This document provides an overview of carbohydrate metabolism. It discusses the major pathways involved including glycolysis, gluconeogenesis, and the citric acid cycle. Glycolysis involves the breakdown of glucose to pyruvate, occurring in the cytosol of cells. Gluconeogenesis is the synthesis of glucose from non-carbohydrate precursors, primarily occurring in the liver and kidneys. Glucose transport into cells is regulated by insulin-dependent and independent mechanisms. The citric acid cycle is the final common pathway for carbohydrates, fats, and proteins, where acetyl CoA is oxidized to carbon dioxide. Carbohydrates provide a major source of energy for cells through these metabolic pathways.

1. BIOCHEMISTRY
[B. Pharm – I Yr.]
Topic: Carbohydrate metabolism
Umesh Kumar
Assistant Professor
Dept. of Pharm. Chemistry
Hygia Institute of Pharmaceutical Education and Research

2. CONTENTS
• Carbohydrate metabolism
• Metabolism
• Carbohydrate metabolism
• Major pathways of Carb. Metabolism
• The cell
• Entry of glucose into the cell
• Glycolysis
• Introduction
• Salient features
• Pathway

3. What is Metabolism
• Metabolism is the process by which your body
converts food into energy.
• This is a set of chemical reactions involved in
maintaining the living state of the cells and the
organism.
• During this complex process, calories in food and
beverages are combined with oxygen to release the
energy your body needs to function.
• Even when you're at rest, your body needs energy for
all its "hidden" functions, such as breathing,
circulating blood, adjusting hormone levels, and
growing and repairing cells.

4. Carbohydrate metabolism (Ref; U. Satyanarayana)
• Carbohydrates are the major source of energy for the living cells.
• The monosaccharide glucose is the central molecule in carbohydrate metabolism
since all the major pathways of carbohydrate metabolism are connected with it.
• The other monosaccharides important in carbohydrate metabolism are fructose,
galactose and mannose
• The official spokesperson of carbohydrate metabolism, ‘glucose’. Speaks,
“I burn myself to provide fuel to life!
Generated through gluconeogenesis by my friends;
Engaged in the synthesis of lipids, amino acids;
Deranged in my duties due to diabetes mellitus.”

5. Major pathways of carbohydrate metabolism
1. Glycolysis (Embden-Meyerhof pathway): The oxidation of glucose to
pyruvate and lactate.
2. Citric acid cycle (Krebs cycle or tricarboxylic acid cycle): The oxidation of
acetyl CoA to CO2. Krebs cycle is the final common oxidative pathway for
carbohydrates, fats or amino acids, through acetyl CoA.
3. Gluconeogenesis: The synthesis of glucose from non-carbohydrate precursors
(e.9. amino acids, glycerol etc.)
4. Glycogenesis: The formation of glycogen from glucose
5. Glycogenolysis: The breakdown of glycogen to glucose
6. Hexose monophosphate shunt (pentose phosphate pathway or direct
oxidative pathway): This pathway is an alternative to glycolysis and TCA cycle
for the oxidation of glucose (directly to carbon dioxide and water).

7. The cell (Diagram)

8. Entry of Glucose into Cell
• Glucose concentration is very low in the cells
compared to plasma (for humans < 100 mg/dl).
• However, glucose does not enter the cells by
simple diffusion.
• Two specific transport systems are recognized for
the entry of glucose into the cells;
• Insulin-independent transport system of glucose
• Insulin-dependent transport system
Glucose transporters:
In recent years, at least six glucose transporters (GLUT-l to
GLUT-5 and GLUT-7) in the cell membranes have been
identified.

9. GLYCOLYSIS
(Embden-Meyerhof Pathway)

10. Introduction
• Glycolysis is derived from the Creek words (glycose-sweet or sugar; lysis-dissolution).
• The complete pathway of glycolysis was elucidated in 1940.
• This pathway is often referred to as Embden-Meyerhof pathway (E.M. pathway) in honour of the
two biochemists who made a major contribution to the knowledge of glycolysis.
Definition
“Glycolysis is defined as the sequence of reactions converting glucose (or glycogen) to pyruvate or
lactate, with the production of ATP”.

11. Salient features of Glycolysis
• Occurs in cytosol and Enzymes of this pathway are present in Cytosomal fraction of the cell.
• Glycolysis occurs in aerobic and anaerobic both the conditions.
• Glycolysis is a major pathway for ATP synthesis in tissues lacking mitochondria, e.g. erythrocytes,
cornea, lens etc.
• Glycolysis is very essential for brain which is dependent on glucose for energy.

12. Reactions of Glycolysis
• The pathway can be divided into three distinct phases
1. Energy investment phase or priming stage
2. Splitting phase
3. Energy generation phase

13. Overview of glycolysis cycles

16. GLUCONEOGENESIS
(Synthesis of glucose from non-carbohydrate sources)

17. Introduction
• The synthesis of glucose from noncarbohydrate compounds is known as gluconeogenesis.
• The major substrates/precursors for gluconeogenesis are lactate, pyruvate, glucogenic amino acids,
propionate and glycerol.
• Gluconeogenesis occurs in the cytosol of the cell and all the precursors produced in mitochondria.
• Gluconeogenesis mostly takes place in liver (about 1 kg glucose synthesized everyday) and, to some
extent, in kidney matrix (about one-tenth of liver capacity).

18. Pathway

20. Importance of Gluconeogenesis
Glucose occupies a key position in the metabolism and its continuous supply is absolutely essential to
the body for a variety of functions;
1. Brain and central nervous system/ erythrocytes, testes and kidney medulla are dependent on glucose
for continuous supply of energy. Human brain alone requires about 120 g of glucose per day, out of
about 160 g needed by the entire body.
2. Glucose is the only source that supplies energy to the skeletal muscle, under anaerobic conditions.
3. ln fasting even more than a day, gluconeogenesis must occur to meet the basal requirements of the
body for glucose and to maintain the intermediates of citric acid cycle. This is essential for the
survival of humans and other animals.
4. Certain metabolites produced in the tissues accumulate in the blood, e.g. lactate, glycerol,
propionate etc. Gluconeogenesis effectively clears them from the blood

21. THANK YOU
HYGIA GROUP OF INSTITUTIONS
GHAILA ROAD, GAAZIPUR BALRAM,
FAIZULLAHGANJ, LUCKNOW