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32 Cards in this Set
- Front
- Back
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What happens if your diet does not contain enough galactose?
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UDP glucose can be turned into UDP galactose by UDP hexose epimerase
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What enzymes are involved with galactose metabolism?
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1. galactokinase (phosphorylate galactose)
2. Uridylyl transferase 3. UDP hexo epimerase 4. phosphoglucomutase This reaction basically changes galactose into glucose 6-P so that it can be used by glycolysis. |
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What is galactosemia?
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Problem with the function of galactose-1-phosphate uridylyl transferase. Dx: low transferase activity in RBC. In deficient patients there is galactose conversion to galactitol=cataracts
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What are the basic steps to galactose metabolism?
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galactose to galactose 1-P to glucose 1-P to glucose 6-P (then it enters glycolysis)
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What are the two pathways for fructose metabolism?
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1. In most tissue phosphorylation yeilds F-6-P (glycolytic intermediate)
2. In the LIVER-fructokinase makes F-1-P, aldolase B makes glyceraldehyde-phosphorylated (ATP dependent) to glyceraldehyde-3-P. BYPASSES PFK-1 |
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What is fructose intolerance?
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Genetic disease causes F-1-P accumulation (as does intravenous fructose feeding) from a deficiency in Aldolase B. This depleates the liver's supply of inorganic phosphate which leads to drop in [ATP] which activates glycolysis and lactate.
Pts rapidly develop a strong distaste for anything sweet |
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T/F Metabolism of fatty acids cannot yield a net increase in glucose. WHY/WHY NOT
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True. Pyruvate is converted to acetyl CoA in an IRREVERSIBLE reaction (pyruvate dehydrogenase)
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Why is alanine important to pyruvate?
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Pyruvate is teh ketoacid corresponding to alanine. Transamination of pyruvate to ala is important in muscle reverse reaction occurs in liver. This can be an important precursor for glycogenesis. Alanine can be used to transfer carbon from muscle to liver.
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What is acetyl CoA made from and what three things can it turn into?
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It is made from pyruvate in an irreversible reaction, ketones or beta oxidation. It can make fatty acids, ketone bodies/acetoacetate, and when combine with oxaloacetate it forms citrate!
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What can pyruvate turn into (four things)?
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1. alanine (transamination)
2. lactate (lactate dehydrogenase) 3. acetyl CoA (pyruvate dehydrogenase) 4. oxaloacetate (Carboxylation-married to acetyl CoA for TCA cycle) |
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What are the pathways that fructose can be metabolized?
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1. In most tissue fructose is metabolized to enter glycolysis through F-6-P (a glycolytic intermediate)
2. In the liver it is phosphorylated by fructokinase to F-1-P, cleaved by aldolase B to yeild glyceraldehyde which is then phosphorylated in an ATP dependent reaction to glyceraldehyde-3-P (by pass PFK-1 step). p. 201 |
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Why is pyruvate coupled to the TCA cycle?
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The end products of pyruvate matabolism are used as substrates in the TCA cycle. Mainly Acetyl CoA (oxidized by the tca cycle) and oxaloacetate which is also needed to use Acetyl CoA
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What happens when pyruvate is carboxylated?
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Forms OAA-important for maintaining substrate concentrations in the TCA cycle.
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What reaction involving pyruvate generates NAD+?
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The decarboxylation to acetaldehyde pulls off a CO2 then the alcohol dehydrogenase creates NAD+ and the end product is ethanol.
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What happens to pyruvate concentrations with strenuous exercise?
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Oxygen is consumed and the pyruvate generated by glycolysis can no longer be oxidized in the TCA cycle. The excess pyruvate is then converted to lactate.
p. 206 |
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What can pyruvate be non-oxidatively decarboxylated to?
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acetalaldehyde (by pyruvate decarboxylase
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What happens when there is a large amount of NADH in the cell? Why does this happen (involving ethanol)?
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the catabolism of ethanol results in production of NADH. Cells have a limited amount of NAD+ so when there is a lot of NADH the [NAD+]/[NADH] ratio is low. This drives LDH towards lactate. Glycerol to glucose also does not happen.
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What cells use lactate?
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Red muscle fibers, heart, kidney, liver
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What cells produce lactate? Why
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Mature RBC, white muscle fibers, brain, GI tract, skin. They do not have mitochondria to break down lactate.
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What is the end product of glycolysis in anaerobic conditions?
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lactate
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Where does pyruvate get oxidized? How does it get there?
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Pyruvate gets oxidized in the mitochondrial matrix. The transport protein PYRUVATE-H+-SYMPORT brings it into the mitochondria
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What is PDC? What does it do? Where does it happen? What are its subunits?
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Pyruvate dehydrogenase complex
oxidative decarboxylation occurs in mitochondrial matrix subunits are E1, E2, and E3 |
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What cofactors are needed for PDC to work (list in order)?
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1. Thiamine pyrophosphate (TPP)
2. Lipoic Acid 3. CoA 4. FAD 5. NAD+ |
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What coenzyme assists with the decarboxylation of pyruvate?
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TTP-produces a hydroxyethyl group
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What two substrates are needed fir Acetyl-CoA
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CoA and pyruvate
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What coenzyme assis with the oxidation of lipoamide in PDC's action?
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FAD
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What coenzyme reoxidizes the FADH2 in PDC?
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NAD+
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What are the five steps in the sequence of reactions catalyzed by PDC?
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1. E1 with TTP decarboxylate pyruvate and from a hydroxyethyl-TTP intermediate
2. hydroxyethyl is transferred to E2 and lipoamide group oxidized to acetyl group, lipoamide group reduced 3. E2 transfers acetyl to CoA 4. Lipoamide group of E2 regenerated-uses FAD 5. E3 reoxidized-uses NAD produces NADH |
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What 2 enzymes control PDC?
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Kinase-phosphorylates E1 causes inactivation
Phosphatase-leads to active form PDC is subject to both allosteric and covalent modification. |
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In the fed state, does it make sense to have PDC on or off? What enzyme activates PDC?
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Have it on so that glucose gets converted into fatty acids. It is activated by the phosphatase.
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What factors stimulate PDC kinase and what does this do for PDC?
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kinase is stimulated by: acetyl-CoA, ATP, and NADH. This inactivates PDC.
Ultimately dependend on the acetyl-CoA/CoA and NADH/NAD ratio lots of NADH doesn't work, |
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What factors inhibit PDC kinase?
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acetyl- CoA, NADH, ATP
Ultimately dependend on the acetyl-CoA/CoA and NADH/NAD ratio lots of NADH doesn't work, |
