Questions for TCA, ETC, Oxidative Phosphorylation

What happens to hepatic citrate levels when pyruvate dehydrogenase is inhibited during fasting

Citrate production is reduced as less acetyl-CoA is available from pyruvate.

Why is citrate exported from the mitochondria into the cytosol in the fed state

To serve as a carbon source for fatty acid synthesis and a signal to inhibit glycolysis.

How does the liver prevent osmotic swelling from excess G6P accumulation

By converting G6P into glycogen or funneling it into glycolysis or the pentose phosphate pathway.

Why is allosteric regulation of PFK-1 by ATP considered fast and reversible

Because ATP binding directly alters the enzyme's conformation without requiring signaling cascades.

What enzyme of glycolysis is inhibited by high levels of ATP

Phosphofructokinase-1 (PFK-1).

Why is NAD+ regeneration important in glycolysis

Because glyceraldehyde-3-phosphate dehydrogenase requires NAD+ to produce 1

How does the cell regenerate NAD+ when oxygen is limited

By converting pyruvate to lactate via lactate dehydrogenase.

How does G6PD deficiency affect the cell’s response to oxidative stress

It reduces NADPH production

What two enzymes produce NADPH for cellular use

Glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase.

What is NADPH used for in the cell

It is used in biosynthetic reactions

What is the effect on ATP yield when DHAP is converted to G3P

Two NADH and four ATP are produced from the two G3P molecules.

What happens to ATP yield when triose phosphate isomerase is absent

Only one G3P is produced

What is the fate of DHAP when it is reduced to glycerol phosphate

It is used for triglyceride biosynthesis

What happens to glycolysis when NAD+ is unavailable

Glycolysis halts at the G3P step due to lack of NAD+ for the dehydrogenase reaction.

What is the consequence of shunting 1

3-BPG to 2

How does the TCA cycle respond to low energy states

Isocitrate dehydrogenase and α-KG dehydrogenase are activated by ADP and Ca2+.

Why is the electron transport chain tightly coupled to ATP synthesis

To ensure efficient use of the proton gradient for ATP production.

What does the chemiosmotic hypothesis propose

That the proton gradient across the inner mitochondrial membrane drives ATP synthesis.

How many protons are required to produce 3 ATP via ATP synthase

About 10 protons per complete F₀ rotation.

How is ATP exported from the mitochondria to the cytosol

Through an electrogenic antiport that swaps ATP out for ADP in.

Why does Complex II of the ETC not pump protons

Because it only transfers electrons from FADH₂ to coenzyme Q without contributing to the proton gradient.

How does liver convert all excess glucose to citrate and what happens to the citrate

Glucose is metabolized via glycolysis to pyruvate which enters mitochondria and becomes acetyl CoA that combines with oxaloacetate to form citrate which exits the mitochondria and is used for fatty acid and cholesterol synthesis

How does the hepatocyte manage the osmotic pressure of increased osmolality of G6P

It rapidly converts G6P into downstream glycolytic intermediates or stores it as glycogen to reduce osmotic stress

In glycolysis how does elevated ATP feedback to limit cellular rate of consumption of glucose

ATP allosterically inhibits phosphofructokinase 1 which is the rate determining enzyme in glycolysis

What enzyme of glycolysis requires NAD+ and how is cytosolic NAD+ restored when glycolysis produces NADH

Glyceraldehyde 3 phosphate dehydrogenase requires NAD+ and NAD+ is regenerated via the reduction of pyruvate to lactate or via the mitochondrial malate shuttle

What two enzymes produce NADPH for cellular use and what is NADPH used for in the cell

Glucose 6 phosphate dehydrogenase and 6 phosphogluconate dehydrogenase produce NADPH which is used for reductive biosynthesis and protection against oxidative stress

What is the yield of ATP in glycolysis when DHAP isomerizes to a second equivalent of G3P

2 ATP net

What is the yield of ATP in glycolysis when triose phosphate isomerase is not present

0 ATP net

What is the yield of ATP in glycolysis when DHAP is reduced to glycerol phosphate for TAG biosynthesis

0 ATP net

What is the yield of ATP in glycolysis when NAD+ is unavailable to support oxidation of G3P

0 ATP net

What is the yield of ATP in glycolysis when 1 3 BPG is isomerized to 2 3 BPG inside RBCs

0 ATP net