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Biological Chemistry > Carbohydrates > Flashcards

Carbohydrates Flashcards

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1
Q

What are carbohydrates formed from

A

carbon dioxide and water

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2
Q

What is the carbohydrate empirical formula

A

(CH20)n, where n =3

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3
Q

How many stereoiosmers can a molecule with n chiral centres have

A

2^n

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4
Q

Characteristics of monosaccharides

A

colourless, crystalline solids, water soluble, sweet tasting, exist in open chain and ring structures

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5
Q

What are the 2 families of simple sugars (monosaccharides)

A

aldoses (aldehyde), ketoses (ketones)

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6
Q

What are epimers

A

carbohydrates that differ in the location of one of the -OH groups in one location

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7
Q

What is an L configuration

A

rotates light in an anticlockwise direction

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8
Q

What is D configuration

A

rotates light that is polarised in a clockwise direction

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9
Q

What determines if the aldose/ketose is an L/D

A

The spatial orientation of C5 groups

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10
Q

Monosaccharide: aldoses

A

6 carbon sugar (hexose). Carbonyl group at the end of the chain (aldehyde), reducing sugar, asymmetric chrial centres at C2, C3, C4 and C5

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11
Q

Monosaccharide: ketoses

A

6 carbon sugar (hexoses). Carbonyl position at C2 (ketone), asymmetric chiral centres at C3, C4 and C5

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12
Q

What is an anomer

A

OH group differs at acetal/hemiacetal carbon

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13
Q

Monosaccharide: ring formation

A

Aldotetroses and monosaccharides > 5C exist as cyclic structures. Covalent bond between carbonyl group and oxygen from OH. Produces another chiral centre

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14
Q

Monosaccharide: Glycosidic bond formation

A

O-glycosidic bonds are formed when a hydroxyl group reacts with the anomeric carbon. Determines structure of oligo- and polysaccharides. Non reducing sugar

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15
Q

How are N-glycosidic bonds formed

A

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

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16
Q

Conformation of pyranose rings

A

saturated carbons produce non-planar structures. Axial substituents sterically hinder each other

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17
Q

What is the difference between the chair and boat form

A

In the chair conformation, the 2nd, 3rd, 5th and 6th carbon atoms lie on one plane whereas the 1st carbon is above the plane and 4th carbon is below the plane. In the boat conformation, 1st, 2nd, 4th and 5th carbons are in one plane while the 3rd and 6th carbons are bent in the same plane outside of the plane.

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18
Q

What is a furanose rings

A

consists of four carbon and one oxygen atom with the anomeric carbon to the right of the oxygen. Not planar. Conformation is known as envelope form

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19
Q

What is an oligosaccharide

A

short chain of monosaccharides, less than 20 residues

20
Q

Difference between homopolymer and hetropolymer

A

homopolymer - identical monosaccharides. Heteropolymer - vairable monosaccharides

21
Q

Role of sugars

A

energy source, structural (cell wall, exoskeletons), information (recognition - glycolipids)

22
Q

Why do sugars have different roles

A

diverse structural forms, 3 diff amino acids, 3 diff hexoses

23
Q

Why is a polysaccharide used as an energy source

A

compact granule, bonding means less osmotic pull, little water associated with it

24
Q

What is the storage molecule for plants and animals

A

plants - starch. Animals - glycogen.

25
Q

Structure of starch

A

homopolymer of alpha D glucose. alpha 1-4 linkages. amylose is unbranched. Amylopectin is branched and has alpha 1-6 linkages every 30 residues

26
Q

Structure of glycogen

A

homopolymer of alpha D glucose, alpha 1-4 linkages. Branched. Alpha 1-6 linkages every 10 residues

27
Q

What is an alpha linkage

A

bond from the anomeric carbon of the first monosaccharide unit is directed downward

28
Q

What is a beta linkage

A

occurs when 2 carbons have different stereochemistry

29
Q

examples of homopolymers that provide structural support

A

cellulose (beta 1-4 linked glucose), chitin (beta 1-4 linked N acetyl glucosamine)

30
Q

Heteropolymers that provide structural support

A

bacterial cell wall (beta 1-4 linked NAG and NAM)

31
Q

Example of a glycoconjugate

A

connective tissue - various monosaccharide linked by beta glycosidic bonds

32
Q

State the properties of cellulose

A

unbranched. Beta 1-4 links allowing for long straight chains. Parallel chains interact by hydrogen bonding forming fibrils which have high tensile strength.

33
Q

Describe the structure of chitin

A

homopolymer of N-acetylglucosamine. beta 1-4 glycosidic bonds. Different from cellulose by C2 having an acetylated amino group. Parallel chains interact by hydrogen bonding leading to high tensile strength

34
Q

What are preoteoglycans

A

glycans (95%) carbohydrates with a but of protein associated with it (5%)

35
Q

What is the polysaccharide chain glycosaminoglycan (GAG)

A

monosaccharide + amino suagr (N-acetylglucosamine or N-acetylgalactosamine). They attach to core protein which can attach to long filaments of hyaluronan to form assemblies that can interact with fibrous matrix proteins. Forms cross-linked meshwork giving strength and resilience

36
Q

What is the difference between gram-positive and gram-negative bacteria

A

positive retain a dye and have cross-linked multilayered proteoglycans where as negative don’t retain the dye and only have a single layer

37
Q

Connective tissue features

A

collagen (fibrous element -strength). Proteoglycans (ground substance - elastic properties of joints)

38
Q

Glycoproteins and glycolipids features

A

oligosaccharide associated with proteins and lipids. Play important roles in recognition and communication

39
Q

Sugar fingerprinting

A

sugar residues of our cells are specific to us and allow more structural variety than proteins. Important for tissue typing, defining blood groups and mount immune response

40
Q

What enzyme synthesise oligosaccharide

A

glycotransferase

41
Q

How do A and B antigens differ

A

by 1 monosaccharide - N acetylgalactose (A) or galactose (B) linked alpha 1,3 to O antigen

42
Q

How does glycosyltransferase differ types A and B

A

adds specific sugars that differ by 4 alpha alpha out of 354 alpha alpha

43
Q

What are lectins

A

ubiquitous proteins that recognise and bind specific carbohydrate structures and can be divided on the basis of their amino acid sequences and biochemical properties

44
Q

Function of lectins

A

cell-cell recognition and adhesion processes. Recognises and removes old erythrocytes. Pathoegns utilise them for adhesion/toxin entry

45
Q

What are selectins

A

carbohydrate-binding transmembrane proteins expressed on platelets (P-selectins), leukocytes (L-selectins) and endothelial cells (E- and P-selectins). Their role is to mediate the first steps of the recruitment of leukocytes from the blood stream in a series of pathologic situations

46
Q

Influenza virus

A

Hemagglutinin (lectin) recognises sialic acid residues on host surface of glycoproteins. After penetrating the membrane neuraidase breaks the glycosidic bond to release the virus. Tamiflu and relenza inhibit the enzyme

Biological Chemistry (12 decks)

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