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mcat biochemistry > Carb metabolism 1 > Flashcards

Carb metabolism 1 Flashcards

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MCAT flashcards
1
Q

Glucose transporters

A
  • GLUT1
    • low km; high enzyme affinity
    • brain, red blood cells
  • GLUT2
    • high km; low enzyme affinity; no response at normal glucose conc.
    • liver and pancreas cells
  • GLUT4
    • Insulin dependent for extra glucose entry
    • low km
    • muscles, adipose cells
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2
Q

enzymes of glycolysis

A
  • Hexokinase/ GLucokinase
    • Isomerase
    • Phosphofructokinase
    • Aldolase
    • glycerolaldehyde-3-phosphate dehydrogenase
    • 3 phosphoglycerate kinase
    • Mutase
    • Enolase
    • Pyruvate Kinase
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3
Q

Hexokinase/ GLucokinase

A
  • Phosphorylate glucose to prevent escape
    - Glucokinase is only in liver and pancreas (high Km) (insulin induced)
    - Hexokinase is in all cells (low Km) (G6P inhibited)
    - Irreversible step
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4
Q

Phosphofructokinase

A
  • Irreversible step
    - rate limiting enzyme
    - PFK-1 inhibited by citrate, ATP, lack of PFK-2
    - Insulin activates PFK-2 but Glucagon inhibits thereby inhibiting PFK-1
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5
Q

Aldolase

A
  • Triose isomerase q

- switches DHAP with GAP

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6
Q
  • glycerolaldehyde-3-phosphate dehydrogenase
A
  • produces 1,3-BPG and NADH
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7
Q
  • 3 phosphoglycerate kinase
A
  • produces 3-PG

- a type of substrate level phosphorylation where you don’t need oxygen to produce ATP

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8
Q
  • Mutase
A
  • Produces 2-PG
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9
Q
  • Enolase
A
  • Produces phosphoenolpyruvate and H2O
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10
Q
  • Pyruvate Kinase
A
  • Irreversible step
    - another substrate level phosphorylation
    - stimulated by F-1,6-BP
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11
Q

Fermentation

A
  • produces NAD+ and lactic acid (lactate) or Ethanol
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12
Q

Important Intermediates of Glycolysis

A
  • DHAP: In TAG synthesis, isomerized to glycerol-3-P and used as backbone
    • 1,3-BPG and PEP: generates ATP by substrate level phosphorylation
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13
Q

Irreversible enzymes

A
  • Glucokinase or Hexokinase
  • Phosphofructokinase-1 (PFK-1)
  • Pyruvate Kinase
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14
Q

Rate limiting enzymes

A
  • Phosphofructokinase
  • Glycogen synthase
  • glycogen phosphorylase
  • glucose -6-phosphate dehydrogenase
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15
Q

Substrate level phosphorylation intermediates

A
  • 1,3 bisphosphoglycerate

- Phosphoenolpyruvate

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16
Q

Glycolysis in Erythrocytes

A
  • Only anaerobic glycolysis occurs
    production of 2,3-BPG by the enzyme bisphosphoglycerate mutase
    ↑ 2,3-BPG → decrease oxygen affinity in Hemoglobin A
17
Q

Galactose Metabolism

A
  • Sourced by Lactose
    phosphorylated by Galactokinase
    converted to glucose 1 phosphate by galactose-1-phosphate uridyltransferase and an epimerase
18
Q

Fructose Metabolism

A

phosphorylated by Fructokinase
cleaved into DHAP and glyceraldehyde by aldolase B
- tHis occurs past the rate-limiting enzyme PFK-1 which means its unregulated

19
Q

PYRUVATE DEHYDROGENASE

A

irreversible
converts pyruvate into acetyl-CoA
- Made of 3 enzymes and 5 coenzymes
- 1st enzyme has TPP (Thiamine pyrophosphate)
- 2nd enzyme has CoA and lipoic acid
- 3rd enzyme has NAD and FAD

20
Q

Glycogen

A
  • liver glycogen is for blood glucose levels

- muscle glycogen is for muscle activity

21
Q

Glycogenesis

A
  • Begins with the core, glycogenin
22
Q

Glycogen synthase

A
  • creates 1,4 glycosidic linkages
  • stimulated by insulin and G6p
  • inhibited by epinephrine and glucagon
23
Q

Branching enzyme

A
  • Glycosyl 4:6 Transferase
  • creates 1,6 glycosidic bonds
  • By hydrolyzing a 1,4 linkage
24
Q

Glycogenolysis

A
  • Glycogen Phosphorylase
    - only breaks 1,4 glycosidic bonds
    - activated by glucagon in liver
    - activated by AMP in muscle
    • Debranching enzymes (4:4 transferase) then (1,6 Glucosidase)
      • Also breaks 1,4 glycosidic bonds but only the ones close to branching point and puts it on the core polymer
      • technically breaking a 1,4 bond and making another 1,4 bond
      • 1,6 glucosidase breaks the branching point, releasing a free glucose with no phosphate
25
Q

gluconeogenesis

A
  • maintain blood glucose
  • stimulated by glucagon and epinephrine
  • substrates for this process are Glycerol (after phosphorylation), lactate (lactic acid), alanine
    • pyruvate is also known as the ketoacid of alanine because when alanine gives off its amino group, it becomes pyruvate
      Gluconeogenesis requires ATP provided from Beta oxidation of fatty acids
26
Q

Enzymes that are needed to be reverse gluconeogenesis

A
  • Pyruvate Carboxylase
    • Phosphoenolpyruvate carboxykinase
    • Fructose-1,6-Bisphosphatase
      • Glucose-6-phosphatase
27
Q

Pyruvate Carboxylase

A

reversal of pyruvate into PEP

    - product is Oxaloacetate
    - OAA is metabolized to malate by malate dehydrogenase 
    - malate is exported from mitochondria
    - Then converted back to OAA by malate dehydrogenase
    - Stimulated by Acetyl-CoA (after Beta oxidation of fatty acids)
28
Q

Phosphoenolpyruvate carboxykinase

A

reversal of pyruvate into PEP

    - Product is PEP
    - stimulated by glucagon
29
Q

Fructose-1,6-Bisphosphatase

A

reversal of F-1,6-BP into F-6-P

    - stimulated by ATP
    - inhibited by PFK-2 and AMP
30
Q

Glucose-6-phosphatase

A

only present in liver not muscle
part of ER membranefacing the lumen
removes phosphate
reversal of glucokinase

31
Q

PENTOSE PHOSPHATE PATHWAY

A

produces NADPH
produces pentose sugar (R5P)
- Made of two phases/parts
- oxidative
- produces NADPH
- irreversible/ one way
- rate limiting step is the first enzyme glucose -6-phosphate dehydrogenase
- stimulated by insulin, and NADP+
- inhibited by NADPH
- Nonoxidative
- reversible/ two ways
- produces various sugars; glycolysis intermediates (GAP, F6P, etc)
- enzymes within this phase that allow for reversibility:
- transketolase- uses TPP as cofactor
- transaldolase

32
Q

NADPH

A

for reducing detox enzymes( Glutathione (natural antioxidant) reduction),
biosynthesis of Nitric oxide, fatty acids, and cholesterol

33
Q

R5P

A

for nucleotide biosynthesis

mcat biochemistry (7 decks)

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