Biology Cellular Respiration and Photosynthesis Flashcards

What is the primary reason why the theoretical ATP yield from glucose oxidation is never achieved in living cells?

Answer: Proton leakage, variable P/O ratios, and energy costs of membrane transport reduce efficiency

Real ATP yields are lower than theoretical maxima because protons leak across the inner membrane, P/O ratios vary, and ATP/ADP transport across the mitochondrial membrane consumes some proton-motive force.

In the context of the Calvin cycle, what does the term 'regeneration of RuBP' refer to?

Answer: The ATP-dependent conversion of Calvin cycle intermediates back into ribulose-1,5-bisphosphate

Regeneration of RuBP is the third stage of the Calvin cycle, where ATP is used to convert 5-carbon intermediates (ribulose-5-phosphate) back into RuBP so CO2 fixation can continue.

Which regulatory molecule activates phosphofructokinase-1 (PFK-1), signaling that the cell needs more energy?

Answer: AMP (adenosine monophosphate)

AMP activates PFK-1, the key regulatory enzyme of glycolysis, signaling low energy charge and stimulating glucose breakdown to generate more ATP.

What structural feature of the inner mitochondrial membrane dramatically increases its surface area for ATP synthesis?

Answer: Cristae (infoldings of the inner membrane)

Cristae are extensive infoldings of the inner mitochondrial membrane that greatly increase its surface area, accommodating more ETC complexes and ATP synthase molecules.

What is the fate of the G3P (glyceraldehyde-3-phosphate) molecules produced in the Calvin cycle?

Answer: About 5/6 of G3P is used to regenerate RuBP, and 1/6 exits to form glucose or other organic molecules

For every 6 G3P produced (from 3 turns of the Calvin cycle), 5 are used to regenerate RuBP and only 1 net G3P exits to be used for glucose synthesis or other biosynthesis.

Brown adipose tissue generates heat instead of ATP during cold exposure. Which protein is responsible for this thermogenesis?

Answer: Thermogenin (uncoupling protein 1, UCP1)

Thermogenin (UCP1) creates a proton channel that allows H+ to leak back across the inner mitochondrial membrane without going through ATP synthase, dissipating the proton gradient as heat.

Which statement correctly describes the difference between P680 and P700 in the light reactions?

Answer: P680 is the reaction center of PSII with a stronger oxidizing power; P700 is the reaction center of PSI with a weaker oxidizing power

P680 in PSII has a stronger oxidizing power (more positive redox potential) allowing it to oxidize water, while P700 in PSI has a weaker oxidizing power but produces a powerful reductant to ultimately reduce NADP+.