5.7.4 the link reaction & Krebs cycle

Question 1

decarboxylation

Answer 1

removal of carboxyl group from substrate molecule

Question 2

dehydrogenation

Answer 2

removal of hydrogen atoms from substrate molecule

Question 3

substrate-level phosphorylation

Answer 3

production of ATP from ADP & Pi during glycolysis & Krebs cycle

Question 4

where is pyruvate from glycolysis transported to

Answer 4

across outer & inner mitochondrial membranes via specific pyruvate-H+ symport into the matrix

Question 5

symport

Answer 5

transport protein that transports 2 ions or molecules in same direction

Question 6

what happens to pyruvate in the links reaction & Krebs cycle

Answer 6

1. pyruvate converted into 2C acetyl group during link reaction
2. acetyl group oxidised during Krebs cycle

Question 7

where does the link reaction occur

Answer 7

mitochondrial matrix

Question 8

what happens to pyruvate in the link reaction

Answer 8

becomes decarboxylated & dehydrogenated, catalysed by pyruvate dehydrogenase

Question 9

is ATP produced in the link reaction

Answer 9

no

Question 10

describe the steps involved within link reaction

Answer 10

1. carboxyl group removed from pyruvate - decarboxylation
2. decarboxylation & dehydrogenation of pyruvate (to produce NADH) produces acetyl group
3. acetyl group combines with coenzyme A producing acetyl coenzyme A

Question 11

how many times does the link reaction occur for 1 glucose molecule

Answer 11

2x (2 pyruvate produced in glycolysis)

Question 12

products of the link reaction for 1 molecule of glucose

Answer 12

• 2 acetyl CoA
• 2 carbon dioxide (CO2)
• 2 NADH

Question 13

link reaction for 2 molecules of pyruvate (1 glucose molecule) as an equation

Answer 13

2 pyruvate + 2NAD + 2CoA —> 2CO2 + 2NADH + 2 acetyl CoA

Question 14

where does the Krebs cycle occur

Answer 14

mitochondrial matrix

Question 15

role of reduced coenzymes produced in Krebs cycle

Answer 15

carry hydrogen atoms to electron transport chain on cristae (oxidative phosphorylation)

Question 16

describe the 6 steps of the Krebs cycle

Answer 16

1. acetyl group (2C) from acetyl CoA combines with 4C oxaloacetate = citrate (6C)
2. citrate decarboxylated & dehydrogenated producing 5C compound & one molecule of carbon dioxide, as well as NADH
3. 5C compound decarboxylated & dehydrogenated producing 4C compound & one molecule of carbon dioxide, as well as NADH
4. substrate-level phosphorylation producing 1 molecule of ATP
5. 4C compound dehydrogenated producing different 4C compound & FADH
6. rearrangement of atoms in 4C compound (catalysed by isomerase enzyme) followed by dehydrogenation, regenerate a molecule of oxaloacetate & cycle continue

Question 17

how many turns of Krebs cycle for 1 molecule of glucose

Answer 17

2

Question 18

products of Krebs cycle for 1 glucose

Answer 18

for 1 glucose:
- 4 carbon dioxide
- 6 NADH
- 2 FADH
- 2 ATP

Question 19

name 4 different coenzymes

Answer 19

• FAD
• NAD
• ATP
• acetyl coenzymes A