Glycolysis And Control

Question 1

What is glycolysis and what is the pathway called

Answer 1

Splitting of glucose into pyruvate x 2

The EMBDEN MAYERHOF PARNAS PATHWAY

Question 2

Why is glycolysis important

Answer 2

Only source of energy in anaerobic respiration

Question 3

Name the 3 stages of glycolysis

Answer 3

Investment

Splitting

Energy yield

Question 4

How many ATP molecules are used / hydrolysed in investment and how many gained

Answer 4

2

4 are gained

Question 5

What first happens to glucose and which enzyme is involved

Answer 5

Glucose is phosphorylated

Glucose 6 phosphate produced

Hexokinase enzyme uses atp hydrolysis to phosphorylate glucose

Question 6

Why is it important for cells that glucose is phosphorylated

Answer 6

Phosphate is negatively charged which stops glucose leaking out of cells as much

Question 7

What ion does hexokinase need and also any other enzyme to phosphorylate glucose etc

Answer 7

Mg++

Needed to stop the other 2 phosphates being hydrolysed (only 1 phosphate added)

Question 8

Why is hexokinase better than glucokinase in phosphorylation of molecules like glucose

Answer 8

Because gluco kinase has a higher KM which means lower affinity to the molecules than hexokinase

Question 9

Which carbon is phopshorylated on glucose by hexokinase atp hydrolysis

Answer 9

6 C

Forms CH2OPO3-

Question 10

What happens to glucose 6 phosphate when produced by hexokinase

Answer 10

Isomerisation (change in structure)

Into fructose 6 phosphate

Question 11

Explain the steps of how aldose sugar glucose 6 P turns into a ketose sugar fructose 6 P

Answer 11

The ring opens to form an exposed aldehyde group ( h c=o h)

This isn’t stable so forms an internal ester with C2OH

This forms a ketone

Then the C2 double O forms internal bond with another O

The ring closes to form a furanose 5C sugar

= fructose 6 phosphate (6c is phosphorylated)

Question 12

What happens to fructose 1 phosphate (5c ring) after isomerisation

Answer 12

Phospho fructo kinase will phosphorylate C1 aswell as C6 (using atp hydrolysis and mg++)

Forms a fructose 1, 6 bisphosphate

Question 13

Why does fructose 1 6 bisphosphate split into 2 x 3c molecules instead of being a furanose 5c ring

Answer 13

Because of the symmetry and the 2 negative charges on phosphates cause repulsion

Question 14

What happens in splitting (include the 2 enzymes involved)

Answer 14

Fructose 1 6 bisphosphate (6c) is split into 
Dihydroxyacetone phosphate (x2) 

BY ALDOSE ENZYME

this then converts to glyceraldahyde 3 phosphate (x2) 3C

This is done using triose phosphate isomerase

Question 15

Which enzyme converts dihydroxyacetone phosphate 3C into glyceraldahyde 3 phosphate

Answer 15

Triose phosphate isomerase

Question 16

What is the gain of ATP in the energy yield stage of glycolysis

Answer 16

2 for each glyceraldahyde 3 phosphate (x2) = 4

Question 17

What is the first step in energy yield converting glyceraldahyde 3 phosphate

Answer 17

Glucose 3 phosphate dehydrogenase Enzyme

Allows conversion of NAD to NADH which oxidises(H removed from G3p)

G3p also gains a free phosphate to form

1,3 bisphosphoglycerate

Question 18

Where are the phosphates located on 1,3 bisphoshoglycerate converted from G3P

Answer 18

C1 and C3

Question 19

What is 1,3 bisphosphoglycerate converted to and how

Answer 19

3 phoshpoglycerate

Converted by removing a phosphate which binds to ADP to form a new ATP molecules (substrate level phosphorylation)

Question 20

Which enzyme dephosphorylates 1,3 bisphosglycerate to form a new ATP molecule

Answer 20

Phosphoglycerate kinase

Question 21

How does 3 phosphoglycerate turn into 2 phosphoglycerate

Answer 21

Phosphoglycerate mutase converts the PO group from C3 to C2 (central C)

Question 22

What happens to 2 phosphoglycerate produced by phosphoglycerate mutase enzyme

Answer 22

It is converted to phosphoenolpyruvate

H2O is removed from it by enolase enzyme

Question 23

Why is h20 removed from 2 phosphoglycerate

Answer 23

Increases energy production by adding another double bond

Question 24

Which enzyme dephosphorylates phosphoenolpyruvate to produce ATP and pyruvate

Answer 24

Pyruvate kinase

Question 25

How many substrate level phosphorylation are there in glycolysis

Answer 25

4

Question 26

Why is controlling glycolysis important

Answer 26

To link supple of atp with demand or if needed for storage

To allow cells to respond to the environment

Question 27

Which type of enzymes are used to control catabolic reactions

Answer 27

Rate limiting enzymes (slow rate of reactions)

Question 28

How do you limit rate of enzymes (4 ways)

Answer 28

1- control amount of enzyme

2- allosteric inactivation of the enzyme

3- covalent modification via kinase or phosphatase

4- controlling enzymes access to substrate

Question 29

How is enzyme access to substrate limited

Answer 29

Via compartmentalisation

Either substrate or enzyme stick to one area

Question 30

Which 3 enzymes are controlled in glycolysis

Answer 30

Hexokinase

Phosphofructo kinase

Pyruvate kinase

Question 31

How is hexokinase inactivated when too much Glucose 6 phosphate is present

Answer 31

Allosterically inactivated via negative feedback

Question 32

Why is glucose 6 phosphate important

Answer 32

Because it is used as a glycogen store important for muscles etc

Question 33

What allows phosphofructokinase activity (turning fructose 1 phosphate into fructose 1,6 bisphosphate)

Answer 33

Low ATP/energy levels

Adenylate cyclase production of AMP activates the phosphofructokinase

Question 34

Which 3 things in too much presence stops phosphofructokinase

Answer 34

ATP (not needed anymore)

Low ph indicating too much lactate produced by pyruvate

Citrate increase in the Krebs cycle

Question 35

How is pyruvate kinase action increased (phosphoenolpyruvate into pyruvate)

Answer 35

The accumulation of fructose 1 6 bisphosphate in the investment stage of glycolysis causes activation of pyruvate kinase

Question 36

How does fructose 2 6 bisphosphate presence allow for activation of phosphofructokinase

Answer 36

It decrease PFK affinity for atp and citrate which decrease its activity