Glycosis

[aka Embden-Meyerhof pathway]

Takes place in cytoplasm.

Symbols used

substrate

[enzyme involved]

---> new mebolite

(NB: ===> denotes irreversible conversion)

Stages of glycosis

Glucose (6C)

[Hexokinase/glucokinase]

===> glucose 6-phosphate
* -1 x ATP

[Phosphohexose isomerase]

---> Fructose 6-phosphate

[Phosphofructokinase]

===> Fructose 1,6-phosphate (6C)
* -1 x ATP

[Aldolase]

---> Glyceraldehyde 3-phosphate (3C)
+ Dihydroxyacetone phosphate (3C)

Glyceraldehyde 3-phosphate is then

[Glyceraldehyde 3-phosphate dehydrogenase]

---> 1,3 bisphosphoglycerate
* +1 x NADH+H+

[Phosphoglycerate kinase]

---> 3-phosphoglycerate
* +1 x ATP

[Phosphoglycerate mutase]

---> 2-phosphoglycerate

[Enolase]

---> Phosphoenolpyruvate
* +1 x H2O

[Pyruvate kinase]

===> Enol-pyruvate
* +1 x ATP

[Spontaneous]

===> Keto-pyruvate

Anaerobic condition

NADH+H accumulates due to lack of oxidative phosphorylation.

Thus,

Pyruvate

[Lactate dehydrogenase]

---> Lactate
* NADH+H oxidised to NAD+

Overall effect of glycolysis

For every molecule of glucose,

-2 x ATP
+4 x ATP
+2 x NADH+H
2 pyruvate is produced.

If anaerobic condition, pyruvate is reduced to lactate to regenerate NAD+.

Overall ATP production = 2

Other notes on glycolysis

Hexokinase and glucokinase

As glucose enters cells, it is converted into glucose 6-phosphate by hexokinase
-> Allows more glucose uptake by reducing intracellular concentration of glucose

Liver has an additional enzyme, glucokinase

More specific for glucose
Increased by insulin and decreased in starvation
Higher Km
-> Has effect only when glucose level is high
Provides glucose in excess of that required for glycolysis
-> Allows glycogenesis and lipogenesis

Lactate

Lactate is produced to regenerate NAD+ when oxygen supply is inadequate.

When oxygen supply is restored, lactate is:

metabolised in the citric cycle or
(in liver) used in gluconeogenesis