carbohydrates and glycolytic pathway.. periodontics
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Good morning…
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
Thank You…