Chapter 18 Resources (scored 92%)

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Biological Sciences
BIOL 2083
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Chapter 18 Carbohydrate MetabolismVocabularyBiotin a CO2 carrier molecule Cori Cycle a pathway in carbohydrate metabolism that links glycolysis in the liver with gluconeogenesis in the liver Debranching Enzyme an enzyme that hydrolyzes the linkages in a branchedchain polymer such as amylopectinGluconeogenesis the pathway of synthesis of glucose from lactateHexose Monophosphate shunt a synonym for the pentose phosphate pathway in which glucose is converted to fivecarbon sugars with concomitant production of NADPHPhosphorolysis the addition of phosphoric acid across a bond such as the glycosidic bond in glycogen giving glucose phosphate and a glycogen remainder one residue shorter it is analogous to hydrolysis addition of water across a bond Pentose Phosphate Pathway a pathway in sugar metabolism that gives rise to fivecarbon sugars and NADPHSubstrate Cycling the control process in which opposing reactions are catalyzed by different enzymesTransaldolase an enzyme that transfers a twocarbon unit in reactions of sugarsChapter 18 Carbohydrate MetabolismChapter SummaryHow does the breakdown of glycogen take place Glycogen can readily be broken down to glucose in response to energy needs Glycogen phosphorylase uses phosphate to break an a14 linkage yielding glucose1phosphate and a glycogen molecule shorter by one glucose Debranching enzyme aids in the degradation of the molecule around the a16linkagesHow is glycogen formed from glucose When an organism has an available supply of extra glucose more than is immediately needed as a source of energy extracted in glycolysis it forms glycogen a polymer of glucose Glycogen synthase catalyzes the reaction between a glycogen molecule and UDPglucose to add a glucose molecule to the glycogen via an a14 linkage Branching enzyme moves sections of a chain of glucoses so that there are a16 branch pointsHow is glycogen metabolism controlledControl mechanisms ensure that both formation and breakdown of glycogen are not active simultaneously a situation that would waste energyWhy is oxaloacetate an intermediate in gluconeogenesis The conversion of pyruvate the product of glycolysis to glucose takes place by a process called gluconeogenesis which is not the exact reversal of glycolysis Glycolysis involves three irreversible steps One of these irreversible steps is the conversion of phosphoenolpyruvate to pyruvate It is favorable to convert pyruvate to oxaloacetate to facilitate the conversion to phosphoenolpyruvateWhat is the role of sugar phosphates in gluconeogenesis The hydrolysis of sugar phosphates is energetically favorable so these steps have the effect of reversing the early energy requiring steps of glycolysisHow does control of key enzymes control carbohydrate metabolismGlycogen synthase and glycogen phosphorylase are reciprocally controlled by phosphorylation Glycolysis and gluconeogenesis are controlled at several points with phosphofructokinase and fructose bisphosphatase being the most important
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