Glycolysis: Preparatory Phase

Question 1

in word form, what is step one of preparatory phase

Answer 1

enzyme 1 hexokinase: glucose is phosphorylated on position 6. ATP donates the phosphate

Question 2

is step one reversible

Answer 2

no, it is irreversible since ATP is consumed

Question 3

what happens to the stability of glucose once phosphorylated

Answer 3

it is destabilised

Question 4

what happens to delta G in step one

Answer 4

becomes large and negative since ATP donates the Pi

Question 5

what is the purpose of Mg2+ in step one

Answer 5

it “shields” the terminal phosphate of ATP and this prevents it from hydrolysis by H20, and this enables nucleophilic attack by OH on C6 of glucose

Question 6

write a note on hexokinase

Answer 6

works via induced fit. it is a regulatory enzyme of glycolysis. It has a U shaped clamp-like structure. There is a conformational change where the clamp closes by binding of D-glucose

It is a dimer, and has 4 isoforms made from different genes. The phosphorylation of glucose by HK traps glucose inside of cells for metabolism

Question 7

what is step 2 of prep phase

Answer 7

Phosphohexose isomerase:
Glucose 6- phosphate isomerises to fructose 6-phosphate

Question 8

describes what happens in step two, and the nature of the reaction

Answer 8

glucose 6-phosphate isomerises to fructose 6-phosphate

this reaction is in a near equilibrium state (reversible). there is a small change in free energy. it is reversible isomerisation of an aldose to ketose, where the atoms are shuffled to move carbonyl from C1 to C2 to allow next reaction

Question 9

what happens in the his residue to allow step 2 to occur

Answer 9

active sit opens ring structure

Question 10

what is step 3 of glycolysis

Answer 10

phosphofructokinase-1

fructose 6-phosphate is phosphorylated to fructose 1-6-bisphosphate