Krebbs Cycle

Question 1

What happens to pyruvate before it can enter the Krebbs cycle?

Answer 1

pyruvate must be converted into acetyl coenzyme A

Question 2

What molecules are created when pyruvate is converted into acetyl CoA?

Answer 2

2 x Acetal CoA

CO₂

NADH

Question 3

What does the pyruvate dehydrogenase complec do?

Answer 3

converts pyruvate into acetyl CoA, CO₂, and NADH

Question 4

What are the three reactions of pyruvate dehydronase complex?

Answer 4

1. The pyruvates carboxyl group is removed creating a CO₂
2. The remaining 2-carbon fragment is oxidized, forming acetyl. The extracted electrons are transferrred to NAD+. A transport protein allows protein to tracerse from the cytosol through a channel in the outer mitochondrial membrane.
3. acetyl is attached to co-enzyme A forming acetyl-CoA

Question 5

What molecules are made when pyruvate is oxidised ?

Answer 5

2 acetyl CoA

2 CO₂

2 NADH

Question 6

What other names are there for the Krebbs cycle?

Answer 6

citric acid cycle

tricarboxylic cycle

Question 7

How many molecules of:

NADH

FADH₂

ATP

are produced in once cycle of the Krebbs cycle?

Answer 7

1 ATP

3 NADH

1 FADH₂

Question 8

How many steps does the Krebbs cycle have?

Answer 8

8

Question 9

Step one of the Krebbs:

enzyme responsible

what happens?

Answer 9

citrate synthase combines acetyl CoA and Oxaloacetate to form citrate

Question 10

Step 2 Krebbs:

What enzyme

What happens?

Answer 10

Aconitase converts citrate into its isomer Isocitrate

Question 11

Step 3: Krebs Cycle:

What enzymes?

What happens?

Answer 11

Isocitrate is oxidises by the enzyme iscocitrate dehydrogenase forming alpha-ketogluterate

NAD+ is reduced to NADH

CO₂ molecule is produced

Question 12

What does isotrate dehydrogenase do?

Answer 12

removes hydrogen atoms from molecules

Question 13

Step 4 Krebbs cycle:

What enzymes

What happens

Answer 13

The enzyme complex alpha-ketogluterate dehydrogenase attaches CoA to alpha-ketogluterate by an unstable bond to form succinyl CoA.

NAD+ is reduced to NADH

CO₂ molecule produced.

Question 14

Step 5: Krebbs Cycle

What enzymes

What happens

Answer 14

The coenzyme A is now displaced by a free phosphate group which is imediatly transferred to GDP forming GTP by the enzyme succinyl CoA synthase

The GTP is converted into ATP by nucleoside-diphosphate Kinase

Question 15

Step 6 Krabbs

What enzymes

What happens

Answer 15

The enzyme succinate dehydrogenase oxidizes succinate by transfering 2 hydrogens to FAD forming FADH₂ and fumerate

Question 16

What is FAD

Answer 16

flavin adenine dinucleotide

Question 17

Step 7: Krebbs cycle:

What enzyme

What happens

Answer 17

The enzyme fumerase facilitates the addition of a water moeulce to fumerate forming Malate

Question 18

Step 8: Krebbs

What enzyme

What happens

Answer 18

The enzyme Malate dehydrogenase oxidises Malate to reduce NAD+ to NADH and regenerates Oxaloacetate

Question 19

What is the ballance sheet of the Krebbs cycle per acetyl CoA? and at what steps are they released?

CO₂

GTP

NADH

FADH₂

Answer 19

What is the ballance sheet of the Krebbs cycle per acetyl CoA? and at what steps are they released?

2: CO₂ (steps 3 & 4)
1: GTP or ATP (steps 5)
3: NADH (steps 3,4, & 8)
1: FADH₂ (step 6)