Functions of Insulin

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Functions of Insulin:

Functions of Insulin

INTRODUCTION:

INTRODUCTION Insulin > protein hormone > by islets of langerhans > pancreas Anabolic hormone > growth & development

HISTORY:

HISTORY Canadian scientist (1921) Fredrick G. Banting Charles H. Best extracted insulin from dog’s pancreas

STRUCTURE OF INSULIN:

STRUCTURE OF INSULIN Insulin Polypeptide hormone 51 amino acids Two chains A chain 21 a.a. B chain 30 a.a. Held by interchange disulfide bridges

BIOLOGICAL EFFECTS OF INSULIN:

BIOLOGICAL EFFECTS OF INSULIN

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INSULIN – Hormone Associated with Energy Abundance 1.Effect on Carbohydrate Metabolism A. Promotes Muscle Glucose Uptake and Metabolism -Storage of Glycogen in Muscle B. Promotes Liver Uptake, Storage and Use of Glucose Mechanisms: a. inactivates liver phosphorylase b. causes enhanced uptake of glucose from the blood by the liver cells (by increasing the activity of the enzyme glucokinase

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C. increases activity of enzyme glycogen synthase , that promote glycogen synthesis - Glucose is released from the liver between meals Lack of insulin activates Phosphorylase , which causes splitting of glycogen into glucose phosphate - Insulin promotes Conversion of Excess Glucose into fatty Acids and Inhibits Gluconeogenesis in the liver

Effect on carbohydrate metabolism:

Effect on carbohydrate metabolism  Glucose uptake Skeletal muscles Cardiac muscles Adipose tissue Mammary glands

Effect on carbohydrate metabolism (contd):

Effect on carbohydrate metabolism ( contd ) Insulin independent tissues Brain RBC Testis Kidney Retina Intestinal mucosal cells

CARBOHYDRATE METABOLISM:

CARBOHYDRATE METABOLISM Metabolism Net Effect Effect on important enzyme Glycolysis Increased Glucokinase Phosphofructokinase Pyruvate kinase Glycogenesis Increased Glycogen synthatase HMP shunt Increased Glucose 6-phosphate dehydrogenase Gluconeogenisis Decreased Pyruvate carboxylase Phosphoenol Pyruvate carboxylakinase Glucose 6-phosphatase Glycogenolysis Decreased Glycogen phosphorylase

INSULIN MEDIATED GLUCOSE UP TAKE:

INSULIN MEDIATED GLUCOSE UP TAKE

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C. Lack of Effect of Insulin on Glucose Uptake and Usage by the Brain

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2. Effect on Fat Metabolism A.Insulin promotes Fat Synthesis and Storage - Storage of Fat n the Adipose Cells a. insulin inhibits the action of hormone-sensitive lipase b. insulin promotes glucose transport through the cell membrane into the fat cells

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B. Insulin deficiency Causes Increase Metabolic Use of Fat causing a . Lipolysis of Storage Fat and Release of Free Fatty Acids b. Increase Plasma Cholesterol and Phospholipid c. Excess Usage of Fats during Insulin Lack Causes Ketosis and Acidosis

Lipid Metabolism:

Lipid Metabolism Metabolism Net effect Effect on important enzymes Lipogenesis Increased DeNovo FA Synthesis Increased Acetyl CoA carboxylase Avalbility of NADPH Adipose tissue Increased Provide α -glycerol-3-PO 4 Lipoprotein lipase Lipolysis Decreased Hormone sensitive lipase Ketogenesis Decreased HMG CoA synthetase Lipoprotein Increased Utilization of VLDL & LDL

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3. Effect of Insulin on Protein Metabolism A. INSULIN PROMOTES PROTEIN Synthesis and Storage a. stimulates transport of amino acids into the cells ( valine, leucine, isoleucine, tyrosine, phenylalanine ) b. increases the translation of messenger RNA, forming new proteins c. increases the rate of transcription of DNA genetic sequences in cell nuclei d. inhibits catabolism of proteins e. depresses the rate of gluconeogenesis

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B. Insulin Lack Causes Protein Depletion and Increased Plasma Amino Acids - protein wasting is one of the most serious of all effects of severe diabetes mellitus C. Insulin and Growth Hormone Interact Synergistically to Promote Growth INSULIN PROMOTES PROTEIN FORMATION AND PREVENTS DEGRADATION OF PROTEINS

Protein Metabolism:

Protein Metabolism Metabolism Net Effect Effect on important enzymes Protein synthesis Increased RNA polymerase Amino acids up take Protein degradation Decreased Transaminases Deaminases

CELL GROWTH & DEVELOPMENT:

CELL GROWTH & DEVELOPMENT Promote cell growth and development Mediated by Epidermal growth factors. Platelet derived growth factor. Prostaglandings .

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