Carbohydrates

Question 1

functions of monosaccharides and disaccharides

Answer 1

energy stores, fuel, metabolic intermediates
structural backbones in nucleic acids (ribose, deoxyribose)

Question 2

functions of polysaccharides

Answer 2

storage molecules, structural elements, cellular recognition functions (glycoproteins for example)

Question 3

two types of sugar and their functional groups

Answer 3

aldoses - aldehyde functional group
ketoses - ketone functional group

Question 4

what is meant by poly-alcohol?

Answer 4

sugars are poly-alcohols as they contain multiple -OH groups

Question 5

general formula for monosaccharide

Answer 5

CnH2nOn

Question 6

which optical isomer predominates in naturally occuring sugars?

Answer 6

D configuration

Question 7

how to recognise D/L configuration of sugar

Answer 7

fischer projection
look at penultimate carbon (second to furthest from terminal aldehyde / ketone group)
-OH group on right = D
-OH group on left = L

Question 8

epimers

Answer 8

isomers that differ at only one chiral centre

Question 9

name two epimers of glucose

Answer 9

Galactose (differs at C4)
Mannonse (differs at C2)

Question 10

what type of ring closure is seen in aldoses?

Answer 10

hemiacetyl ring closure
(try drawing structure)

Question 11

what type of ring closure is seen in ketoses?

Answer 11

hemiketal ring closure
(try drawing structure)

Question 12

what are anomers

Answer 12

stereoisomers differing in the arrangement of groups around the anomeric carbon

Question 13

position of anomeric carbon on aldose

Answer 13

C1

Question 14

position of anomeric carbon on ketose

Answer 14

C2

Question 15

difference between a- and B- anomers of glucose

Answer 15

a-anomer - OH on anomeric carbon (C1) on opposite side of ring to C6

B-anomer - OH on anomeric carbon (C1) on same side of ring as C6

Question 16

difference between a-anomer and B-anomer of pyranose sugar

Answer 16

a-anomer - OH on anomeric carbon (C2) below ring (C1 and C6 on same side of ring)
B-anomer - OH on anomeric carbon (C2) above ring (C1 and C6 on oppsite sides of ring)

Question 17

which anomer of glucose is favoured at equilibrium and why?

Answer 17

B-anomer
because: hexose ring in chair conformation. On B-anomer, -OH on anomeric carbon is in equatorial position - less sterically hindered so more favourable. On a-anomer the -OH is in the axial position, less favourable due to 1,3 diaxial interactions

Question 18

ratio of a-anomer to B-anomer at equilbibrium

Answer 18

1/3 : 2/3

Question 19

name for six membered sugar ring

Answer 19

pyranose

Question 20

five membered sugar ring

Answer 20

furanose

Question 21

which type of glycosidic linkage attaches alcohol groups to modified monosaccharides?

Answer 21

O-linkage

Question 22

which type of glycosidic linkage attaches amine groups to modified monosaccharides?

Answer 22

N-linkage

Question 23

importance of phosphorylated monosaccharides

Answer 23

forms reactive intermediates that are important for metabolism
also, phosphorylation makes sugars anionic

Question 24

what kind of reaction forms the glycosidic bond between two monosaccharides?

Answer 24

dehydration reaction, removal of H2O

Question 25

which glycosidic linkage joins glucose and galactose monomers in lactose?

Answer 25

Gal-B-1,4-Glc

Question 26

which linkage joins glucose monomers in maltose?

Answer 26

Glc-a-1,4-Glc

Question 27

which linkage joins glucose and fructose monomers in sucrose?

Answer 27

a-Glc-1,2-B-Fru

Question 28

Describe the structure of glycogen

Answer 28

branched homopolymer of glucose a-1,4 linkages branching via a-1,6 linkages every 8-12 units forms open helical structure

Question 29

Describe the structure of starch

Answer 29

contains two homopolymers of glucose: amylose - unbranched, a-14 glycosidic linkages amylopectin - branched via a-1,6 linkages every 24-30 units forms open helical structure

Question 30

Describe the structure of cellulose

Answer 30

unbranched homopolymer of glucose B-1,4 linkages forms long straight chains H-bonding between parallel chains forms fibrils - high tensile strength

Question 31

Describe the structure of chitin

Answer 31

unbranched homopolymer of GlcNAc (acetylglucosamine)

Question 32

Describe the structure of peptidoglycan

Answer 32

heteropolysaccharide of two modified monosaccharide monomers (N-acetylmuramic acid, N-acretyl-D-glucosamine) B-1,4 linkages crosslinking between polysaccharide chains with oligopeptides

Question 33

in which biological structure is peptidoglycan found?

Answer 33

bacterial cell wall

Question 34

N-linked glycosidic bonds are found in which glycoproteins

Answer 34

oligosaccharide joined to aspariagine residue

Question 35

O-linked glycosidic bonds are found in which glycoproteins?

Answer 35

oligosaccharides joined to serine or threonine

Question 36

where does N-linked glycosylation occur

Answer 36

begins in lumen of endoplasmic reticulum, continues in Golgi complex

Question 37

where does O-linked glycosylation occur?

Answer 37

entirely in the Golgo complex