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CMB311 Ch.25 Test With
Complete Solution
What is cellular respiration (aerobic respiration)? What are the three stagesof cellular respiration (aerobic respiration)? What is oxidative phosphorylation?
- ANSWER - metabolic process leading to uptake of O2 and release of CO producing ATP
- Acetyl-CoA production
- Acetyl-CoA oxidation (citric acid cycle)
- Electron transport chain and oxidative phosphorylation-> re oxidation of the reduced cofactors is coupled to the synthesis of large amounts of ATP
What is glycolysis? How does it fit into the "three stages of aerobic respiration"? - ANSWER - Glycolysis is the initial stage of cellular respiration, occurring in the cytoplasm
How many ATP, NADH and pyruvate molecules does it produce (from one glucose)? What are the fates of pyruvate from glycolysis? - ANSWER - 2 ATP, 2 NADH, 2 Pyruvate
What are the basics of glycolysis? - ANSWER - incomplete glucose oxidation
- happens in cytoplasm
- 1 glucose (6-carbon) splits to form 2 molecules of pyruvate(3-carbon)
- no carbon released
- 2 NAD+ reduced to 2 NADH
What is glycolysis "preparation" phase? What are the five reactions in the prep phase? What are the substrates, products, enzymes, and special characters for each reaction? What are the structures of the molecules involved in each reaction? - ANSWER - glucose mol converted to two triose phosphate mol. (glyceraldehyde 3-phosphate, GAP) at the expense of 2 ATP
STEP 1- formation of glucose 6-phosphate-- ATP hydrolysis drives the rxn (couple rxn cost 1 ATP)
- negative charge traps
- intro pyruvate
STEP 2- Isomerization-- make C1 avail for phosphorylation, prepare for cleavage
STEP 3- second phosphorylation-- "commitment step"; cost 1 ATP; fructose 6-phosphate (F-1), fructose 1,6-biphosphate (6-bisP), phosphofructokinase- (PFK-1)
STEP 4- Adol cleavage(actual glycolytic rxn)-- proceeds in forward direction bc rxn products removed quickly, "pulling" the rxn in the direction of the cleavage; 6-bisP-> dihydroxyacetone phosphate + glyceraldehyde 3-phosphate
STEP 5- Isomerization-- ketose<-> aldose; triose phosphate isomerase
What is glycolysis "payoff" phase? What are the five reactions in the payoff phase? What are the substrates, products, enzymes, and special characters for each reaction? What are the structures of the molecules involved in each reaction? - ANSWER
ANSWER feeder pathways
Why metabolic pathways need to be regulated? What are the control points in glycolysis - ANSWER - to control the rate of the respective pathway and whether it is turned on or shut off
-phosphofructokinase-
-pyruvate kinase
What is hexokinase? What are isoenzymes (isozymes)? What are the two types of hexokinase isozymes? How are they different? Is hexokinase inhibited by glucose-6-phosophate in liver? - ANSWER - used to keep glucose in the cell: enzymes introducing PO4 on glucose, using ATP
- hexokinases I-III
- low Km: .1 mM, located in all tissues except liver
- inhibited by glucose 6-phosphate
- glocokinase
- high Km: 10 mM, primarily in liver (pancreas, small intestine, and brain)
- not inhibited by glucose 6-phos
Why we say that phosphofructokinase regulation is complex? How does fructose-2,6-biosphosphate regulate phosphofructokinase (positive or negative) - ANSWER - ATP is required, ut if high, can also bind to allosteric site and inhibit PFK-
- this is relived by AMP, which competes with ATP for binding at the
allosteric site
- Fructose-2,6-bisphosphate is a positive allosteric regulator of phosphofructokinase-1 (PFK-1), activating the enzyme. (allosteric activator)
26 - ANSWER
What are the general properties of glycogen? - ANSWER - highly branched
- made in animals, starch made in plants
- only one reducing end
(breakdown starts from the non reducing ends)
How is glycogen broken down? What is the major enzyme? What does glycogen phosphorylase do? What molecule does the reaction catalyzed by glycogen phosphorylase release? (product) - ANSWER - glycogen phosphorylase
- works on non reducing end of glycogen, releases a glucose 1-P
- cleaves by addition of orthophosphate to yield glucose 1-phosphate
- cleavage of a bond by the add of orthophosphate= "phosphorolysis"
- orthophosphate splits the glycosidic linkage between C-1 and C-
What do transferase and debranching enzyme do? (brief) - ANSWER - shifts 3 glucose residues from one outer to another
- exposes a single glucose residue joined by a alpha-1,6-Gloucosidase
- free glucose molecule is released
Once glucose-1-phosphate is released, what happens next? - ANSWER -
Does glucose-1-phosphate need to be "activated" first (to be added to glycogen)? - ANSWER yes
What are the different general properties of glycolysis and gluconeogenesis, respectively? - ANSWER - glycolysis- catabolic, oxidative (NADH reduced), yields energy (net 2ATP), spontaneous, exergonic
- gluconeogenesis is the anabolic pathway that synthesizes glucose from non carbohydrate carbons such as pyruvate, lactate, glycerol, glucogenic amino acids
- mainly in liver
- non spontaneous, endergonic, requires energy, anabolic
What is gluconeogenesis? Is it an "exact reversal" of glycolysis? - ANSWER NO
What are the three "irreversible" steps of glycolysis? What does "irreversible" mean? How are they actually "reversed" in gluconeogenesis?Using what four enzymes? - ANSWER irreversible (cannot use the same enzyme)
1.) phosphoenolpyruvate to pyruvate + ATP (pyruvate kinase)
2.) fructose-6-phosphate to fructose-1,6-biphosphate (phosphofructokinase-1)
3.) glucose to glucose-6-phosphate (hexokinase)
How about the seven "reversible reactions"? Does gluconeogenesis use the same seven enzymes as in glycolysis? - ANSWER yes
What molecules can be used to do gluconeogenesis? (produce sugar) - ANSWER pyruvate, lactate, glycerol, glycogenic amino acids
What is the major site (organ) of gluconeogenesis? - ANSWER liver
In gluconeogenesis starting from pyruvate, how does pyruvate change into phosphoenolpyruvate (PEP)? What are the two steps and the enzymes used? Where does the first step happen? (mitochondria or cytoplasm).What is the entire process involving both mitochondria and cytoplasm? - ANSWER - pyruvate enters mitochondria
- pyruvate-> oxaloacetate using 1ATP (requires biotin (CO2 carrier))
- decarboxylation of oxaloacetate is couple w/ phosphorylation by GTP to give PEP
-oxaloacetate-> malate in mitochondrial matrix (reduction, using NADH)
- malate shuttled into cytoplasm and converted to oxaloacetate (oxidation, generating NADH)
pyruvate in, malate out
fermentation- energy yielding anaerobic breakdown of a carb breaks down into acids, gases, or alcohol in the absence of oxygen or electron transport chain
Is glycolysis an anaerobic process? Does glycolysis need NAD+? Which reaction needs NAD+? - ANSWER -itself is anaerobic but it can be part of aerobic respiration, in which the NAD+ is regen in the electron transport chain, which uses O
How can NAD+ be generated anaerobically? Which molecule is reduced to regenerate NAD+? - ANSWER - under anaerobic conditions: cannot send NADH to electron transport, cannot deoxidize NADH to NAD+ by O2, therefore: lattice acid fermentation, alcohol fermentation
- pyruvate needs to be reduced
How can pyruvate be used to generate lactate or ethanol? What is the"purpose" for this pyruvate reduction for the organism? Do muscles generate lactate during vigorous exercise? Do we generate ethanol? - ANSWER - under anaerobic conditions, regen of NAD+ is reduction of pyruvate to lactate
-fermentation of pyruvate to lactate regen both the NAD+ mols used in glycolysis
- true for both microorganisms and muscles
-two rxn lead to the production of ethanol: decarboxylation of pyruvate to acetaldehyde, reduction of acetaldehyde to ethanol
Fermentation is used in the process of making what food products? - ANSWER alcohol
What enzymes are used in pyruvate reduction? What are the cofactors for pyruvate decarboxylase? - ANSWER -Thiamine and Thiamine Pyrophosphate (TTP)
Do we have alcohol dehydrogenase? What do we use it for? - ANSWER - yes, we only use it for the reverse rxn, to detoxify ethanol
Look at the three stages of aerobic respiration, what is the step between glycolysis and Citric Acid Cycle (TCA Cycle) - ANSWER - pyruvate to acetyl-CoA
How is pyruvate converted to acetyl-CoA? Where in the cell does it happen? Is this an oxidative decarboxylation reaction? What happens in this reaction? What is the enzyme complex for this reaction (which contains three enzymes)? What are the five cofactors used in this reaction? - ANSWER - oxidative decarboxylation in mitochondrial matrix (irreversible)
- decarboxylation of alpha-keto acid
- FMN, FAD = oxidized forms
- FMNH2, FADH2 = reduced forms
Lipoic Acid
- can carry an acetyl (acyl)
Coenzyme A
- Can carry an acetyl (acyl)
- Acetyl-CoA has a high acyl-group transfer potential = hydrolysis releases energy
- acetyl-coa is a thioester
How is PDH reaction? Is it an alpha-keto acid decarboxylation or beta-keto acid decarboxylation? Does it release CO2? How does it compare to pyruvate->ethanol reaction? - ANSWER - decarboxylation of pyruvate and transfer of hydroxyethyl group to TPP
- oxidation of the hydroxyethyl group to acetyl group (lipoate receives both electrons and acetyl group), oxidizing agent is lipoic acid, E
- transacetylation (from lipoate to CoA) CoA-SH, with E
- re oxidation of reduced lipoate, HS-Lip-SH reoxidizes back to oxidized lipoic acid by FAD, with E
- re oxidation of FADH2 to FAD by NAD+ with E
Does the product of PDH reaction, acetal-CoA, have a high acyl-group transfer potential? (Does its hydrolysis release a lot of energy?) - ANSWER Pyruvate -> PDH -> Acetyl CoAPyruvate -> acetaldehyde -> ethanol
Acetyl-CoA has a high acyl-group transfer potential= hydrolysis releases energy
How does PDH reaction happen? Which group is converted to CO2? How are the five coenzymes involved in this reaction (order of reactions)? Which carbon (in pyruvate) attaches to TPP? What is the "electron transfer"process?
- ANSWER 1) Thiamine Pyrophosphate
lipoic acid oxid
FAD -> FADH
NAD+ -> NADH
28 - ANSWER
What is the central role of the TCA Cycle? Is it "amphibolic"? Why? - ANSWER
- It plays a central role in aerobic metabolism. yes bc does both.
- The TCA cycle oxidizes Acetyl group and sends the electrons to the electron
When a glucose or a pyruvate molecule is fully catabolized, all carbons are oxidized to CO2, in what pathways are they oxidized? (after we learn TCA cycle, you should understand this.) - ANSWER Glucose Catabolism (Glycolysis)
Pyruvate Decarboxylation
Citric Acid Cycle (Krebs Cycle)
What are the 8 intermediates of the TCA cycle? What is the entrance molecule of the TCA cycle? (this molecule enters the TCA cycle, not one of the intermediates) - ANSWER enter: citrate
- citrate synthase
- aconitase
- isocitrate dehydrogenase
- alpha- Ketoglutarate dehydrogenase complex
- succinyl CoA synthetase
- fumarase
- malate dehydrogenase
exit: oxaloacetate
What are the eight reactions of the TCA Cycle? What are the substrates, products, enzymes, and special characters for each reaction? What are the structures of the molecules involved in each reaction? (All the reactions are
important) - ANSWER Step 1 - citrate synthesis
deltaG= -32.2 kj/mol
Step 2 - isocitrate formation, citrate to isocitrate
Step 3 - oxidativede carboxylation, isocitrate to alpha-ketoglutarate, decarboxylate of beta-keto acid, -20.9 kj/mol
Step 4 - oxidative decarboxylation; alpha-ketoglutarate to succinyl CoA
Step 5 - Substrate level phosphorylation; succinyl-CoA hydrolysis-> succinate, -2.9 kj/mol
Step 6 - alkyl chainoxidation; only rxn in TCA cycle that happens on mitochondria inner mem., all other happen in matrix
Step 7 - hydration of fumarate to form malate, -3.8 kj/mol
Step 8 - formation of oxaloacetate; most endergonic, non spontaneous, the product is effectively removed in step 1 (thirster hydrolysis)
"pulls" this rxn to happen, 29.7 kj/mol
How is Krebs Cycle regulated? - ANSWER - highly regulated entrance + oxidative decarboxylation rxns
- ATP/NADH
- immediate product
- distant product
Where does fatty acid beta-oxidation happen (in which organelle)? - ANSWER - the mitochondria (some in peroxisomes)
How is triacylglycerol is broken to release fatty acids? What is the enzyme? - ANSWER - lipases catalyze hydrolysis of bonds between fatty acids and the rest of tricylglycerols
How does fatty acid get "activation"? what is the reaction, what is the enzyme, and where does this reaction happen (in which organelle)? - ANSWER - on the outer mitochondrial membrane, a fatty acid must be activated before transport into formation of acyl-CoA (catalyzed by acyl-CoA synthetase)
How are "activated" fatty acids (Acyl-CoA) transported into the mitochondria? - ANSWER - acyl-CoA -> Acyl-carnitine by carnitine acyltransferase I
- acyl-carnitine enters mitochondrial matrix by carnitine translocate across the mitochondrial inner mem.
- acyl-carnitine -> acyl-CoA by carnitine acyltransferase II in the mitochondrial matrix
What is exactly fatty acid beta-oxidation? What are the products? Why it is
called beta-oxidation? - ANSWER - beta-oxidation: a series of reactions that cleaves carbon atoms '2 at a time from the CoA(carboxyl) end , releasing acetyl-coa, FADH2, NADH
- 8 cyclee of beta oxidation, releases 9 '2-carbon' units
What are the four reactions in a complete cycle of beta-oxidation? (four steps, know what happens in each step) Are you able to recognize the reactants and products (and their structures) for each step? - ANSWER 1.) oxidation: of them alpha, beta carbon-carbon single bond to a carbon-carbon double bond
2.) hydration: of the carbon-carbon double bond
3.) oxidation: of the beta-hydroxyl group to a carbonyl group
4.) cleavage: of the carbon chain using another CoA-SH
What are the stages of fatty acid complete oxidation? Is beta-oxidation the end of fatty acid oxidation? - ANSWER - beta-oxidation of acyl-chain-> acetyl-CoA
- oxidation of acetyl-CoA->CO
- electron transfer->ATP
- beta-oxidation of acyl-chain-> NADH, FADH
- electron transfer-> ATP
