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SFM - Biochem - Quiz 1 > (L3) - Carbohydrate Metabolism > Flashcards

(L3) - Carbohydrate Metabolism Flashcards

1
Q

What cell types exclusively use glucose as their fuel source?

L3 S8

A
  • RBCs

- Brain (non-starvation)

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2
Q

What are the different types of glucose transporters, where are they found and what are their affinities?

L3 S10-11 LO1

A

GLUT1:

  • found in all cells; especially high in RBCs and brain
  • high affinity (Km: 1mM)

GLUT2:

  • found in liver and pancreas
  • low specificity (Km: 10mM)

GLUT3:

  • found in neurons
  • high affinity (Km: 1mM)

GLUT4:

  • found in skeletal muscle, adipose tissue, and heart
  • intermediate affinity (Km: 5mM)
  • INSULIN REGULATED vesicle fusion
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3
Q

What is the net yield of glycolysis per molecule of glucose?

L3 S13 LO1

A
  • 2 ATP
  • 2 NADH
  • 2 Pyruvate
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4
Q

What is the first phase of glycolysis and what occurs during it?

A

Investment
-use 2 ATP to trap glucose

Net reaction:
Glucose + 2 ATP -> fructose 1,6-BP

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5
Q

What does hexokinase do?

L3 S14 LO1

A

Converts glucose to glucose 6-P using ATP

Found in all cells

Inhibited by glucose-6P (feedback inhibition)

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6
Q

What does glucokinase do?

L3 S14 LO1

A

Converts glucose to glucose 6-P using ATP

Found only in the liver and pancreas

No feedback inhibition by glucose 6-P

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7
Q

What does phosphofructokinase do?

L3 S14

A

RATE LIMITING

Converts fructose 6-P to fructose. 1,6-BP

Inhibited by ATP and citrate

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8
Q

What is the second phase of glycolysis and what occurs during it?

L3 S15 LO1

A

Splitting
-goes from 1 6C molecule to 2 3C molecules

Net reaction:
-Fructose 1,6-BP -> 2 Glyceraldehyde 3-P

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9
Q

What does aldolase do?

L3 S15 LO1

A

Splits fructose 1,6-BP into DHAP and G3P

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10
Q

What does triose phosphate isomerase do?

L3 S15

A

Interconverts DHAP and G3P

G3P is used in next step of glycolysis

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11
Q

What is the third phase of glycolysis and what occurs during it?

L3 S16 LO1

A

Recoup/payoff

  • 4ATP and 2NADH are generated
  • pyruvate is generated

Net reaction:
-2 G3P + 4 ADP + 2 NAD+ -> 2 Pyruvate + 4 ATP + 2 NADH

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12
Q

What does glyceraldehyde 3-P dehydrogenase do?

L3 S16 LO1

A

Converts G3P to 1,3-BPG

Generates NADH

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13
Q

What does phosphoglycerate kinase do?

L3 S16 LO1

A

Converts 1,3-BPG to 3-phosphoglycerate

Generates ATP

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14
Q

What does pyruvate kinase do?

L3 S16 LO1

A

Converts phosphoenolpyruvate to pyruvate

Generate ATP

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15
Q

What are the regulated steps of glycolysis?

L3 S19 LO1

A
  • hexokinase/glucokinase
  • phosphofructokinase-1
  • pyruvate kinase
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16
Q

How is hexokinase/glucokinase regulated?

L3 S20-21 LO1

A

Hexokinase is inhibited by G6P

Glucokinase is minimally affected by G6P

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17
Q

How is PFK-1 regulated?

L3 S22-23 LO1

A

Insulin actives phosphatases which activates PFK-2’s kinase activity and activates PFK-1

Glucagon activates PKA which activates PFK-2’s phosphorylase activity and inactivates PFK-1

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18
Q

What is Tarui disease?

L3 S24 LO1

A

GSD VII

Deficiency in PFK-1 (rate limiting enzyme of glycolysis)

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19
Q

How is pyruvate kinase regulated?

L3 S25 LO1

A

Activated by F1,6BP and insulin (activation of phosphatases)

Inhibited by ATP and glucagon (activation of PKA)

20
Q

What are the possible fates of G6P?

L3 S27-28

A
  • Glycolysis (pyruvate)
  • Glycogen synthesis (glycogen)
  • Pentosephosphate pathway (ribose)
21
Q

How do defects in glycolysis affect RBCs?

L3 S31-32 LO1

A

Glycolysis is only means of ATP production for RBCs

Failure of glycolysis leads to hemolytic anemia.

22
Q

What is Fanconi-Bickel syndrome?

L3 S37 LO1

A

Mutation in GLUT2 transporter (liver and pancreatic β cells

Results in inability to take up glucose efficiently in those cells

23
Q

What steps of glycolysis must be bypassed in gluconeogenesis?

L3 S42 LO2

A

Hexokinase/glucokinase
-bypassed by glucose 6-phosphatase

Phosphofructokinase
-bypassed by fructose 1,6-bisphosphatase

Pyruvate kinase
-bypassed by PEP carboxylase and pyruvate carboxylase

24
Q

What factors regulate glycolysis and gluconeogenesis?

L3 S44 LO2

A

High energy signals (ATP, glucagon) inhibit glycolysis and stimulate gluconeogenensis

Low energy signals (ADP/AMP, insulin) stimulate glycolysis and inhibit gluconeogenesis

25
Q

What does pyruvate carboxylase do?

L3 S45 LO2

A

Converts pyruvate to oxaloacetate

26
Q

What does malate dehydrogenase do?

L3 S46 LO46

A

Converts mitochondrial oxaloacetate into malate which can leave the mitochondria

Malate is converted back into oxaloacetate in the cytoplasm

27
Q

What does phsophoenolpyruvate kinase do?

L3 S47 LO2

A

Converts oxaloacetate to PEP using GTP

28
Q

What does fructose 1,6-bisphosphatase do?

L3 S47 LO2

A

RATE LIMITING

Converts fructose 1,6-bisphosphatase to
fructose 6-P

29
Q

What does glucose 6-phosphatase do?

L3 S47 LO2

A

Dephosphorylates G6P to glucose

ONLY found in liver, kidneys, SI, and pancreas

30
Q

What is GLUT7?

L3 S48 LO2

A

Removes glucose from the ER after being produced by glucose 6-phosphatase

31
Q

What is the Cori cycle?

L2 S49 LO2

A

Links lactate production in muscles and RBCs to glucose production in liver

32
Q

What is Von Gierke disease?

L3 S54 L2

A

GSD1a

Deficiency in glucose 6-phosphatase

Results in inefficient release of glucose from the liver and build of of stored glycogen in liver

33
Q

What is the significance of fructose metabolism on glycolysis?

L3 S63 LO3

A

Fructose enters glycolysis as G3P, after rate limiting step. High consumption of fructose is linked to obesity because of this.

34
Q

What is the significance of galactosemia?

L3 S65 LO3

A

Due to deficiency in galactose 1-P uridyltransferase (GALT) that results in accumulation of galactose.

Excess galactose is converted to galactitol which can accumulate in the eyes leading to cataracts

35
Q

What is the rate limiting step of the PPP?

L3 S69-70 LO4

A

Glucose 6-phosphate dehydrognase

36
Q

What is the first step of the PPP?

L3 S68 LO4

A

Oxidative phase

Contains rate limiting step

Produces NADPH and ribulose 6-phosphate

37
Q

What is the second step of the PPP?

L3 S68 LO4

A

Non-oxidative

Products shunt to glycolysis/gluconeogenesis or nucleotide synthesis

38
Q

What are the main products of PPP and what are they used for?

L3 S73 LO4

A

Ribose 5-P:
-used in nucleotide synthesis

NADPH:
-Used as a reducing agent in anabolic reactions

39
Q

What are the non-reducing and reducing ends of glycogen?

L3 S75 LO5

A

Reducing:

  • 1’ end
  • connected to glycogenin
  • does not grow

Non-reducing:

  • 4’ end
  • site for growth and shortening
40
Q

What is phosphoglucomutase?

L3 S79 LO5

A

Converts glucose 6-P into glucose 1-P

41
Q

What does UDP-glucose pyrophosphorylase do?

L3 S79 LO5

A

Converted glucose 1-P into UDP-glucose, the building block of glycogen

42
Q

What does glycogen synthase do?

L3 S80 LO5

A

RATE LIMITING glycogen synthesis

Forms α-1,4 glycosidic bonds elongating glycogen

43
Q

What does glucosyl 4:6 transferase do?

L3 S80 LO5

A

Takes roughly 7 glucose chain from glycogen and adds it onto the side of the chain via a 1,6 glycosidic bond

44
Q

What does glycogen phosphorylase do?

L3 S82 LO5

A

RATE LIMITING glycogenolysis

Breaks glycogen from non-reducing end into glucose 1-P

45
Q

What does debranching enzyme do?

L3 S83 LO5

A

Removes distal 3 of 4 remaining glucose of a branch and adds to end of chain

46
Q

What does α-1,6-glucosidase do?

L3 S83 LO5

A

Cleaves last glucose of branch generating a glucose

47
Q

How do fed and fasting states regulate glycogenesis and glycogenolysis?

L3 S87 LO5

A

Fed state:

  • high insulin and glucose
  • trigger dephosphorylation of glycogen synthase (activating) and glycogen phosphorylase (inactivating)

Starving state:

  • high glucagon, low glucose
  • triggers phosphorylation of glycogen synthase (inactivating) and glycogen phosphorylase (activating)

SFM - Biochem - Quiz 1 (16 decks)

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