MCB 2000 Final Exam Questions And Answers (Verified And Updated)

MCB 2000 Final Exam Questions And Answers (Verified And Updated) When does the synthesis of lipid occur? - answerHigh I/G ratio, excess calorie intake (excess carbons from glucose or excess dietary protein) What tissues are involved in the synthesis of lipids? - answerLiver (primary site in humans - 90%), adipose tissue How are the structures of triglycerides and phospholipids similar? - answerBoth contain a glycerol backbone w/ 2 fatty acids attached, BUT PL attach a phosphate group w/ alcohol or polar head group and TG attaches a third fatty acid What determines the fate of acetyl CoA? How? - answerInsulin: if levels are high makes fatty acids, if levels are low (diabetic) makes ketone bodies (used by brain for energy reducing reliance on glucose) What happens if carb intake is restricted? - answerInsulin level is restricted and the body thinks it's in a fasted state, so it breaks down fat for energy What is needed for fatty acid synthesis? (3) - answerAcetyl CoA, NADPH, high I/G How is OAA used in FA synthesis in regards as an energy source? - answerOAA is converted back to malate (malic enzyme) which is converted back to pyruvate (malate dehydrogenase) and forms NADPH in the process Why is OAA converted back to malate after it was split by citrate lyase to produce OAA and acetyl CoA for FAS? - answerOAA needs to go back to the mitochondria for TCA, but cannot cross the mitochondrial membrane Fatty acid synthesis integrates what 3 pathways? - answerGlycolysis, TCA cycle - citrate synthase, pentose phosphate pathway (ALL occur in the fed state in the liver) How many acetyl CoA's are activated in FA synthesis? - answer7 (first one doesn't get activated) How are fatty acids (16C) formed from acetyl CoA (2C)? - answerATP is consumed (activation step), activated acetyl CoA is converted to malonyl CoA (acetyl CoA carboxylase), malonyl CoA is decarboxylated and donates 2C which are used for FAS along with NADPH which powers the chain to grow to 16C (palmitate) How many ATPs are needed for the activation step of FAS? - answer7 How is acetyl CoA an allosteric regulator? - answer(+) for pyruvate carboxylase - pyruvate forms OAA when there's too much acetyl CoA and little OAA bc OAA needs to bind first to citrate synthase, (-) for PDC - pyruvate naturally goes through PDC to make acetyl CoA and makes too much Why does pyruvate carboxylase and PDC fluctuate and how is this related to FAS? - answerBoth products from each process (OAA and acetyl CoA) are needed to make citrate which can exit the mitochondria and dissociate into acetyl CoA and OAA (citrate lyase rxn), the acetyl CoA which is now in the cytoplasm can be used for FAS What happens to ATP when citrate that exits the mitochondria to the cytoplasm is cleaved into OAA and acetyl CoA for FAS? - answerATP is hydrolyzed Where does NADPH come from for FAS (2 sources)? - answerPentose-phosphate pathway (converting G-6-P to F-6-P turns NADP+ to NADPH) and malic enzyme (converting malate to pyruvate turns NADP+ to NADPH) What is the second activation/rate limiting step of pre-FAS? What happens? - answerAcetyl CoA carboxylase - ATP, biotin, and bicarbonate are added to acetyl CoA to form malonyl CoA (consuming ATP) which decarboxylates (losing CO2 and carboxyl) and donates 2C (acetyl CoA) for fatty acid synthesis Why is acetyl CoA carboxylase (ACC) considered irreversible and committed? - answerThere's no other place malonyl CoA can go except FAS How is ACC hormonally regulated pre-FAS? - answerFasted: AMP activates AMPK which converts ATP to ADP donating a phosphate onto ACC which inactivates it Fed: Insulin stimulates protein phosphatase 2A to remove the phosphate from ACC activating it How is ACC allosterically regulated? - answerCitrate triggers polymerization of inactive dimers activating ACC (more citrate = more acetyl CoA = more malonyl CoA) Palmitoyl CoA causes depolymerization bc it's the end product of FAS and inactivates ACC (feedback inhibition: have product = no need to form more) Which regulation of ACC hormonal or allosteric allows for FAS to occur quicker? - answerAllosteric bc citrate builds up faster in the fed state than insulin and is used to make acetyl CoA for FAS What are the 3 types of reactions in lipogenesis (extension of the fatty acid chain) - answerCondensation, reduction, dehydration reactions