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Biochemistry (BY1BC1) > Week 5 (Carbohydrate Polymers) > Flashcards

Week 5 (Carbohydrate Polymers) Flashcards

1
Q

What are carbohydrates composed of?

A

Carbon, hydrogen and oxygen

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2
Q

What is a monosaccharide?

A
  • One sugar residue
  • Any of the class of sugars (e.g. glucose) that cannot be hydrolysed to give a simpler sugar
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3
Q

What is a disaccharide?

A

Two monosaccharide units

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4
Q

What is an oligosaccharide?

A

More than two monosaccharides (from three to six simple monosaccharide units)

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5
Q

What is a polysaccharide?

A

Lots of monosaccharide molecules bonded together

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6
Q

How are carbohydrates stored in plant cells?

A

As the complex carbohydrate starch

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7
Q

What is the function of carbohydrates in plant cells?

A
  • act as structural elements
  • supply energy (in the form of simple sugars)
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8
Q

How are carbohydrates stored in animal cells?

A

Stored as glycogen

however they also occur as both simple and complex sugars

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9
Q

What are the function of carbohydrates in animal cells?

A
  • Storage of glucose, in the form of polymers like glycogen, makes it slightly less accessible for metabolism; however, this prevents it from leaking out of the cell or creating a high osmotic pressure that could cause excessive water uptake by the cell
  • Carbohydrates form a part of genetic material like DNA and RNA in the form of deoxyribose and ribose sugars
  • Act as recognition elements e.g, blood groups, cell markers
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10
Q

How many arrangements of a simple disaccharide comprising two glucose residues be joined together?

A

Eleven

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11
Q

Approximately how many different monosaccharides exist?

What does this give rise to?

A
  • 200
  • This gives rise to millions of different polymers
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12
Q

What extends the range of polysaccharide possibilities?

A

Functional group inter conversion

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13
Q

Explain the structure, function and properties of glycogen

A
  • used by animals to store glucose
  • a large branched polymer of glucose
  • alpha-1,4- glycosidic binds
  • branches formed by alpha-1-6- glycosidic bonds
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14
Q

What is the advantage of branching in glycogen?

A
  • Branching increases solubility and makes the sugar more accessible
  • Furthermore, branching creates a large number of terminal residues, the sites of action of glycogen phosphorylase and synthase. Thus, branching increases the rate of glycogen synthesis and degradation.

(Glycogen branching requires a single transferase activity. Glycogen debranching requires two enzyme activities: a transferase and an α-1,6 glucosidase)

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15
Q

What is the structure of amylose?

A
  • unbranched glucose chains with alpha-1,4- glycosidic bonds
  • left handed helix with 6 glucose units per turn
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16
Q

What is the structure of amylopectin?

A
  • branched
  • one alpha-1-6 linkage per 30 alpha 1-4 linkages
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17
Q

What is the purpose of the alpha 1-4 linkages in glycogen and starch?

A

The alpha 1-4 linkages of glycogen and starch produce molecules with hollow helices

  • well suited to forming accessible surface stores
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18
Q

What is the main differences in the structure of amylopectin and glycogen?

A
  • Glycogen has more branching and shorter branches
  • Amylopectin has less frequent branching but longer side chains
  • Amylopectin is an insoluble form whereas glycogen is a soluble form
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19
Q

What is the function of dextran?

A
  • A storage polysaccharide in yeasts and bacteria
20
Q

What is the structure of dextran?

A
  • Nearly all linkages in the main chain are alpha 1-6
  • Depending upon the species occasional branches formed by: Alpha 1-2 linkages, Alpha 1-3 linkages (most common) and Alpha 1-4 linkages
21
Q

What is the function of cellulose?

A
  • major polysaccharide of plants
  • has a structural rather than nutritional role
22
Q

What is the structure of cellulose?

A
  • an unbranched polymer of glucose residues joined by beta 1-4 linkages
  • this particular configuration allows cellulose to form very long straight chains
  • each glucose molecule is rotated 180 degrees relative to its neighbours (This means that the repeating unit is cellobiose, not glucose)
  • Intrachain hydrogen bonds form between the ring oxygen of one residue and the hydrogen of the C3 hydroxyl of a neighboring residue. (Interchain hydrogen bonds occur between hydroxyl and oxygen atoms on adjacent chains)
  • H bonds are formed between different strands (Several cellulose chains come together to form a crystalline or paracrysatalline lattice, which is stabilized by both intrachain (intramolecular) and interchain (intermolecular) hydrogen bonds.)
  • fibrils are formed by parallel chains
  • the linear structure is ideal for forming fibres having a high tensile strength (several dozen such chains lie against each other and are bonded together to form what is known as a cellulose fibril)
23
Q

What are glycoasaminoglycans?

A
  • disaccharide repeating units containing a derivative of an amino sugar:

Glucosamine Or Galactosamine

  • at least one of the sugars in the repeating unit has a negatively charged carboxylate or surface group
24
Q

What are the major glycosaminoglycans?

A
  • chondroitin 6-sulphate
  • keratan sulphate
  • heparin
25
Q

What is heparin synthesised as?

A
  • synthesised as a non-sulfated proteoglycan
  • this is then deacelated and sulfated
  • incomplete modification leads to a mixture of variously sulfated consequences
26
Q

Describe the chemical structure of heparin

A
27
Q

What are proteoglycans?

A
  • A diverse class of proteins contains one or more covalently linked glycosaminoglycan chains

E.g. the proteoglycan in the extracellular matrix of cartilage

28
Q

Explain the composition of cartilage

How does this help with its funcition?

A
  • A very long filament of hyaluronate in the middle

keratin sulfate and chondrotin sulfate chains are covalently attached (through serine chains) to a polypeptide backbone called core protein

  • about 140 of these proteins are noncovalently bound at intervals of 30 nm to the long filament of hyaluronate
  • this interaction is promoted by a small link protein
  • cartilage can cushion compressive forces because these highly hydrated polyanions spring back together after being deformed

(Lots of negative charges close together which can repel each other- when there is no pressure on the cartilage they are far apart (expanded state) when you walk the cartilage is compressed and the negative charges are pushed close together)

29
Q

Describe the physical structure of cartilage

A
  • Hyaluronate is the main thread that runs down the middle
  • Core proteins in the chains that come out at the sides
  • Chondroitin sulfate and keratan sulfate attached to the core protein
  • Link protein hold the various structures together
  • Lots of negative charges close together which can repel each other- when there is no pressure on the cartilage they are far apart (expanded state) when you walk the cartilage is compressed and the negative charges are pushed close together
30
Q

What two ways can oligosaccharides and proteins be linked to form glycoproteins?

A
  • N- linked glucoses (saccharide chains) via asparagine amino groups
  • O linked glycine via threonine or serine hydroxyls
31
Q

How are N- linked glycans usually attached to protein?

A
  • Through N- actetylglucosamine
  • Sometimes through N-acetylgalacosamine to side chain amino group in an asparagine residue
32
Q

How are O linked glycans usually attached to protein?

A
  • by an O-glycosidic bond between N-acetylgalactosamine and the hydroxyl group of threonine or serine residue
  • in a few cases, collagen, hydroxylysine or hydroyproline is employed
33
Q

What are blood group substances?

A
  • a set of antigenic oligosaccharides attached to the surface of red cells
  • on some cells the antigens are attached as O- linked glycans to membrane proteins
  • alternatively, the oligosaccharide may be linked to a lipid molecule to form a glycolipid.
  • The lipid portion of the molecule helps anchor the antigen in the outside surface of erythrocyte membranes
  • these oligosaccharides determine the blood group types in humans.
  • Their presence in a blood sample is detected by blood typing
  • determining wether antibodies to a particular antigen cause red cells of that blood sample to agglutinate
34
Q

Explain the oligosaccharides corresponding to the blood types A, B and O

A

(The R group is the anchoring point to the surface of the red blood cell)

  • almost all humans can produce the type O saccaride. There are 4 carbohydrate building blocks joined together
  • addition of either galactose (to make type B) or N-acetylgalactosamine (to make type A) requires special enzymes
  • some individuals posses one or other of these enzymes
  • a few heterozygous can produce both.
  • The heterozygous individuals have type AB blood with both A and B oligosaccharides present on cell surfaces
35
Q

How can oligosaccharides act as cell markers?

A
  • the surface of many cells are nearly covered with saccharides attached to either lipids or proteins in the cell membrane
  • these act as recognition sites by binding to particular proteins e.g. lectins (carbohydrate-binding proteins that are highly specific for sugar groups of other molecules)
36
Q

What is the difference between heparin and heparin sulfate?

A

Heparan sulfate is like heparin but has few N- and O- sulfate groups and more N- acetylcholine groups

37
Q

Why can cartilage cushion compressive forces?

A

These highly hydrated polyanions spring back after being deformed

38
Q

Why are oligosaccharides used as cell markers?

A

They can offer up a massive variety of structures in relatively short chains -Monomers - linkages - branching patterns

39
Q

How many different possibilities of tri saccharides are there?

A

In a tri-saccharide several thousand permutations are possible

40
Q

What is the difference between heparan sulfate and heparin?

A

Heparan sulfate is like heparin but has fewer N- and O-sulfate groups and more N-acetyl groups

41
Q

Draw the structure of Dermatan Sulfate

A
42
Q

Draw the structure of Hyaluronate

A
43
Q

Name some sugar residues commonly found in glycoproteins

A
44
Q

Why are oligosaccharides so often used as celluar markers?

A

They can offer up a massive variety of structures in relatively short chains

45
Q

Describe the structure and properties of chondroitin 6-sulphate

A
  • Disaccharide repeating unit
  • Glucose is usually CH2OH however this structure has gone up 2 oxidation levels to a caboxylic acid in one component
  • Under physiological conditions the carboxylic acid is depronated to COO-
  • In the other componet what was the CH2OH is effectively now the ester of sulfuric acid which would also be deprotonated in physiological pH: CH2OSO​3-
  • At the bottom of this component what was the OH group would have become an amino group and then an amide group
46
Q

Name some carbohydrates commonly attached to protein

A

Biochemistry (BY1BC1) (17 decks)

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