Question

Normal human blood plasma, glucose concentration is ~5mM. Explain (state pathway(s) and key enzyme(s) in processing glucose in muscle cells) the fate(s) of glucose once it is delivered by blood plasma to myocytes (muscle cells).

Answer 1

Glycolysis :- Divided into 2 different phase--- a) Preparatory phase b) Payout phase

In preparatory phase the ATP molecules are consumed and in payout phase the ATP molecules are synthesized

A) Preparatory phase

Reaction 1

Glucose is phosphorylated by hexokinase to form glucose-6-phosphate (G6P). The negative charge effectively traps G6P in the cell as it cannot pass through the membrane.

Reaction 2

In reaction two, G6P is converted into fructose-6-phosphate by glucose isomerase.

Reaction 3

Fructose-6-phosphate is phosphorylated by phosphofructokinase into fructose-1,6-bisphosphate. This creates an unstable molecule that will split spontaneously to form two 3 carbon molecule and consumes our second molecule of ATP.

Reaction 4

By reaction 4, the energy consumption of the ‘investment phase’ is complete and two ATP molecules have been consumed.

Here, fructose-1,6-bisphosphate is converted into two triose sugars by fructose-bisphosphate aldolase.. Namely, these triose sugars are glyceraldehyde-3-phosphate (GA3P) and dihydroxyacetone phosphate (DHAP).

Reaction 5

DHAP is converted into a second molecule of GA3P. The 2 molecules of GA3P then enter the second stage of glycolysis, the payout phase.

B) Payout Phase

Reaction 6

In reaction 6, GA3P is converted into 1,3-bisphosphoglycerate (1,3-BPG) by glyceraldehyde phosphate dehydrogenase. This yields a molecule of NADH, formed by the reduction of NAD+.

Reaction 7

Here, 1,3-BPG is converted into 3-phosphoglycerate (3PG) by phosphoglycerate kinase. This generates a molecule of ATP.

Reaction 8

3PG is converted into 2PG by phosphoglycerate mutase.

Reaction 9

2PG is converted into phosphenolpyruvate by enolase.

Reaction 10

Phosphenolpyruvate is converted into pyruvate by pyruvate kinase, which yields our second molecule of ATP.

Fate of Glucose :-

GLUCOSE Pentose phosphate pathway Enzyme Hexokinase Glycolysis Enzyme Glucose-6-phosphotase ATP production Glucose-6-phosphate Glycogen synthesis Hexose biosynthesis pathway Glycogen