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Science for Medicine A > Carbohydrates > Flashcards

Carbohydrates Flashcards

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1
Q

Major carbohydrates in the diet

A

Glucose
Galactose
Fructose

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2
Q

Carbohydrates are_____

A

Highly oxidisable (H atoms)
Major source of energy
used for structural and protective functions
Cell to cell communications (receptors on RBC)

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3
Q

Stored as

A

Starch in plants

Glycogen in animals

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4
Q

Disaccharides

A

Maltose
Lactose
Sucrose

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5
Q

Glycosidic bond

A

Covalent bond between hydroxyl group (OH) and the anomeric group of another monosaccharide

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6
Q

Anomeric carbon

A

Carbon number 1

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7
Q

Features of anomeric carbon

A

Stabilises the structure of glucose

Only residue that can be oxidised

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8
Q

Maltose is____

A

a breakdown product of starch
found in beer
found in baby foods as natural sweeteners

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9
Q

Lactose is____

A

Main sugar in milk

Formed from galactose and glucose

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10
Q

Sucrose

A

Common table sugar
Only made by plants
25% of dietary carbohydrate
Sweetener is most processed food

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11
Q

Homopolysaccharides

A

single monomeric specie

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12
Q

Heteropolysaccharides

A

two or more monomer species

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13
Q

Starch contains____

A

two types of glucose polymer: amylose and amylopectin

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14
Q

Amylose

A

D glucose residues

(a1-4) linkage

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15
Q

Amylopectin

A

Branched

(a1-4) and (a1-6) every 24-30 residues

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16
Q

Amylose and amylopectin form____

A

Alpha helices

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17
Q

Glycogen

A

(a1-4) and (a1-6) every 8-12 resides- more extensively branched

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18
Q

More branched =

A

More reducing ends = more easily broken down and built up

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19
Q

Why store glucose in polymers

A

Compactness
Readily synthesised
Osmotically inactive

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20
Q

Glycoprotein

A

Class of proteins with carbohydrate covalently attached

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21
Q

Glycosaminoglycans (GAG)

A

Long unbranched polymers made from repeating units of hexuronic acid and an amino sugar

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22
Q

Proteoglycans

A

Proteins that are covalently bonded with GAGs
ECM
Part of connective tissue

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23
Q

Mucopolysaccharidoses

A

Group of disorders caused by the absence or malfunction of enzymes that are required for the breakdown of GAG

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24
Q

Example of Mucopolysaccharidoses

A

Hurler Syndrome
Dementia
Clouding of cornea
Arterial wall thickening

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25
Q

Mouth digestion

A

Salivary amylase

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26
Q

Stomach digetsin

A

No carbohydrate digestion

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27
Q

Jejunum digestion

A

Isomaltase- hydrolyses (a1-6 bonds)
Glucoamylase- removes glucose from non-reducing ends
Sucrase- hydrolyses sucrose
Lactase- hydrolyses lactose

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28
Q

Absorption of glucose

A

Na+ glucose symporter- driven by high extracellular Na+

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29
Q

Glucose uniporter:

A

GLUT2 faciltates efflux of glucose into blood

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30
Q

Fructose absorption

A

GLUT 5

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31
Q

Cellulose and Hemicellulose

A

Oligosaccharides
Cannot be digested in the gut
Increases faecal bulk and decreases transit time
Polymers are broken down by the gut bacteria which yield CH4 and H2

32
Q

Disaccharides deficiencies

A 
Genetic
Intestinal infection
Inflammation of gut lining
Drug injury to wall of gut
Surgical removal
33
Q

Lactose Intolerance

A

Most common disaccharidase deficiency

34
Q

How is glucose absorbed into gut?

A

Diffuses through the intestinal epithelium
Enters portal blood to liver
Phosphorylated to Glucose-6-phosphate to trap it

35
Q

Glucokinase

A

Liver
High Km-
High Vmax-

36
Q

Hexokinase

A

Everywhere
Low Km
Low Vmax

37
Q

Km

A

Low Km- high affinity

High Km- low affinity

38
Q

Vmax

A

Low Vmax- Low rate of conversion

High Vmax- High rate of conversion

39
Q

Glycogen

A

In liver when blood glucose falls converted to glucose

In skeletal muscle converted to lactate

40
Q

What enzyme begins Glycogenesis

A

Glycogenin

41
Q

Phosphoglucomutase

A

Glucose-6-phosphate to Glucose-1-phosphate

42
Q

UDP-glucose phosphorylase

A

Catalyses the synthesis of UDP-glucose from UTP and Glucose-1-phosphate

43
Q

Glycogen Synthase

A

Extends the glucose chains forming (a1-4) glycosidic bonds

44
Q

Glycogen-branching enzymes

A

After a number of glucoses have been joined in a straight chain (a1-4), branching enzymes break one of the a1-4 bonds and transfers a block of residues to a more interior site in the glycogen molecule (a1-6)

45
Q

Glycogenin

A

A primer than contains 8 glucosyl units and glycogen synthase extends this molecule

46
Q

Degradation of Glycogen

A

Glucose monomers are removed one at a time from the non-reducing ends as G-1-P
The glucose is removed then phosphorylated

47
Q

Glucose Phosphorylase

A

Removed glucose from non-reducing end and phosphorylates it

48
Q

Glucosidase

A

Removes final glucose

49
Q

Hexokinase

A

Glucose to G-6-P

50
Q

Glucose-6-Phosphatase

A

Removal of glucose from G-6-P to produce glucose

51
Q

Phosphoglucomutase

A

Glucose-6-P to Glucose-1-P

52
Q

Cori Cycle (Liver)

A

Lactate&raquo_space; Pyruvate&raquo_space;Glucose (gluconeogensis)

53
Q

Cori cycle ( Muscle)

A

Glucose&raquo_space;Pyruvate»(lactate dehydrogenase)Lactate (glycolysis)

54
Q

Key enzymes of Gluconeogenesis

A
  1. Pyruvate Carboxylase
  2. PEP Carboxykinase (PEPCK)
  3. Fructose 1,6 Bisphosphatase
  4. Glucose-6-Phosphatase
55
Q

Purpose of 4 key reactions in gluconeogenesis

A

Bypass non-reversible reaction

56
Q

Lactate to Pyruvate

A

Lactate dehydrogenase

57
Q

Pyruvate to Oxaloacetate

A

Pyruvate carboxylase

58
Q

Oxaloacetate to PEP

A

PEP carboxykinase

59
Q

F-1,6 BP to F-6-P

A

Fructose 1,6 Bisphosphatase

60
Q

G-6-P to glucose

A

Glucose-6 Phosphatase

61
Q

Final step of Gluconeogenesis

A

Occurs in lumen of ER

G-6-P shuttled out of enzyme embedded in cytoplasmic membrane

62
Q

Fructose and Galactose can__

A

enter glycolysis at various points

63
Q

Pentose Phosphate Pathway

A

produces NADPH for all organisms

64
Q

Starting molecule for PPP

A

G-6-P

65
Q

Purpose of PPP

A 
Fatty acid synthesis
Steroid synthesis
Antioxidant
Drug metabolism
Produces precursors for ATP, RNA and DNA
66
Q

2 Phases of PPP

A

Oxidative- linear (irreversible)

Non-oxidative (reversible)

67
Q

Non-oxidative

A

produces a lot of NADPH

68
Q

Oxidative

A

Generates NADPH and produces pentoses

69
Q

In liver ethanol is broken down which requires____

A

NAD+

70
Q

Consequence of limited amount of NAD+

A

inhibits gluconeogenesis

71
Q

Reaction A and B of gluconeogenesis require____ to convert pyruvate to PEP and Lactate to pyruvate

A

NAD+

72
Q

Drinking alcohol inhibits gluconeogenesis and leads to

A

Increased lactate in blood and decreased blood glucose

73
Q

G-6-P dehydrogenase

A

generates NADPH

Clears peroxidase from RBCs

74
Q

G-6-P dehydrogenase deficiency

A

Low NADPH levels
Peroxidase not cleared
Oxygen forms free radicals and damages cells

75
Q

Citric Acid Cycle

A

Occurs in mitochondrial matrix
Indirectly produces large amounts of ATP
Gateway to aerobic metabolism
Removes electrons and passes it on to form NADH and FADH2

76
Q

Citric Acid Cycle process

A 
Pyruvate 
(PYRUVATE DEHYDROGENASE)
Acetyl CoA
Citrate
a-ketoglutarate
Succinyl CoA
Oxaloacetate
77
Q

Entry to cycle is controlled by_____

A

Pyruvate dehydrogenase- acetyl CoA and ATP negative regulate
Isocitrate dehydrogenase- ATP and NADH negative regulate
a-ketoglutarate dehydrogenase- ATP and NADH negative regulate

Science for Medicine A (31 decks)

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