Glycolysis from handout

Question 1

Describe PFK as a control site in glycolysis

Answer 1

PFK is allosterically inhibited by ATP. Once ATP binds to allosteric sites, the PFK will have reduced affinity towards F6P. Therefore, glycolysis is inhibited, since G6P did not proceed into becoming F6P.

Question 2

Purpose of Muscle Glycolysis

Answer 2

To generate ATP to power contraction

Question 3

How is glycolysis stimulated in relation to the energy charge of the cell?

Answer 3

The energy charge of the cell, which is the ratio of ATP and AMP regulates glycolysis. When there’s a decreased energy charge, there’s an increased demand for ATP.

Question 4

Relation of levels of ATP and the PFK

Answer 4

High levels of ATP may result in the inhibition of PFK and, therefore inhibition of glycolysis.

Question 5

What does a decreased ATP/AMP ratio?

Answer 5

Increases ATP activity.

[This just means that there’s a need for more. MAKE MOREE]

Question 6

What do pH levels do with PFK activity?

Answer 6

decreased pH level = decreased PFK activity

pH decreases during anaerobic. This produces lactic acid excessively, hence the low pH level.

Question 7

What inhibits the hexokinase?

Answer 7

G6P [its product]

This just signals that: I DON’T NEED GLUCOSE NO MORE!

Question 8

What will happen to glucose when Hexokinase is inhibited?

Answer 8

Glucose remains in the blood.

Question 9

What if there’s a high concentration of G6P, what would you assume is happening in the process?

Answer 9

Feedback Inhibition of PFK by G6P: When the concentration of G6P rises, it acts as a feedback inhibitor of PFK. This inhibition slows down the conversion of fructose-6-phosphate (F6P) to fructose-1,6-bisphosphate (F1,6BP), thereby reducing the rate of glycolysis.

Feedback Inhibition of Hexokinase by G6P: Concurrently, the elevated levels of G6P also inhibit hexokinase, the enzyme that phosphorylates glucose to form G6P in the initial step of glycolysis. This inhibition reduces the rate of glucose phosphorylation and further contributes to the buildup of G6P.

Question 10

This controls the efflux (exit) from glycolytic pathway

Answer 10

Pyruvate kinase

Question 11

How is Pyruvate Kinase inhibited?

Answer 11

• ATP [allosterically]
• Alanine

Question 12

How does ATP inhibit PK?

Answer 12

When the energy charge of the cell is high, PK is inhibited

[Note: Too much energy charge means TOO much ATP. No need to produce more]

Question 13

How does Alanine inhibit PK?

Answer 13

Acts as a signal.

The increased/presence of Alanine means Building blocks are abundant.

This is because the inhibition of pyruvate kinase (PK) by alanine is part of a complex regulatory mechanism known as the glucose-alanine cycle, which involves the interconversion of amino acids and glucose intermediates.

Question 14

How does the liver maintain blood glucose?

Answer 14

When there’s an increase in glucose, the liver stores them as glycogen.

When there’s a decreased level of glucose, the liver releases them

Question 15

Explain: “Liver uses glucose to generate reducing power for biosynthesis”

Answer 15

Reducing power such as NADH and NADPH, which are necessary for the synthesis of other molecules

Question 16

Functions of Glycolysis in the liver

Answer 16

1. Maintain blood glucose
2. Generate reducing power for biosynthesis
3. Synthesizing building block for some molecules

Question 17

The enzyme that is primarily responsible for phosphorylation glucose in the liver

Answer 17

Glucokinase

Question 18

When do glucokinase phosphorylate glucose?

Answer 18

ONLY when glucose is abundant

Question 19

How is the low affinity of glucose in the liver necessary?

Answer 19

Because of the low affinity, the liver won’t hold onto the glucose as much. Therefore, it will have the freedom to be used by the brain and muscles first during limited supply.

Question 20

In the liver, this is an allosteric activator of PFK1.

Answer 20

F-2,6-BP

This opposes ATP inhibition.
[F-2,6-P: GO ON PFK1!]

Question 21

Is fructose-2,6-bisphosphate a glycolysis intermediate?

Answer 21

No! It was just synthesized from fructose-6-P by PFK2.

Question 22

PFK2 is a bifunctional enzyme with 2 domains, what are those?

Answer 22

kinase domain
Phosphatase domain

Question 23

In cells with adequate O2 supply, glucose is oxidized into ______.

Answer 23

CO2

Question 24

In cells with no O2 supply, what will happen?

Answer 24

PDH is inhibited by NADH/NAD ratio
pyruvate is reduced into lactic acid allowing the process to continue

Question 25

Aiah had an increased level of Lactic acid but is in a normal condition. What is your assumption?

Answer 25

Aiah is currently exercising hence the elevated lactate

Question 26

What does increased NADH concentration prevent in glycolysis in the liver?

Answer 26

Prevents pyruvate from being oxidized into the TCA cycle.

Pyruvate is directed instead to be reduced as lactic acid

Question 27

If other pathways that use G6P are blocked, what will happen?

Answer 27

G6P is shunted into glycolysis. There’s no other way but into the anaerobic way.

Question 28

Where are the enzymes of glycolysis can be seen?

Answer 28

Cytosol

Question 29

Which cells can use glucose as energy?

Answer 29

ALL