Introduction: In the previous lecture we discussed the structure of prokaryotic and eukaryotic cells. Cellular integrity is maintained at the expense of energy produced by a set of chemical reactions, collectively known as metabolism. It is a summation of two different types of chemical processes:

Anabolism , the reactions which are responsible for formation of new compounds. It is alternatively known as biosynthetic pathway.

Catabolism , the reactions which are responsible for utilization of organic nutrients to produce energy in the form of ATP, NADH, FADH. ATP is the readily available form of energy whereas NADH and FADH needs to go mitochondria for ATP generation. Although carbohydrate, protein and fat undergo catabolism to produce energy but carbohydrate is most preferred choice for this purpose and henceforth topic of choice to discuss in the current course.

Carbohydrate Metabolism- Post digestion, food material is digested into the amino acid, fatty acid and glucose. All these final digestion products are absorbed by intestine and enter into the blood stream. Glucose enters into blood and distribute to the different organs for storage purpose but liver is the prime site for storage. Glucose is converted into the glycogen with the help of an enzyme glycogen synthase . Glucose is oxidized into the glycolysis and Kreb's cycle to produce ATP and other reducing equivalent to produce energy.

Glycolysis- Glycolysis is central to carbohydrate metabolism and it is the universal pathway found in prokaryotic or eukaryotic cells. It is a breakdown of 6 membered glucose into two 3 membered carbon suger to feed Kreb's cycle (in the presence of oxygen) or to send for anaerobic oxidation (in the absence of oxygen). Hence, it plays a crucial role for adopation of a living organism under differet types of stress conditions. The glycolysis is a 10 step chemical reaction to enable glucose for its optimal oxidation. All these reactions are given in Figure 5.1.

STEP-1: Phosphorylation of glucose- Glucose produced after glycogen breakdown is phosphorylated by glucokinase (in liver) or hexokinase in all other tissues especially in muscles. In the phosphorylation reaction, phosphate ( γ-phosphate ) group of ATP is transferred to glucose to form glucose-6-phosphate. The phosphorylation reaction of glucose to produce glucose-6-phosphate marks the molecule for glycolysis. One molecule of ATP is utilized in this step.