Glycolysis

Glycolysis Process

  • Glycolysis is a cytoplasmic pathway which breaks down glucose into two three-carbon compounds and generates energy.
  • The process involves the conversion of glucose (six-carbon) to pyruvate (three- carbon). This conversion happens in ten steps and is catalyzed by different enzymes.
  • The first five steps of glycolysis require energy, thus are called the energy investment phase. They include phosphorylation of glucose and its conversion to fructose and further phosphorylation.
  • Steps six to ten release energy, hence they are the energy payoff phase. Here, D-Glyceraldehyde-3-phosphate (G3P) is formed and two molecules of G3P are converted to pyruvate.
  • Conversion of G3P to pyruvate, in the presence of enzymes, releases energy which is utilized to form ATP (Adenosine Triphosphate) and NADH (Nicotinamide adenine dinucleotide ).

Importance of Glycolysis

  • Glycolysis is considered the universal energy extraction process, as it occurs in all organisms from simple bacteria to complex eukaryotes.
  • It serves as the initial process in fermentation. The anaerobic conversion of glucose to lactate when oxygen is scarce provides a valuable mechanism for muscles and other tissues.
  • The ATP generated during glycolysis is utilized for other biological processes while the NADH contributes to further ATP synthesis in the oxidative phosphorylation process.

Factors Affecting Glycolysis

  • Glycolysis depends on the availability of glucose. The more glucose available, the more ATP can be generated.
  • Certain hormones, such as insulin and glucagon, also regulate glycolysis. Insulin stimulates glycolysis in the liver and muscle cells while glucagon has an inhibitory effect.
  • Enzymes involved in glycolysis act as catalysts, so a change in enzyme activity can significantly change the rate of glycolysis.

Regulation of Glycolysis

  • Glycolysis is audited at the phosphofructokinase stage to ensure that glucose is converted to fructose-1,6-biphosphate only when it is needed.
  • This process is regulated through feedback inhibition, where the end product of glycolysis (ATP) inhibits the early stages of the process when its concentration is high.
  • In the presence of oxygen and the cell has enough ATP, glycolysis is inhibited and glucose is stored in the form of glycogen. However, when ATP levels decrease and ADP levels increase, glucose is broken down to produce ATP.