M1: Glycolysis Part 2 L3

Question 1

How is ATP energy stored in the cell?

Answer 1

It’s stored as creatine phosphate.

Question 2

Why is ATP stored as creatine phosphate in the cell?

Answer 2

Because cells cannot store free ATP since it inhibits ATP synthase. Creatine phosphate allows for quick access of ATP when it is needed.

Question 3

When is creatine phosphate made and describe the process of its production.

Answer 3

It’s made in times of rest when we don’t need abundant ATP. When ATP is made by ATP synthase in the matrix of the mitochondria, it is then transported to the other side of the membrane by the AAC carrier (ATP/ADP carrier). It is then used as a substrate for creatine kinase along with creatine to produce creatine phosphate.

Question 4

What’s the second step of glycolysis?

Answer 4

Glucose-6-Phosphate Fructose-6-Phosphate (F6P)

it’s an equilibrium reaction driven by the abundance of substrates (not a regulatory step).

Question 5

What’s step 3 of glycolysis?

Answer 5

Fructose-6-phosphate + ATP –PFK1, Mg2+—> Fructose-1,6-bisphosphate (FBP) + ADP
(PFK1 = phosphofructokinase1)
This step is physiologically irreversible (highly exergonic) and highly regulated.

Question 6

What step of glycolysis commits cells to metabolize glucose?

Answer 6

Step 3: F6P -> FBP by PFK1

Question 7

What are the activators and inhibitors of PFK1?

Answer 7

Allosteric activators: AMP & F2,6BP (Fructose-2,6-bisphosphate)
Allosteric inhibitors: ATP & Citrate

Question 8

Describe the two states of PFK1 and what is bound to it in each state.

Answer 8

Tense inactive state: ATP is allosterically bound (substrate sites not accessible)
Relaxed active state: Relaxed when ATP is removed or when AMP and F2,6BP is bound

Question 9

Is ATP or AMP more potent at modulating PFK1?

Answer 9

AMP -> Overcomes the ATP inhibition of PFK.

Question 10

What does the adenylate kinase enzyme do and what is the reaction?
(see example L3.1 slide 21)

Answer 10

It regenerates ATP from 2 molecules of ADP.

2ADP -> ATP + AMP (reversible)

Question 11

What is the biochemical consequence of adenylate kinase’s function?

Answer 11

It keeps ATP abundant for exercise and generates AMP which activates PFK1 for glycolysis.

Question 12

What inhibits Fructose-1,6-bisphosphatase (FBPase1)?

Answer 12

AMP and Fructose-2,6-Bisphosphate (F2,6BP)

Question 13

What would happen if the PFK and FBPase substrate cycle was not regulated by AMP and F2,6BP?

Answer 13

The cycle would be futile because it would consume ATP.

Question 14

What side reaction of glycolysis makes Fructose-2,6-bisphosphate (byproduct)?

Answer 14

Fructose-6-phosphate ——PFK2——> Fructose-2,6-bisphosphate

Question 15

What is the role of PFK2 (kinase domain) in glycolysis?

Answer 15

It has an indirect role by catalyzing the reaction that makes F-2,6-BP which modulates (activates) PFK1.

Question 16

What are the two domains of PFK2?

Answer 16

Kinase domain (PFK2) and phosphatase domain (FBPase2).

Question 17

Describe what happens to the PFK1 FBPase substrate cycle in the liver after fasting or prolonged exercise.
(see L3.1 slide30)

Answer 17

there is a decease in [blood glucose], which causes an increase in [glucagon] because alpha cells in the pancreas detect low blood glucose and secrete glucagon. This causes a rise in [cAMP] which activates PKA. PKA phosphorylates PFK2, causing it to be inactive (no longer makes F-2,6-BP from F6P). The lack of F-2,6-BP causes the substrate cycle to favour gluconeogenesis.

Question 18

Describe what happens to the PFK1 FBPase substrate cycle in the heart after heart stress.
(see L3.1 slide30)

Answer 18

Increased stress in the heart causes an increase in [epinephrine] which causes an increase in [cAMP] which activates PKA. PKA in the heart, phosphorylates PFK2 which activates it and causes an increase in the production of Fructose-2,6-bisphosphate. F2,6BP activates PFK1 and inactivates FBPase which causes the substrate cycle to favour glycolysis.

Question 19

What is step 4 of Glycolysis?

Answer 19

Fructose-1,6-bisphosphate (FBP) to GAP + DHAP (reversible).

Aldolase cleaves FBP (6 carbons) into two different 3 carbon molecules. This is where the pathway splits.

Question 20

What is step 5 of glycolysis?

Answer 20

GAP —reversibly—> DHAP
Triose phosphate isomerase converts DHAP to GAP because GAP is quickly consumed through glycolysis. Therefore, the reaction is favoured in the direction of GAP production to maintain equilibrium.
1 Glucose makes 2 GAPs.

Question 21

What is step 6 of glycolysis?

Answer 21

GAP + Pi + NAD+ 1,3-Biphosphoglycerate (1,3-BPG) + NADH + H+
GAPDH= Glyceraldehyde-3-phosphate dehydrogenase

This step is where the 2 NADH/glucose in glycolysis comes from.

Question 22

Why is 1,3-BPG a high energy intermediate?

Answer 22

Because it has 2 phosphate groups therefore it is unstable.

Question 23

What is step 7 of glycolysis?

Answer 23

1,3-BPG + ADP –reversibly–> 3-phosphoglycerate (3PG) +ATP

This step produces 2 ATPs per glucose.

Question 24

What is step 8 of glycolysis?

Answer 24

3-phosphoglycerate (3PG) –reversibly–> 2-phosphoglycerate (2PG) by phosphoglycerate mutase

Question 25

What is step 9 of glycolysis?

Answer 25

2-phosphoglycerate (2PG) –reversibly–> phosphoenolpyruvate (PEP) by enolase
PEP is a high energy intermediate.

Question 26

What type of intermediate is used in order to generate ATP?

Answer 26

A high energy intermediate.

Question 27

What is step 10 of glycolysis?

Answer 27

phosphoenolpyruvate (PEP) + ADP + Mg2+ + K+ —- pyruvate kinase (PK)—-> pyruvate +ATP
Irreversible reaction.
Generation of 2ATPs and 2 pyruvates/glucose.

Question 28

What allosteric modulators regulate pyruvate kinase?

Answer 28

Activator: Fructose-1,6-bisphosphate
Inhibitor: ATP

Question 29

What hormonal modulators inhibit pyruvate kinase (PK) in the liver?

Answer 29

Inhibitor: Glucagon (increase in glucagon increases cAMP which activates PKA which phosphorylates PK which inhibits it).

Question 30

What is faster at producing ATP: anaerobic glycolysis or mitochondrial oxidative phosphorylation?

Answer 30

Anaerobic glycolysis.

Question 31

How much ATP is made from aerobic glycolysis + mitochondrial oxidative phosphorylation?

Answer 31

32 ATP

Question 32

How much ATP is generated from anaerobic glycolysis?

Answer 32

2ATP

Question 33

Explain how pyruvate is turned into lactate in the muscle in the absence of oxygen.

Answer 33

Pyruvate + NADH —> L-Lactate + NAD+

Question 34

What happens to lactate once it is made in the muscle and what is the cycle called?
(L 4.1 slide28)

Answer 34

It circulates to the liver through the blood where it is turned back into glucose. And the glucose goes back to the muscle to be turned into lactate. This is called the Cori cycle.