Glycolysis

Question 1

What is the first step of glycolysis? What enzymes are involved, and what type of reaction is occurring?

Answer 1

Glucose converted to glucose-6-phosphate using hexokinase. Phosphorylation occurs as ATP is split to Pi and ADP.

Question 2

What reaction of glycolysis is irreversible- why is this?

Answer 2

Phosphorylation of glucose- this commits the cell to the subsequent reaction and the negative charge traps the glucose inside the cell

Question 3

What is the second step of glycolysis? Why does this occur?

Answer 3

Glucose-6-phosphate to fructose-6-phosphate, using phosphoglucose isomerase. When cleaved, the fructose can be split into equal halves.

Question 4

What is the third step of glycolysis?

Answer 4

Fructose-6-phosphate is converted to fructose-1,6-bisphosphate using phosphofructokinase (PFK). One ATP is hydrolysed to form Pi and ADP

Question 5

Why is regulation of phosphofructokinase needed?

Answer 5

It is needed to control the entry of sugars into the glycolysis pathway- to control the metabolic pathway

Question 6

How many ATP molecules are used in the first half of glycolysis? During what stages?

Answer 6

2: Phosphorylating glucose in step 1 and phosphorylation of fructose-6-phosphate in step 3 using PFK

Question 7

What happens in step 4 of glycolysis?

Answer 7

Fructose-1,6-bisphosphate is hydrolysed, using aldolase, to form dihydroxyacetone phosphate, and glyceraldehyde-3-phosphate.

Question 8

What happens to dihydroxyacetone phosphate, formed from step 4 of glycolysis?

Answer 8

Isomerisation: triose phosphate isomerase (TPI) converts it to glyceraldehyde-3-phosphate, so there are 2x GP

Question 9

What is the only fatal glycolytic enzymopathy?

Answer 9

Deficiency in triose phosphate isomerase- sufferers die within the first 6 years of their lives.

Question 10

What does a kinase enzyme do?

Answer 10

Transfers phosphate groups

Question 11

What occurs in step 6 of glycolysis?

Answer 11

The 2 glyceraldehyde-3-phosphates are oxidised, using glyceraldehyde-3-phosphate dehydrogenase.
NAD+ becomes NADH, as Pi is added to GP, forming 1,3-bisphosphoglycerate (x2)

Question 12

What is the importance of the formation of NADH? When does this occur during glycolysis?

Answer 12

NADH is needed to generate more ATP during oxidative phosphorylation within the mitochondria.
NADH is made when glyceraldehyde-3-phosphate is oxidised to form 1,3-bisphosphoglycerate.

Question 13

What occurs during step 7 of glycolysis?

Answer 13

1,3-bisphosphoglycerate has 1 phosphate group removed, using phosphoglycerate kinase. This forms ATP from ADP, and 3-phosphoglycerate.

Question 14

What occurs during step 8 of glycolysis?

Answer 14

3-phosphoglycerate undergoes isomerisation to form 2-phosphoglycerate, using phosphoglycerate mutase

Question 15

What occurs during step 9 of glycolysis?

Answer 15

2-phosphoglycerate undergoes dehydration, to form phosphoenolpyruvate, using the enzyme enolase.

Question 16

What is the last step of glycolysis?

Answer 16

Phosphoenolpyruvate has 1 phosphate removed, using pyruvate kinase. This forms pyruvate, and ATP from ADP.

Question 17

What is the net gain of ATP from glycolysis of one glucose molecule? Explain why this occurs

Answer 17

2 ATP molecules:
One ATP is used to phosphorylate glucose, and another to phosphorylate fructose-6-phosphate.
When 1,3-bisphosphoglycerate becomes 3-phosphoglycerate, one Pi is removed to form ATP (x2). When phosphoenolpyruvate becomes pyruvate, one Pi is removed and added to ADP, forming ATP (x2).

Question 18

What are the products from glycolysis of one glucose molecule?

Answer 18

2 ATP & 2 NADH (from oxidation of 2 molecules of glyceraldehyde-3-phosphate)

Question 19

Where does glycolysis occur?

Answer 19

In the cytosol

Question 20

Is glycolysis aerobic or anaerobic?

Answer 20

Anaerobic- it takes place even when there is no oxygen

Question 21

What 2 main concepts occur during glycolysis?

Answer 21

First, the formation of 2 high energy compounds (G3P) using ATP.
Then, the splitting of these compounds to generate ATP

Question 22

What types of reaction are occurring in all 10 steps of glycolysis (in order)?

Answer 22

1) Phosphorylation/group transfer
2) Isomerisation
3) Phosphorylation/group transfer
4) Hydrolysis
5) Isomerisation
6) Redox & phosphorylation/group transfer
7) Group transfer (phosphate removal)
8) Isomerisation
9) Dehydration (group removal)
10) Group transfer (phosphate removal)

Question 23

What is the only part of glycolysis that requires the coenzyme NAD+?

Answer 23

The oxidation of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate, forming NADH also

Question 24

Why is glucose-6-phosphate committed to the rest of the metabolic pathway?

Answer 24

Glucose-6-phosphate will not bind to the glucose transporter proteins, so will not leave the cell

Question 25

Why is transportation of NADH into the mitochondria needed?

Answer 25

So, during oxidative phosphorylation more reduced cofactors can be reoxidised, forming more ATP. Also, the NAD+ made can be used for glycolysis (anaerobic conditions in particular)

Question 26

How is NADH transported into the mitochondria?

Answer 26

Only the electrons are moved!! The glycerol phosphate shuttle for the skeletal muscle and brain, and the malate-aspartate shuttle for the liver, kidney and heart

Question 27

How do shuttles work?

Answer 27

Cytoplasmic and mitochondrial forms of the same enzyme, to translocate high energy electrons.

Question 28

Why can NADH not move into the mitochondria?

Answer 28

Inner membrane is impermeable to NADH/NAD+, so the electrons alone are moved

Question 29

How may defects in TCA cycle occur? What occurs due to these defects?

Answer 29

Mutations of TCA genes coding for certain enzymes reduces activity of the TCA cycle. So, lactate generation tends to occur even when there is abundant oxygen.