Glycolysis

Glycolysis

Glycolysis is the simply the process of breaking down a sugar such as Gluclose into energy and pyruvate.

The chemical equation for respiration is:

C6H12O6  +    6O2        ==>         6CO2                +     6H20  + ATP

Glucose       Oxygen                 Carbon dioxide           Water     Energy

the main stages of glycolysis are:

Stage One: To trap the glucose in the cell and destabilise it structure.

Stage Two: To break down the glucose into smaller components.

Stage Three: Harvest the energy to form ATP molecules and pyruvates.

As this topic is very complicated and difficult to make it simpler with less rambling. I am going to break glycolysis into ten simple steps!

STEP ONE:

The phosphorylation of glucose, glucose moves into the cell with the help of a membrane transporter and once inside the cytoplasm it undergoes phosphorylation process that is catalysed by protein kinases called hexokinase. 

This step is important as:

-Makes glucose polar which traps the glucose into the cell.

-The negatively charged phosphate group stops the glucose from moving across the cell membrane.

-The addition of a charged moiety on the glucose destabilises the structure and increases its energy which makes it more reactive and more likely to undergo glycolysis.

Some information on the enzyme hexokinase:

-Hexokinase depends on the presence of a divalent metal atom such as Mg2+

-Glucose moves into the active site of hexokinase which creates a induced fit, which seals off water out and stops ATP from being hydrolysed and it also places the glucose sugar more closer to the ATP.

STEP 2:

Enzyme phosphogluclase isomerase transforms on aldose (glucose 6 phosphate) into a ketose (fructose 6 phosphate)

STEP 3:

The OH group on carbon one of fructose 6 phosphate is phosphorylised by ATP and catalysed by PFK enzyme.

Phosphofructokinase (PFK) adds a second phosphoryl group on the sugar which commits the sugar to glycolysis. 

STEP 4:

Here we can see the breakdown of gluclose into smaller components. The aim of stage 2 is to cleave the fructose 1,6 bisphosphat inot two 3 carbon molecules called Glyceraldehyde 3- phosphate (GAP).

An enzyme called aldolase catalyse the breakdown of fructose 1.6 bisphosphate into two different 3 carbon moleculates called glyceraldehyde 3 phosphate and Dihydroxyacetone phosphate (DAP) 

The glyceraldehyde lies directly on the glycolysis pathway which means it can go directly onto stage 3 of glycolysis without any problems, however Dehydroxyacetone phosphate (DAP) does not so needs to be modified. To prevent the loss of energy potential the DAP must to be converted to GAP.

STEP 5:

An enzyme called triose phosphate isomerase catalyse the rapid and reversible conversion of DAP to GAP. 

TPI catalyses the conversion of the ketose (DAP) into aldose (GAP) via an intermolecular redox reaction in which a hydrogen is transferred from carbon one to carbon 2.

STEP 6:

This is stage three where glycolysis aims to harvest the energy in glyceraldehyde 3 phsophate to form ATP, NADH and pyruvate molecules.

The initial process involves the conversion of the glyceraldehyde 3 phsophate (GAP) into 1.3 Bisphoglycerate this reaction is catalysed by anenzyme called Glyceradlehyde 3 phosphate dehydrogenase.

STEP 7:

The transfer to ADP of the high energy phosphate group that was generated in step  6 to make ATP. It is catalysed by the enzyme phosphoglycerate kinase.

STEP 8:

The left over phosphate ester linkage in 3 phosphoglycerate which has a very low free energy of hydrolysis is moved to carbon 2 from carbon 3 to create 2 phosphoglycerate.

It is catalysed by the enzyme phosphoglycerate mutase.

STEP 9:

The removal of water from 2 phosphoglycerate which creates a high energy enol phosphate linkage. It is also catalysed by enolase enzyme.

STEP 10:

The transfer to ADP of the high energy phosphate group that was generate in step 9 creates glycolysis. This is catalysed by the pyruvate kinase enzyme. 

The whole process: 

TIP: ... and that is it! Learning this the first time round can be quite tricky! From all the diagrams and names it does look puzzling but with practice and going over it a number of time you will get the hang of it! I personally found this topic the hardest in biology and I have written the notes in a very simple and concise way! I have attached a additional video which I have found useful in understanding this topic.