TCA & OxPhos

Question 1

What is the TCA cycle also known as?

Answer 1

Krebs or citric acid cycle

Question 2

What are the main roles of the TCA cycle?

Answer 2

• Oxidative role: Produces NADH and FADH2 for ATP generation
• Synthetic role: Provides intermediates for biosynthesis

Question 3

Which coenzymes are produced in the TCA cycle?

Answer 3

• NADH
• FADH2

Question 4

List some essential intermediates provided by the TCA cycle.

Answer 4

• Oxaloacetate (OAA)
• Citrate
• α-Ketoglutarate
• Succinyl-CoA

Question 5

What is the purpose of anaplerotic reactions in the TCA cycle?

Answer 5

To replenish the cycle and prevent depletion of intermediates

Question 6

How is the TCA cycle regulated?

Answer 6

• Substrate supply
• Allosteric effectors
• Control of gene expression

Question 7

What is the significance of ATP in the body?

Answer 7

ATP is not stored in large amounts; it must be continually produced to meet energy demands

Question 8

What does PDH convert pyruvate into?

Answer 8

Acetyl CoA

Question 9

What cofactors are required for the Pyruvate Dehydrogenase Complex (PDC)?

Answer 9

• Thiamine Pyrophosphate (TPP)
• Lipoate
• Coenzyme A (CoA)
• FAD
• NAD⁺

Question 10

What is the first step of the PDC process?

Answer 10

E1 – Decarboxylation of Pyruvate

Question 11

What role does lipoate play in the PDC?

Answer 11

• S-S lipoate: Accepts the acetyl group
• SH-SH lipoate: Becomes reduced and must be reoxidized

Question 12

What is the function of E3 in the PDC?

Answer 12

Regeneration of oxidized lipoate

Question 13

What is the primary function of the citric acid cycle?

Answer 13

Harvesting high-energy electrons from carbon fuels and providing precursors for biosynthesis

Question 14

What type of reactions do dehydrogenases catalyze in the TCA cycle?

Answer 14

Oxidation reactions

Question 15

What happens during the formation of NADH in the TCA cycle?

Answer 15

NAD⁺ is reduced to NADH, often coupled with decarboxylation

Question 16

Which three enzymes act as key regulatory checkpoints in the TCA cycle?

Answer 16

• Pyruvate Dehydrogenase (PDH)
• Isocitrate Dehydrogenase (IDH)
• ATP Synthase

Question 17

What inhibits Pyruvate Dehydrogenase (PDH)?

Answer 17

• High ATP
• NADH
• Acetyl-CoA

Question 18

What activates Isocitrate Dehydrogenase (IDH)?

Answer 18

ADP

Question 19

In which part of the cell does oxidative phosphorylation occur?

Answer 19

Inner mitochondrial membrane

Question 20

What is the role of the malate-aspartate shuttle?

Answer 20

Transfers electrons from cytosolic NADH into the mitochondria

Question 21

What is produced when malate is oxidized back to oxaloacetate in the mitochondria?

Answer 21

Mitochondrial NADH

Question 22

How does the glycerol 3-phosphate shuttle function?

Answer 22

Transfers electrons from NADH to FAD in the mitochondria, producing FADH2

Question 23

What is the total proton pumping summary for NADH in the electron transport chain?

Answer 23

• Complex I → 4 H⁺
• Complex III → 4 H⁺
• Complex IV → 2 H⁺
  Total: 10 H⁺ per NADH

Question 24

Why does Complex II not pump protons?

Answer 24

It does not release enough energy for active proton translocation

Question 25

How many ATP does FADH2 yield per molecule?

Answer 25

~1.5 ATP

Question 26

What is the only enzyme that participates in both the citric acid cycle and the electron transport chain?

Answer 26

Succinate dehydrogenase (Complex II)

Question 27

What is the role of Complex II (Succinate Dehydrogenase) in cellular respiration?

Answer 27

It participates in both the citric acid cycle and the electron transport chain, oxidizing succinate to fumarate and transferring electrons to CoQ. ## Footnote Complex II does not pump protons but is crucial for linking the TCA cycle with oxidative phosphorylation.

Question 28

How many ATP does FADH₂ yield compared to NADH?

Answer 28

FADH₂ yields ~1.5 ATP per molecule, while NADH yields ~2.5 ATP. ## Footnote This difference is due to the bypass of Complex I by FADH₂.

Question 29

What are the consequences of succinate dehydrogenase (SDH) dysfunction?

Answer 29

It can lead to severe metabolic and mitochondrial disorders, including neurodegenerative diseases, metabolic syndromes, and cancers. ## Footnote Mutations in SDH genes (SDHA, SDHB, SDHC, SDHD) are linked to these conditions.

Question 30

What is the function of the proton gradient in oxidative phosphorylation?

Answer 30

It creates a concentration and charge difference across the mitochondrial membrane, driving ATP synthesis through ATP synthase. ## Footnote Protons are pumped from the mitochondrial matrix to the intermembrane space by Complexes I, III, and IV.

Question 31

What is the role of ATP-ADP translocase?

Answer 31

It facilitates the exchange of ATP and ADP across the mitochondrial membrane as an antiporter. ## Footnote This ensures a continuous supply of ADP for ATP production.

Question 32

What is the effect of dinitrophenol on oxidative phosphorylation?

Answer 32

It uncouples oxidative phosphorylation by causing proton back diffusion, lowering the voltage. ## Footnote Dinitrophenol is a well-known uncoupler.

Question 33

What is the impact of cyanide on cellular respiration?

Answer 33

It inhibits cytochrome c oxidase (Complex IV), blocking the electron transport chain. ## Footnote This results in a halt of ATP production.

Question 34

What alternative pathway can pyruvate take instead of being converted to Acetyl-CoA?

Answer 34

Pyruvate can be carboxylated to form oxaloacetate (OAA) by the enzyme Pyruvate Carboxylase. ## Footnote This reaction requires biotin as a cofactor.

Question 35

How is PDH activated?

Answer 35

PDH is active when PDH phosphatase dephosphorylates it, which occurs when ATP is low or insulin is high. ## Footnote This promotes energy production.

Question 36

What inhibits PDH activity?

Answer 36

PDH is inhibited when it is phosphorylated by PDH kinase in response to high ATP, NADH, or acetyl-CoA levels. ## Footnote This conserves energy when sufficient energy is available.

Question 37

What are the outputs of the TCA cycle related to NADH formation?

Answer 37

NADH is formed in three steps: * Isocitrate → α-Ketoglutarate (via Isocitrate Dehydrogenase) * α-Ketoglutarate → Succinyl-CoA (via α-Ketoglutarate Dehydrogenase) * Malate → Oxaloacetate (via Malate Dehydrogenase) ## Footnote These reactions involve oxidative decarboxylation and generate CO₂.

Question 38

How is FADH₂ formed in the TCA cycle?

Answer 38

FADH₂ is formed from the oxidation of succinate to fumarate by Succinate Dehydrogenase. ## Footnote This is the only step in the cycle that produces FADH₂.

Question 39

What is produced during substrate-level phosphorylation in the TCA cycle?

Answer 39

GTP is produced from the conversion of Succinyl-CoA to Succinate via Succinyl-CoA Synthetase. ## Footnote GTP can be converted to ATP.

Question 40

What regulates the flux through the TCA cycle and oxidative phosphorylation?

Answer 40

It is regulated by substrate supply, allosteric effectors, covalent modification, and protein synthesis. ## Footnote This regulation ensures ATP synthesis matches ATP hydrolysis.

Question 41

What is the significance of brown adipose tissue?

Answer 41

It generates body heat and is especially abundant in newborns and hibernating mammals. ## Footnote Brown adipose tissue plays a role in thermoregulation.

Question 42

What is the primary function of the TCA cycle?

Answer 42

The TCA cycle is responsible for the oxidation of acetyl-CoA to produce reducing equivalents (NADH and FADH₂) for the electron transport chain. ## Footnote This process also generates CO₂ as a waste product.

Question 43

Fill in the blank: The enzyme that catalyzes the conversion of pyruvate to oxaloacetate is _______.

Answer 43

Pyruvate Carboxylase

Question 44

True or False: Complex II pumps protons across the mitochondrial membrane.

Answer 44

False