GRE Subject Test: Biochemistry, Cell, and Molecular Biology : Cellular Respiration and Photosynthesis

Study concepts, example questions & explanations for GRE Subject Test: Biochemistry, Cell, and Molecular Biology

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All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources

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Example Questions

Example Question #2 : Help With The Electron Transport Chain

Which of the following is true regarding the final electron acceptor in the electron transport chain?

Possible Answers:

It is a byproduct of anaerobic respiration

It only picks up electrons

It picks up electron and protons

It contributes to the production of energy

Correct answer:

It picks up electron and protons

Explanation:

The final electron acceptor in electron transport chain is oxygen. The electrons traverse along the electron transport chain and ultimately end up being taken up by an oxygen atom. Upon accepting electrons, the oxygen atom becomes negatively charged and attracts protons (hydrogen atoms). An oxygen atom binds to two hydrogen atoms and forms water.

Energy production in ETC is facilitated by the generation of the proton gradient by the proton pump. This gradient is utilized by ATP synthase to produce ATP. Oxygen does not play a role in this process. Anaerobic respiration is a type of respiration that occurs in the absence of oxygen. Examples of anaerobic respiration include glycolysis and fermentation.

Example Question #3 : Help With The Electron Transport Chain

Anaerobic respiration occurs in the __________ and aerobic respiration occurs in the __________.

Possible Answers:

cytosol . . . cytosol

cytosol . . . mitochondria

mitochondria . . . mitochondria

mitochondria . . . cytosol

Correct answer:

cytosol . . . mitochondria

Explanation:

Cellular respiration has three main processes: glycolysis, Krebs cycle, and electron transport chain. Glycolysis is an anaerobic process whereas Krebs cycle and ETC are aerobic processes. A molecule of glucose enters the cell and undergoes glycolysis in the cytosol. Some of the products of glycolysis are transported to mitochondria where they undergo Krebs cycle and then, eventually, the electron transport chain; therefore, anaerobic respiration occurs in the cytosol and aerobic respiration occurs in the mitochondria.

Anaerobic respiration produces very little ATP and the ATP produced is not sufficient to power all of the active processes in a cell. Aerobic respiration, particularly ETC, produces a lot of ATP. This is why mitochondria is called the “powerhouse” of the cell. Note that the products of glycolysis can undergo another type of anaerobic respiration called fermentation. This also produces very little ATP.

Example Question #5 : Help With The Electron Transport Chain

Which of the following is true regarding electron transport chain (ETC)?

I. Proton pump generates ATP

II. Electron affinity of  and  is lower than the carriers in ETC

III. Electrochemical gradient of sodium facilitates production of ATP

Possible Answers:

I only

I and II

II only

II and III

Correct answer:

II only

Explanation:

Electron transport chain is a series of electron carriers located on the inner membrane of the mitochondria. Electrons traverse across these electron carriers and this motion allows for the proton pump to generate a proton gradient across the inner membrane. This gradient is generated by pumping protons from the inside of the mitochondria to the periplasmic space (space between inner and outer mitochondrial membranes). The excess protons in the periplasmic space are transported back into the mitochondria and this movement facilitates the generation of ATP by the ATP synthase. Note that ATP is generated by ATP synthase, not the proton pump.

 and  are electron carriers that carry electrons from glycolysis and Krebs cycle. These carriers enter the ETC and donate their electrons to the carriers in ETC. This occurs because ETC carriers have higher affinity for electrons. Remember that each subsequent carrier in ETC has a higher affinity for electrons, so that it is able to snatch the electron from the previous carrier. As mentioned, the ATP generation is facilitated by the proton gradient, not the sodium gradient.

Example Question #31 : Cellular Respiration And Photosynthesis

What directly drives ATP synthase to generate ATP from ADP and inorganic phosphate? 

Possible Answers:

Proton gradient

Electron transfer

Phosphorylation 

Reduction of  to 

Ubiquitination

Correct answer:

Proton gradient

Explanation:

The correct answer is proton gradient.  and  donate electrons to electron transport chain complexes and pass them along the membrane, causing protons  to move from the mitochondrial matrix to the intermembrane space. The high proton concentration gradient causes protons to travel through the inner mitochondrial transmembrane ATP synthase to equilibrate the gradient. Passing of protons through ATP synthase promotes synthesis of ATP from ADP from inorganic phosphate. 

Example Question #2 : Help With The Electron Transport Chain

Cytochrome C is a small protein localized to the inner mitochondrial membrane that has an important role in the last steps of the electron transport chain. What is cytochrome C's primary role in the electron transport chain? 

Possible Answers:

Cytochrome C catalyzes the conversion of 2 ADP to 2 ATP, thus contributing to the energetic gain in the electron transport chain

Cytochrome C removes electrons from complex IV and transfers them to molecular oxygen in the mitochondria

Cytochrome C accepts electrons from complex IV and directly transfers these electrons to molecular oxygen

Cytochrome C accepts electrons from complex II and shuttles them to Complex III, which is required for further activation of complex IV

Cytochrome C accepts electrons from complex III in the mitochondrial membrane and transfers them to complex IV

Correct answer:

Cytochrome C accepts electrons from complex III in the mitochondrial membrane and transfers them to complex IV

Explanation:

Cytochrome C is responsible for accepting the electrons generated in the bc1 complex (complex III) and transferring them over to complex IV. In other words, cytochrome C oxidizes complex III and is oxidized by complex IV. This is required to then add those electrons to molecular oxygen, which forms water and contributes to the proton gradient required for ATP production. 

Example Question #101 : Biochemistry

What is the final electron acceptor in the electron transport chain?

Possible Answers:

Cytochrome C

Correct answer:

Explanation:

The final electron acceptor in the electron transport chain is oxygen gas. one oxygen gas molecule will accept 4 electrons and combine with 4 protons in order to create 2 water molecules. This reaction is the reason water is a byproduct of aerobic cellular respiration.

Example Question #2 : Help With The Electron Transport Chain

Krebs cycle occurs in the __________ and the electron transport chain occurs in the __________.

Possible Answers:

cytoplasm . . . mitochondrial matrix

mitochondrial inner membrane . . . mitochondrial matrix

mitochondrial matrix . . . cytoplasm

mitochondrial matrix . . . mitochondrial inner membrane

Correct answer:

mitochondrial matrix . . . mitochondrial inner membrane

Explanation:

Glycolysis, the first step in metabolism of carbohydrates, occurs in the cytoplasm. The products of glycolysis (pyruvate and NADH) are transported to the mitochondrial matrix. The products undergo series of reactions called the Krebs cycle. The products of Krebs cycle and NADH from glycolysis enter the inner mitochondrial membrane and go through the electron transport chain (ETC). During ETC, oxidative phosphorylation generates most of the ATP used by the cells.

Example Question #101 : Biochemistry

Which of the following molecule(s) undergoes reduction during the electron transport chain?

Possible Answers:

None of these are reduced

Both of these are reduced

Oxygen

NADH

Correct answer:

Oxygen

Explanation:

Reduction is the process of gaining electrons. In electron transport chain (ETC), electron carriers such as NADH and  donate electrons to the electron carriers in the ETC. These electrons are transported to subsequent molecules. The final acceptor of electrons in ETC is oxygen, which accepts electrons and gets converted into water. Since electrons are being lost from them, NADH and  are oxidized in the ETC. On the other hand, oxygen accepts electrons and is reduced in the electron transport chain.

Example Question #32 : Cellular Respiration And Photosynthesis

Oligomycin is an inhibitor of ATP synthase. Which of the following will you observe in the cells of a patient taking oligomycin?

I. There will be a higher concentration of protons in the intermembrane space

II. Proton pump will no longer be functional

III. ATP production will be decreased

Possible Answers:

I and II

III only

I, II, and III

I and III

Correct answer:

I and III

Explanation:

The question states that oligomycin inhibits ATP synthase. Recall that ATP synthase (found on the inner mitochondrial membrane) generates ATP by transporting protons from the intermembrane space (space between inner and outer mitochondrial membrane) into the mitochondria. Inhibiting this will prevent the transport of protons and will, subsequently, lead to a buildup of protons in the intermembrane space.

Proton pumps are also found on the inner mitochondrial membrane. They function to pump out protons from the inside of mitochondria to the intermembrane space, thereby providing the proton gradient for ATP synthase to generate ATP. Halting ATP synthase will cause proton pump to stop pumping protons into the intermembrane space (due to the increase in protons in intermembrane space).

ATP synthase is the major generator of ATP; therefore, halting ATP synthase via oligomycin will decrease the amount of ATP generated.

Example Question #103 : Biochemistry

During ATP synthesis in mitochondria, protons move directly through __________.

Possible Answers:

Outer mitochondrial membrane

F1 subunit of ATP synthase

Ubiquinone

Cytoplasmic cellular membrane

F0 subunit of ATP synthase

Correct answer:

F0 subunit of ATP synthase

Explanation:

The F0 subunit of ATP synthase is where protons flow through to create ATP. This mechanism involves a rotation of the subunit, producing ATP with each turn. ATP synthase is part of oxidative phosphorylation, the greatest ATP producing segment of cellular respiration.

All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources

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