L15- Glycolysis

Question 1

What’s the main conversion in glycolysis?

Answer 1

1 glucose —> 2 Pyruvate

Question 2

What can pyruvate be further metabolized into?

Answer 2

Anaerobic conditions- Lactate (muscles) or ethanol (microorganisms)

Aerobic conditions- Acetyl CoA

Question 3

What is the net energy generation of glycolysis?

Answer 3

• 2 ATPs are produced
• 2 NAD+ reduced to 2 NADH

Question 4

What’s the glycolysis equation?

Answer 4

Glucose + 2 ADP + 2NAD+ + 2Pi —->

2 Pyruvate + 2ATP + 2NADH + 2 H+ +2H20

Question 5

How is pyruvate metabolized to ethanol?

Answer 5

Two reactions are required, catalysed by:

1. Pyruvate decarboxylase
2. Alcohol dehydrogenase

Puravate—-> Acetaldehyde—->Ethanol
1 2

(acetaldehyde = ethanal)

Question 6

Why is pyruvate made into lactate in muscles rather than ethanol?

Answer 6

Muscles lack pyruvate decarboxylase (which miscroorganisms have).

Musces have lactate dehydrogenase which converts pyruvate to lactate.

Question 7

What do the anaerobic metabilizing reactions of pyruvate generate?

Answer 7

They regenerate NAD+ for use by GAPDH in glycolysis. Hence glycolysis can continue to generate ATP.

Question 8

Which steps of glycolysis are irreverible and why?

Answer 8

Steps 1,3 and 10.

They have large ∆G. The other steps ∆G is close to zero and these ar reversible.

Question 9

What regulates glycolysis?

Answer 9

1. Metabolites in the pathway (feedback inhibition)
2. Availability of substrates
3. Hormonal regulation (linked to kinases and phosphatases)

Question 10

What does hexokinase catalyse?

Answer 10

An irreversible step at the start of glycolysis.

Glucose to glucose 6-phosphate

Question 11

What is hexokinase inhibited by?

Answer 11

Glucose 6-phosphate (its product)

When enough product is made, negative feedback

Question 12

What happens differently in the liver for the 1st raction of glycolysis?

Answer 12

A seperate enzyme is used0 GLUCOKINASE.

Not inhibited by its product. Important because high levels of glucose 6 -phosphate needed in the liver for glycogen storage.

Question 13

How is phosphofructokinase-1 (PFK-1) inhibited?

Answer 13

ATP is a substrate and inhibitor of PFK-1.

AMP acitvates PFK-1 by relieving the ATP inhibition.

Elevated citrate also inhibits PFK1.

Question 14

How is pyruvate kinase regulated? (step 10)

Answer 14

It’s inhibited by ATP (a product). Feedback inhibition.

Activated by fructose 1,6 bisphosphate - feed forward activation

Question 15

What is GLUT?

Answer 15

A family of 6 passive hexose transporters

Question 16

How does insulin affect the GLUT fam?

Answer 16

Glucose uptake mediated by GLUT4 is stimulated by insulin

The other GLUT transporters mediate glucose transport in and out of cells in the absence of insulin

Question 17

What are the general inhibitors of glycolysis?

Answer 17

High ATP/citrate conc., low blood glucose levels

Question 18

What are the general activators?

Answer 18

High AMP, high levels of bloog glucose

Question 19

What is made when these other sugars enter glycolysis?

Answer 19

a. Fructose- glyceraldehyde 3 phosphate
b. Galactose- glucose 6 phosphate
c. Mannose- fructose 6-phosphate

Question 20

What are the steps of glycolysis?

Answer 20

Glucose
Glucose 6 phosphate
Fructose 6 phosphate
Fructose 1,6 phosphate
Glyceraldehyde 3-phosphate
1,3 biphosphoglycerate
3 phosphoglycerate
2 phosphoglycerate
phosphoenolpyruvate
Puruvate

Question 21

What are the enzyme in each step of glycolysis?

Answer 21

1. Hexokinase/glucokinase
2. Glucose 6-phosphate isomerase
3. Phosphofructokinase 1
4. Aldolase
5. Glyceraldehyde 3 phosphate dehydrogenase (and triose phosphate isomerase)
6. Phosphoglycerate kinase
7. Phosphoglycerate mutase
8. Enolase
9. Pyruvate kinase