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Biochemistry > Carbohydrates > Flashcards

Carbohydrates Flashcards

1
Q

Functions of carbohydrates

A
  • Supply of carbon for synthesis
  • Form structural components (in cells/ tissues)
  • Energy storage
    • Starch
    • Glycogen
  • Energy for:
    • DNA
    • RNA
    • ATP
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2
Q

Give the categories of carbohydrate

A
  • Monosaccharides
  • Disaccharides (2 monosaccharides)
  • Oligosaccharides (3-10 monosaccharides)
  • Polysaccharides (10+ monosaccharides)
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3
Q

Give the classifications of monosaccharide

A
  • Triose (3C)
  • Tetrose (4C)
  • Pentose (5C)
  • Hexose* (6C)

*Can form a 5-membered ring

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4
Q
A

Glyceraldehyde

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5
Q
A

Dihydroxyacetone

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6
Q
A
  • Ribose
  • Deoxyribose
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7
Q
A

Ribulose

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8
Q
A
  • Glucose
  • Galactose
  • Mannose
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9
Q
A

Fructose

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10
Q

Monosaccharide classification is based on…

A

Functional groups

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11
Q

The functional group of aldoses

A

Aldehyde group (CHO)

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12
Q

The functional group of ketoses

A

Ketone group (CO)

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13
Q

Optical rotation: Plane of polarised light rotation

A
  • Right: +
  • Left: -
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14
Q

Anomers

A
  • Epimers occurring after cyclization
  • Alpha-D-(+)-glucopyranose
  • Beta-D-(+)-glucopyranose
  • Reflect a change at the:
    • Hemiacetal carbon (C1)
    • Hemiketal carbon (C1)
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15
Q

Location of -OH group in alpha/beta-D-(+)-glucopyranose

A

At C1:

  • Alpha: Below the ring
  • Beta: Above the ring
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16
Q

Glucose structure

A
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17
Q

Galactose structure

A
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18
Q
A

Mannose structure

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19
Q

Sugar acids

A
  • Aldehyde at C1 is oxidised to a -COOH group

E.g:

  • Gluconic acid
  • Glucuronic acid
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20
Q

Aminosugars

A
  • Amino group substitutes for 1 or 2 of the -OH
  • The amino group may be acetylated
  • Example: Glucosamine
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21
Q

Sugar alcohols

A
  • Lack of an aldehyde/ketone group
  • Reduced to alcoholic groups
  • E.g:
    • Ribitol (by reducing ribose)
    • Sorbitol (by reducing glucose)
    • Mannitol (by reducing mannose)
    • Xylitol (by reducing xylose)
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22
Q

Monosaccharides are bound by a…

A

Glycosydic bond

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23
Q

Composites of maltose

A

α-D-glu + α-D-glu

(α-1,4 glycosidic bond)

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24
Q

Composites of Cellobiose

A

β-D-glu + β-D-glu

(β-1,4 glycosidic bond)

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25
Q

Composites of Lactose

A

β-D-gal + β-D-glu

(β-1,4 glycosidic bond)

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26
Q

Composites of sucrose

A

α-D-glu + β-D-fru

(α-1, β-2 glycosidic bonds)

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27
Q

Examples of oligosaccharides

A

Dextrines:

  • Amylo-
  • Malto-
  • Erithro-
  • Acro-
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28
Q

Sources of sucrose

A
  • Sugar beet
  • Sugar cane
  • Sugar maple
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29
Q

Oligosaccharides used in…

A
  • Milk constituents
  • Prebiotics - digested by the microbial flora
  • Glycolipids/glycoproteins of membranes
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30
Q

Starch and glycogen are examples of…

A

Homopolysaccharide

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31
Q

Composite of starch

A
  • 20% amylose
  • 80% amylopectin
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32
Q

Describe the branching of starch

A

Branching occurs on the 25th glucose monomer

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33
Q

Glycogen

A
  • Animal storage product
  • Branching
  • Non-water soluble
  • Branching at 8-10th glucose monomer
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34
Q

Glycosidic bonds between monomers are degraded by…

A

Amylase

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35
Q

Cellulose

A
  • Non water soluble
  • Found in plant walls
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36
Q

Describe the bonding of cellulose

A
  • Beta-D-glucose bound by beta 1,4 glycosidic bond
  • Hydrogen bonding
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37
Q

How is cellulose degraded by herbivores?

A

Presence of bacterial cellulase in the rumen

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38
Q

Examples of heteropolysaccharides

A
  • Hyaluronic acid
  • Chondroitin sulphate
  • Heparin

Contain beta 1,3 glycosidic bond

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39
Q

Hyaluronic acid composition

A

Repeating monomers:

  • D-glucuronate
  • N-acetyl-D-glucosamine
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40
Q

Hyaluronic acid is degraded by…

A

Hyaluronidase

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41
Q

Where is hyaluronidase found?

A

In the coat of the ovum

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42
Q

Chondroitin sulphate composition

A

Alternating units:

  • D-glucuronate
  • N-acetyl-D-galactosamine

Vitamin A has a role in the binding of the sulphate group

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43
Q

Where is chondroitin sulphate found?

A
  • Cartilage
  • Bone
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44
Q

Heparin composition

A

Repeating units:

  • D-glucuronate
  • D-glucosamine
  • Has an extended helical conformation*
  • Known as a clearing factor*
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45
Q

The carbohydrate portion of glycoproteins differs from that of glycosaminoglycans in that it is…

A
  • Shorter
  • Often branched
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46
Q

Cori cycle

A
  • Synthesis of glucose-6-phosphate via gluconeogenesis
  • Glucose-6-phosphate → Glucose
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47
Q

Anaerobic substrate for gluconeogenesis

A

Lactate

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48
Q

Glycogenesis (GG)

A
  • Synthesis of glycogen from glucose
  • Liver, muscle cytoplasm
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49
Q

Glycogenolysis (GGL)

A
  • Degradation of glycogen to blood glucose
  • Liver cytoplasm
50
Q

Aim of carbohydrate metabolism in the liver

A

Elevation of blood glucose (not storage)

51
Q

Which process is shown?

A

Glycogenesis

52
Q

During glycogenesis, glycogen synthase acts as a…

A

Regulatory enzyme

52
Q

Compare hexokinase and glucokinase activity

A
  • Hexokinase:
    • Non-hepatic
    • Low Km
    • High activity
  • Glucokinase:
    • Hepatic
    • High Km
    • Low activity
53
Q

Which enzyme catalyses branching of the glycogen chain (glucogenesis)

A

Transglucosidase

54
Q

The branched structure of glycogen allows…

A

Rapid release of glucose simultaneously from every non-reducing end of every branch

55
Q

Glucose produced from glycogenolysis is transported by…

A

GLUT2 transporter into the circulation

56
Q

Glycogenolysis occurs in the…

A
  • Liver
  • (Kidney)
57
Q

Energy balance of glycogenesis

A

Loss of 2 ATP per glucose stored

Glucose storage needs energy

58
Q

Energy balance of glycogenolysis

A

No energy gain/utilisation

59
Q

Regulation of glycogenesis + glycogenolysis

A
  • 2 reactions with opposite directions → Cascade mechanism
  • 2 types of regulation:
    • Slow, hormonal
    • Fast, allosteric
60
Q

Process of cascade mechanism

A
  1. Messenger molecules (hormones) induce →
  2. Cellular answer by second messenger molecules

Intensity of cellular reaction can be 1000-10000 times higher

61
Q

Steps of hormonal regulation

A
  1. Glucagon/adrenalin-binding receptors bind hormones → First messengers
  2. Inactive GDP → active with hormone binding
  3. GTP bound to α-subunit​
  4. Activated α-subunit​ dissociates
  5. Adenylate cyclase activated
  6. GTP → GDP
  7. α-subunit​ inactivated
62
Q

Adenylate cyclase catalyses which reaction?

A

ATP → PPin + AMP → cAMP

63
Q

Which enzyme degrades cAMP to form AMP?

A

Phosphodiesterase

64
Q

cAMP-dependent protein kinase A (PKA) is activated by…

65
Q

Give the effects of cAMP during hormonal regulation of glycogenolysis

A
  1. cAMP activates PKA
  2. Active PKA activates GPK
  3. Active GPK activates GP beginning glycogenolysis
66
Q

Describe the structure of PKA

A
  • 2 catalytic subunits
  • 2 regulatory subunits
67
Q

If the regulatory subunits are bound to the catalytic subunits, the PKA enzyme is…

68
Q

Enzyme for phosphorylation

A

Protein kinase

69
Q

Enzyme for dephosphorylation

A

Phosphoprotein phosphatase

70
Q

Give the steps of glycogenesis-glycogenolysis

A
  1. Glycogen phosphorylase active by phosphorylation
  2. Glycogen synthase active by dephosphorylation
71
Q

Title the figure

A

Regulation by phosphorylation

72
Q

Compound A

  • Name
73
Q

Process 1

  • Enzyme
  • Reactions
A
  • Glycogen phosphorylase
  • Pi →
74
Q

Compound B

  • Name
A

Glucose-1-phosphate

75
Q

Process 2

  • The fate of the compound
A

Enters into glycogenolysis

76
Q

Process 3

  • Reactions
A

UTP → PPi

77
Q

Compound C

  • Name
A

UDP-glucose

78
Q

Process 4

  • Enzyme
  • Reactions
A
  • Glycogen-synthase
  • → UDP
79
Q

Enzyme A1

  • Name
A

Glycogen phosphorylase

Active, phosphorylated form

80
Q

Process 5

  • Enzyme
A

Phosphoprotein-phosphatase

Dephosphorylated

81
Q

Enzyme A2

  • Name
A

Glycogen phosphorylase

Inactive, dephosphorylated

82
Q

Process 6

  • Enzyme
A

Protein kinase

Phosphorylated

83
Q

Which hormone can regulate glycogenesis/glycogenolysis?

84
Q

Hormonal regulation of glycogenesis by insulin

A
  1. Insulin receptor → PIP3
  2. PIP3 activates PKB
  3. Active PKB activates phosphodiesterase
  4. This degrades + decreases cAMP
  5. Dephosphorylation
  6. Activation of glycogen synthase
  7. Glycogenesis
85
Q

Insulin:

  • Stimulation of glycogen synthesis
  • Inhibition of glycogen degradation
A
  1. Insulin bound to the receptor
  2. PI3-K activated
  3. PIP2 → PIP3 second messenger
  4. PKB inactive → PKB active
  5. Phosphodiesterase inactive → Active
  6. cAMP → AMP
  7. PKA active → Inactive
  8. Glycogen synthase → Active
  9. Glycogen phosphorylase → Inactive
86
Q

Give the steps of parallel regulation of glycogenolysis and glycogenesis in the liver + muscle

A
  1. Glycogen phosphorylase active → Inactive
  2. Phosphodiesterase activated by insulin
  3. Glycogen synthase active → inactive
  4. Adenylate cyclase activated by glucagon + adrenalin
  5. Step 1 repeats
87
Q

Allosteric regulation of glycogenolysis + glycogenesis is present in which organs?

A

Liver + muslce

88
Q

The allosteric inhibitor of glycogen phosphorylase in the liver

89
Q

During allosteric regulation, 2 P groups of GP enzyme favour binding of…

A

Phosphoprotein phosphatase

90
Q

Allosteric activator of glycogen phosphorylase in the muscle.

A

Ca2+

Binds to glycogen phosphorylase kinase

91
Q
A

Carbohydrates

  • Glucose
  • Fructose
  • Galactose
92
Q
A

Glucose-6-phosphate

93
Q
A

Glucose

To blood and brain

94
Q
A

Glycogen

Stored in liver cells

95
Q
A

Pyruvic Acid

96
Q
A

Glycolysis

97
Q
A

Gluconeogenesis

98
Q
A

Glycogenesis

99
Q
A

Glycogenolysis

100
Q
A

Lactic acid

101
Q

Glycolysis

A

Degradation of glucose to pyruvate

or anaerobically to lactate

102
Q

Gluconeogenesis

A

Production of glucose from non-carbohydrate sources

in the liver

103
Q

Give the parts of glycolysis

A
  1. Preparatory part
  2. Energy conserving part
104
Q

Energy production + end product of anaerobic glycolysis

A
  • 2 ATP (starting with glucose)
  • 3 ATP (starting with glycogen)
  • Product = Lactate
105
Q

Energy production + end product of aerobic glycolysis

A
  • 6 ATP (Starting with glucose)
  • 7 ATP (Starting with glycogen)
  • End product = Pyruvate
106
Q

Role of lactate in meat quality

A
  1. PSE (Pale, soft, exudative) (Pork)
  2. DFD (Dark, firm, dry) (Beef)
107
Q

Pasteur effect

A

Pyruvic acid → Lactic acid

  • Aerobic environment: No lactate production
108
Q

Energy from gluconeogenesis is used in…

A
  • Brain
  • Testes
  • Erythrocytes
  • Adrenal medulla
109
Q

In ruminants, gluconeogenesis takes place…

A

Continuously

110
Q
A

Lactic acid

111
Q
A

Pyruvic acid

112
Q
A
  • Glycerol
  • Amino acids
113
Q
A

6 ATP → 6 ADP

114
Q
A

Glucose-6-phosphate

115
Q
116
Q
A

Glycogenesis

117
Q
118
Q

Name the pathway

A

Gluconeogenesis

119
Q

Give the energy gain of oxidation from one glucose molecule in glycolysis/citrate cycle

Biochemistry (21 decks)

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