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MCBM Part 1 > Mitsouras - Carbohydrates > Flashcards

Mitsouras - Carbohydrates Flashcards

1
Q

what are the 3 functions of carbohydrates

A
  1. metabolism (fuel/energy source)
  2. structural components of nucleic acids and enzyme cofactors
  3. modify other biomolecules (glycoconjugates)
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2
Q

how are carbohydrates classified

A

by number of carbons (triose, tetrose, pentose, and hexose) –> (CH2O)n n= # of Carbon atoms

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3
Q

which 3 hexoses are of particular interest

A

glucose, fructose, and galactose

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4
Q

what is the smallest unit of a carbohydrate

A

monomers

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5
Q

what are the 2 most oxidized functional groups

A

aldehyde (aldose) or keto group (ketose)

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6
Q

what is an isomer

A

same chemical formula but different 3D structures - asymmetric carbon has 4 different chemical groups

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7
Q

what is D-glucose and how many isomers does it have

A

C6H12O6 - m (asymmetric carbons) =4 so there are 16 isomers (2^m isomers)

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8
Q

what are the 3 types of isomers

A

epimers, entaniomers, and anomers

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9
Q

what is a epimer

A

different configurations around a single asymmetric carbon (not around carbonyl C)

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10
Q

what is an entaniomers

A

isomers that are mirror images of each other

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11
Q

what is an anomer

A

formed by cyclization of monosaccharides: alpha (below ring) or beta (above plane)

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12
Q

what C are galactose and glucose epimers at

A

C-4

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13
Q

what C are glucose and mannose epimers at

A

C-2

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14
Q

what form enantiomer do almost all sugars occur in the human

A

D anantiomers

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15
Q

what monosaccharides can exist as a ring structure

A

5+ carbons (99% are rings)

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16
Q

what happen in cyclization

A

the aldehyde or keto group reacts with OH group

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17
Q

what is pyranose

A

a 6-membered ring (5 carbons and 1 oxygen)

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18
Q

what is furanose

A

5-membered ring (4 carbons and 1 oxygen)

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19
Q

how do anomers (alpha and beta) forms interconvert

A

by mutarotation

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20
Q

what are disaccharides

A

dimers - 2 monosaccharides linked by glycosidic bond

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21
Q

what are the components and type of glycosidic bond in sucrose

A

glucose + fructose (table sugar)

glucose α (1 → 2) fructose

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22
Q

what are the components and type of glycosidic bond in lactose

A

galactose + glucose (milk and dairy)

galactose β (1 → 4) glucose

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23
Q

what are the components and type of glycosidic bond in maltose

A

glucose + glucose

glucose α (1 → 4) glucose

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24
Q

what are the components and type of glycosidic bond in isomaltose

A

glucose + glucose

glucose α (1 → 6) glucose

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25
Q

what are the functions of polysaccharides

A

metabolic fuels and energy sources (common: glycogen, starch, and cellulose)

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26
Q

what type of bond does glycogen contain (liver and muscle)

A

Glucose (linear chain) α(1,4) and glucose (branchpoints) α (1,6)

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27
Q

what type of bond does starch from plants have in amylose

A

(unbranched) Glucose α(1,4)

28
Q

what type of bond does starch from plants have in amylopectin

A

(branched) glucose α(1,4) and α (1,6)

29
Q

what type of bond does cellulose from plants have (fiber-undigestible)

A

(unbranched) β (1,4) bonds

30
Q

what are the 2 parts in the digestive process for dietary carbohydrates

A

digestion- mechanical (chewing and mixing foods) and chemical - cleavage of glycosidic bonds by glycosidases (breakdown of food)

31
Q

what are polysaccharides (starch and glycogen) broken down into and what breaks them down

A

oligosaccharides, tri- and disaccharides in mouth by salivary α-amylase

32
Q

what bonds does salivary α-amylase break in the mouth

A

glucose a(1,4) bonds cleaved =>oligosaccharides (a-dextrins), tri & disaccharides

33
Q

what breaks down the oligosaccharides into tri- and disaccharides

A

pancreatic α-amylase in the small intestine

34
Q

what bonds does pancreatic α-amylase break in the small intestine

A

glucose a(1,4) bonds cleaved => trisaccharides & disaccharides

35
Q

what is D-glucose polymer

A

plant origin and composed of amylose and amlyopectin (unbranched) - not digestible fiber in diet

36
Q

what bonds of amylopectin are cleaved by the brush border disaccharides in the internal mucosa

A

glucose a(1,6) glucose bonds

37
Q

what do the brush boarder disaccharides break down in sucrose

A

glucose α(1,2) fructose bonds

38
Q

what do the brush boarder disaccharides break down in lactose

A

galactose β (1,4) glucose bonds

39
Q

what do the brush boarder disaccharides break down in maltose

A

glucose α(1,4) glucose bonds

40
Q

what do the brush boarder disaccharides break down in isomaltose

A

glucose α(1,6) glucose bonds

41
Q

where do glucose, fructose, and galactose get absorbed

A

in the gut

42
Q

how do the monosaccharides go into circulation

A

from the intestinal epithelium into circulation by transporters

43
Q

what happens to blood glucose levels after the monosaccharides enter circulation

A

blood glucose levels increase - onset of fed state and insulin signaling cascade

44
Q

why is transport of monosaccharides critical

A

to lower blood glucose levels after a meal and prevent hyperglycemia

45
Q

what are 2 types of transportation for monosaccharides

A

facilitated and active transport

46
Q

what is facilitated transport

A

down the concentration gradient (high glucose: extracellular -> low glucose: intracellular) NO ATP required

47
Q

what is active transport

A

against concentration gradient (low glucose: intracellular -> high glucose: extracellular) Needs ATP

48
Q

when is there a high affinity

A

active at low (fasting) and high (fed) glucose concentrations

49
Q

when is there a low affinity

A

active at high (fed) glucose concentrations

50
Q

what is the specificity of a monosaccharide transporter

A

which type of monosaccharide is transported (glucose,fructose, or galactose)

51
Q

what is the affinity of a monosaccharide transporter

A

sensitivity of the transporter

52
Q

what is the capacity of monosaccharide transporters

A

what concentrations of glucose saturates the transporter

53
Q

when is there a low capacity

A

saturated at low glucose levels

54
Q

when is there a high capacity

A

saturated at hight glucose levels

55
Q

what are the 4 properties of monosaccharide transporters

A

specificity, affinity, capacity, and hormonal regulation

56
Q

what is the hormonal regulation of monosaccharide transporters

A

insulin-dependent transporters -> transport in presence of insulin

57
Q

what do basal glucose uptake transporters do

A

constant supply at both high and low blood glucose

58
Q

what do insulin-dependent uptake transporters do

A

important in fed state during insulin signaling to lower blood glucose levels

59
Q

what do high-capacity glucose uptake transporters do

A

equilibrate intracellular with blood glucose levels in fed state in glucose-sensing organs

60
Q

what do Na+ dependent co-transporters do

A

(ATP required) for complete absorption of glucose from GI to circulation (low glucose -> high glucose)

61
Q

what is the tissue-specificity and function of GLUT1

A

most cell types (RBCs, brain) but not kidney or SI - glucose and galactose transporter, high affinity, basal glucose uptake

62
Q

what is the tissue-specificity and function of GLUT2

A

hepatocytes, pancreatic b-cells, SI, and kidney - glucose, galactose, fructose transporter
high capacity, low affinity
glucose sensor: exports glucose into blood after uptake from lumen of SI

63
Q

what is the tissue-specificity and function of GLUT3

A

most tissues/organs (brain, testes, placenta)
glucose and galactose transporter
high affinity and basal glucose uptake

64
Q

what is the tissue-specificity and function of GLUT4

A

skeletal muscle and adipocytes
glucose transporter
high affinity and insulin dependent

65
Q

what is the tissue-specificity and function of GLUT5

A

SI, sperm, kidney, brain, muscle, adipocytes
fructose transporter
high affinity

66
Q

what is the tissue-specificity and function of GLUT7

A

membrane of ER in heaptocytes

glucose transporter, transports free glucose from ER to cytoplasm to be taken by GLUT2

67
Q

what is the tissue-specificity and function of SGLUT1

A

epithelial cells of SI and apical surface of kidney tubules
glucose, galactose co-transporter with Na+
uptake of sugar from lumen of SI against gradient

MCBM Part 1 (29 decks)

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