Hey everyone!! Welcome back to my blog! Today we will be moving on to the topic Glycolysis which is another major topic in this course and requires a lot of detail and attention. This blog post will be focused on phase one of glycolysis which is known as the Energy Investment Phase. Before we get into this phase let us do a little background into glycolysis.


Glycolysis takes place in the cytosol of a cell. There are two phases in glycolysis: Energy investment phase & Energy generation phase. Overall, there are 10 enzymes in glycolysis, and 5 in each phase. I decided to explain this using points to make sure the concepts and main points are clear. Happy Learning!

Reaction 1

·         First priming reaction

·         Enzyme- Hexokinase

·         Enzyme transfers a phosphate group from ATP to glucose (phosphorylation) producing glucose-6-phosphate

·         Irreversible reaction

·         No transporters in the cell for glucose-6-phosphate

Reaction 2

·         Enzyme- Phosphohexoisomerase

·         Enzyme converts glucose-6-phosphate into its isomer fructose-6-phosphate

·         Conversion of an aldose sugar to a ketose sugar

Reaction 3

·         Second priming reaction

·         Enzyme- Phosphofructokinase-1

·         The enzyme PFK-1 uses an ATP molecule to transfer a phosphate group to fructose-6-phosphate to form fructose-1,6-bisphosphate

·         Its bisphosphate and not diphosphate because the phosphate groups are on different carbons

Reaction 4

·         Enzyme- Aldolase

·         The enzyme Aldolase splits fructose-1,6-bisphosphate into two sugars. These two sugars are isomers of each other. 

·         Two sugars: Dihydroxyacetone-phosphate & Glyceraldehyde-3-phosphate

Reaction 5

·         Enzyme- Triose phosphate isomerase

·         The enzyme Triose phosphate isomerase quickly converts the molecules of Dihydroxyacetone-phosphate and Glyceraldehyde-3-phosphate

·         At this point there is a net investment of energy from two ATP molecules in the breakdown of glucose

The first half of glycolysis uses two ATP molecules in the phosphorylation of glucose, which is then split into two 3C molecules. See image below for the overall reactions of phase 1. Click image for larger image.


Once again, thanks for viewing my blog. Look out for part two of this post! Like, Comment, Follow!


Featured Image:

Youtube: BiochemJM


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