BIOCHEMISTRY-CARBOHYDRATE METABOLISM CHAPTER 2.pptx

CARBOHYDRATE METABOLISM
UNIT II
11-04-2024 BIOCHEMISTRY_CHAPTER 2 1

Central molecule
in
Carbohydrate metabolism
Chemical reactions, occurring in the living system, referred as metabolism
The fasting blood glucose level in normal individuals is 70-100 mg/dl
Major pathways of carbohydrate metabolism-
Glycolysis, Citric acid cycle,
Gluconeogenesis, Glycogenesis,
Glycogenolysis & Hexose monophosphate
shunt

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.
3. Gluconeogenesis : The synthesis of glucose from non-carbohydrate
precursors (e.g.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

GLYCOLYSIS
• Glycolysis is derived from the Greek words glycose—sweet or sugar;
lysis—dissolution.
• This pathway is often referred to as Embden-Meyerhof pathway (E.M.
pathway).
Glycolysis is defined as the sequence of reactions
converting glucose (or glycogen) to pyruvate or lactate,
with the production of ATP.

•This pathway is utilized by all the cells and tissues to get energy, which is stored in the
form of ATP and NADH.
•It occurs in both prokaryotes and eukaryotes.
•It is employed in both aerobic and anaerobic respiration.
•The process of glycolysis occurs in cytosol, so it is a very important process of energy
generation for those organisms, who do not possess mitochondria.
•Even intermediates of the glycolysis process are utilised in other metabolic pathways,
•Glycolysis interconnects with other processes such as lactate and ethanol fermentation..
•When there is a high demand of energy in muscles and there is an insufficient supply of
oxygen, anaerobic glycolysis pathway is used to generate energy.
•As most of the reactions are reversible, glucose is generated back from pyruvate by the
process of gluconeogenesis.
SIGNIFICANCE

CITRIC ACID CYCLE
 The citric acid cycle (Krebs cycle or tricarboxylic acid—TCA cycle) is
the most important metabolic pathway for the energy supply to the body.
 About 65-70% of the ATP is synthesized in Krebs cycle.
 Citric acid cycle essentially involves the oxidation of acetyl CoA to CO2
and H2O

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•Krebs cycle or Citric acid cycle is the final pathway of oxidation of glucose, fats and amino acids
•Many animals are dependent on nutrients other than glucose as an energy source
•Amino acids (metabolic product of proteins) are deaminated and get converted to pyruvate and other
intermediates of the Krebs cycle.
•Fatty acids undergo 𝞫-oxidation to form acetyl CoA, which enters the Krebs cycle
•It is the major source of ATP production in the cells. A large amount of energy is produced after
complete oxidation of nutrients
•It plays an important role in gluconeogenesis and lipogenesis and interconversion of amino acids
•Many intermediate compounds are used in the synthesis of amino acids, nucleotides, cytochromes and
chlorophylls, etc.
•Vitamins play an important role in the citric acid cycle. Riboflavin, niacin, thiamin and pantothenic
acid as a part of various enzymes cofactors (FAD, NAD) and coenzyme A
•Regulation of Krebs cycle depends on the supply of NAD+ and utilization of ATP in physical and
chemical work
•The genetic defects of the Krebs cycle enzymes are associated with neural damage
SIGNIFICANCE

Pentose phosphate pathway (PPP) or Hexose mono-phosphate (HMP)
shunt
Pathway used to create products essential in the body for many reasons.
The HMP shunt is an alternative pathway to glycolysis and is used to
produce ribose-5-phosphate and (NADPH).
This pathway occurs in the oxidative and non-oxidative phases, each
comprising a series of reactions.
The sequence of reactions are divided into two types.
I)oxidative reaction phase
II) Non-oxidative reaction phase

Significance of Pentose phosphate pathway
HMP is only the cytoplasmic pathway that generates NADPH
NADPH is produced in this pathway acts as reducing agent during
biosynthesis of various molecules eg. fattyacids. Eg nucleotides are
synthesized from ribose-5-phsophate.
Pentose phosphate pathway is very essential for cell lacking
mitochondria (eg.RBCs) for generation of NADPH.
NADPH is also used to reduce Hydrogen peroxide in cell.
Generating two important products—pentoses and NADPH—
needed for the biosynthetic reactions and other function

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is a
condition in which red blood cells break down when the
body is exposed to certain drugs or the stress of infection. It
is hereditary, which means it is passed down in families.

A glycogen storage is a
metabolic disorder caused
by an enzyme deficiency
affecting glycogen synthesis,
glycogen breakdown, or
glucose breakdown,
typically in muscles and/or
liver cells.
GLYCOGEN STORAGE DISEASES
Rare glycogen disorders VIII, IX, X and
XI have been identified. They are due to
defects in the enzymes concerned with
activating and deactivating liver
phosphorylase

 Gluconeogenesis closely resembles the reversed pathway of glycolysis,
although it is not the complete reversal of glycolysis.
 Essentially, 3 (out of 10) reactions of glycolysis are irreversible.
 The seven reactions are common for both glycolysis and gluconeogenesis .
 The three irreversible steps of glycolysis are catalysed by the enzymes,
namely hexokinase, phosphofructokinase and pyruvate kinase.
Gluconeogenesis (GNG) is a metabolic pathway that results in the generation
of glucose from certain non-carbohydrate carbon substrates.
Although most gluconeogenesis occurs in the liver

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