describe various steps of glycolysis
Answers
Glycolysis is derived from the Greek words (glykys = sweet and lysis = splitting). It is a universal catabolic pathway in the living cells.
Glycolysis can be defined as the sequence of reactions for the breakdown of Glucose (6-carbon molecule) to two molecules of pyruvic acid (3-carbon molecule) under aerobic conditions; or lactate under anaerobic conditions along with the production of small amount of energy.
This pathway was described by Embden, Meyerhof and Parnas. Hence, it is also called as Embden-Meyerhof pathway (EM pathway).
glycolysis
Site of Glycolysis
Glycolysis occurs in the cytoplasm of virtually all the cells of the body.
Types of Glycolysis
There are two types of glycolysis.
Aerobic Glycolysis: It occurs when oxygen is plentiful. Final product is pyruvate along with the production of Eight ATP molecules.
Anaerobic Glycolysis: It occurs when oxygen is scarce. Final product is lactate along with the production of two ATP molecules.
Steps of Glycolysis
Glycolysis is an extramitochondrial pathway and is carried by a group of eleven enzymes. Glucose is converted to pyruvate in 10 steps by glycolysis.
The glycolytic patway can be divided into two phases:
Preparatory Phase :
This phase is also called glucose activation phase. In the preparatory phase of glycolysis, two molecules of ATP are invested and the hexose chain is cleaved into two triose phosphates.
During this, phosphorylation of glucose and it’s conversion to glyceraldehyde-3-phosphate take place. The steps 1, 2, 3, 4 and 5 together are called as the preparatory phase.
Payoff Phase :
This phase is also called energy extraction phase. During this phase, conversion of glyceraldehyde-3-phophate to pyruvate and the coupled formation of ATP take place.
Because Glucose is split to yield two molecules of D-Glyceraldehyde-3-phosphate, each step in the payoff phase occurs twice per molecule of glucose. The steps after 5 constitute payoff phase.
Step 1 : Uptake and Phosphorylation of Glucose
glycolysis-step-1
Glucose is phosphorylated to form glucose-6-phosphate.
The reaction is catalysed by the specific enzyme glucokinase in liver cells and by non specific enzyme hexokinase in liver and extrahepatic tissue. The enzyme splits the ATP into ADP, and the Pi is added onto the glucose.
Hexokinase is a key glycolytic enzyme. Hexokinase catalyses a regulatory step in glycolysis that is irreversible.
Hexokinase, like many other kinases, requires Mg2+ for its activity.