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66 Cards in this Set
- Front
- Back
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What is the goal of glycolysis? |
Partial oxidation of glucose |
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What happens to glucose in glycolysis? |
One 6-carbon poly-hydroxy aldehyde is oxidized to two 3-carbon alpha keto carboxylic acids (pyruvate)
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What about glucose was so evolutionarily favorable? |
1) It can be formed from formaldehyde under prebiotic conditions 2) Stable ring form due to equitorial d or alpha form |
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What enzyme breaks down glucose in the mouth and gut? What are they breaking down? |
Alpha-amylase break down starch and glycogen |
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What glucose polymer is indigestible by mammals? |
Cellulose |
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What does the energy requiring phase of glycolysis achieve? |
Splitting of glucose into 2 interconvertible 3-C sugars which end up as 2 glyceraldehyde 3 phosphates from 1 glucose |
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What are the energy requiring enzymes in phase 1 of glycolysis? What do these enzymes achive? |
1) Hexokinase phosphorylates glucose to glucose 6-phosphate to trap it in the cell 2) Phosphofructokinase converts Fructose 6-phosphate into fructose 1-6, bisphosphate so that it can be split into 2 3-C molecules |
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What does the second phase of glycolysis achieve?q |
2 molecules of glyceraldehyde 3-phosphate are oxidized to pyruvate and generate 2 ATP per glucose |
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What enzyme of glycolysis produce high-energy electrons as NADH? What does this enzyme do? |
1) Glyceraldehyde 3-phosphate dehydrogenase oxidizes the aldehyde hydrogen with NAD+ and replaces it with inorganic phosphate producing NADH Oxidative phosphorylation |
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What enzymes produce energy as ATP in the second phase of glycolysis? What do these enzymes do? |
1) Phosphoglycerate kinase replaces one of the phosphoryl groups 1,3-bisphosphoglycerate with a COO- yielding 3-phosphoglycerate and converting ADP to ATP (Substrate level phosphorylation) 2) Pyruvate Kinase replaces the phosphoryl group of phosphoenolpyruvate with a carbonyl shifting the double bond from C=C to C=O and yielding final pyruvate |
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Why is hexokinase's conversion of glucose into G-6P not glycolysis commiting? |
It can be used in glycogen synthesis, pe |
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Describe how hexokinase binds glucose |
Induced fit |
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Describe the mechanism of phosphoglucose isomerase |
1) The enzyme opens the ring 2) Abstraction of C2 and e- pushing so that the aldehyde carbonyl abstracts a hydrogen 3) Electronic addition of hydrogen from enzyme and formation of ketone at C2 with loss of proton 4) Ring closing |
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What form of catalysis does phosphoglucose isomerase use and how? |
General Acid base catalyst by abstracting hydrogen from C2 and donating it to C1 |
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What does aldolase do? |
Splits Fructose 1-6,bisphosphate into DHAP which is isomerized into glyceraldehyde 3-phosphate and generates another glyceraldehyde 3-phosphate |
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What enzyme isomerizes the products of Fructose 1,6-bisphosphate clevage? What does the isomerization achieve? |
Triose phosphate isomerase converts DHAP into GAP by converting a ketone to an aldhyde |
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Describe the mechanism of Triose phosphate isomerase |
1) Abstraction of H+ from C1 and e- pushing so that the C2 carbonyl abstracts a proton to form OH 2) Abstraction of H+ from C1 OH to form enediol 3) electronic addition to C2 with formation of aldehyde at C1 |
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What is the function of Glu 165 in triose phosphate isomerase? What is it's initial charge? |
Abstracts proton from C1 and donates it back to C2 Acid-base catalyst COO- |
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With is the function of His 95 is triose phosphate isomerase? What is its initial charge? |
Donate proton to C2 and abstraction from C1 OH Acid-base catalyst Neutral |
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Why would urea affect TPI catalysis? |
Inhibits acid-base catalysis through hydrogen bonding |
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What is the function of the thioester intermediate is glyceraldehyde phosphate dehydrogenase? |
It couples the oxidation and acyl-phosphate formation reactions to reduce the large free energy change |
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Describe the mechanism of glyceraldehyde 3 phosphate dehydrogenase? |
1) Cys recruits G3P to form hemithioacetal 2) NAD+ is reduced by abstracting aldehyde H- with concomitant abstraction of H+ from OH to form carbonyl thioester intermediate 3) NADH is replaced by NAD+ which polarizes the thioester 4) Phosphorylation of polarized thioester, and cleavage of thioester bend |
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What is the role of Histidine in glyceraldehyde 3-phosphate dehydrogenase? |
Abstraction of H+ from hemithioacetal to allow thioester formation and then donation of H+ to reduce sulfur of the thioester bond and cleavage Acid-base catalyst |
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What is the role of NAD+ is glyceraldehyde 3-phosphate dehydrogenase? |
Electron acceptor Base catalyst |
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Together, phosphoglycerate mutase, enolase, and pyruvate kinase, achieve what? and how? |
1) transfer of phosphoryl to C2 for increased (-) (-) repulsion 2) Dehydration 3) Dephosphorylation All this to make a high-phosphate transfer molecule and produce ATP |
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What are the 3 fates of pyruvate |
1) Fermentation to ethanol and lactate 2) Complete oxidation of CO2 and H2O |
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What 2 enzymes achieve the conversion of Pyruvate into ethanol and how? |
1) Pyruvate decarboxylase decarboxylates pyruvate to aldehyde 2) Alcohol dehydrogenase reduces acetaldehyde by oxidizing NADH |
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What enzyme is responsible for the conversion of pyruvate into lactate and how? |
Lactate dehydrogenase reduces pyruvate to lactate by oxidizing NADH |
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What is the point of oxidizing NADH in fermentation? |
Regeneration of NAD+ allows for more formation of ATP anaerobically for use by glyceraldehyde 3-phosphate dehydrogenase |
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How can we use dietary fructose in glycolysis? |
Phosphprylate it to fructose-6-phosphate from adipose tissue Convert it into DHAP from the liver |
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What cofactors and conditions are needed for aldolase? |
An acid and a Zn |
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What is the net output of the oxidation of 1 glucose to 2 molecules of pyruvate? |
2 ATP + 2 NADH |
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Why can't cells use the breakdown of glucose to pyruvate to generate energy without further fermentation or respiration? |
We need to regenerate NAD+ for use by glucose-3 phosphate dehydrogenase |
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How do we generate energy from lactose? |
Lactase breaks it into galactose and glucose Galactose is them converted into G-6P |
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How do we generate energy from sucrose? |
Invertase breaks the disaccharide into 2 glucose |
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What enzymes allow us to use fructose via the fructose 1-phosphate pathway? What is their end product? |
Fructose kinase Fructose 1-phosphate aldolase Triose Kinase Glyceraldehyde 3-phosphate |
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How do we convert Galactose into glucose 6-phosphate? |
1) Phosphorylate to Galactose 1-phosphate 2) Form UDP-Galactose from UDP-Glucose forming Glucose 1-phosphate 3) Epimerize UDP-Galactose to UDP-Glucose to be used in step 2 4) Isomerize glucose 1-phosphate to glucose 6-phosphate At the expense of 1 ATP |
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What is the primary site of gluconeogenesis in mammals? |
Liver |
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What are the 3 enzymes at the irreversible steps of gluconeogenesis? |
Glucose-6-phophatase Fructose-1,6-bisphospatase Pyruvate Carboxylase and PEPCK |
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What are the 3 enzymes at the irreversible steps of glycolysis? |
Hexokinase
Phosphofructosekinase Pyrvuate kinase |
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What are the 3 irreversible steps of gluconeogenesis and glycolysis? |
Glucose <--> Glucose 6-phosphate Fructose 6-phosphate <--> Fructose 1,6-bisphosphate Phosphoenolpyruvate <--> Pyruvate |
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Why is phosphoglycerate kinase a thermodynamically unfavorable reaction in gluconeogensis but not glycolysis? |
Phosphoenolpyruvate requires ATP in this direction |
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What is unique about how PEPCK and Pyruvate carboxylase use energy in the conversion of Pyruvate to phosphoenolpyruvate? |
Pyruvate carboxylase and phosphoenol pyruvate carboxykinase can use alternate energy sources like GTP instead of ATP |
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Glycolysis converts phosphoenolpyruvate into pyruvate in glycolysis, but this is irreversible, so how does gluconeogenesis circumvent this issue? |
Pyruvate carboxylase forms oxaloacetate as an intermediate which PEPCK converts into phosphoenolpyruvate |
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Describe the form and function of biotin. Where is it found? |
Prosthetic group of Pyruvate Carboxylase Amide linked to a lysine Activated carrier of CO2 Found in mitochondrial enzyme |
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How does Biotin bind CO2? |
CO2 is phosphorylated then attached to the ring nitrogen in biotin |
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What carrier is necessary for biotin carboxylation? |
Acetyl CoA |
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What enzyme catalyzes the first commited step in gluconeogenesis? What does it do? |
PEPCK = Phosphoenolpyruvate carboxykinase converts oxaloacetate into phosphoenolpyruvate at the expense of GTP
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How does oxaloacetate participate in gluconeogensis if it is formed in the matrix? |
Oxaoacetate is reduced to malate at the expense of NADH and sent through a malate channel to the cytoplasm where it is oxidized to oxaloacetate to reform NADH |
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Describe the components of the active site of PEPCK |
Arginine residue Mn2+ |
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What is the function of Arg and Mn2+ in PEPCK's active site?
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Non covalently binds Oxaloacetate and terminal phosphate of ATP Promotes decarboxylation Stabilizes enolate ion intermediate |
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How is oxaloacetate phosphorylated? |
Decarboxylation leads to enolate of pyruvate, who's lone electrons of C2 oxygen attack the terminal phosphate of ATP |
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How do we get from Phosphoenol pyruvate to Fructose 1,6-bisphosphate? |
Simply the reverse of glycolysis. Direction is govered by [products]/[substrates] |
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What is the rate limiting enzyme of gluconeogenesis? What does this achieve? |
Fructose 1,6-bisphosphatase converts Fructose 1,6-bisphosphate into fructose 6-phosphate which is readily isomerized to glucose 6-phosphate |
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What enzyme completes gluconeogensis and where is this found? |
Glucose 6-phospatase dephosphorylates glucose 6-phosphate in the ER and then transports it to the cytoplasm then out of the cell |
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How are Glyocgen breakdown, synthesis, and glycolysis coordinated? |
Low blood sugar raises glucagon which raises cAMP which raises PKA, which increases glycogen breakdown and decreases both glycogen synthesis and glycolsys |
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High levels of what promotes glycolysis? |
Fructose-2,6-bisphosphate AMP Fructose-1-6-bisphosphate |
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High levels of what inhibits glycolysis? |
ATP Citrate H+ Alanine |
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High levels of what promotes gluconeogenesis? |
Citrate Acetyl CoA |
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High levels of what inhibits gluconeogenesis? |
Fructose-2-6-bisphosphate AMP ADP |
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How does fructose 2,6-bisphosphate regulate glycolysis and gluconeogenesis under low blood sugar conditions? |
Under low blood sugar conditions glucagon stimulates PKA which activates Fructose bisphosphatase 2 which increases levels of F6P which stimulates phosphoprotein phosphatase activates PFK2 activating glycolysis |
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How does negative feedback and feedforward stimulation regulate glycolysis and gluconeogenesis? |
G6P negatively affects hexokinase Fructose-1,6-bisphosphate positively affects pyruvate kinase |
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What factor enables aerobic respiration in a growing tumor? |
Hypoxia inducible factor stimulates VEGF and angiogenesis |
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What 2 compounds can effect PEPCK gene transcription? |
Insulin inhibits PEPCK cAMP activates PEPCK |
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Describe the cori cycle |
Liver glucose enters the blood and travels to the muscle where it is converted to pyruvate then lactate which travels to the liver to be regenerated to pyruvate and then glucose |
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What is the purpose of the cori cycle |
The liver shares the metabolic stress of exercise by undergoing gluconeogenesis as the muscle undergoes glycolysis |
