What Is Glycolysis?

What are the steps in glycolysis and what do they do? The breakdown of food molecules in glucose and other simple sugars is what fuels the reactions which take place inside of our bodies.

Glycolysis is responsible for the production of ATP (adenosine triphosphate) through the degradation of glucose. Glycolysis does not use molecular oxygen, and occurs in the cytosol of cells. Glycolysis can happen in aerobic and anaerobic organisms. It is hypothesized that the reason glycolysis can proceed without molecular oxygen is that the mechanism was initiated before earth's atmosphere contained the element. There has not been any reason for the process to convert to simply aerobic mechanisms. Glycolysis not only produces ATP but also intermediates that are important for biosynthetic processes later on in the metabolic process.

There are ten steps in glycolysis:

The first step involves the phosphorylation of the glucose molecule, by ATP, which creates a sugar phosphate. The glucose molecule stays inside of the cell, due to the negative charges on the phosphate. These negative charges don't allow passage through the plasma membrane.

The next step involves the relocation of the carbonyl oxygen from carbon 1, to carbon 2. This is done through a reversible isomerization, and creates a ketose. The hydroxyl group which is now located on the first carbon, is phosphorylated through ATP. The fructose 1,6-biphosphate, which happens to be a six carbon sugar, is cleaved. This cleaving causes the creation of two three-carbon molecules.



One of the previously produced three-carbon molecules, glyceraldehyde proceeds immediately through glycolysis. However, dihydroxyacetone phosphate is restructured, or isomerized to become glyceraldehyde 3-phosphate, and it as well can not proceed through glycolysis.

Next, in step six, both glyceraldehydes are oxidized to form an NADH and a proton. Then, the enzyme phosphoglycerate kinase uses the power of glyceraldehyde oxidation to create an ATP molecule. The phosphate ester linkage is moved from carbon 3 to carbon 2 through the enzyme phosphoglycerate mutase. This results in a molecule of 2-phosphoglycerate. From this molecule, one molecule of water is extracted, forming phosphoenolpyruvate.

This extraction of water allow for the formation of a very high-energy phosphate linkage. This linkage transfers energy to an ADP, forming an ATP. The final product of glycolysis is therefor two molecules of NADH, four molecules of ATP, and two molecules of three carbon sugars (pyruvate).

From step six on, there is energy generation going on, which indicates the beginning of ATP and NADH synthesis. In aerobic organisms, the NADH molecules produced transferred their electrons, or energy, into the electron transport chain. In anaerobic organisms, fermentation takes place instead of the electron transport chain.

There are five different key reactions that were described above. Phosphoryl transfer was the transfer of a phosphoryl group from ATP to an intermediate in glycolysis, or the transfer of a phosphoryl group to an ADP from an intermediate, which is aided by a kinase. A phosphoryl shift is when the phosphoryl group is moved from one oxygen to another, which is aided by mutase. Isomerization which is the chemical change of an aldose to a ketose or vice versa, aided by an isomerase. Dehydration is the removal of a water molecule, which is aided by a dehydratase. Aldol cleavage is during the reversal of an aldol condensation, a carbon-carbon bond is split, by the help of an aldolase.

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