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46 Cards in this Set
- Front
- Back
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What are the effects of insulin on protein?
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Insulin promotes the uptake of amino acid uptake of cells ad the conversion of these amino acids into protein and it inhibits the breakdown of the proteins that are already in the cells
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Where is insulin formed?
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Most of proinsulin is cleaved in the Golgi apparatus to make insulin
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What are the components of insulin?
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Insulin is made of A and B chains connected by disulifide linkages and the C chain peptide ( the connecting peptide)
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What is the function of C peptide?
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C peptide binds to a membrane receptor and activated two systems: Na-K ATPase and endothelial nitric oxide
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What laboratory test can determine the amount of natural insulin that is being produced?
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Measurement of C-peptide levels by radioimmunoassay can be used in insulin- treated diabetic patients to determine how much of their own natural insulin they are still making.
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What is the plasma half-lie of insulin?
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6 minutes; it is usually cleared from the circulation within 10 to 15 minutes
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What organ is mainly responsible for removing circulating insulin?
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The liver degrades insulin with the enzyme insulinase and to a lesser extent in the kidneys and muscles
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Describe the insulin receptor.
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The insulin receptor is a combination of four subunits help together by disulfide linkages: 2 alpha subunits that lie entirely outside the cell membrane and 2 beta subunits that penetrate through the membrane, protruding into the cell cytoplasm
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What changes occur to the insulin receptor when insulin binds to the receptor?
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Insulin binds to the alpha subunits on the outside of the cell, and the portions of the beta subunit that protrude into the cell become autophorylated
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What are the consequences of the autophosphorlyation of the beta subunits?
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Autophosphorylation of the beta subunits of the receptor activates a local tyrosine kinase this causes the phosphrylation of insulin receptor substrates (IRS)
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What are the most prolonged effects of insulin stimulation?
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There are changed rates of MRNA translation at the ribosomes to form new proteins and changed rates of DNA transcription in the cell nucleus
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What are the most immediate effects of insulin stimulation?
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The membranes of about 80% of the body's cells markedly increase their uptake of glucose and the cell membrane becomes more permeable to many amino acids, K ions, and phosphate ions
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What tissue does not increase their uptake of glucose with insulin stimulation?
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most neurons in the brain
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The normal resting muscle depends on _______ for its energy.
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fatty acids
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What are the two conditions that muscles use large amounts of glucose?
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Moderate or heavy exercise
In the few hours after a meal |
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How can muscles increase the uptake of glucose without insulin doing moderate or heavy exercise?
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Exercising muscle fibers become more permeable to glucose even in the absence of insulin because of the contraction process itself
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How can brain tissue uptake glucose in the absence of insulin/
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Most of the brain cells are permeable to glucose and can use glucose with the intermediation of insulin
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What is the critical level when hypoglycemic shock develops?
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20 to 50 mg/ 100 ml
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What is hypoglycemic shock?
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Progressive nervous irritability that leads to fainting, seizures, and even coma
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What is the principal enzyme that lets glucagon split liver glycogen into glucose?
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Liver phosphorylase
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what is the effect of insulin on liver phosphorylase?
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Insulin inactivates liver phosphorylase?
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How does insulin enhance the uptake of glucose by the liver cells?
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It increases the activity of glucokinase.
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How does insulin promote glycogen synthesis?
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Insulin increase the activities of glycogen synthase.
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How is function of glycogen synthase?
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It is responsible for polymerization of the monosaccharide units to form the glycogen molecules
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How does free glucose enter the blood during an insulin deficiency?
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Glucose phosphatase is activated by the insulin lack and dephosphorylates the glucose to allow the free glucose to diffuse back into the blood.
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What is the fate of the excess glucose after the glycogen stores are used up?
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Insulin promotes the conversion of excess glucose into fatty acids and these are packaged as triglycerides into VLDLs
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What is the role of insulin in the fat deposition?
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It transports glucose into adipose cells mainly for providing substrate for the glycerol portion of the fat molecule
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How does insulin function as a fat sparer?
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Insulin increases the utilization of glucose by most of the body's tissues and automatically decreases the body's utilization of fat
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What is the amount of liver glycogen that inhibits more glycogen synthesis?
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When the liver concentration reaches 5 -6 %.
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Describe the pathway of glucose to fatty acid.
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Glucose is split to pyruvate inthe glycolytic pathway and the pyruvate is converted to acetyl CoA. Acetyl CoA is the substrate for fatty acids
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What are the activating ions for acetyl CoA carboxylase?
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Excess Isocitrate and citrate ions formed by the citric acid cycle when excess glucose is used for energy. These ions activate acetyl CoA carboxylase.
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What is the function of Acetyl CoA carboxylase?
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The enzyme is required to carboxylate acetyl CoA to form malonyl- CoA
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What is the first sat of fatty acid synthesis?
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Taking acetyl CoA to make malonyl CoA
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In what form is triglycerides released in the blood?
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They are packaged in lipoproteins AKA VLDL
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How does insulin help move triglycerides from the blood into adipose tissue?
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Insulin activates lipoprotein lipase in the capillary walls of the adipose tissue
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What is the difference between hormone sensitive lipase and lipoprotein lipase?
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Lipoprotein lipase is found in the capillary walls and hormone sensitive lipase is found inside the adipocyte.
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What is the relationship between insulin and hormone sensitive lipase?
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Insulin inhibits the action of hormone sensitive lipase. This prevents additional trigylcerides from being released in the blood
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What is the role of hormone sensitive lipase?
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It causes the hydrolysis of the trigylcerides already stored in the fat cells
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what is the main function of glucose once it is transported into the adipocyte?
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It forms large quantities of alpha-glycerol phosphate. Alpha gylcerol phosphate supplies the glycerol that combines with fatty acids
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How does insulin deficiency also cause a rise in plasma cholesterol?
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Insulin deficiency causes an activation of hormone- sensitive lipase which floods the blood with free fatty acids. The uptake of free fatty acids by the liver leads to increased phospholipids and cholesterol
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Why does insulin deficiency also cause excess increases in acetoacetic acid?
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In the absence of insulin but in the presence of increased fatty acids --> the liver cells carnitine mitochondrial transport is increased leading to beta oxidation of fatty acids --> large amounts of acetyl CoA --> a large part of the excess of acetyl CoA is condensed to acetoacetic acid
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Name the ketone bodies.
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Acetoacetic acid
Beta-hydroxybutyric acid acetone |
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Why do the levels of ketone bodies rise with insulin deficiency.
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Once large amounts of fatty acids have been beta-oxidized to large amounts of acetyl CoA which condense to acetoacetic acid. These large amounts of acetoacetic acid would normally be shunted to the peripheral cells for conversion back into acetyl CoA.
Insulin deficiency causes decreased utilization of acetoacetic acid. |
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Name the proteins that are strongly transported by insulin.
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Phenylalanine
Leucine Isoleucine valine tyrosine |
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What are the effects of insulin on mRNA and DNA?
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Insulin increases the translation of mRNA by turning on the ribosomal machinery
Insulin increases the rate of transcription of selected DNA genetic sequences --> increased RNA and more protein synthesis |
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What is the effect of insulin on proteins?
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Insulin stimulates the transport amino acids into the cells and inhibits the catabolism of proteins
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