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Carbohydrates

Presented By Dr. Guru Ram (I Year Post Graduate)

Department Of Periodontics

Contents• Introduction •Functions•Classification•Metabolism

•Glycolysis •Krebs cycle •Gluconeogenesis•Hexose MonoPhosphate shunt (HMP

shunt)•Glucogenesis and Glycogenolysis

•Carbohydrates Related To Dental Plaque

Introduction

ClassificationCarbohydrates

Monosaccharides

Disaccharides

oligosaccharides

Polysaccharides

Hetero

Homo

MonosaccharidesMonosaccharides

Number of C- atoms

Monosaccharides

Physical properties

Stereoisomerism

CHO

C

CH2OH

HO H

CHO

C

CH2OH

H OH

CHO

C

CH2OH

HO H

CHO

C

CH2OH

H OH

L-glyceraldehydeD-glyceraldehyde

L-glyceraldehydeD-glyceraldehyde

Optical Activity

•Levorotatory

•Dextrorotatory

•Racemic mixture

Epimers

Chemical Properties

Furanose form of fructose

•β-D-Ribose

•β-D-Deoxyribose

•β-D- Galactose

•β-D- Glucose

•β-D-Fructose

Disaccharides

Disaccharides

Reducing Non Reducing

Reducing Sugars

•Maltose •Lactose

Non Reducing Sugars•Sucrose•Trehalose

Oligosaccharides

Raffinose

Polysaccharides

Polysaccharides

Homo Hetero

Homopolysaccharides

•Starch

•Glycogen

•Cellulose

Amylose

Amylopectin

Starch- amylose

Starch- amylopectin

Glycogen

• Heteroglycans• Polysaccharides composed of different type of sugars or their derivatives.

1) Mucopolysaccharides : Repeating units of amino sugars more commonly known as Glycosaminoglycans (GAG).

Ground substance of collagen, elastin.Eg. Hyaluronic acid, chondratin sulphate, heparin, keratan sulphate.

Heteropolysaccharides

2 ) Glycoproteins : Several proteins are covalently bonded to carbohydrates. The carbohydrate content varies from 1 to 90 %.

They are widely distributed, and act as enzymes, hormones, transport proteins.

Metabolism Of Carbohydrates

•Catabolism

•Anabolism

Glucose?????Glucose acts as the central molecule in carbohydrate

metabolism as : - Instant source of energy

- Easily synthesized

- Stored as glycogen in body

Glycolysis (Embden- Mayerhof-Parnas

pathway){Glycos- sugars, lysis-dissolution}

Takes place in all cells of the body but mainly in liver and muscles.

Enzymes are present in cytosomal fraction of the cell.

Can occur in Anaerobic : lactate Aerobic : pyruvate

Major pathway of ATP synthesis for tissues lacking mitochondria eg. Erythrocytes, cornea.

Glycolysis

3 phases : 1) Energy investment phase or priming phase

2) Splitting phase

3) Energy generation phase

Energy investment

phase

Splitting phase

Energy Generation Phase

Glycolysis: Generation of ATP

Under anaerobic conditions: 2 ATP are synthesized Under aerobic conditions : 6ATP are synthesized

Pyruvate to Acetyl CoA Pyruvate is converted to acetyl CoA by oxidative decarboxylation.

Irreversible reaction ,catalysed by multienzyme complex pyruvate dehydrogenase complex(PDH), found only in mitochondrion.

It requires 5 cofactors: Thymine pyrophosphate lipoamide FAD coenzyme A NAD+

6 ATP are produced in this step.

Citric Acid Cycle: ( Krebs cycle or Tricarboxylic acid-TCA cycle)

Sir Hans Krebs (1900−1981) . He was awarded the Nobel Prize in Medicine in 1953.

Citric Acid CycleStep I- Condensation reactionCitrate synthetaseStep II - isomerisation

Aconitase

Isocitrate dehydrogenase

Step IV – oxidative decarboxylationFive cofactors:Thymine pyrophosphateLipoamideNAD+FADCoA

α-ketoglutarate dehydrogenase complex.

Succinate thiokinase

Succinate dehydrogenase

Malate dehydrogenase

fumarase

Reaction catalysed by

Method of production of ATP

No. of ATP produced

Isocitrate dehydrogenase

Oxidation of 2 NADH 6

α ketoglutarate dehydrogenase

Oxidation of 2 NADH 6

Succinate thiokinase

Oxidation at substrate level

2

Succinate dehydrogenase

Oxidation of FADH2 4

Malate dehydrogenase

Oxidation of 2 NADH 6

TOTAL 24

Total number of ATP generated from oxidation of 1 molecule of glucose:

Glycolysis 8 ATP

Conversion of pyruvate to 6 ATPAcetyl CoA

Citric acid cycle 24 ATP

TOTAL 38 ATP

Relation With Periodontium

•TCA cycle is ACTIVE in basal and

parabasal layers

•Glucose – 6- phosphatase activity is more

towards surface

•Glycogen concentration is inversily

related to degree of keratinization and

inflammation

•Laminin (glycoprotien)- basal lamina

•The enzymes of the glycolytic cycle: phosphohexoisomerase, aldolase, phosphoglycerokinase and glucose-6-phosphatase were determined in the gingiva, periosteum and periodontium of the mandibular incisor region in the guinea pig and compared with their activities in the liver, kidneys, adrenals, pituitary and testes of the same animal.

{E.H. Charreau, J.A. Kofoed, A.B. Houssay: Enzymes of glycolytic cycle in periodontal tissues of the

guinea pig. Archives of Oral Biology}

Gluconeogenesis

Synthesis of glucose from non-carbohydrate compounds is known as gluconeogenesis.

The major substrates/ precursors are: Lactate Pyruvate Glucogenic aminoacids Propionate Glycerol.

1. Intake of high protein diet

2. During muscular exercise, large amounts of lactic acids is produced, liver picks up the Lactic acid and converts into glucose & glycogen via Cori cycle.

3. During starvation, tissue proteins are broken down and amino acids are utilized for gluconeogenesis.

Regulation of Gluconeogenesis- Glucagon by α-cells

- Availability of substrates

- Alcohol consumption interferes - hypoglycemia

Hexose Monophosphate shunt (HMP shunt)

Also known as Pentose phosphate pathway Phosphogluconate pathway

Alternative pathway to Glycolysis and TCA cycle for oxidation of glucose.

Enzymes located in cytosol

Oxidative phase

Non oxidative phaseRibulose- 5 - phosphate

Glyceraldehyde-3 phosphate

Fructose- 6 phosphate

TPP and Transketolase

Reversal of glycolysis

Glycogenesis

Glycogenolysis • Degradation of stored glycogen in liver and muscle to

glucose.

• Site- cytosol.

• Glycogen is degraded by breaking α-1,4 and β-1,6 glycosidic bonds.

Glycogen Storage DiseasesEnzyme defect

Type I: von Gierke’s disease

Glucose-6-phosphate

Type II: Pompe’s disease Lysosomal α-1,4 glucosidase

Type III: Cori’s disease or limit dextrinosis

Amylo α-1,6 glucosidase (debranching enzyme)

Type IV: Andersen’s disease or amylopectinosis

Glucosyl 4-6 transferase (branching enzyme)

Type V: McArdle’s syndrome

Muscle glycogen phosphorylase

Type VI: Her’s disease Liver glycogen phosphorylase

Type VII: Tauri’s disease Muscle and erythrocyte phosphofructokinase 1

Digestion and Absorption

Digestion Occurs largely in the intestine and briefly in mouth.

In mouth : During mastication, salivary amylase acts on starch cleaves α-1,4-glycosidic bonds.

In small intestine : Pancreatic α amylase acts on starch (specially on α-1,4-glycosidic bonds) to form oligosaccharides and disaccharides (maltose, isomaltose)

Absorption

Glucose accounts for 80% of total monosaccharides

Absorption sites : Duodenum and upper jejunum.

Rate of absorption Galactose > glucose > fructose

Selective permeability : Facilitates absorption of smaller molecules Prevents bigger molecules from being absorbed.

Active transport: Membrane transport system involving active absorption by conc. gradient. This transport is facilitated along with Na+ .(glucose-

Na+ symport) This process requires metabolic energy which is provided by the Na+-K+ ATPase enzyme.

Interaction Between Carbohydrates And Dental

Plaque :Sucrose in the food causes plaque to be copiously produced and of gelatinous nature with much extracellular polysaccharide matrix.

Extracellular polysaccharides help plaque adhere to smooth surfaces and prevent the buffering action of saliva.

References• Carranza’s Clinical Periodontology 10th Edition

• Essentials Of Biochemistry By U Satyanarayana 2nd Edition.

• Harper’s Biochemistry 24th Edition

• Fundamentals Of Biochemistry By Ambika Shanmugan 6th

Edition

• Basic And Dental Applied Biochemistry 2nd Edition RAD

Williams.

• Organic And Biochemistry For Today Spencer L. Seager /

Michael R. Slabaugh 4th Edition

•E.H. Charreau, J.A. Kofoed, A.B. Houssay: Enzymes of glycolytic cycle in periodontal tissues of the guinea pig. Archives of Oral Biology:Volume 11, Issue 7, July 1966, Pages 709–715.

References

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