Glycolysis

Introduction

For survival, almost every living organism we see around us breathes and respires. Despite their diversity in biological characteristics, the molecular reactions involved in respiration are largely the same.

Simply explained, glycolysis is the breakdown of glucose, which can occur with or without the presence of oxygen. In the presence of oxygen, glycolysis is the first stage of cellular respiration. Glycolysis allows cells to create ATP in the absence of oxygen through a fermentation process.

Definition of Glycolysis

Considered the first stage of cellular respiration . Glycolysis is the process of breaking down glucose to produce energy. Glycolysis is a series of reactions that split glucose into two three-carbon molecules called pyruvates and extract energy from it. Glycolysis is an old metabolic mechanism that developed many years ago and is found in the vast majority of living creatures today.

Ten steps of Glycolysis

Glycolysis is a high-energy process. It has two phases: one that absorbs energy and the other that releases it. Adenosine triphosphate is used to release the energy (ATP).

During glycolysis, two molecules of pyruvate, two molecules of ATP, two molecules of NADH and two molecules of water are formed. Glycolysis happens in the cytoplasm. A total of eleven enzymes are involved in the breakdown of sugar. The 10 steps of glycolysis are organised by the sequence in which particular enzymes act on the system.

Glycolysis takes place in the cytoplasm of the cell . Glycolysis produces two ATP molecules in total (two are used during the process and four are produced).

Let us find out more about the ten steps of glycolysis:

Step 1

In the cytoplasm of a cell, the enzyme hexokinase phosphorylates or adds a phosphate group to glucose. A phosphate group from ATP is transferred to glucose throughout the process, resulting in glucose 6-phosphate or G6P. During this phase, one molecule of ATP is consumed.

Step 2

Phosphoglucoisomerase is an enzyme that converts G6P to its isomer fructose 6-phosphate or F6P. Isomers share the same chemical formula but differ in their atomic configurations.

Step 3

To create fructose 1,6-bisphosphate or FBP, the enzyme phosphofructokinase transfers a phosphate group to F6P using another ATP molecule. So far, two ATP molecules have been used.

Step 4

Fructose 1,6-bisphosphate is broken into a ketone and an aldehyde molecule by the enzyme aldolase. Glyceraldehyde 3-phosphate (GAP) and dihydroxyacetone phosphate (DHAP) are isomers of each other.

Step 5

The enzyme triose-phosphate isomerase transforms DHAP to GAP in a short amount of time (these isomers can interconvert). The next phase of glycolysis requires GAP as a substrate.

Step 6

In this reaction, the enzyme glyceraldehyde 3-phosphate dehydrogenase (GAPDH) performs two purposes. GAP is first dehydrogenated by transferring one of its hydrogen (H+) molecules to the oxidising agent nicotinamide adenine dinucleotide (NAD+), resulting in NADH + H+.

GAPDH then joins the oxidised GAP with a phosphate from the cytosol to generate 1,3-bisphosphoglycerate (BPG). This process of dehydrogenation and phosphorylation is carried out on both molecules of GAP generated in the previous phase.

Step 7

Phosphoglycerokinase is an enzyme that transfers a phosphate from BPG to a molecule of ADP to create ATP. This happens to each and every BPG molecule. Two 3-phosphoglycerate (3 PGA) molecules and two ATP molecules are produced in this process.

Step 8 

The enzyme phosphoglyceromutase moves the P from the third to the second carbon of the two 3-PGA molecules, resulting in two 2-phosphoglycerate (2 PGA) molecules.

Step 9 

To make phosphoenolpyruvate, the enzyme enolase removes a molecule of water from 2-phosphoglycerate (PEP). From Step 8, this happens for each molecule of 2 PGA.

Step 10

Pyruvate kinase is an enzyme that transfers a P from PEP to ADP to produce pyruvate and ATP. This occurs for each PEP molecule. This process produces two pyruvate molecules and two ATP molecules.

Krebs cycle

One of the most significant reaction sequences in biochemistry is the Krebs cycle, commonly known as the citric acid cycle or the tricarboxylic acid cycle. Not only are the molecules produced in these reactions responsible for the majority of the energy needs in complex organisms, but they can also be used as building blocks for a variety of important processes, such as the synthesis of fatty acids, steroids, cholesterol, amino acids for protein building and the purines and pyrimidines used in DNA synthesis. Lipids (fats) and carbohydrates, which both create the chemical acetyl coenzyme-A, provide energy for the Krebs cycle (acetyl-CoA).

The TCA cycle was first discovered in pigeon muscle tissue. All eukaryotic and prokaryotic cells are affected. It is found in the matrix of the mitochondrion in eukaryotes. It occurs in the cytoplasm of prokaryotes.

A glucose molecule must first be transformed to acetyl-CoA before the Krebs cycle can begin. This procedure produces two acetyl-CoA molecules, which are then fed into the cycle. As a result, for every original glucose, the cycle repeats twice, generating double the products illustrated below.

One “round” of the TCA cycle provides  products:

• GTP 
• 3 NADH 
• FADH2 

Conclusion

Glycolysis is vital in the cell since glucose is the body’s primary source of energy. For example, glucose is the brain’s sole source of energy. The body needs to maintain a consistent supply of glucose in the blood to sustain appropriate brain function.