Biochemistry - glycolysis

3 stages of glycolysis

Stage 1 - glucose is trapped and destabilised to glucose 6-phosphate; Stage 2 - glucose 6-phosphate is converted into two three-carbon molecules; Stage 3 - ATP is produced from the breakdown of these molecules.

purposes of glycolysis

fast production of atp, pushing the atp:adp ratio away from equilibrium

Trapping and destabilisation of glucose

Hexokinase enzyme buries and dissolves the substrate in the active site, so when ATP is hydrolysed it is favourable for the phosphate to be transferred to glucose instead of entering the aqueous environment. This forms glucose 6-phosphate.

Glucose 6 Phosphate to fructose 6 phosphate

adds a carbon to the glucose structure, converting it into a fructose structure through isomerization. This reaction is catalysed by phosphoglucose isomerase and makes it more symmetrical

fructose 6 phosphate to fructose 1,6, bisphosphate

This reaction involves the phosphorylation of fructose 6-phosphate, adding a second phosphate group to form fructose 1,6-bisphosphate. It is catalyzed by the enzyme phosphofructokinase and makes the molecule more symmetrical

Breakdown to 3 carbon units

fructose 1,6 is cleaved into two three-carbon molecules, dihydroxyacetone phosphate and glyceraldehyde-3-phosphate. This reaction is facilitated by the enzyme aldolase.

DHAP GA3P equilibrium

At equilibrium, dihydroxyacetone phosphate (DHAP) is at a much higher concentration than glyceraldehyde-3-phosphate (GA3P). However the constant use of GA3P makes it favourable to convert DHAP to GA3P

DHAP to GA3P conversion

the isomerization of dihydroxyacetone phosphate (DHAP) to glyceraldehyde-3-phosphate (GA3P), catalyzed by the enzyme triose phosphate isomerase.

GADPH reaction

GA3P is phosphorylated by NAD+ and pi, resulting in the formation of 1,3-bisphosphoglycerate and the reduction of NAD+ to NADH. This reaction is catalyzed by the enzyme glyceraldehyde-3-phosphate dehydrogenase. A sulfur in the active site forms an unstable thioester intermediate with GA3P preventing an energy trough .