Citric Acid Cycle

Question 1

What is the citric acid cycle/tricarboxylic acid cycle/krebs cycle?

Answer 1

The common pathway by which all fuel molecules are broken down into carbon dioxide and water

Question 2

How is acetyl Coenzyme A formed?

Answer 2

Coenzyme A formed from pantotheinic acid forms a high energy bond with pyruvate. During this reaction TWO molecules of NADH are given off and TWO molecules of CO2 are also produced.

Question 3

Describe how the citric acid cycle works

Answer 3

1) Condensation of the Acetyl group (2 carbons) from acetyl Coenzyme A with oxaloacetate (4 carbons) to from citrate (6 carbons)
2) Citrate is then decarboxylated (removal of CO2) twice to form a 5-Carbon then a 4-Carbon molecule. It is then further oxidised untill it forms the origional 4-Carbon molecule oxaloacetate

Question 4

During the citric acid cycle what compounds are formed

Answer 4

• Two molecules of Carbon Dioxide
• One molecule of GTP (which can instantly be converted into a molecule of ATP)
• Three molecules of NADH
• One molecule of FADH2

Question 5

What is the full name for FAD, what is it’s role and what vitamin is it derived from?

Answer 5

• Flavin Adenine Dinucleotide
• Role is to shuttle electrons to the electron transport chain
• Produced from riboflavin (Vit B2)

Question 6

Where does the breakdown of pyruvate and the citric acid cycle occur?

Answer 6

In the matrix of the mitochondria

Question 7

What does the electron transport chain consist of?

Answer 7

Three large protein complexes which are linked together by molecules that shuttle electron to the next complex

Question 8

What feeds electrons into the electron transport chain? and at what point do they feed these electrons

Answer 8

NADH and FADH2. NADH feeds electrons into the start of the chain (complex one). FADH2 feeds electrons to the electron shuttle after complex one

Question 9

The respirator chain is a target for what chemical agents?

Answer 9

Rotenon, Antimycin A and cyanide and carbon monoxide which will block the final step (where hydrogen combines with oxygen to form water

Question 10

What occurs in the electron transport chain?

Answer 10

Electrons are passed down the chain from higher energy states to slower energy states and therefore provide energy to move hydrogen ions across the membrane into the intermembrane space. This generates a proton gradient.

Question 11

What is used to generate ATP?

Answer 11

The return flow of hydrogen ions through ATP synthase in the inter mitochondrial membrane

Question 12

The oxidation of NADH and FADH2 generates hoe many molecules of ATP?

Answer 12

NADH - 3 molecules

FADH2 - 2 molecules

Question 13

How any molecules of ATP and NADH are produced by glycolysis?

Answer 13

2 of ATP (net energy) and 2 of NADH

Question 14

How any molecules of ATP, NADH and FADH2 are produced by the citric acid cycle?

Answer 14

2 of ATP
6 of NADH
2 of FADH

Question 15

What is the maximum yield of ATP after mitochondrial oxidative phosphorylation

Answer 15

4 ATP from other parts of cycle.
2 cytoplasmic NADH x 1.5-2.5ATP/NADH - 3-5 ATP
8 mitochondrial NADH x 2.5ATP/NADH- 20 ATP
2 FADH2 x 1.5ATP/FADH2 - 3 ATP

SO TOTAL IS 30-32 ATP