CARBOHYDRATES

-Dr. Rushikesh K Joshi

MPT ( Neuro.)

Introduction

Carbohydrates are composed of carbon, hydrogen and oxygen.

CARBOHYDRATES – “hydrates of carbon..“

Emperical formula for carbohydrates can be written as (CH2O)n… n=1,2,3…….

Contd..

Examples- GlucoseFructosegalactoseStarchcellulose etc....

Functions of carbohydrates Dietary sources of energy (calorific

value 4cal/gm) for all organisms.

Precursors of organic compounds like fats, amino acids...

Carbohydrates ( as glycoprotein and glycolipids) participate in the structure of cell membrane and cellular functions..

Contd..

These are storage form of energy for energy in the form of GLYCOGEN..

Structural components of many organisms like cell walls of bacteria, cellulose of plants.

Sources of carbohydrates

Classification of carbohydrates

Carbohydrates are divided into FOUR main groups depending upon the number of MONOMER units (e.g- CH2O) present in the molecule.

Broadly the carbohydrates are classified into four groups as follows -->

Monosaccharides

Also called as ‘SIMPLE’ SUGARS… They are the simplest form of

carbohydrates, which cannot be further hydrolysed into simpler forms.

Emperical formula – Cn H2n On Monosaccharides can be further

divided into following…

Contd..

Depending upon the number of carbon atoms , they can be subdivided into Monosaccharides

Trioses

Tetroses

Pentoses

Hexoses

Heptoses

Contd..

Trioses – 3 carbons Tetroses – 4 carbons Pentoses- 5c Hexoses – 6 c Heptoses- 7c

Further if we see, if this can combine with either an aldehyde or with ketone group..

Disaccharides

These are those sugars which gives 2 molecules of monosaccharides on hydrolysis.

These two units of monosaccharides are joined by a GLYCOSIDIC BOND.. !!!

Examples – maltoselactosesucrose

Contd..

Maltose glucose + glucose

Lactose glucose + galactose

Sucrose glucose + fructose

Oligosaccharides

These are those sugars which yield 3-10 monosaccharide units on hydrolysis..

Examples- Raffinose Stachyose

Contd..

Raffinose fructose + galactose + glucose

Stachyose 2(galactose) + glucose + fructose

Polysaccharides

These are those sugars which yield more than 10 molecules of monosaccharides on hydrolysis.

Polysaccharides can be further classified into two types based on the type of monosaccharide units present in the chain of molecules.

Polysaccharides

Homopolysaccharides

Heteropolysaccharides

Contd..

Homopolysaccharides – Also known as ‘ homoglycans’. These are the polymers of the same monosaccharide units.Examples-

StarchGlycogenInulin Cellulosedextrin

Contd..

Heteropolysaccharides – also known as ‘ heteroglycans’ .

these are polymers of different monosaccharide units.

Examples- heparinchondroitin sulphate

In short…

Metabolism

Metabolism all chemical reactions in the body.

But, further it is important to understand that reactions can be of mainly two types.

They can either be synthetic in nature or they can be reactions which breakdown

Based on this concept, there are two main types

Contd..

Reactions

Anabolic( synthetic)

Catabolic (breakdown)

Anabolism

Chemical reactions that combine simple substances into more complex molecules

This reactions help in the synthesis of substances in the body

E.g – Formation of peptide bonds between amino acids formation of PROTEINS..

-Glucose into GLYCOGEN..

Catabolism

The chemical reactions that breakdown complex organic compounds into simple ones.

E.g – Digestion of food molecules breakdown of bonds release of energy.- generally these reactions are hydrolysis reactions that release chemical energy..

Carbohydrate metabolism

This includes the metabolism of glucose.

During digestion, polysaccharides and disaccharides are HYDROLYSED into monosaccharides ( glucose), fructose and galactose.

These monosaccharides are ultimately converted into glucose in the LIVER cells.

Fate of carbohydrates

ATP Production- calorific value of glucose is 4Kcal/gm..

Amino acid synthesis- glucose used to form amino acids proteins.

Glycogenesis- liver stores excess glucose by converting it into glycogen by Glycogenesis. Later, when decrease in blood glucose glycogen converted to glucose by glycogenolysis.

Contd..

Lipogenesis- if glycogen storage is filled up, liver cells can transform the glucose to glycerol and fatty acids formation of triglycerides ( lipogenesis)

Glycolysis

It is also known as EMP pathway ( Embden-Meyerhof Parnas pathway)

In glycolysis, a molecule of glucose is degraded in a series of enzyme catalyzed reactions to yield two molecules of PYRUVATE.

During this reactions, some of the free energy liberated from glucose is conserved in the form of ATP.

Contd.. This process of catabolism of glucose occurs

either in presence of oxygen to pyruvic acid(i.e pyruvate ) ( AEROBIC GLYCOLYSIS) or during the lack of oxygen to lactate ( i.e lactic acid) (ANAEROBIC GLYCOLYSIS).

GLYCOLYTIC ENZYMES are present in the extramitochondrial compartment of the cell.

Aerobic glycolysis occurs in all the tissues like liver, kidney and erythrocytes.

While anaerobic glycolysis takes place only in MUSCLE.

Importance of glycolysis

Energy production Produces ATP even in absence of

Oxygen (anaerobic glycolysis). This allows skeletal muscles to perform efficiently even when aerobic oxidation becomes insufficient.

Deficiency of pyruvate kinase produces the disease haemolytic anemia.

Energy production

Glucose to glucose-6-phosphate -1 ATP Fructose-6-phosphate to fructose 1,6-

diphosphate -1 ATP Glyceraldehyde 3-phosphate to 1,3-

biphosphoglyecradehyde 2NADH2 2*3ATP= 6ATPs

Phosphoglycerate kinase 2ATP Pyruvate kinase2ATP NET YIELD= 6+2+2-1-1=8ATPs.

Metabolism as a whole..

TCA cycle(Kreb’s/Citric acid) Site of reaction- mitochondria Consists of a series of reactions in

mitochondria which catalyses the oxidation of Acetyl CoA and giving out ENERGY..

It is the FINAL COMMOM PATHWAY for metabolism of carbohydrates, fats and proteins.

It is mechanism by which much of free energy is liberated .

Production of Acetyl coA from pyruvate(AEROBIC CONDITION)

• Pyruvate

2molecules

Production of Lactic acid from pyruvate(AN-AEROBIC CONDITION)

• PYRUVATE

Major functions of kreb’s cycle most of the CO2 made in human

tissues through this cycle. Source of coenzymes for further

chain reactions Provides precursors for the synthesis

of proteins and fatty acids. Components of this cycle controls

the other enzyme systems.

Energy production

Isocitrate Alpha keto glutarate - 1NADH23ATPs

Alpha keto glutaratesuccinyl CO-A1NADH23ATPs

Succinyl coAsuccinate 1GTP1ATP Succinatefumarate1FADH22ATPs Malateoxaloacetate1NADH23ATPs NET YIELD OF ATP 3+3+1+2+3=

12ATPs

Contd..

So, now we know that 1molecule of pyruvate gives 12ATPs.

As we know that in glycolysis, 2pyruvate molecules are produced.

So, 2molecules of acetyl coA is produced.

NET PRODUCTION from 2acetyl coA will be 12*2= 24ATPs

NET YIELD DURING COMPLETE OXIDATION OF 1 MOLECULE OF GLUCOSE

38 MOLECULES OF ATP Glycolysis8ATP Pyruvateacetyl coA 6ATP TCA Cycle 24 ATP

Biological significance of citric acid cycle

Plays dual role oxidation + synthesis

Catabolic + anabolic Catabolic oxidation of

carbohydrates. Lipids and proteins release of energy

Anabolic biosynthesis of amino acids and glucose.