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922 > Sugar Metabolism > Flashcards

Sugar Metabolism Flashcards

1
Q

The breakdown of starch (polysaccharides) to oligosaccharides mostly takes place where?

A

intestines

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2
Q

What is soluble (branched) starch called?

A

amylopectin

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3
Q

What is insoluble (not branched) starch called?

A

amylose

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4
Q

Alpha-amylase acts as an ________ meaning it only cuts internal bonds (cuts molecule somewhere in the middle)

A

endo-glycosidase

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5
Q

Alpha-amylase specifically cuts which bonds?

A

1-4-alpha-glycosidic bonds

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6
Q

Where are two places where alpha-amylase are produced?

A

pancreas, saliva

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7
Q

Does alpha-amylase create mostly di/trisaccharides or monosaccharides?

A

di/trisaccharides

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8
Q

Which bonds can the sucrase-isomaltase complex cut?

A

1-4-alpha-glycosidic, 1-6-alpha-glycosidic, alpha-1-beta-2-glycosidic

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9
Q

Does the sucrase-isomaltase complex create mostly di/trisaccharides or monosaccharides (ie glucose, fructose)?

A

monosaccharides

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10
Q

The sucrase-isomaltase complex are glycosidases of the intestinal __________ membrane.

A

brush-border

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11
Q

An anomer is said to be ______ if the R/S designation at the anomeric C is the same as the R/S designation at the highest number chiral center.

A

beta

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12
Q

An anomer is said to be ______ is the R/S designation at the anomeric C is different from the R/S designation at the highest number chiral center.

A

alpha

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13
Q

IN a structure, what is an easy way to identify the anomeric C?

A

the carbon connected to 2 oxygens

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14
Q

When is a sugar considered a “reducing” sugar?

A

if it has a free anomeric center

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15
Q

Are invert sugars sweeter than normal sugars?

A

yes

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16
Q

What bond can lactase cut?

A

beta-glycosidic (makes glucose and galactose)

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17
Q

Where are the lactase and trehalase glycosidases found?

A

intestinal brush-border membrane

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18
Q

What bond in trehalose can trehalase cut?

A

alpha-1-alpha-1-glycosidic bond

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19
Q

Does acarbose act systemically?

A

no

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20
Q

How does acarbose work?

A

competitively inhibits alpha-glucosidase activities (of alpha-amylase and sucrase-isomaltase complex) so few carbs in intestines broken down (used to treat type II diabetes)

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21
Q

What are four ways glucose can be transported across the membrane?

A

simple diffusion, facilitated diffusion (passive, uses channel), active transport (requires energy), pinocytosis/phagocytosis

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22
Q

Why can simple diffusion not occur in the blood-brain barrier?

A

tight junctions in BB barrier

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23
Q

Are the active sodium-glucose transporters symport or antiport?

A

symport

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24
Q

The facilitated transport of glucose is activated by ________.

A

insulin (insulin binds to surface receptor, causes expression of glucose transporters on surface)

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25
Q

The uniport glucose transporter (facilitated transport of glucose) is called what?

A

GLUT1

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26
Q

The Na/K/ATPase pump brings Na+ molecules _____the cell and K+ molecules ______ the cell.

A

out of and in to

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27
Q

Can glycolysis occur in every cell type?

A

yes

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28
Q

Where in the cell does glycolysis take place?

A

cytosol

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29
Q

What are the products of glycolysis?

A

2 ATP, 2 NADH/H+, pyruvate

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30
Q

What happens to the pyruvate from glycolysis in aerobic cells?

A

transported to mitochondria, where it’s oxidized by oxygen to carbon dioxide to generate lots of ATP

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31
Q

What happens to the pyruvate from glycolysis in anaerobic cells?

A

reduced to lactate to regenerate NAD+

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32
Q

Glycolysis provides “high energy” _______ intermediates suitable for substrate level phosphorylation.

A

phosphate

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33
Q

What regulates glycolysis in the liver and adipose tissue?

A

glucagon, insulin

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34
Q

What are the two phases of glycolysis?

A

preparative phase, ATP-generating phase

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35
Q

In the preparative phase of glycolysis, glucose is converted to what?

A

fructose-1,6-bisphosphate (FBP)

36
Q

How much ATP is consumed in the preparative phase of glycolysis?

A

2 ATP

37
Q

In the ATP-generating phase of glycolysis, triosephosphates are converted to what?

A

pyruvate

38
Q

How much ATP is produced in the ATP-generating phase of glycolysis?

A

4 ATP

39
Q

In glycolysis, all the intermediates between glucose and pyruvate are ____________.

A

phosphorylated

40
Q

What is the 1st enzyme of the glycolytic pathway?

A

hexokinase (aka glucokinase)

41
Q

What is the role of hexokinase in glycolysis?

A

converts glucose to glucose-6-phosphate (G6P)

42
Q

Why is the 6 position in glucose the most reactive?

A

it is a primary alcohol

43
Q

What is the 2nd enzyme in the glycolytic pathway?

A

phosphoglucose isomerase

44
Q

What is an isomer?

A

same molecular formula, different structure

45
Q

What is the role of phosphoglucose isomerase in glycolysis?

A

converts a pyranose (6-membered sugar ring) into furanose (5-membered ring, requires carbonyl group to be shifted from position 1 to position 2, aka taking an aldehyde and turning it into a ketone via an ene-diol intermediate)

46
Q

What is the 3rd enzyme in the glycolytic pathway?

A

phosphofructokinase

47
Q

What is the role of phosphofructokinase in glycolysis?

A

converts fructose-6-phosphate into fructose-1,6-bisphosphate

48
Q

What is the 4th enzyme of glycolysis?

A

aldolase

49
Q

What does aldolase catalyze?

A

aldol or retrol-aldo reaction

50
Q

What is an aldol?

A

compound with both an aldehyde (or ketone) and an alcohol group

51
Q

What is the role of aldolase in glycolysis?

A

converts fructose-1,6-bisphosphate into glyceraldehyde-3-P and dihydroxyacetone-P

52
Q

What is the role of triosephosphate isomerase in glycolysis?

A

interconverts between dihydroxyacetone-P and glyceraldehyde-3-P

53
Q

If triosephosphate isomerase didn’t work, what would the effect be on glycolysis?

A

glycolysis would yield less energy (because can’t interconvert between products so only half would go through the cycle)

54
Q

Fructose-1,6-bisphosphate is bound to aldolase as a ________ (Schiff base).

A

imine

55
Q

What is considered the most sophisticated enzyme of glycolysis?

A

glyceraldehyde-3-phosphate dehydrogenase

56
Q

What do glyceraldehyde-3-phosphate dehydrogenase do in glycolysis?

A

adds phosphate group without using ATP (generates mixed anhydride, generates energy in the form of reduced NADH/H+)

57
Q

Which glycolysis enzyme is responsible for removing a phosphate from the mixed anhydride created by glyceraldehyde-3-phosphate dehydrogenase, thus producing ATP?

A

phosphoglycerate kinase

58
Q

What is a mutase?

A

enzyme that moves functional group from one position to another in the same molecule

59
Q

What glycolysis enzyme catalyzes the transformation of 2-phosphoglycerate into phosphoenolpyruvate (PEP), a dehydration reaction (elimination of water)?

A

enolase

60
Q

What glycolysis enzyme is used to convert PEP into pyruvate and ATP?

A

pyruvate kinase (uses keto-enol tautomers)

61
Q

What is the reduced form of NAD+?

A

NAD

62
Q

What is the reduced form of NADH?

A

NADH/H+

63
Q

What are the two “shuttle” mechanisms that can be used to move the protons from NADH/H+ across the mitochondrial membrane for aerobic metabolism (since NADH/H+ can’t move across it by itself)?

A

glycerol-3-P, malate-aspartate shuttles

64
Q

How does the glycerol-3-P NADH/H+ shuttle work?

A

dihydroxyacetone-P (DHAP) picks up hydrogens from NADH/H+ (converts it back to NAD+), changing to glycerol-3-P, which then crosses the membrane and transfers hydrogens to FAD inside the membrane, changing it to FAD(2H) which can enter the electron transport chain

65
Q

What is a disadvantage to using the glycerol-3-P shuttle to make FAD(2H) that can enter the transport chain instead of finding a way to use NADH/H+ in the chain?

A

FAD(2H) makes less ATP in the chain than NADH/H+

66
Q

How does the malate-asparatate shuttle work?

A

oxaloacetate picks up hydrogens from NADH/H+ (converts it back to NAD+), changing to malate, which crosses the membrane and gives its hydrogens to NAD+ (converts back to oxaloacetate) already inside the membrane (byproduct of TCA cycle), which creates NADH/H+ that can enter the electron transport chain; the oxaloacetate can’t cross the membrane, so reacts with glutamate to form aspartate which can cross the membrane (outside, aspartate reacts with alpha-ketoglutarate to form glutamate and oxaloacetate again)

67
Q

The malate-asparatate shuttle reactions are __________ reactions (mutual conversions of amino into keto groups)

A

transamination

68
Q

In anaerobic glycolysis, how is NADH reoxidized?

A

lactate dehydrogenase reaction

69
Q

In the anaerobic metabolism of yeast, how is NADH reoxidized?

A

alcohol dehydrogenase reaction

70
Q

The ______ is the only place where gluconeogenesis can be done to produce free glucose.

A

liver

71
Q

Can red blood cells do aerobic metabolism?

A

no

72
Q

What is the rate-limiting enzyme of the glycolytic pathway?

A

phosphofructokinase-1 (PFK-1)

73
Q

What two substances inhibit phosphofructokinase-1 enzymes (rate-limiting glycolysis enzyme)?

A

ATP, citrate

74
Q

What are three substances that stimulate phosphofructokinase-1 enzymes (rate-limiting glycolysis enzyme)?

A

AMP, ADP, fructose-2,6-bisphosphate

75
Q

What enzyme converts fructose into fructose-1-phosphate in the pathway to utilizing fructose for energy?

A

fructokinase

76
Q

What enzyme converts fructose-1-phosphate into glyceraldehyde in the pathway to utilizing fructose for energy?

A

aldolase B

77
Q

How many inherited disorder of fructose metabolism are there?

A

two (essential fructosuria, hereditary fructose intolerance)

78
Q

What is the name of the pathway used to interconvert fructose and glucose?

A

polyol-pathway (moves carbonyl from 1 to 2 position used redox sequence)

79
Q

UDP-glucose serves as an activated molecule for ____________.

A

glycosyltransfer

80
Q

The transformation from glucose-1-phosphate to UDP-glucose is an example of an _______ exchange reaction.

A

anhydride

81
Q

_______________ is a major metabolism to change drugs and other xenobiotics to facilitate their excretion from the body (makes the more water-soluble, inactivates drugs).

A

glucuronidation

82
Q

UDP-glucose serves as a precursor of UDP-__________, which is important in glucuronidation reactions.

A

glucuronate

83
Q

What is an epimerisation reaction?

A

change of one stereocenter of a sugar molecule into the opposite stereochemistry

84
Q

What kind of reaction is needed to convert between glucose and galactose?

A

epimerisation (sequential redox)

85
Q

What is galactosemia?

A

genetic disease characterized by inability to convert galactose to glucose

86
Q

How many forms of galactosemia are there?

A

three (classical, non-classical, type III)

922 (4 decks)

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