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Macromolecules > Carbohydrates > Flashcards

Carbohydrates Flashcards

1
Q

What are carbohydrates ?

A
  • most abundant biomolecules on Earth
  • complex organic molecules formed from carbon dioxide and water which are used as a source of chemical energy by living organisms
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2
Q

What is the empirical formula of carbohydrates ?

A

(CH2O)n where n is greater than or equal to 3

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3
Q

What are monosaccharides ?

A

Simple sugars

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4
Q

What are oligosaccharides ?

A

Short chains of monosaccharides which are less than 20 residues

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5
Q

What are polysaccharides ?

A

Consists of hundreds or thousands of monosaccharide units

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6
Q

What are the properties of monosaccharides ?

A
  • colourless and crystalline solids
  • water soluble
  • most are sweet tasting
  • open chain and ring structures
  • two families : aldehydes and ketones
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7
Q

Why are most monosaccharides sweet tasting ?

A

They interact with the protein receptors on the tongue and form hydrogen bonds with them

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8
Q

Summarise the properties of glucose

A
  • 6 carbon sugar (hexose)
  • aldose
  • reducing sugar - reduces copper 2 into copper 1 and forms a red brick ppt in Benedict’s reagent
  • asymmetrical with chiral centres at C2, C3, C4 and C5
  • the L and D configuration is based on spatial orientation of C5 groups
  • 16 possible isomers
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9
Q

What is an epimer ?

A

A molecule which has 2 different stereoisomers because only 1 carbon attachment is different

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10
Q

What are the epimers of glucose ?

A
  • D mannose (C2)
  • D galactose (C4)
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11
Q

Are mannose and galactose epimers of each other ?

A

No because 2 carbons are different and not one

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12
Q

Summarise the properties of fructose

A
  • hexose sugar
  • ketone sugar (carbonyl group at C2 position)
  • reducing sugar because the hydroxyl group can be oxidised to another carbonyl which is then reduced
  • asymmetrical - chiral centres at C3, C4 and C5
  • L and D configurations based on spatial orientation of C5
  • 8 possible isomers
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13
Q

What are anomers ?

A
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14
Q

What type of rings are pyranose rings ?

A

Hexagonal rings e.g. glucose

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15
Q

What type of rings are furanose rings ?

A

Pentagonal rings e.g. fructose

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16
Q

What is derivatisation ?

A

Hydroxyl groups can be derivatised which means they can be replaced by substituents

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17
Q

What can hydroxyl groups be replaced by ?

A
  • addition of a phosphate group e.g. ATP is the energy currency of cells
  • addition of sulphate groups e.g. heparin reduces blood clotting
  • addition of amine groups e.g. glucosamine is found in connective tissue
  • addition of hydrogen or alkyl groups e.g. deoxyribose found in DNA
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18
Q

How do O-glycosidic bonds form ?

A
  • form when a hydroxyl group reacts with the anomeric carbon
  • non reducing sugar because the anomeric carbon is trapped by the glycosidic bond and so it can’t be reduced
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19
Q

How do N-glycosidic bonds form ?

A

They form when the anomeric carbon reacts with a nitrogen atom e.g. nucleotides and glycoproteins

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20
Q

What are disaccharides ?

A

2 monosaccharides linked covalently by an O-glycosidic bond

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21
Q

Give some examples of disaccharides

A
  • Lactose
  • Trehalose
  • Maltose
  • Sucrose
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22
Q

Briefly describe lactose

A
  • disaccharide
  • made of ß D galactose and glucose
  • found in milk
  • reducing sugar because there is at least 1 free anomeric carbon
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23
Q

Briefly describe trehalose

A
  • non reducing sugar
  • found in insects
  • 2 alpha glucose with 1-1 linkage
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24
Q

Briefly describe maltose

A
  • important in hydrolysis of starch
  • glucose 1-4 linkage
  • reducing sugar
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25
Q

Briefly describe sucrose

A
  • non reducing sugar
  • found in plants
  • glucose and fructose (1-2)
26
Q

How do polysaccharides vary ?

A
  • the monosaccharide units involved
  • chain length
  • type of bonds linking the units
  • degree of branching
27
Q

What are homopolymers ?

A

Identical monosaccharides

28
Q

What are heteropolymers ?

A

Variable monosaccharides

29
Q

What are the roles of sugars ?

A
  • energy source
  • structural function
  • important in information
30
Q

Which carbohydrates can be used an energy source ?

A
  • monosaccharides
  • disaccharides
  • starch
  • glycogen
  • ATP
31
Q

What are the structural functions of sugars ?

A
  • cell walls
  • exoskeletons
  • connective tissue
32
Q

Why do sugars have so many roles ?

A
  • diverse structural forms
  • 3 hexose sugars can form 1056 different trisaccharides because each hydroxyl group can react with an anomeric carbon
33
Q

Why are polysaccharides mostly used for storage ?

A
  • compact granules
  • bonding means less osmotic pull and so more can be stored in a small space
  • little water associated with it
34
Q

Give some examples of storage polysaccharides

A
  • starch
  • glycogen
35
Q

Describe the structure of starch

A
  • homopolymer of alpha D glucose
  • the alpha D glucose molecules are linked together by 1-4 linkages
  • unbranched = amylose
  • branched = amylopectin > 1-6 linkage every 30 residues
36
Q

Describe the structure of glycogen

A
  • more compact than amylopectin
  • branched > 1-6 linkage every 10 residues
37
Q

What is the importance of alpha linkages ?

A

They provide the coiled structure which is good for storage carbohydrates

38
Q

What do all structural sugars have in common ?

A

They all have ß linkages which provides a linear structure allowing hydrogen bonding which adds to the tensile strength

39
Q

What are the structural homopolymers ?

A
  • cellulose (ß1-4 linked glucose)
  • chitin (ß1-4 linked N-acetylglucosamine)
40
Q

What are the structural heteropolymers ?

A

Bacterial cell walls (ß1-4 linked peptidoglycan)

41
Q

Describe the structure of cellulose

A
  • unbranched polymer of glucose joined by ß1-4 linkages
  • the ß configuration allows the formation of very long straight chains
  • parallel chains can interact by hydrogen bonds forming fibrils
  • fibres have high tensile strength
42
Q

What is the most abundant biological molecule on Earth ?

A

Cellulose

43
Q

What is chitin used for ?

A

Insect exoskeleton

44
Q

Describe the structure of chitin

A
  • very similar to cellulose
  • differs from cellulose by the replacement of C2 hydroxyl group with an acetylated amino group
  • parallel chains interact by hydrogen bonding leading to high tensile strength
45
Q

Describe the structure of bacterial cell walls

A

ß1-4 linked

46
Q

What are glycosaminoglycans ?

A
  • family of heteropolysaccharides composed of repeating disaccharide units
  • anioinic
  • one of the monosaccharides is always either N-acetylgalactosamine or N-acetylglucosamine
  • the other sugar is mostly an uronic acid (C6 carboxylic acid)
  • it is a component of the extracellular matrix
47
Q

Where is connective tissue found ?

A
  • bone
  • teeth
  • cartilage
  • skin
  • blood vessels
48
Q

Describe the structure of connective tissue

A
  • made of collagen which is fibrous so provides strength
49
Q

What are proteoglycans ?

A
  • glycans with a bit of protein associated with it (95% carbohydrates and 5% protein)
50
Q

What are glycoproteins and glycolipids ?

A
  • oligosaccharides associated with proteins and lipids
  • play important roles in recognition and communication
51
Q

Describe the importance of sugar in fingerprints

A
  • sugar residues of our cell surfaces which are unique to us (recognise self from non self)
  • sugars allow more variety than proteins
  • important for tissue typing
  • define blood groupings
  • mounts an immune response
52
Q

How do the blood groups differ ?

A
  • glycosyltransferases add specific sugars/carbohydrates to the base antigen which causes differentiation
  • common foundation is known as the O antigen
  • O phenotype is a result of a mutation resulting in no active glycosyltransferase
53
Q

How do the A and B blood groups differ ?

A
  • A blood group has the addition of N-acetylgalactose
  • B blood group has the addition of galactose
  • there is a type A and type B glycosyltransferase
54
Q

Which blood group is the universal recipient ?

A

AB

55
Q

Which blood group is the universal donor ?

A

O

56
Q

What are mucins ?

A
  • proteins found in the mouth to help with digestion
  • they contain lots of carbohydrates
  • they increase the viscosity of the fluid in which they are dissolved
  • aid the delivery of the food to the gullet and ease its passage
57
Q

What are lectins ?

A
  • proteins which recognise and bind specific carbohydrate structures
  • serve a wide variety of cell to cell recognition and adhesion processes
58
Q

Give some functions of lectins

A
  • lectins recognise old red blood cells and remove them
  • viral pathogens utilise lectins for adhesion or toxic entry into host cells
59
Q

What are selectins ?

A

They are a family of lectins involved in cell to cell recognition and adhesion e.g. the movement of T lymphocytes to a site of infection or inflammation

60
Q

Summarise the roles of carbohydrates in the influenza virus

A
  • hemagglutinin (lectin) recognises sialic acid residues on the host surface glycoproteins
  • after penetrating the membrane, neuramidase (sialidase) breaks the glycosidic bond to release the virus
  • without neuramidase, the virus is non invasive

Macromolecules (4 decks)

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