TAMU BICH 411 - Exam 3 Study Guide (14 pages)

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Exam 3 Study Guide

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Exam 3 Study Guide


A review of chapters 22-24.

Study Guide
Texas A&M University
Bich 411 - Comprehen Biochem Ii
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Bich 411 1st Edition Exam 3 Study Guide Lectures 1318 Chapters 22 24 Chapter 22 lectures 13 15 Gluconeogenesis forming glucose from metabolites necessary for the body to maintain its own energy mostly in the endoplasmic reticulum of the liver and kidneys gluconeogenesis can use pyruvate lactate glycerol amino acids and all TCA intermediates fatty acids can t be used note that it s not just reversed glycolysis when one is on the other is off reciprocal regulation see figure 22 1 it relates glycolysis and gluconeogenesis gluconeogenesis uses steps 2 and 4 9 of glycolysis to produce glucose pyruvate carboxylase and PEP carboxylase replace pyruvate kinase Fructose 1 6 bisphosphatase replaces phosphofructokinase Glucose 6 phosphatase replaces hexokinase Unique Gluconeogenesis reactions Step 1 pyruvate HCO3 ATP oxaloacetate ADP Pi with Pyruvate Carboxylase Requires ATP and bicarbonate It is also very biotin dependent biotin linked with lysine Acetyl coA is an allosteric activator Also note that when ATP or acetyl CoA concentrations are high pyruvate enters gluconeogenesis This reaction is the initiation of gluconeogenesis Step 2 Oxaloacetate GTP PEP GDP CO2 with PEP carboxylase This reaction gets its energy from decarboxylation and GTP hydrolysis Step 3 Fructose 1 6 Bisphosphate H2O Fructose 6 Phosphate Pi with Fructose 1 6Bisphosphatase Fructose 1 6 Bisphosphatase is regulated by citrate positively and fructose2 6 bisphosphatase and AMP negatively Step 4 Glucose 6 Phosphate Glucose with Glucose 6 Phosphatase This involves 3 transport proteins T1 is responsible for taking Glucose 6 phosphate to the endoplasmic reticulum T2 exports glucose to the cytosol T3 exports inorganic phosphates to the cytosol GLUT 2 transporter takes the glucose out of the endoplasmic reticulum and cell Net equation 2 pyruvate 4ATP 2 GTP 2 NADH 2 H 6 H2O 1 glucose 4 ADP 2 GDP 6 Pi 2 NAD Metformin stimulates the glucose transporters 3 Mercaptopicolinate and hydrazine inhibit the oxaloacetate PEP reaction Chlorogenic acid inhibits glucose 6 phosphatase S 3483 does the same Cori cycle The liver is very important during exercise Lactate is reoxidized in the liver by lactate dehydrogenase LDH to pyruvate The pyruvate is eventually converted to glucose note that the liver has high NAD NADH while the muscle has low NAD NADH Regulation For glucose 6 phosphatase the more substrate the more enzyme is activated the other regulators are allosteric acetyl CoA AMP citrate Fructose 2 6 bisphosphate memorize figure 22 8 Glycogen at the end of gluconeogenesis glucose becomes glycogen branched polymers This involves glycogenolysis glycogen comes from anything consumed that s starch broken down by alpha amylase endoglycosidase breaks alpha 1 4 bonds internally Stops 4 units before branch debranching enzyme cleaves four remaining units limit dextrin Transfer the three outer glucose groups cleaves the remaining glucose Glycogenolysis releases a glucose 1 phosphate rearranges glycogen and converts glucose 1phosphate to glucose 6 phosphate The fate of glucose 6 phosphate depends on what is needed It can enter glycolysis like if you re running become glucose if you re hungry or starving or enter the pentose phosphate pathway electrons for biosynthesis or ribose for making nucleic acids special note Tissue glycogen stored in the liver and muscle is where the energy comes from when broken down Glycogen phosphorylase cleaves glucose from non reducing ends remember that alpha amylase cleaves internal bonds These have cleave differently The produce sugarphosphate is a good glycolysis substrate The product Glucose 1 phosphate doesn t go to ATP Glycogen synthesis derivitizing glucose activates it UDP glucose pyrophosphorylase causes phosphoanhydride exchange the reaction involves spontaneous hydrolysis End result is UDP glucose activated form of glucose for synthesis of glycogen glycogenin protein initiates glycogen formation Glucose is added to OH on Tyrosine Sugar units added glycogen synthase via alpha 1 4 bonds UDP glucose loses glycosyl units to C 4 hydroxyl of glycogen strand an oxonium intermediate is involved The branching enzyme is responsible for forming the branches Glycogen synthesis Net reaction Glucose 6 Phosphate ATP Glycogenn H2O Glycogenn 1 ADP 2 Pi Enzymes involved phosphoglucomutase UDP glucose pyrophosphorylase Inorganic pyrophosphatase glycogen synthase nucleotide diphosphokinase Issues with diabetes ligation disease in diabetes glucose can form Schiff base linkages which undergo Amadori rearrangements to form Glycation end products AGEs irreversible measure glycated hemoglobin for diagnostics RAGE receptor for advanced glycation end products protein in immune systems can trigger intracellular responses in diabetics Glycogen Metabolism glycogen metabolism is highly regulated involves glycogen phosphorylase GP and glycogen synthase GS reciprocal regulation both regulations involve phosphorylation GP is activated by AMP turns on inhibited by ATP glucose 6 Phosphate and caffeine turn off GS is stimulated by glucose 6 phosphate regulated by covalent modification GS I dephosphorylated form insensitive to glucose 6 P GS D phosphorylated form can be activated by glucose 6 phosphate dephosphorylation by phosphatase like PP1 activates GS and inactivates GP Insulin binding of insulin triggers protein kinase cascades GS stimulated has several effects job is to lower blood sugar wants to dump glucose out of blood to glycogen ATP amino acids etc glucose uptake activates glycogen synthase Hormone regulation glycogen metabolism regulated by hormones like insulin glucagon epinephrine and glucocorticoids insulin stimulates glycogen synthesis gets rid of glucose glucagon and epinephrine cause glycogen breakdown want to increase glucose Figure 22 20 is helpful to know for the quiz glucagon acts in liver and fat tissue activates glycogen breakdown and gluconeogenesis maintenance reactions epinephrine acts in liver and muscles activates glycolysis fight or flight reactions Glucocorticoids act on liver skeletal muscle and fatty tissue Cortisol is catabolic acts on skeletal muscle protein breakdown and liver gluconeogenesis Example Problems practice these for the test if fructose 1 6 bisphosphate is high what is effect on glycolysis and gluconeogenesis It increases glycolysis What is effect of increased blood glucose concentration Gluconeogenesis turns off glycolysis turns off Glycogen synthesis increases What is effect of high insulin

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