Details carbohydrate metabolism

1. Carbohydrate Digestion
,absorption and transportation

2. Digestion of carbohydrate
Digestion:
It is a process involving the hydrolysis of large and complex organic
molecules of foodstuffs into smaller and preferably water-soluble
molecules which can be easily absorbed by the gastrointestinal tract
for utilization by the organism.

4. Digestion of carbohydrate
 The principal dietary carbohydrates are polysaccharides (starch,
glycogen)disaccharides( lactose, sucrose) and monosaccharides
(glucose, fructose)
 Digestion of carbohydrates occurs briefly in mouth and largely in the
intestine.
 The hydrolysis of glycosidic bonds is carried out by a group of
enzymes called glycosidase
 These enzymes are specific to the bond, structure and configuration
of monosaccharide units.

6. Digestion in Mouth
 Saliva contains carbohydrate splitting enzyme salivary
amylase(ptyalin)
 Action of salivary amylase:
• It is a-amylase requires Cl- ions for activation and optimum
pH (6.7)
• Salivary amylase hydrolyses a (1-4) glycosidic bands of
polysaccharides producing smaller molecules like a limit
dextrin, Maltose, Isomaltose and maltotriose,

7. Digestion in stomach
 Salivary amylase action stops in stomach when pH
falls to 3.
 No carbohydrate splitting enzyme in gastric juice.
 Thus, no carbohydrate digestion take place in
stomach.

8.  Digestion in Duodenum:
food bolus in duodenum mixes with pancreatic juice
Pancreatic juice contains pancreatic a amylase.
Action of pancreatic amylase:
• It is an amylase, optimum pH 7.1, requires cl- ions.
• It specifically hydrolyses (a 1-4glycosidic bonds and not an
a(1-6 bond)
• It produce disaccharide ( maltose, Isomaltose and
oligosaccharides)
Digestion in small Intestine.

9. Digestion in small Intestine.
Digestion in Jejunum:
• The final digestion of di- and oligosaccharide to
monosaccharides primarily occurs at the mucosal lining of the
upper jejunum.
• These enterocyte secrete juice which contains
oligosaccharidases and disaccharidases( e.g maltase, sucrase ,
lactase, isomaltase).
Action of intestinal juice:
Oligosaccharidase: it hydrolyses oligosaccharide and liberate
free glucose.
Disaccharidase : it will act on specific disaccharide and release
respective monosaccharides.

11. Carbohydrate Absorption
 The principal monosaccharides produced by the digestion of
carbohydrates are glucose, fructose and galactose.
 Of these, glucose accounts for nearly 80% of the total
monosaccharides
 Different sugars possess different mechanisms for their
absorption and also has different in their rate of absorption.
 Glucose is transported into the intestinal mucosal cells by a
carrier mediated and energy requiring process.

12. Mechanism of absorption.

15. Mechanism of glucose absorption

22.  Treatment:
The best treatment for lactose intolerance is
elimination of lactose from the diet.( i.e. severe
restriction of milk and diary products)

23.  Glucose concentration is very low in the cells compared to
plasma.
 Two specific transport systems are recognized for the entry of
glucose into the cells.
 1. Insulin- independent transport system of glucose
This is a carrier mediated uptake of glucose which is not
dependent on the hormone insulin.
This is operative in hepatocytes , erythrocyte and brain with
glucose transporter like GLUT 1,GLUT 2, GLUT3.
2. Insulin-dependent transport system of glucose:
This occurs in muscle and adipose tissue with glucose
transporter like glut 4.
Entry of glucose into cells

27.  Carbohydrate is major source of energy for the living
cells.
 The monosaccharide glucose is the central molecule
in carbohydrate metabolism.
 The fasting blood glucose level in normal individuals
is 70-100mg/dl .it is efficiently maintained at this level.
 Liver plays a key role in monitoring and stabilizing
blood glucose levels.
 Thus Liver may be appropriately considered as
glucostat monitor.
Carbohydrate metabolism.

28. Glycolysis
Citric acid cycle
Gluconeogenesis
Glycogenesis
Glycogenolysis
Hexose monophosphate shunt
Major pathways of carbohydrate
metabolism.

29. 1. Definition
2. Salient feature
3. Location
4. Reaction
• Energy investment phase
• Splitting phase
• Energy generation phase
1. Energetics
2. Regulations
Glycolysis

30. This pathway is often referred to as Embden-
Meyerhof 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 to pyruvate or lactate, with the
production of ATP.
Glycolysis

31.  Glycolysis takes place in all the cells of the body.
 Glycolysis occurs in the absence of oxygen(anaerobic)
or in the presence oxygen(aerobic).
 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.
 Reversal of glycolysis reactions will be important for
the gluconeogenesis.
Salient Features

32.  Glycolysis take place in the cytosol of all cells.
Location

33.  The pathway is divided into three distinct phases
A) Energy investment phase
B) Splitting phase
C) Energy generation phase.
Reactions of glycolysis.

34. Energy investment
phase
Energy generation
phase
Splitting phase

35. Lactate
dehydrogenase

36. Aerobic Glycolysis energetics Anaerobic Glycolysis energetics
Total ATP invest/utilised= 2 ATP Total ATP invest/utilised= 2 ATP
Total ATP synthesised : 2ATPx2=4ATP Total ATP synthesised : 2ATPx2=4ATP
Total ATP from NADH :2NADH x2.5=5ATP NADH is used for conversion of pyruvate
to lactate.
Net total ATP : 9 ATP – 2 ATP =7ATP Net total ATP : 4ATP -2ATP = 2ATP
Energetics

37.  The three enzyme namely
 Hexokinase
 Phosphofructokinase
 Pyruvate kinase
 Hexokinase:
 Hexokinase is inhibited by
Glucose 6-phosphate.
Regulation

38. Phosphofructokinase

39.  Glucagon
 cAMP

 protein kinase
 Pyruvate kinase a Pyruvate kinase-P
 (active enzyme) Inactive enzyme
 phosphatase
 Pi
Pyruvate kinase
+