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MCAT Supplementary > Metabolism > Flashcards

Metabolism Flashcards

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MCAT flashcards
1
Q

GLUT 2

A
  • low affinity transporter (Km = 15mM)
  • captures excess glucose in 1st order kinetics
  • appears in hepatocytes and pancreatic cells (signals insulin release with glucokinase)
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2
Q

GLUT 4

A
  • high affinity transporter (Km = 5mM)
  • appears in muscle & adipose tissue (more recruited in presence of insulin)
  • muscles turn glucose to glycogen, adipose turns it into DHAP -> G3P -> triacylglycerol
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3
Q

Hexokinase/Glucokinase

A

Hexokinase - all tissue, low Km, inhibited by G6-P
Glucokinase - hepatocytes/beta islet, high Km, induced by insulin (liver)
- both are irreversible

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4
Q

PFK-1/PFK-2

A

PFK-1: Fru 6-P -> Fru 1,6-BP

  • inhibited by ATP/citrate, activated by AMP
  • irreversible

PFK-2: Fru 6-P -> Fru 2,6-BP

  • activated by insulin, inhibited by glucagon
  • activates PFK-1 to override PFK-1 ATP inhibition
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5
Q

GAP Dehydrogenase

A

GAP + NAD + Pi -> 1,3-BPG + NADH

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6
Q

3-PG Kinase

A

1,3-BPG + ADP -> 3-PG + ATP (payoff)

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7
Q

Pyruvate Kinase

A

PEP + ADP -> pyruvate + ATP

  • irreversible
  • activated by Fru 1,6-BP
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8
Q

Fermentation

A

Used to regenerate NAD+ when ETC unavailable

  • mammals: pyruvate -> lactate (lactate dehydrogenase)
  • yeast: pyruvate -> ethanol + CO2
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9
Q

Galactose Mechanism

A

Gal -> Gal 1-P by Galactokinase

Gal 1-P -> Glu 1-P by Uridyltransferase + Epimerase

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10
Q

Fructose Mechanism

A

Fru -> Fru 1-P by Fructokinase

Fru 1-P -> DHAP + Glyceraldehyde by Aldolase B

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11
Q

Pyruvate Dehydrogenase Complex

A

(1) Pyruvate Dehydrogenase - oxidation to release CO2, needs TPP (vit B1)
(2) Dihydrolipoyl Transacetylase - oxidation of 2C, transfer to lipoic acid, then transfer to acetyl-CoA
(3) Dihydrolipoyl Dehydrogenase - lipoic acid oxidized by FAD -> FADH2, then NAD+ -> NADH

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12
Q

Possible Fates of Pyruvate

A

Lactate, Acetyl-CoA, Oxaloacetate

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13
Q

Glycogenesis Enzymes

A

Glycogen Synthase: rate-limiting, forms alpha 1,4 bond
- stimulated by G6-P/insulin, inhibited by epi/glucagon

Branching Enzyme

G-6P becomes G-1P by mutsage then becomes UDP-Glucose before Glycogen Synthase

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14
Q

Glycogenolysis Enzymes

A

Glycogen Phosphorylase: rate-limiting, breaks alpha 1,4 bond

  • activated by glucagon (liver), AMP/epi (muscle)
  • inhibited by ATP

Debranching Enzyme - cannot move whole branch so leftover part becomes free glucose

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15
Q

Gluconeogenesis Substrates

A

G-3P from stored triacylglycerol
Lactate & Glucogenic AA
Propionyl CoA from odd-chain FA

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16
Q

Gluconeogenesis Promotion/Inhibition

A

Gluconeogenesis is promoted by glucagon/epi and inhibited by insulin

  • also requires ATP in liver via B-oxidation
  • acetyl-CoA that inhibits PDH complex comes from B-oxidation
17
Q

4 Accessory Enzymes of Gluconeogenesis

A
  • lactate dehydrogenase (to pyruvate)
  • alanine amnotransferase (to pyruvate)
  • G-3P dehydrogenase (to DHAP)
  • pyruvate carboxylase (mito. pyruvate to OAA to malate, which can go to cytoplasm using malate-asp shuttle)
18
Q

3 Bypasses of Gluconeogenesis

A

Phosphoenolpyruvate Carboxykinase (PEPCK)

  • located in cytoplasm, OAA -> PEP with GTP
  • induced by glucagon and cortisol

Fructose-1,6-Bisphophatase

  • located in cytoplasm, rate-limiting, reverse of PFK-1
  • activated by ATP, inhibited by AMP & Fru 2,6-BP

Glucose-6-Phosphatase - only in liver ER, NOT muscle

19
Q

Insulin stimulates

A

Glycolysis, Glycogenesis, Aerobic Respiration, FA Synthesis, Pentose Phosphate Pathway

20
Q

Pentose Phosphate Pathway Overall

A
  • occurs in cytoplasm of all cells
  • turns G6-P into Ribulose 5-P (creates 2 NADPH) using Glucose-6-P Dehydrogenase (stim by insulin)
  • Ribulose 5-P can become Ribose 5-P (for nucleotides)
  • RIbose 5-P can become Fru 6-P or GAP by Transketolase (TPP)/Transaldolase
21
Q

NADPH Functions

A
  • electron donor for FA/cholesterol synthesis
  • cellular bleach production
  • maintenance of reduced glutathione (radical removal)
22
Q

Non-PDH Ways to Make Acetyl-Coa

A
  • B-Oxidation: cytosol activation: Fa-CoA using ATP energy, carnitine transport from cytosol then reformation in mitochondria
  • AA -> ketone bodies -> acetyl-Coa
  • ethanol using alcohol/aldehyde dehydrogenase
23
Q

Citrate Synthase

A

OAA ->

MCAT Supplementary (1 decks)

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