Carbohydrates

Question 1

Classification of carbohydrates

Answer 1

Monosaccharides, oligosaccharides and polysaccharides.

Question 2

Monosaccharide structure + examples

Answer 2

Simple sugar that consists of only one polyhydroxy aldehyde or polyhydroxyketone, many of them are sweet, water soluble.

Glucose, Galactose and Fructose

Question 3

Oligosaccharides structure + examples

Answer 3

Polymers formed of 2-10 monosaccharides that can be separated by hydrolysis. Named disaccharides, trisaccharides etc depending on the number of monomers. Generally sweet taste and water soluble.

Sucrose, Lactose, maltose

Question 4

Polysaccharides structure + examples

Answer 4

Large molecules formed by the assembly of monosaccharides arranged in linear or branched chains. In general insoluble in water, tasteless and amorphous.

Starch, cellulose, glycogen

Question 5

Different types of monosaccharide sugar + examples

Answer 5

aldose- contains a carbonyl group on the end of the chain, glucose, galactose

ketose- contains a carbonyl group in the middle of the chain, fructose

Question 6

Two forms of ring and how they are formed

Answer 6

Pyranose- between 1 aldehyde group and 5 hydroxyl group to create a hemiacetal. Reaction of an aldehyde and an alcohol. six membered ring. OH attacks the carbonyl

Furanose- reaction of an alcohol and a ketone- forms a hemiketal. Contains 4 carbons and one oxygen atom in ring and the other carbons on either side. five membered ring

Question 7

Two shape considerations

Answer 7

Chair and boat- both planar conformations

Question 8

Why does the chair shape form more often?

Answer 8

More stable due to the lack of steric interference between groups of the apical points. Boat contains orbitals that clash which are of higher energy.

Question 9

Maltose glycosidic bond

Answer 9

alpha 1,4

Question 10

Cellular glycosidic bond

Answer 10

beta 1,4

Question 11

Lactose glycosidic bond

Answer 11

beta 1,4

Question 12

Amylopectin glycosidic bond

Answer 12

alpha 1,4 and alpha 1,6

Question 13

3 polysaccharides and structures

Answer 13

Starch- formed of alpha glucose, 1,4 glycosidic bonds form a coiling molecule with intramolecular hydrogen bonds.

Glycogen- formed of alpha glucose, 1,4 glycosidic bonds- similar to starch however more highly branched.

Cellulose- formed of beta glucose, beta 1,4 glycosidic bonds, form parallel chains with intermolecular hydrogen bonds forming strong microfibrils.

Question 14

Structures of monosaccharides in cells

Answer 14

Always phosphorylated by ATP, often carbon 6. Always a ring structure, apart from trioses.

Question 15

Lectin function

Answer 15

Carbohydrate binding protein. Have a role in recognition on the cellular and molecular level.

Question 16

Main reaction of sugar molecules

Answer 16

Act as a reducing agent if they have a free carbonyl group

Question 17

What must ketones first undergo?

Answer 17

Tautomerism

Question 18

What form must the sugars be in?

Answer 18

Open chain, not a ring.

Question 19

How does a blood test work?

Answer 19

Use glucometers to test blood sugar levels. Glucose is oxidised by glucose oxidase to hydrogen peroxide and D-gluconolactone.

Electronic meters use an electrode to take up the electrons that are released. Current measured is proportional to the concentration of glucose in the blood.

Colourimetric strips use peroxidase to change colour upon reaction with the hydrogen peroxide produced.

Question 20

Glycoprotein definition

Answer 20

Compounds formed of conjugated proteins with prosthetic groups that are carbohydrates.

Question 21

How do glycoproteins differ from proteoglycans?

Answer 21

Glycoproteins have shorter and more branched carbohydrate chains.

Question 22

Proteoglycan structure

Answer 22

Proteins that are heavily glycosylated. Basic proteoglycan unit consists of a core protein with one or more covalently attached glycosaminoglycan chains. Point of attachment for the carbohydrate chains is serine residue.

Question 23

Proteoglycan function

Answer 23

Mainly in the ECM, form large complexes to other proteoglycans such as hyaluronic acid and to fibrous components such as collagen.

Combination of proteoglycans and collagen form cartilage.

GAG chains contain negatively charged sulphates which attract water, therefore can be compressed at the joints and protect.

GAGs are very large, therefore provide large structural scaffold.

Question 24

Proteoglycan structure in cartilage

Answer 24

Protein core aggrecan acts as linking protein attaching GAGs in intervals on the hyaluronic acid

Question 25

Different types of glycosylation

Answer 25

N-linked and O-linked

Question 26

Glycosylation definition

Answer 26

A process in which a carbohydrate is attached to a hydroxyl group of another molecule. Often with glycans being attached to proteins.

Question 27

N-linked glycosylation explained

Answer 27

Sugars attached to the protein on the nitrogen on asparagine. 1. Processing steps include removal of some of the original sugar molecule during trimming. 2. addition of new sugars at the non reducing end of the glycan 3. Lipid linked precursor formed first in the cytoplasm and then undergoes second phase in the lumen of the ER. 4. Core structure occurs in the lumen during translation.

Question 28

N-linked trimming in more detail

Answer 28

1. exoglycosidases cleave sugars from non reducing end 2. series of mannosidases remove mannose linked alpha 1,2 3. high mannose olligosaccharides (glycans containing 5-9 mannose sugars) 4. complex glycans are built on a core containing 3 mannose residues and GlnNAc residues.

Question 29

Two main forms of o-linked proteins

Answer 29

proteoglycans and mucins

Question 30

How do glycans attach?

Answer 30

attach to serine/threonine or tyrosine OH group

Question 31

Dolichol phosphate function

Answer 31

Function as a membrane anchor for the formation of an oligosaccharide with glucose, mannose and N-acetylglucosamine. Oligosaccharide is transferred from the dolichol phosphate to asparagine on polypeptide chains

Question 32

4 examples of proteoglycans

Answer 32

Hyaluronic acid, chondroitin, derma tan and keratin sulphate

Question 33

Hyaluronic acid structure + function

Answer 33

Glycosaminoglycan is a disaccharide formed of G-glucuronic acid linked to N-acetylglucosamine. Each unit is bound to the next to form a polysaccharide. forms a highly viscous solution with lubricating properties- associated with many connective tissues

Question 34

Chondroitin sulfate structure and function

Answer 34

N-acetyl-D-glucosamine and glucuronic acid. Important component in cartilage and bone- provides resistance from compression

Question 35

Dermatan sulphate structure and function

Answer 35

L- iduronic acid and N-acetyl-D-glucosamine Found in skin and connective tissue of various organs.Role in coagulation, cardiovascular disease and wound repair.

Question 36

Keratan sulfate structure and function

Answer 36

No uronic acid- formed of galactose and acetylated glucosamine, esterified by sulphate Found in cornea and cartilage.- act as a dynamic buffer in corneal hydration and shock absorber in cartilage

Question 37

Glycogen structure + function

Answer 37

Energy store in animals, fungi and bacteria. Glucose linked together linearly by 1,4 glycosidic bonds. Branches are linked o changes by 1,6 bonds. Each glycogen granule has its core glycogenin protein

Question 38

Starch structure + function

Answer 38

energy store in plants. Formed of two components: amylose which is unbranched and amylopectin which is branched. Branches are longer and less frequent compared to glycogen.

Question 39

Cellulose structure and function

Answer 39

Structural component in plant cell walls, withstand pressure Parallel chains formed of beta glucose with string hydrogen bond intermolecular forces between chains, forming microfibrils.

Question 40

Function of glycoproteins

Answer 40

marker proteins e.g glycoprotein of the ovule the zone pellucida contains oligosaccharides recognised by sperm, allowing the interaction of gametes prior to fertilisation. . Binds to toxins, preventing them from invading cells

Question 41

Explain blood groups

Answer 41

The surface of red blood cells and other cells contain glycoproteins and glycolipids. The antigenic determinant of these molecules lies in the carbohydrate moiety. Antigenic glycans built up on the ends of polylactosamine chains by the action of a fucosyltransferase which generates H antigens. Individials with an O group only have H antigens. Blood type A individuals contain polylactosamines with an extra N-acylglucosamine residue added to the terminal galactose. B type, Galactose resided is added

Question 42

What is the Bombay phenotype?

Answer 42

Individuals lack genes for fucosyl transferase, therefore cannot form terminal disaccharide fucose-galactose present in H antigens, therefore have no antigens on their red blood cells.

Question 43

Role of carbohydrates in synthesis of lipids

Answer 43

Synthesised from acetyl CoA which is formed from the breakdown of carbohydrates.

Question 44

Role of carbohydrates in synthesis of proteins

Answer 44

Amino acids components obtained from glucose during glycolysis

Question 45

Role of carbohydrates in synthesis of nucleotides

Answer 45

Phosphorylated ribose-5-phosphate derived from glucose-6-phosphate which is obtained from glucose during glycolysis in the cytoplasm