. 
C)  Copper is an essential metal for the reaction. 
D)  For every electron passed to Complex IV, two protons are consumed from the matrix (N) side. 
E)  In order to generate two water molecules, Complex IV must go through the catalytic cycle two times. E

Question 4

Which statement is TRUE regarding the reduction potential of mitochondrial glycerol 3 phosphate dehydrogenase?

Accepted Answer

A)  It will be higher than those of both NADH and Complex III. 
B)  It will be lower than those of both NADH and Complex III. 
C)  It will be higher than that of NADH but lower than that of Complex III. 
D)  It will be lower than that of NADH but higher than that of Complex III. 
E)  No conclusion can be drawn regarding its reduction potential. 
A)  It will be higher than those of both NADH and Complex III. 
B)  It will be lower than those of both NADH and Complex III. 
C)  It will be higher than that of NADH but lower than that of Complex III. 
D)  It will be lower than that of NADH but higher than that of Complex III. 
E)  No conclusion can be drawn regarding its reduction potential.

Question 5

Which of the following electron carriers is NOT able to transfer one electron at a time?

Accepted Answer

A)  NADH 
B)  FMN 
C)  FAD 
D)  ubiquinone 
E)  heme 
A)  NADH 
B)  FMN 
C)  FAD 
D)  ubiquinone 
E)  heme

Question 6

Describe the role of hypoxia-inducible factor (HIF-1) in reducing reactive oxygen species (ROS).

Accepted Answer

Hypoxia-inducible factor 1 (HIF-1) is a

Question 7

Which molecule can reduce the proton gradient in mitochondria?

Accepted Answer

A)  Pi-H+ symporter 
B)  ATP synthase 
C)  pyruvate translocase 
D)  All of the answers are correct. 
E)  None of the answers is correct. 
A)  Pi-H+ symporter 
B)  ATP synthase 
C)  pyruvate translocase 
D)  All of the answers are correct. 
E)  None of the answers is correct.

Question 8

Which statement is CORRECT concerning the mitochondrial ATP synthase?

Accepted Answer

A)  It can synthesize ATP after it is extracted from broken mitochondria. 
B)  It catalyzes the formation of ATP even though the reaction has a large positive $\Delta$G'°. 
C)  It consists of Fo and F1 subunits, which are transmembrane (integral) polypeptides. 
D)  It is actually an ATPase and only catalyzes the hydrolysis of ATP. 
E)  When it catalyzes the ATP synthesis reaction, the $\Delta$G'° is actually close to zero. 
A)  It can synthesize ATP after it is extracted from broken mitochondria. 
B)  It catalyzes the formation of ATP even though the reaction has a large positive $\Delta$G'°. 
C)  It consists of Fo and F1 subunits, which are transmembrane (integral) polypeptides. 
D)  It is actually an ATPase and only catalyzes the hydrolysis of ATP. 
E)  When it catalyzes the ATP synthesis reaction, the $\Delta$G'° is actually close to zero.

Question 9

Discuss three lines of evidence that support the theory that mitochondria evolved from endosymbiontic bacteria.

Accepted Answer

1) Genetic evidence: Mitochondria have t

Question 10

Which statement regarding oxidative phosphorylation is TRUE?

Accepted Answer

A)  The rate of electron transport is independent of the magnitude of the proton electrochemical gradient. 
B)  ATP synthase utilizes oxidized cofactors. 
C)  Proton transfer through the Fo subunit of ATP synthase is required in order for ATP synthesis to occur. 
D)  The addition of an uncoupler decreases the rate of re-oxidation of NADH and FADH2, therefore decreasing the rate of the citric acid cycle. 
E)  All of the statements are true. 
A)  The rate of electron transport is independent of the magnitude of the proton electrochemical gradient. 
B)  ATP synthase utilizes oxidized cofactors. 
C)  Proton transfer through the Fo subunit of ATP synthase is required in order for ATP synthesis to occur. 
D)  The addition of an uncoupler decreases the rate of re-oxidation of NADH and FADH2, therefore decreasing the rate of the citric acid cycle. 
E)  All of the statements are true.

Question 11

Mutations in mitochondrial genes do NOT play a role in:

Accepted Answer

A)  adult onset diabetes. 
B)  cystic fibrosis. 
C)  hypertrophic cardiomyopathy. 
D)  Leber's hereditary optic neuropathy. 
E)  myoclonic epilepsy. 
A)  adult onset diabetes. 
B)  cystic fibrosis. 
C)  hypertrophic cardiomyopathy. 
D)  Leber's hereditary optic neuropathy. 
E)  myoclonic epilepsy.

Question 12

In which pairing are both transporters symports?

Accepted Answer

A)  adenine nucleotide translocase and phosphate translocase 
B)  phosphate translocase and pyruvate translocase 
C)  pyruvate translocase and adenine nucleotide translocase 
D)  adenine nucleotide translocase and glutamate-aspartate transporter 
E)  glutamate-aspartate transporter and phosphate translocase 
A)  adenine nucleotide translocase and phosphate translocase 
B)  phosphate translocase and pyruvate translocase 
C)  pyruvate translocase and adenine nucleotide translocase 
D)  adenine nucleotide translocase and glutamate-aspartate transporter 
E)  glutamate-aspartate transporter and phosphate translocase

Question 13

Which cofactor is MOST commonly involved as a cosubstrate in catabolic reactions where a metabolite is oxidized?

Accepted Answer

A)  NAD+ 
B)  FAD 
C)  NADPH 
D)  NADH 
E)  coenzyme Q 
A)  NAD+ 
B)  FAD 
C)  NADPH 
D)  NADH 
E)  coenzyme Q

Question 14

The ATP synthase F1 portion contains many subunits arranged in a cyclic pattern, yet we cannot really describe it as having cyclic symmetry. Why?

Accepted Answer

ATP synthase is a complex enzyme that pl

Question 15

Which statement is TRUE regarding the gamma ($\gamma$) subunit of ATP synthase?

Accepted Answer

A)  It contains mostly $\alpha$-helical regular secondary structure. 
B)  It exists as a dimer in the F1 portion of ATP synthase. 
C)  It prevents the F1 portion from rotating relative to the FO portion. 
D)  It interacts with the a and b subunits of the FO portion. 
E)  It binds protons as part of the proton translocation process. 
A)  It contains mostly $\alpha$-helical regular secondary structure. 
B)  It exists as a dimer in the F1 portion of ATP synthase. 
C)  It prevents the F1 portion from rotating relative to the FO portion. 
D)  It interacts with the a and b subunits of the FO portion. 
E)  It binds protons as part of the proton translocation process.

Question 16

Explain briefly the current model for how the proton motive force that is generated by electron transport is used to drive the ATP synthesis reaction.

Accepted Answer

The current model for how the proton mot

Question 17

For each of the following explain whether they are transported into or out of the mitochondrion and comment briefly on the mechanism for each:
(1) NADH
(2) Inorganic phosphate
(3) ADP

Accepted Answer

(1) NADH is transported into the mitocho

Question 18

What mechanism accounts for mitochondrial inheritance in sexual reproduction in animals?

Accepted Answer

A)  Male gametes do not contain mitochondria. 
B)  Mitochondria from male gametes do not enter the ovum. 
C)  Female mitochondria are able to outcompete male mitochondria. 
D)  Male mitochondria are degraded after fertilization. 
E)  Male and female mitochondria merge after fertilization to form hybrids. 
A)  Male gametes do not contain mitochondria. 
B)  Mitochondria from male gametes do not enter the ovum. 
C)  Female mitochondria are able to outcompete male mitochondria. 
D)  Male mitochondria are degraded after fertilization. 
E)  Male and female mitochondria merge after fertilization to form hybrids.

Question 19

When the $\Delta$G'° of the ATP synthesis reaction is measured on the surface of the ATP synthase enzyme, it was found to be close to zero. Describe briefly why this is so.

Accepted Answer

The Gibbs free energy change (ΔG'°) of a

Question 20

Describe, in simple diagrams and a few words, the chemiosmotic theory for coupling oxidation to phosphorylation in mitochondria.

Accepted Answer

The chemiosmotic theory explains how the

Exam 19: Oxidative Phosphorylation and Photophosphorylation

How do the cytosolic and mitochondrial isozymes of glycerol 3-phosphate dehydrogenase differ from each other?

Upon the addition of 2,4-dinitrophenol (DNP) to a suspension of mitochondria carrying out oxidative phosphorylation linked to the oxidation of malate, what does NOT occur?

Which statement is NOT a feature of Complex IV?

Which statement is TRUE regarding the reduction potential of mitochondrial glycerol 3 phosphate dehydrogenase?

Which of the following electron carriers is NOT able to transfer one electron at a time?

Describe the role of hypoxia-inducible factor (HIF-1) in reducing reactive oxygen species (ROS).

Which molecule can reduce the proton gradient in mitochondria?

Which statement is CORRECT concerning the mitochondrial ATP synthase?

Discuss three lines of evidence that support the theory that mitochondria evolved from endosymbiontic bacteria.

Which statement regarding oxidative phosphorylation is TRUE?

Mutations in mitochondrial genes do NOT play a role in:

In which pairing are both transporters symports?

Which cofactor is MOST commonly involved as a cosubstrate in catabolic reactions where a metabolite is oxidized?

The ATP synthase F1 portion contains many subunits arranged in a cyclic pattern, yet we cannot really describe it as having cyclic symmetry. Why?

Which statement is TRUE regarding the gamma ( γ\gammaγ ) subunit of ATP synthase?

Explain briefly the current model for how the proton motive force that is generated by electron transport is used to drive the ATP synthesis reaction.

For each of the following explain whether they are transported into or out of the mitochondrion and comment briefly on the mechanism for each: (1) NADH (2) Inorganic phosphate (3) ADP

What mechanism accounts for mitochondrial inheritance in sexual reproduction in animals?

When the Δ\DeltaΔ G'° of the ATP synthesis reaction is measured on the surface of the ATP synthase enzyme, it was found to be close to zero. Describe briefly why this is so.

Describe, in simple diagrams and a few words, the chemiosmotic theory for coupling oxidation to phosphorylation in mitochondria.

The Foundations of Biochemistry

Water

Amino Acids, Peptides, and Proteins

The Three-Dimensional Structure of Proteins

Protein Function

Enzymes

Carbohydrates and Glycobiology

Nucleotides and Nucleic Acids

DNA-Based Information Technologies

Lipids

Biological Membranes and Transport

Biosignaling

Bioenergetics and Biochemical Reaction Types

Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway

Principles of Metabolic Regulation

The Citric Acid Cycle

Fatty Acid Catabolism

Amino Acid Oxidation and the Production of Urea

Carbohydrate Biosynthesis in Plants and Bacteria

Lipid Biosynthesis

Biosynthesis of Amino Acids, Nucleotides, and Related Molecules

Hormonal Regulation and Integration of Mammalian Metabolism

Genes and Chromosomes

DNA Metabolism

RNA Metabolism

Protein Metabolism

Regulation of Gene Expression

Filters

The ATP synthase F₁ portion contains many subunits arranged in a cyclic pattern, yet we cannot really describe it as having cyclic symmetry. Why?

Which statement is TRUE regarding the gamma ( $\gamma$ ) subunit of ATP synthase?

When the $\Delta$ G'° of the ATP synthesis reaction is measured on the surface of the ATP synthase enzyme, it was found to be close to zero. Describe briefly why this is so.