TCA cycle

Question 1

Krebs cycle

Answer 1

Citrate acid plays a role in Krebs cycle
It is the central metabolic pathway that connects fats, proteins and carbohydrates.
It generates NADH and FADH2 that can be used to generate more ATP.
It occurs inside the mitochondrial matrix, where ETC is also occuring
- releases stored energy of fat, proteins and carbohydrates through oxidation
- provide many raw materials used elsewhere in the body such as amino acids precursors and NADH

Question 2

Can I keep selling substances for money, officer

Answer 2

Citrate, isocitrate, alpha ketoglutarate, succinyl-CoA, succinate, fumarate, malate and oxaloacetate.

Question 3

Step 1 citrate synthesis, synthase

Answer 3

Oxaloacetate (4C) from the 8th step + acetyl CoA + water forms citrate.
       COO-
          I
       CH2
          I
OH - C - COO-
          I
        CH2
          I
       COO-
Tricarboxylic acid, with alpha C bonded to 2 CH2, OH and COO-.
In this reaction, acetyl-CoA is removed
In this reaction, it is irreversible.
The enzyme is called citrate synthase

Question 4

Step 2 Citrate hydroxylation, isomerization

Answer 4

COO-
          I
       CH2
          I
   H - C - COO-
          I
HO - C - H
          I
       COO-
The OH of citrate is swapped out with H from CH2
Aconitase is the enzyme, water is added and then removed.
In this isomerization, it is reversible

Question 5

Step 3 Alpha ketoglutarate synthesis, dehydrogenase

Answer 5

COO-
    I
 CH2
    I
 CH2
    I
   C = O
    I
COO-
Alpha ketoglutarate (5C)
Isocitrate dehydrogenase is the enzyme
1 NADH, H+ and CO2 are the byproducts.
The reaction is also rate limiting and irreversible. Due to IDH being a allosteric enzyme.
Note produces NADH

Question 6

Step 4 Succinyl-CoA formation, oxidative decarboxylation of alpha ketoglutarate
Dehydrogenase

Answer 6

COO-
   I
 CH2
   I
 CH2
   I
  C = O
   I
 SCoA
Succinyl-CoA (4C)
Alpha ketoglutarate dehydrogenase is the enzyme
Generates NADH, an irreversible reaction
NADH + H+ + CO2 are the products
SCoA is added, and replaces the COO-
This reaction is irreversible.
Note produces NADH, 2.5 ATP equivalent

Question 7

Step 5 Succinate synthesis

Succinyl-CoA Synthase

Answer 7

COO-
 I
CH2
 I
CH2
 I
COO-
Succinate 
The enzyme is succinyl-CoA synthetase 
GTP is formed from GDP + Phosphate ion input into the reaction.
SCoA is released, Succinyl-CoA is hydrolyzed.
From O = C - SCoA to COO-
Substrate level phosphorylation due to high energy thioester bond in succinyl-CoA
Note produce GTP, GTP is ATP equivalent

Question 8

Step 6 Fumarate formation

Dehydrogenase

Answer 8

COO-
   I
 CH
   II
 CH
    I
COO-
Fumarate 
The enzyme is called succinate dehydrogenase.
FAD is converted into FADH2 in this reaction
FAD is a prosthetic group on the enzyme succinate dehydrogenase. FADH2 is 1.5 ATP
Single bond between both CH2 
Hydration of a C-C bond
Note produce FADH2

Question 9

Step 7 Malate formation, Fumarase, Hydration

Answer 9

COO-
           I
OH  - C - H
           I
         CH2
           I
        COO-
    Malate
Water is added to fumarate, OH is added to alpha C, forming COHH. H is added to CH, forming CH2
This reaction is reversible

Question 10

Step 8 Oxaloacetate formation, dehydrogenase

Answer 10

COO-
   I
  C = O
   I 
  CH2
   I
COO-
Oxaloacetate
2 H atoms is released from malate, C = O is formed NAD+ becomes oxidized to NADH and H+.
Malate dehydrogenase 
Products are oxaloacetate, NADH+ and H+.

Question 11

Which step produces GTP

Answer 11

Step 5 from succinyl CoA to succinate

Question 12

Which step produces FADH2

Answer 12

Step 6 Succinate to fumarate, succinate dehydrogenase

Question 13

Which step produces 3 NADH2

Answer 13

Step 3,4 and 8. Isocitrate dehydrogenase, alpha ketoglutarate dehydrogenase and malate dehydrogenase.

Question 14

Anabolic intermediates of Krebs cycle

Answer 14

Each intermediate contains 3 reactive groups

Question 15

Difference between anaerobic and aerobic respiration

Answer 15

Anaerobic respiration such as lactic acid and alcohol fermentation only yield 2 ATPs
Aerobic respiration from glycolysis to krebs cycle to electron transport chain yield 36 ATPs