Carbohydrates

Question 1

Examples of monosaccharides

Answer 1

Glucose, galactose, fructose, all hexoses

Question 2

What is the general formula of simple sugars?

Answer 2

Cn(H20)n (n=3 - 7)

Question 3

Why do sugars exist as stereoisomers?

Answer 3

Chiral carbon atoms

Question 4

What are the anomeric forms of monosaccharides, why?

Answer 4

Alpha: hydroxyl group (carbon 1) is below the ring

Beta: hydroxyl group is above the ring

Question 5

How many chiral centres do hexoses contain?

Answer 5

4

Question 6

What are the two enantiomers named?

Answer 6

D and L

Question 7

What is the pyranose conformation?

Answer 7

Hexoses in six membered ring

Question 8

How is the pyranose conformation formed?

Answer 8

The ring is created by reaction of the 5-hydroxyl group with the 1-aldehyde group creating a hemicetal

Question 9

Where is C6 located in pyranose formation?

Answer 9

Outside the ring, exocyclic

Question 10

What is the furanose ring?

Answer 10

Another arrangement for hexose sugars, 5 membered ring, 2 exocyclic carbons

Question 11

How are furanose rings formed?

Answer 11

Reaction of a ketone with an alcohol, creating a hemiketal.

Question 12

What is a sugar that forms a furanose ring?

Answer 12

Fructose

Question 13

What sugars form pyranose rings?

Answer 13

Glucose (alpha/beta) and galactose

Question 14

What are the two planar conformations of hexoses/pentoses?

Answer 14

Chair and boat

Question 15

What planar conformation is more stable and why?

Answer 15

Chair is usually more stable due to the lack of steric interference between groups at the “apical” points

Question 16

Describe examples of disaccharides , how are they joined?

Answer 16

Sucrose (alpha glucose and beta fructose), maltose (alpha glucose and alpha glucose) and lactose (galactose and glucose)

Glycosidic link

Question 17

What are oligosaccharides?

Answer 17

Monosaccharides joined to form small multimers

Question 18

What makes a sugar reducing?

Answer 18

Open-chain form with an aldehyde group or a free hemiacetal group.

Question 19

What does a reducing sugar do?

Answer 19

Reduces another compound and is itself oxidized; that is, the carbonyl carbon of the sugar is oxidized to a carboxyl group.

Question 20

Describe a 1,4 glycosidic bond

Answer 20

Form between the C1 hemiketal/hemicetal and another -OH group that is opposite in the same molecule attached to the (C4).

Question 21

Describe a 1,6 glycosidic bond

Answer 21

1,6 glycosidic bonds form between the -OH that is joined to exocyclic C6 and the C1 hemiketal/hemicetal.

Question 22

What property do 1,6 glycosidic bonds give?

Answer 22

1,6 glycosidic bonds cause branching within a polysaccharide structure.

Therefore heavily branched polysaccharides contain many 1,6 glycosidic bonds.

Question 23

What are 3 polysaccharides?

Answer 23

Glycogen, starch and cellulose (all made just of glucose)

Question 24

Describe structure and bonding in cellulose, how are its features suited for function?

Answer 24

Beta 1-4 bonds creates long straight chains

Chains line in parallel stabilised by H bonds then fibrils - fibres

Fibres have high tensile strength - oppose osmotic expansion in cells

Question 25

Describe structure and branching of glycogen and starch

Answer 25

Glycogen: Glucose monomers joined by 1-4 mainly but some 1-6, branched structure.

Starch: mixture of amylose (1-4 glucose polymer, helical) and amylopectin (less branching than glycogen, some 1-6)

Question 26

How can you diff between an alpha or beta glycosidic bond?

Answer 26

Z shape e.g. lactose is beta

90 degree bond e.g. sucrose and maltose is alpha

Question 27

What glycosidic bond does lactose have?

Answer 27

Beta

Question 28

What are the structural roles of carbohydrates?

Answer 28

In ECM: proteoglycans consist of a protein backbone attached to GAGs (polysaccharide chains) - proteoglycans provide compression strength

GAGs: repeating dissacharide subunits containing either glucosamine or galactosamine

Question 29

How are GAGs attached to proteins (2 ways)?

Answer 29

GAGs are attached to proteins through an asparagine (N-linked) or serine/threonine (O-linked).

Question 30

What AAs provide N linkages what AAs provide O linkages?

Answer 30

N-linked via asparagine

O-linked via serine/threonine

Question 31

Describe N-linked glycosylation

Answer 31

Removal of some of the original sugar molecules (trimming)

Addition of new sugars at the non-reducing end of the glycan.

Question 32

What are the roles of carbs as biosynthetic precursors?

Answer 32

Involved in AA synthesis, fatty acid synthesis and nucleotide synthesis

Question 33

What conjugates can carbs form?

Answer 33

Glycoproteins and glycolipids

Question 34

What are lectins?

Answer 34

Proteins that bind to sugar molecules.

Question 35

What are the roles of different lectins?

Answer 35

C-type lectins participate cell adhesion

L-selecting on the surface of lymphocytes binds to counter receptors on endothelial cells

P and E selectins are involved in the migration of neutrophils to sites of inflammation

Question 36

An amino acid to which carbohydrate residues are attached in glycoproteins is…

Answer 36

Serine

Question 37

Glycosylation of proteins involves the addition of ——–moieties

Answer 37

Carbohydrate

Question 38

Example of a ketose sugar …

Answer 38

fructose

Question 39

Disaccharide that forms a large amount of intake?

Answer 39

Sucrose