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MCAT BIochem > Carbohydrate Metabolism > Flashcards

Carbohydrate Metabolism Flashcards

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1
Q

Osmotic pressure equation

A

II=iMRT

M=molarity
R=ideal gas constant
T=absolute temperature in kelvin
i=van''t Hoff factor =number of particles obtained from the molecule from a molecule in solution
ex. glucose= 1, NaCl=2
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2
Q

Where is sodium needed to uptake glucose

A

In digestive tract

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3
Q

What is normal glucose concentration in peripheral blood?

A

5.6 mM

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4
Q

GLUT 2

A

Low affinity transporter in hepatocytes and pancreatic cells
Has a high Km value and it will pick up glucose from the liver in proportion to glucose concentration in blood (when blood glucose is high)

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5
Q

What serves as a sensor for glucose release in pancreatic B islets?

A

GLUT 2 and glucokinase enzyme

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6
Q

What does a high Km mean?

A

Low affinity for substrate

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7
Q

GLUT 4

A

In adipose tissue and muscle and responds to glucose concentration in peripheral blood
Low Km

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8
Q

Effect of insulin

A

Stimulates more GLUT 4 transporters to membrane by exocytosis

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9
Q

What order of kinetics are GLUT 4 transporters?

A

Zero order, saturated transporters still permit only a constant rate of glucose influx

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10
Q

How can glucose uptake be increased in muscle and adipose tissue?

A

More GLUT 4 transporters

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11
Q

What happens in liver when blood glucose drops below high Km?

A

Rest enters peripheral circulation

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12
Q

What energy pathway can red blood cells use?

A

Glycolysis

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13
Q

Glycolysis

A

Cytoplasm

Converts glucose into pyruvate releasing energy in 2 phosphorylation and 1 oxidation

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14
Q

Can glycolysis be done anaerobically?

A

Yes

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15
Q

What does hexokinase do?

A

Phosphorylate transported in glucose to make glucose 6-phosphate

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16
Q

What does glucokinase do?

A

Hexokinase in the liver & pancreatic B-islets along with GLUT 2

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17
Q

What inhibits hexokinase?

A

Glucose 6-Phosphate

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18
Q

What inhibits glucokinase?

A

Insulin

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19
Q

Phosphofructokinase-1

A

Rate limiting step

Converts Fructose 6-phosphate to fructose 1,6-bisphosphate use ATP

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20
Q

What inhibits Phosphofructokinase-1

A

ATP (don’t need pyruvate during high energy)
Citrate
Glucagon

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21
Q

What stimulates PFK-1?

A

Insulin

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22
Q

PFK-2

A

Converts an amount of fructose 6-phosphate to fructose 2,6 bisphosphate

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23
Q

What is the effect of fructose 2,6 bisphosphate?

A

Activates PFK-1

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24
Q

What is the effect of glucagon?

A

Inhibits PFK-2 and lowers F2 2,6-BP to inhibit PFK-1

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25
Q

Where is PFK-2 mostly found?

A

Liver

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26
Q

Glyceraldehyde 3-phosphate dehydrogenase

A

Catalyzes oxidation and addition of inorganic phosophate to Glyceraldehyde 3-phosphate

G3P–>to 1,3-bisphosphoglycerate & creation of NADH

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27
Q

3-Phosphoglycerate Kinase

A

1,3 bisphophoglycerate –> 3-phosphoglycerate and ATP

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28
Q

What enzyme uses substrate-level phosphorylation?

A

3-phosphoglycerate kinase

Pyruvate kinase

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29
Q

Pyruvate kinase

A

In presence in O2 only

Phosphoenolpyruvate (PEP) –>Pyruvate

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30
Q

What activates pyruvate kinase?

A

Fructose 1,6 bisphosphate from PFK-1 in feed forward reaction

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31
Q

Lactate dehydrogenase

A

Key fermentation enzyme

Oxidizes NADH to NAD+ so that it can be used by G3P

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32
Q

What is pyruvate turned into in yeast cells?

A

ethanol and carbon dioxide

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33
Q

Dihydroxyacteone phosphate (DHAP)

A

Use in hepatic and adipose tissue for TAG synthesis
Formed from fructose 1,6-bisphosphate
Isomerized to glycerol 3-P –>glycerol

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34
Q

What is used to generate ATP by substrate level phosphorylation?

A

1,3-bisphosphoglycerate (1,3-BPG) and phosphoenolpyruvate (PEP)

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35
Q

Irreversible reactions in glycolysis?

A

Glucokinase/hexokinase
PFK-1
Pyruvate kinase

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36
Q

How much ATP is made in anaerobic glycolysis in erythrocytes?

A

2 ATP

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37
Q

Biphosphoglycerate mutase

A

Produces 2,3-bisphosphoglycerate (2,3-BPG) from 1,3-BPG in glycolysis in erythrocytes
Binds to B-chains of hemoglobin A and decreases affinity for oxygen

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38
Q

What has a higher affinity for oxygen, fetal or maternal hemoglobin?

A

Fetal hemoglobin

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39
Q

Lactase

A

Hydrolylzes lactose to galactose and glucose

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40
Q

Galactoskinase

A

Phosphorylates galactose inside the cell from the liver

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41
Q

What transfers galactose 1-phosphate to glucose 1-phosphate

A

Galactose 1-phosphate uridyltransferase and epimerase

42
Q

Sucrose

A

Fructose and glucose

43
Q

What phosphorylates fructose?

A

Fructokinase

44
Q

What cleaves fructose 1-phosphate into DHAP and glyceraldehyde?

A

aldolase B

45
Q

Is pyruvate dehyrogenase reversible?

A

No

46
Q

What is pyruvate dehydrogenase activated by in the liver?

A

Insulin (Burn glucose when there is food & store it)

47
Q

What pathways can acetyl-CoA take?

A

Fatty acid synthesis if enough ATP is present

Ctiric acid cycle if not enough ATP

48
Q

Glycogen

A

A branched polymer of glucose that stores glucose primarily in liver and muscle

49
Q

What is liver glycogen used for?

A

Used in between meals to prevent low blood glucose

50
Q

What happens during glycogenesis?

A

Glycogenin core protein adds G6P to it and its converted to G1P

51
Q

What does glycogen synthase use to integrate into the glycogen chain?

A

Glycogen 1-phosphate activated by coupling to uridine triphosphate to make UDP phosphate & pyrophosphate

52
Q

Glycogen synthase

A

Rate-limiting enzyme of glycogen synthesis and forms a-1,4 glycosidic bonds in a linear fashion

53
Q

What stimulates glycogen synthase?

A

Glucose 6-phosphate

Insulin

54
Q

What inhibits glycogen synthase?

A

Epinephrine

Glucagon

55
Q

Branching enzyme

A

Introduces a-1,6 linkages into the granule as it grows by hydrolyzing a-1,4-glycosidic linkages and moves them

56
Q

What breaks down glycogen?

A

Glycogen phosphorylase into glucose 1-P

57
Q

What bonds can glycogen phosphorylase not break?

A

a-1.6 bonds

58
Q

What stimulates glucagon?

A

AMP
Epinephrine
Glucagon

59
Q

What inhibits glycogen phosphorylase?

A

ATP

60
Q

Debranching enzyme ( a1,4;a-1,6 transferase)

A

Deconstructs branches in glycogen that have been exposed by glycogen phosphorylase
Moves terminal end of branch point to the core chain

61
Q

Debranching enzyme (a-1,6 Glucosidase)

A

Removes glucose monomer present at the branch point (the a-1,6 linkage

62
Q

Glycogenolysis produces how many free glucose?

A

1

63
Q

Order of formation of glucose?

A

G6P –>G1P –>Glucose

64
Q

Isoform

A

Slightl different versions of the same protein

65
Q

Gluconeogenesis

A

Formation of glucose by the liver

66
Q

What is the effect on blood sugar by glucagon and epinephrine and cortisol and growth hormone?

A

Increase blood sugar

67
Q

What is the effect on blood sugar by insulin?

A

Decrease blood sugar

68
Q

What are sources for gluconeogenesis?

A

Glycerol 3-Phosphate (from fats), Lactate (from anaerobic glycolysis), Glucogenic amino acids *from muscle proteins)

69
Q

Glucogenic amino acids

A

Can be converted into intermediates of gluconeogenesis

All except leucine and lysine

70
Q

Ketogenic amino acids

A

Can be converted into ketone bodies that can be used as alternative fuel during prolonged starvation

71
Q

What kind of fatty acids can yield glucose?

A

Odd-chained

72
Q

What do odd-chained fatty acids yield?

A

Propionyl-CoA that can be turned into glucose

73
Q

Can acetyl CoA be turned back into glucose?

A

No

74
Q

4 Enzymes in gluconeogenesis that circumvent irreversible steps of glycolysis in liver?

A

Pyruvate carboxylase
Phophoenolpyruvate Carboxykinase (PEPCK)
Fructose 1,6 Bisphosphate
Glucose 6-phosphatase

75
Q

Pyruvate Carboxylase

A

Mitochondrial enzyme that is activated by acetyl-CoA

Creates OAA in the mitochondria which is reduced to malate and leaves mitochondria in the malate-aspartate shuttle

76
Q

What signals pyruvate carboxylase to work?

A

Acetyl-CoA from B-oxidation of fatty acids

77
Q

What turns of pyruvate dehydrogenase?

A

A high level of Acetyl-CoA, the cell should stop burning glucose because it has enough

78
Q

What must be used to produce glucose during gluconeogenesis?

A

Fatty acids must be used in the liver because pyruvate dehydrogenase is turned off by acetyl CoA

79
Q

Phosphoenolpyruvate Carboxykinase (PEPCK)

A

In cytoplasm induced by glucagon and cortisol to raise blood sugar
Converts OAA to PEP requires GTP
Circumvents pyruvate kinase
PEP becomes F 1,6 BP

80
Q

Fructose 1,6 Bisphosphatase

A

Reverses action of phosphofructokinase-1 (rate limiting step)
Fructose 1,6 bisphosphate –>Fructose 6-phosphate
Activated by ATP and inhibited by AMP

81
Q

What is the effect of F2,6-BP on gluconeogenesis?

A

Glucagon will lower F2,6-BP and stimulate gluconeogenesis

Insulin will increase F2,6-BP and repress gluconeogenesis

82
Q

What does high AMP mean to gluconeogenesis?

A

Energy is low and can’t make enough to make glucose for the rest of the body

83
Q

What does high ATP mean to gluconeogenesis?

A

Enough energy to make glucose for the rest of the body

84
Q

Glucose 6-Phosphatase

A

In lumen of ER in liver

Glucose 6-Phosphate in ER –>Glucose out of cell

85
Q

Where is there no glucose-6- phosphatase?

A

In skeletal muscle, can’t provide blood glucose

Circumvents glucokinase and hexokinase

86
Q

Why does gluconeogenesis require acetyl-CoA?

A

Inhibit pyruvate dehydrogenase and stimulate pyruvate carboxylase

Links to fatty acid oxidation

87
Q

What gluconeogenic intermediate can glycerol be converted into?

A

DHAP

88
Q

What can acetyl-CoA be converted into as alternative fuel?

A

Ketone bodies

89
Q

Is gluconeogenesis an energy source for the liver?

A

No, requires expenditure of ATP from B-oxidation

90
Q

Pentose phosphate pathway/Hexose monophosphate shunt

A

Produces NADPH

Serves as a source of ribose 5-phosphate for nucleotide synthesis

91
Q

First step of pentose phosphate pathway

A

Glucose 6-phosphate –>Ribulose 5-phosphate and NADPH

BY glucose-6-phosphate dehydrogenase (G6PD)

92
Q

What affect does insulin have on the pentose phosphate pathway?

A

Stimulate G6PD to go through pentose phosphate pathway

93
Q

What is created from ribulose 5-P in the pentose phosphate pathway?

A

Ribose 5-P for nucleotide synthesis and other sugars

94
Q

What can glyceraldehyde 3-P and Fructose 3-P be converted into ?

A

Glycolytic intermediates by transketolases and transaldolases

95
Q

NADH acts primarily as ?

A

A elecron acceptor and oxidizing agent

96
Q

NADPH acts primarily as?

A

A electron donor and reducing agent

97
Q

When is NADPH needed?

A

Biosynthesis (FA and cholesterol)
Immune system
Prevent oxidative damage using glutathione

98
Q

Where does gluconeogenesis take place?

A

In the cytoplasm and mitochondria

99
Q

Which reactions in glycolysis are irreversible?

A

Glucokinase/hexokinase
PFK-1
Pyruvate kinase

100
Q

Is glucokinase/hexokinase a rate-limiting step?

A

No

MCAT BIochem (8 decks)

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