Citric Acid Cycle (Deevska)

Question 1

3 names of Citric Acid Cycle

Answer 1

Krebs cycle, citric acid cycle, TCA cycle

Question 2

Where does TCA cycle intersect with other metabolic pathways?

Answer 2

Catabolic pathways- breakdown of amino acids provides TCA cycle intermediates
Anabolic- some TCA intermediates feed into making other amino acids.

Question 3

What provides most of the energy in the TCA cycle?

Answer 3

NADH and FADH2. These produce ATP through oxidative phosphorylation…
located in mitochondrial matrix very close to ETC…

Question 4

List the steps of TCA cycle…

Answer 4

Pyruvate–Acetyl CoA+Oxaloacetate–Citrate–Isocitrate–Alpha-ketoglutarate–Succinyl CoA–Succinate– Fumarate–Malate–Oxaloacetate…

Question 5

List the irreversible steps of TCA cycle…

Answer 5

1. Acetyl CoA+Oxaloacetate to Citrate via Citrate synthase
2. Isocitrate to Alpha-Ketoglutarate via Isocitrate Dehydrogenase
3. alpha-ketoglutarate to Succinyl CoA via alpha-ketoglutarate dehydrogenase complex

Question 6

What are the 5 different cofactors and what vitamin are they derived?

Answer 6

Thaimine pyrophosphate, TPP (from Thiamine, Vit B1)
Lipoamide (synthesized in human cells)
Coenzyme-A (CoA) (from pantothenic acid, vitamin B5)
FAD (from riboflavin, vitamin B2)
NAD+ (from nicotinamide, vitamin B3/niacin)

Question 7

What 5 molecules activate PDH?

Answer 7

Pyruvate
NAD+
ADP
Ca2+ (muscle)
CoA

Question 8

What 3 molecules deactivate PDH?

Answer 8

Acetyl CoA
NaDH
ATP

Question 9

What is the goal of steps 1,2,3, and 4?

Answer 9

Goal is to degrade Acetyl CoA…

Question 10

Citrate is a feedback inhibitor of what?

Answer 10

PFK-1 Phosphofructokinase-1 used in glycolysis

Question 11

Citrate is a precursor for ______ synthesis?

Answer 11

Fatty acid

Question 12

What is the enzyme of isomeerization of citrate?

Answer 12

Aconitase… Works both directions.

Question 13

What is the Rate Limiting step of TCA cycle?

Answer 13

Step 3… Oxidative phosphorylation of isocitrate. Yields the first NADH. Releases 1 CO2 and 1 C atom lost.

Question 14

alpha ketoglutarate is also produced from what amino acid?

Answer 14

From the metabolism of glutamate.

Question 15

Which step yields the second NADH releases 1 CO2?

Answer 15

alpha ketoglutarate to succinyl CoA via alpha ketoglutarate dehydrogenase complex.

Question 16

What can cause serious central nervous system problems?

Answer 16

Deficiency of niacin or thiamine

Question 17

Alpha ketoglutarate and PDH both require multiple _______ derived from vitamins.

Answer 17

coenzymes

Question 18

alpha-ketoglutarate dehydrogenase complex and PDH both require ______acid.

Answer 18

Lipoic Acid

Question 19

Arsenic poisoning forms a stable_____ with the -SH group in lipoic acid making it unavialable to serve as coenzyme.

Answer 19

thiol

Question 20

What affects the brain and can cause neurological disturbances and even death?

Answer 20

Arsenic poisoning

Question 21

What step in CTA cycle is coupled with phosphorylation of GDP to GTP?

Answer 21

Cleavage of Succinyl CoA to Succinate via Succinate thiokinase… (Substrate level phosphorylation)

Question 22

What step requires FAD?

Answer 22

Oxidation of succinate to fumarate… FADH2 is made… Embedded in inner mitochondrial membrane…

Question 23

What step is a hydration?

Answer 23

Fumarate to L-Malate via fumarase.

Question 24

What steps produce NADH?

Answer 24

step on both sides of alpha ketoglutarate (think about them) and malate to oxaloacetate…

Question 25

How many times will TCA cycle run?

Answer 25

Will run twice because there are two pyruvates…??? not sure… check this…

Question 26

How many ATP are synthesiezed for every NADH?

How many for FADH2?

Answer 26

~3 ATP for NADH.

~2 for FADH2

Question 27

Total ATP breakdown from ETC:
Glycolysis:
TCA:
PDH:

Answer 27

Glycoysis: 2 NADH= 6 ATP
TCA: 3 NADH=9ATP 1FADH2=2 ATP == 11ATP(x2)
PDH: 1NADH= 3 ATP (x2)
38 TOTAL ATP per glucose molecule