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Biochem Exam 3

Terms in this set (72)

Choose all the true statements about the electron transport chain.
The electron transport chain is a series of oxi-redox reactions that occurs in the inner mito. membrane.
In the electron transport chain, a series of reactions moves electrons through carriers.
The products of the electron transport chain are H2O and either NAD+ or FAD.
The electron transport chain (ETC), or respiratory chain, is linked to proton movement and ATP synthesis. Select the statements that accurately describe the electron transport chain. Choose all that apply.
Electron carriers are organized into four complexes of proteins and prosthetic groups.
Electron transfer in the ETC is coupled to proton transfer from the matrix to the intermembrane space.
The outer membrane of the mitochondria is readily permeable to small molecules and H+ ions.
Prosthetic groups, such as iron-sulfur centers, are directly involved with electron transfer.
Electron carriers in the ETC include coenzyme Q and cytochrome c.
Without using a textbook, predict the sequence of electron transport carriers (the sequence of participants in the redox reactions) in the electron transport chain. A table of standard reduction potentials is given for reference.
1. NAD+
2. Coenzyme Q
3. Cytochrome b
4. Cytochrome c
5. Cytochrome a
6. O2

Gradient goes from negative to positive (E0')
Determine which complex of the electron transport chain (respiratory chain) each phrase describes.
Complex I: Electron transfer from NADH to CoQ. NADH dehydrogenase complex.

Complex II: Electron transfer from succinate to CoQ. Succinate dehydrogenase complex.

Complex III: Electron transfer from ubiquinol (QH2, reduced CoQ) to cytochrome c. Cytochrome bc1 complex (CoQ-cytochrome c reductase).

Complex IV: Electron transfer from cytochrome c to O2. Cytochrome oxidase.
When considering free energy change, biochemists define a biochemical standard state, ΔG°', which differs from the chemical standard state, ΔG°. A similar distinction must be made with reduction potentials.

In contrast to the chemical reduction potential, ΔE°, the biochemical standard reduction potential, ΔE°'.

Why might the standard reduction potential for a reaction differ from the reduction potential found in a cell?
Specifies at pH of 7.

Concentrations in the cell might not be 1 M.
ΔG°' = -nFΔE°
n is the number of electrons transferred
F is Faraday's constant, 96.5 kJ·mol-1·V-1
ΔE0' is the difference in reduction potential

ΔG°' units are kJ.mol-1
As part of the malate-aspartate shuttle, the malate-α-ketoglutarate transporter transfers malate formed in the cytosol to the mitochondrion. The malate-α-ketoglutarate transporter is inhibited by n-butylmalonate. When n-butylmalonate is added to an aerobic suspension of kidney cells using glucose as the primary source of energy, ATP synthesis drastically decreases. Select the statements that explain why the addition of n-butylmalonate causes a decrease in ATP synthesis.
Inhibiting the malate-α-ketoglutarate transporter will prevent the regeneration of NAD by the malate-aspartate shuttle in the cytosol, thus forcing the kidney cells to switch to anaerobic glycolysis via lactate fermentation.

If the malate-aspartate shuttle is inhibited, NADH will accumulate in the cytosol, thus limiting the amount of NADH available for the electron-transfer chain. Decreasing the amount of NADH in the mitochondrion will eventually inhibit oxidative phosphorylation.
Although some citric acid cycle enzymes operate primarily in the mitochondria, malate dehydrogenase operates in both the cytosol and the mitochondria. Match each function to cytosolic malate dehydrogenase or mitochondrial malate dehydrogenase.
Cytosolic malate dehydrogenase:

reduces OAA to malate, oxidizes NADH produced in glycolysis to NAD+, transfers reducing equivalents from cytosolic NADH to a molecule that can traverse the inner mitochondrial membrane.

Mitochondrial malate dehydrogenase:

oxidizes malate to OAA, reduces NAD+ to NADH, catalyzes an endergonic reaction to regenerate OAA for the citric acid cycle, transfers reducing equivalents that originate in the cytosol to NAD+ in the mito.
The following statements concern the relationship between mitochondrial hydrogen ion concentration and energy storage as ATP during oxidative phosphorylation. Classify each statement as either accurate or inaccurate.
Accurate:

H+ ions cannot freely pass through the inner mitochondrial membrane.

H+ concentration is lower in the mitochondrial matrix than in the intermembrane space.

The pH in the mitochondral matrix is higher than the pH in the intermembrane space.

H+ ions move through a channel formed by ATP synthase releasing energy to form ATP.
ATP synthase, shown below, uses the proton (H ) gradient to drive ATP synthesis. Put the following steps of ATP synthesis in order from proton transport to the synthesis of ATP:
1. protons from the intermembrane space bind to proton binding sites on c subunits.

2. as the c ring rotates past the a subunit, c subunits release their protons into the matrix.

3. the gamma subunit rotates along with the c subunit.

4. the gamma subunit rotates and interacts with three alpha-beta subunit pairs, causing conformational changes in the beta subunits.

5. each beta subunit binds ADP and Pi, converts ADP+Pi to ATP, and releases ATP once during one turn of the gamma subunit.
The adenine nucleotide translocase (ADP-ATP translocase), a transporter located in the inner mitochondrial membrane, transports ADP and ATP across the membrane. It is an antiporter. (Recall that these adenine nucleotides are negatively charged: ADP3- and ATP4-.) Phosphate translocase is also located in the inner mitochondrial membrane. It transports H and phosphate (H2PO4-) across the membrane. It is a symporter. Answer parts (a), (b), (c), and (d) below.

(a) Which direction is ATP4- transported during times of active oxidative phosphorylation?

(b) What drives the transport of adenine nucleotides?

(c) What is the ratio of ADP to ATP transported by the adenine nucleotide translocase? That is, how many ADP are transported for each ATP transported?

(d) What drives the transport of H2PO4- across the membrane? Which direction is it transported during oxidative phosphorylation?
a) out of the mitochondrial matrix

b) the electrochemical gradient (membrane potential)

c) 1 ADP: 1 ATP

d) H and H2PO4- are transported into the matrix in a process driven by the proton gradient.
The energy derived from the movement of H ions down an electrochemical gradient from the intermembrane space into the matrix is used to drive the synthesis of ATP. How many H ions must be moved into the matrix for the synthesis of 1 ATP?
4 H+ ions/ ATP
Which of the following regulate oxidative phosphorylation under hypoxic conditions?
pH decreases below 6.5 and IF1 exists as a stable dimer capable of inhibiting the ATPase activity of ATP synthase.

The protein inhibitor IF1 binds two ATP synthase molecules and inhibits their ATPase activity.

HIF-1 replaces a subunit of Complex IV of the electron transport chain with a subunit that is more efficient under hypoxic conditions.
Louis Pasteur observed that when oxygen is introduced to cells consuming glucose at a high rate in an anaerobic environment, fermentation ceases and the rate of glucose consumption decreases. This phenomenon is called the Pasteur effect. The basis of this effect is the shift from fermentation to oxidative phosphorylation to regenerate NAD . Additionally, the cells also synthesize ATP through oxidative phosphorylation. In respiration-deficient yeast mutants that lack cytochrome oxidase, the Pasteur effect is not seen. Select the reasons why the absence of cytochrome oxidase eliminates the Pasteur effect?
In the absence of cytochrome oxidase, oxidative phosphorylation will be inhibited and ATP production will decrease drastically. Low ATP levels will maintain the high rate of glucose consumption in the mutant yeast cells.

In the absence of cytochrome oxidase, oxidative phosphorylation will be inhibited and ATP production will decrease drastically. Low ATP levels will maintain the high rate of glucose consumption in the mutant yeast cells.
Which of the following is the major regulator of oxygen consumption during oxidative phosphorylation?
ADP
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