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Biochemistry > Carbohydrates L13 L14 L15 > Flashcards

Carbohydrates L13 L14 L15 Flashcards

1
Q

what forms carbohydrates

A 
carbon
hydrogen 
oxygen
most abundant organic molecules on earth
major energy source for most living things
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2
Q

why are they called carbohydrates

A

hydrated carbons

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3
Q

what is the role and function of carbohydrates

A

structure role and supplying energy in plants

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4
Q

how is glyceraldehyde formed

A

Gycerol remove a hydrogen becomes a monosaccharide

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5
Q

what are the types of glyceraldehyde

A

two different forms of glyceraldehyde (depending on the highlighted OH which side is on)
D form – dextro
Or L form – laevo

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6
Q

what do monosaccharides contain

A

number of hydroxyl groups

carbon covalently bonded to oxygen

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7
Q

what makes a monosaccharide an aldehyde

A

if bonded at end

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8
Q

what makes a monosaccharide a ketone (ketose sugar)

A

if in carbon chain

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9
Q

what is a chiral carbon

A

four different molecules bound to it

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10
Q

what are D and L glyceraldehydes

A

Different compounds
Mirror images of each other
Enantiomers (also stereoisomers)

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11
Q

how do D and L glyceraldehydes differ

A

Rotate polarized light differently: either (+) or (-)
D will rotate it to the right
L will rotate it to the left
Handled differently by enzymes

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12
Q

what are stereoisomers

A

same chemical formula but OH differs where it is in the chain

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13
Q

what is glyceraldehyde

A 
triose sugar (3 carbons)
aldose sugar (aldehyde group)
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14
Q

what is ribose

A 
pentose sugar (5 carbons)
aldose sugar (aldehyde group)
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15
Q

what is glucose

A 
hexose sugar (6 carbons)
aldose sugar (aldehyde group)
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16
Q

what are the main examples of D-versions of hexose sugar

A

D-glucose
D-mannose
D-galactose

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17
Q

how many hexose sugar versions are there

A

8 L

8 D

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18
Q

what is an epimer

A

differ in position of one of their hydroxyl groups

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19
Q

what are examples of epimers

A

glucose and mannose

glucose and galactose

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20
Q

monosaccharide examples

A

glucose
mannose
galactose
fructose

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21
Q

what do monosaccharide aldehyde groups react with

A

tend to react with their own hydroxyl groups

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22
Q

what are most monosaccharides structure

A

most of the time the monosaccharides exist in a cyclic form

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23
Q

in a cyclic form what forms alpha glucose

A

if the hydroxyl group points down on the first carbon

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24
Q

in a cyclic form what forms beta glucose

A

if the hydroxyl group points up on the first carbon

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25
Q

can glucose molecules convert between alpha and beta

A

In solution can convert between the two alpha/beta

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26
Q

what structure can glucose adopt

A

different ‘chair’ and ‘boat’ conformations

Glucose more often found in chain configuration as large groupings are less hindered

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27
Q

what is the structure of simple ‘sugars’

A

based on linear carbon chains with multiple hydroxyl groups (-OH)

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28
Q

what are the most common sugars

A

D form

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29
Q

where is the aldehyde group in aldoses

A

carbon 1

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30
Q

what is the preferred structure of hexose

A

chains prefer to cyclise and form a 6- membered ring

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31
Q

what do hexoses form

A

hexoses such as glucose, mannose and galactose form 6- membered pyranose rings

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32
Q

what does a pentose ribose form

A

5-membered furanose ring

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33
Q

what are ketoses

A

have a carbonyl oxygen on carbon 2 (keto-group)

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34
Q

what are the three most common aldoses

A

Glucose, Mannose and Galactose

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35
Q

how are glucose, mannose and galactose related

A

cyclise in the same way

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36
Q

what are modified monosaccharides important in

A

glycoproteins and cell walls

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37
Q

what can monosaccharides carry

A

phosphates

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38
Q

what is inositol

A

analogue of a monosaccharide

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39
Q

what are inositol phosphates important for

A

cell signalling mechanisms

e.g. muscle contractions

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40
Q

what can monosaccharides join together to form

A 
condensation reaction removes water
through glycosidic bonds
disaccharides - two monomers
oligosaccharides - several monomers
polysaccharides - many monomers
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41
Q

what prevents monosaccharides alternating between alpha and beta

A

when glycosidic bond in ring is no longer free to open

cannot change between the two due to anomeric carbon bound by glycosidic bond

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42
Q

what is the lactose percentage in milk

A

~7%

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43
Q

what breaks down lactose

A

beta galactosidase - lactase

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44
Q

where is beta galactosidase in high amounts

A

in infants digestive system, not in adults

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45
Q

what type of enzyme is beta galactosidase

A

hydrolytic enzyme

catalyses reaction of lactose with water

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46
Q

what is beta galactosidase famous for

A

genetic studies in E.coli

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47
Q

what is an inducible enzyme

A

gene can be ‘turned on’ by lactose in medium

- beta galactosidase

48
Q

what forms a blue colour when beta galactosidase enzyme expressed

A

galactose derivative X-gal releases a blue colour when the beta-galactosidase gene is expressed (‘turned on’)

49
Q

what happens when a foreign gene is inserted into beta galactosidase

A

cant hydrolyse
With foreign gene of interest will be white in colour as blue enzyme wont work
Can be used to identify proteins

50
Q

what is beta galactosidase used for in transgenic animals

A

transgenic animals, the galactosidase sequence can be attached to a ‘transgene’ of interest
The galactosidase enzyme activity is used to show where transgene is being expressed

51
Q

what is sucrose

A

probably the most abundant disaccharide in nature – a heterodimer of glucose and fructose
The glycosidic linkage is 1-2

52
Q

what is sucrose hydrolysed by

A

enzyme ‘Sucrase’ or ‘Invertase

53
Q

where does sucrose hydrolysis occur naturally

A

fruits and honey - a mixture of glucose and fructose is sweeter than sucrose

54
Q

what is dietary glucose used in

A

energy metabolism by the brain

55
Q

where is fructose used

A

tends to become directly incorporated into fat

56
Q

what do foods and confectionaries use high-fructose syrups for

A

sweetener may be more ‘fattening’ than those with ‘sugar’

57
Q

what is maltose

A

homodimer of glucose

58
Q

what is maltose hydrolysed by

A

maltase enzyme

59
Q

what is the bond that links monosaccharides

A

glycosidic bonds

60
Q

where is maltose found

A

usually only found in low amounts, except as a breakdown product of starch -eg in the ‘malting’ process in barley

61
Q

which monosaccharides are ‘reducing’ sugars and why

A

Lactose and maltose are ‘reducing’ sugars as their anomeric carbon can open up
Sucrose is not a reducing sugar as both anomeric carbons are bound to glycosidic bond –When sucrose is split by invertase two reducing sugar are formed

62
Q

what carbon in monosaccharide is used to react to give colour characteristic

A

OH on carbon 1 free to react with copper ion

63
Q

where is the carbonyl group in ketoses

A

carbon 2

64
Q

how is five member furanose ring formed

A

fructose cyclises

65
Q

how can monoscaccharides be modified

A

to include amino acid groups and phosphate groups

66
Q

what does the stereochemistry of glycosidic bonds determine

A

susceptibility to enzymic attack

67
Q

where are oligosaccharides not usually found

A

free in cells or tissues, except as breakdown products of polysaccharides

68
Q

how big are oligonucleotides

A

~5-15 monomers

69
Q

what are the three main types of polysaccharide that carbohydrates are present as

A

cellulose
starch
glycogen

70
Q

what does cellulose do

A

structural in plants

71
Q

what does starch do

A

storage

72
Q

where is glycogen

A

high in liver where stored

73
Q

what is the structure of cellulose compared to glucose

A

Cellulose is a linear homo-polymer of glucose

74
Q

how are glucose monomers joined

A

beta 1-4 glycosidic bonds

75
Q

what is the structure of cellulose monomers joined

A

line up end to end
each neighbouring glucose molecule is rotated 180 degrees
thousands of glycan chains lining up parallel

76
Q

what bond joins cellulose molecules

A

hydrogen

77
Q

where are the hydrogen bonds that join cellulose

A

between hydroxyl groups

78
Q

what gives cellulose support

A

surrounded by other polysaccharides for support

79
Q

what gives cellulose strength and rigidity

A

high strength and rigidity from criss cross structure

80
Q

what reaction is joining the cellulose monomers

A

condensation reaction Water is largely excluded, making solubilisation very difficult

81
Q

what enzyme do most animals not possess, but what does

A

enzymes capable of breaking the 1-4 linkage between glucose units
a few microorganisms and fungi do

82
Q

what do ruminants need to get release of glucose

A

rely on microorganisms with the enzyme that can break the beta 1-4 glycosidic bond
very slow process

83
Q

what can fermentation technology produce

A

cellulase enzyme

84
Q

what is cellulase for

A

valuable to be able to release glucose for foods or for biofuels

85
Q

what is characteristic of de-repressed mutants and cellulase

A

De-repressed mutants have been found that can make large quantities of cellulase

86
Q

what is the growth of a non mutant like with glucose and cellulase present

A

Glucose gets lower as is used up, till too low

Cellulase starts to breaks down materials to make glucose

87
Q

what is the growth of a mutant like with glucose and cellulase present

A

Mutant always has cellulase even when high amount of glucose, to make more glucose

88
Q

how is cellulase made into glucose

A

cut by three enzymes

  • endoglucanase
  • exoglucanse
  • cellobiase
89
Q

what does endoglucanase do

A

initial cut into cellulose chain

90
Q

what does exoglucanase do

A

makes a second cut next to first produces glucose dimer cellobiase

91
Q

what does cellobiase do

A

breaks down bits into individual glucose molecules

92
Q

what is hemicellulose

A

complex polymers of xylan and other monosaccharides

93
Q

what is lignin

A

complex cross-linked polymers of phenolic compounds

94
Q

what can we use biomass for

A
  • Composting
  • Feeding to ruminants
  • Adding ‘cellulase’ and releasing sugars for biofuels
  • Genetically engineering plants to contain their own ‘cellulase’
95
Q

what is chitin

A

an abundant polymer found in crustaceans, insects and fungal cell walls

96
Q

what are the links to join monomers to form chitin

A

beta 1-4 linked homopolymer of glucosamine

97
Q

what are starch and glycogen designed for

A

glucose stores to be rapidly utilised as fuels

98
Q

what is starch’s function

A

plant energy reserves consisting of alpha-amylase and

amylopectin

99
Q

what is alpha-amylase

A

enzyme

linear homopolymer of starch

100
Q

what is amylopectin

A

branched polymer of starch

contains up to a million glucose units

101
Q

where is alpha amylase present

A

present in saliva

102
Q

what does alpha amylase do

A

randomly attacks the long chain, yielding disaccharides (maltose) and trisaccharides

103
Q

what happens to di- and tri- saccharides that are formed

A

further degraded in the small intestine by an alpha - glucosidase

104
Q

in animals what attacks amylopectin

A

alpha and beta - amylase

105
Q

what effect does the attack of alpha and beta amylase have on amylopectin

A

cannot break 1-6 linkage

106
Q

what starch is very resistant to digestion

A

potato

almost crystalline structure

107
Q

what is glycogen with regards to glucose

A

glucose homopolymer

108
Q

what is glycogen function

A

major storage polysaccharide in animal cells

109
Q

what are the glycosidic links in glycogen

A

alpha1-4

alpha 1-6

110
Q

what particles does glycogen form

A

cytosolic

111
Q

what effect does greater branching have on glucose and starch storage

A

more glucose can be packed in smaller volume than in starch

more ‘ends’ capable of being attacked by glycogen phosphorylase

112
Q

where is glycogen phosphorylase

A

liver and muscle

113
Q

what is glycogen phosphorylase

A

highly-regulated enzyme

114
Q

what is glycogen phosphorylase needed for in animals

A

energy production during the ‘fight or flight’ response in animals

115
Q

what does glycogen phosphorylase sense

A

‘energy status’ of the cell (ATP + ADP + AMP) particularly the level of AMP

116
Q

what does the enzyme glycogen phosphorylase respond to

A

stimulation by the nervous system (via Calcium ion release)

stimulation by adrenaline (via phosphorylation)

117
Q

what is glycogen phosphorylase regulated by

A

Ca++, AMP and adrenaline

Biochemistry (13 decks)

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