12.2- LINK REACTION AND KREBS CYCLE

Question 1

What do the pyruvate molecules produced during glycolysis possess?

Answer 1

potential energy that can only be released in Krebs cycle

Question 2

What must first happen to the pyruvate molecules before they enter the Krebs cycle?

Answer 2

must first be oxidised in link reaction

Question 3

Where does the Krebs cycle and link reaction happen in eukaryotic cells?

Answer 3

exclusively inside mitochondria

Question 4

Where is the pyruvate molecules produced in the cytoplasm during glycolysis transported to?

Answer 4

actively transported into matrix of mitochondria

Question 5

What is the pyruvate oxidised to? (link reaction)

Answer 5

acetate

Question 6

How is the pyruvate oxidised to acetate in the link reaction?

Answer 6

3-carbon pyruvate loses a CO2 molecule + 2 hydrogens

these hydrogens accepted by NAD to form reduced NAD, which is later used to produce ATP

Question 7

What does the 2-carbon acetate combine with and what does this produce? (link reaction)

Answer 7

combines with molecule called coenzyme A (CoA) to produce compound called acetylcoenzyme A

Question 8

What is the overall equation for the link reaction?

Answer 8

pyruvate + NAD + CoA -> acetyl CoA + reduced NAD + CO2

Question 9

What does the Krebs cycle involve?

Answer 9

series of oxidation-reduction reactions that happen in matrix of mitochondria

Question 10

What happens to the 2-carbon acetylcoenzyme A from the link reaction? (Krebs cycle)

Answer 10

loses CO2 + hydrogen to give 4-carbon molecule to produce 6-carbon molecule

Question 11

In a series of reactions, what happens to the 6-carbon molecule?

Answer 11

loses CO2 + hydrogen to give 4-carbon molecule + single molecule of ATP produced as a result of substrate-level phosphorylation

Question 12

For each molecule of pyruvate, what does the link reaction and Krebs cycle produce? (3)

Answer 12

reduced coenzymes i.e. NAD + FAD

1 molecule of ATO

3 molecules of CO2

Question 13

What do reduced coenzymes such as NAD + FAD have the potential to do?

Answer 13

potential to provide energy to produce ATP molecules by oxidative phosphorylation and so are important products of Krebs cycle

Question 14

How many pyruvate molecules are produced for each original glucose molecule?

Answer 14

2 pyruvate molecules

Question 15

Are coenzymes enzymes?

Answer 15

no

Question 16

What are coenzymes?

Answer 16

molecules that some enzymes require to function

Question 17

What role do coenzymes play in photosynthesis and respiration?

Answer 17

carry hydrogen atoms form one molecule to another

Question 18

Where is NAD, FAD and NADP important?

Answer 18

NAD- throughout respiration
FAD- Krebs cycle
NADP- photosynthesis

Question 19

What does NAD work with in respiration and what does it do?

Answer 19

dehydrogenase enzymes that catalyse removal of hydrogen atoms from substrates + transfer them to other molecules involved in oxidative phosphorylation

Question 20

Significance of the Krebs cycle- what does it break down?

Answer 20

breaks down macromolecules into smaller ones- pyruvate broken down into CO2

Question 21

Significance of the Krebs cycle- what does it produce?

Answer 21

produces hydrogen atoms that are carried by NAD to electron transfer chain + provide energy for oxidative phosphorylation
this leads to production of ATP that provides metabolic energy for cell

Question 22

Significance of the Krebs cycle- what does it regenerate?

Answer 22

regenerates 4-carbon molecule that combines with acetylcoenzyme A, which would otherwise accumulate

Question 23

Significance of the Krebs cycle- what is it a source of?

Answer 23

source of intermediate compounds used by cells in manufacture of other important substances i.e. fatty acids, amino acids + chlorophyll