18 Questions
What is the yield of ATP per NADH in liver cells and heart cells?
2.5 ATP
What is the maximum number of ATP produced by oxidative phosphorylation per glucose molecule?
28 ATP
What is the energy released per mole of glucose under standard conditions?
686 kcal/mol
What is the approximate efficiency of cellular respiration?
34%
What is the function of the proton-motive force in the mitochondria?
To drive other kinds of work
What is the purpose of the uncoupling protein in brown fat?
To generate heat
What is the result of the buildup of ATP in cells?
Decreased cellular respiration
What is the purpose of the adaptation in hibernating mammals?
To generate heat
What is the approximate percentage of chemical energy in glucose that is lost as heat?
66%
What is the advantage of the adaptation in hibernating mammals?
It allows for maintenance of internal body temperature
Why can't we state an exact number of ATP molecules generated by the breakdown of one molecule of glucose?
Because phosphorylation and the redox reactions are not directly coupled to each other.
What is the approximate number of H+ that must reenter the mitochondrial matrix via ATP synthase to generate 1 ATP?
4 H+
How many ATP molecules can be generated by a single molecule of NADH?
2.5 ATP
How many ATP molecules can be generated by a single molecule of FADH2?
1.5 ATP
Why does the ATP yield vary slightly depending on the type of shuttle used?
Because the shuttle affects the proton-motive force generated.
What is the purpose of electron shuttle systems?
To transport electrons from the cytosol into the mitochondrion.
What happens to the electrons of NADH captured in glycolysis?
They are conveyed into the mitochondrion by electron shuttle systems.
How many ATP molecules can result from each NADH that was originally generated in the cytosol in brain cells?
1.5 ATP
Study Notes
Reasons for Inexact ATP Yield
- Three reasons for inexact ATP yield: phosphorylation and redox reactions not directly coupled, ATP yield varies depending on electron shuttle used, and proton-motive force used for other work
- Ratio of NADH to ATP molecules not a whole number
ATP Yield from NADH
- 1 NADH generates enough proton-motive force for 2.5 ATP synthesis
- Each FADH2 generates enough proton-motive force for 1.5 ATP synthesis
- ATP synthesis takes into account energetic cost of moving ATP from mitochondrion to cytosol
Electron Shuttle Systems
- Mitochondrial inner membrane impermeable to NADH
- Electrons from NADH in cytosol conveyed into mitochondrion by electron shuttle systems
- Electrons passed to FAD or NAD+ in mitochondrial matrix
- ATP yield varies depending on electron shuttle used (1.5 ATP or 2.5 ATP per NADH)
Proton-Motive Force and ATP Yield
- Proton-motive force used for other work, reducing ATP yield
- Maximum ATP yield from oxidative phosphorylation is 28 ATP, plus 4 ATP from substrate-level phosphorylation (total 32 ATP or 30 ATP with less efficient shuttle)
Efficiency of Respiration
- Efficiency of respiration is percentage of chemical energy in glucose transferred to ATP
- 7.3 kcal per mole of ATP stored, with 686 kcal of energy released per mole of glucose
- Efficiency of respiration is approximately 34%
Cellular Respiration and Energy Conversion
- Cellular respiration remarkably efficient in energy conversion
- Comparison to automobile efficiency (25%)
- Remaining energy lost as heat, used to maintain body temperature and dissipated through sweating and cooling mechanisms
Hibernation and Reduced Metabolic Efficiency
- Hibernating mammals reduce metabolic efficiency to generate heat without ATP production
- Brown fat tissue contains mitochondria with uncoupling protein, allowing protons to flow back down concentration gradient without generating ATP
- Adaptation allows for heat generation without buildup of ATP, which would shut down cellular respiration
This quiz explores the reasons why the number of ATP molecules generated by glucose breakdown is inexact, including the decoupling of phosphorylation and redox reactions.
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