Carbohydrates

Question 1

What are the functions of carbohydrates in plants?

Answer 1

Cellulose = structure
Starch = energy reserve

Question 2

What are the functions of carbohydrates in humans? (6)

Answer 2

1. Carb oxidation provides energy
2. Glycogen = short term energy reserve
3. Synthesis of biochemical substances e.g. protein, lipids, nuclei comes acids as they provide carbon
4. Form part of structural framework for DNA and RNA
5. Carbs linked to lipids = structural components of cell membranes
6. Carbs linked to proteins = cell-cell or cell-molecule recognition processes

Question 3

What is the basic empirical formula for carbohydrates

Answer 3

CnH2nOn

Question 4

Define a carbohydrate

Answer 4

A polyhydroxy aldehyde/ketone or compound that produces polyhydroxy aldehyde/ketone

Question 5

What are the 4 classifications of carbohydrates

Answer 5

Monosaccharides
Disaccharides
Oligosaccharides
Polysaccharides

Question 6

Monosaccharide

Answer 6

• contains single polyhydroxy aldehyde or ketone unit e.g. glucose and fructose
• water soluble
• crystalline solids
• often open chain and ring structures

Question 7

E.g. disaccharides (2)

Answer 7

Sucrose (sugar)

Lactose (milk sugar)

Question 8

Oligosaccharides

Answer 8

• contains less than 20 monosaccharides joined together by o-glycosidic bonds
• usually associated with proteins or lipids

Question 9

Polysaccharides

Answer 9

• 20+ monosaccharides bonded together

Question 10

Heteropolymer

Answer 10

Chain of variable monosaccharides

Question 11

Homopolymers

Answer 11

Chain of identical monosaccharides

Question 12

How can you tell if a molecule can be chiral

Answer 12

• central carbon is bonded to 4 groups
• the 4 groups must all be different
• ring structures can be chiral if the substituents in the ring are different and the 2 halves of the ring are different

Question 13

Chiral

Answer 13

Molecule that’s mirror images are not super impossible

Question 14

Achiral

Answer 14

Molecule whose mirror images are superimposable

Question 15

Do monosaccharide tend to right handed or left handed molecules

Answer 15

Right
(Plants only produce right hand)
BUT
Amino acids are always left handed

Question 16

Enantiomers

Answer 16

Stereoisomers who are nonsuperimposable images of eachother

L and D forms determined by configuration at high numbered chiral centre

Question 17

Diastereomers

Answer 17

Stereoisomers that are not nonsuperimposable images of eachother

Question 18

Epimers

Answer 18

Diastereomers whose molecules differ only in the configuration at one chiral centre

Question 19

Ho do enantiomers differ?

Answer 19

Their interactions with plane polarised light
(Single enantiomer light rotated counter/clockwise depending on enantiomer)
Their interactions with other chiral substances

Question 20

Constitutional isomer

Answer 20

Isomers in which the atoms have different connectivity

Question 21

Skeletal isome

Answer 21

Isomers with different carbon atom arrangements and different hydrogen atom arrangements

Question 22

Positional isomers

Answer 22

Isomers that differ in the location of the functional group

Question 23

Functional group isomers

Answer 23

Isomers that contain different functional groups

Question 24

Stereoisomers

Answer 24

Isomers with atoms of the same connectivity but that differ in orientation in space

Question 25

Cis trans isomers

Answer 25

Stereoisomers that result from rotation amount chemical bonds (Sometimes possible when ring or double bond present)

Question 26

Describe aldoses

Answer 26

- 6C sugar - carbonyl group at the end of the chain - reducing sugars - 16 possible isomers

Question 27

Describe ketoses

Answer 27

- 6C sugar - carbonyl group at C2 position - 8 possible isomers - reducing sugars

Question 28

What is an anomeric carbon

Answer 28

Carbon bonded to the OH group and oxygen atom in a ring structure

Question 29

Describe monosaccharide ring structure

Answer 29

Monosaccharides >5 carbons tend to be cyclic structures Covalent bond takes place between carbonyl group and the oxygen of the hydroxyl group Produces a chiral centre There are 2 possible stereoisomers depending on whether OH group formed on top (beta) or bottom (alpha)

Question 30

What are anomers

Answer 30

Cyclic monosaccharides that only differ in the positions of the substituents on the anomeric carbon

Question 31

Describe pyranose rings

Answer 31

- ring with 6 carbons and an oxygen not planar but either boat or chair form - due to saturation of carbons and its tetrahedral geometry - axial substituents sterically hinder eachother

Question 32

Describe furanose rings

Answer 32

Mono ring structure with 5 carbons and an oxygen atom | - not planar = envelope form

Question 33

Monosaccharide derivatisation

Answer 33

- hydroxyl groups replaced with substituents - addition of phosphate group - addition of sulphate group - addition of amine groups - addition of hydrogen or alkyl groups

Question 34

Monosaccharide bonding

Answer 34

via glycosidic bonds - o glycosidic bond formed when hydroxyl group reacts with anomeric carbon (N glycosidic bonds formed when anomeric carbon reacts with nitrogen )

Question 35

What are the 3 main roles of sugars (with e.g.s )

Answer 35

Can fill so many roles as so diverse Energy source (e.g. ATP, starch, glycogen) Structure ( cells walls, exoskeletons, connective tissue) Information: recognition (glycoproteins and glycolipids) and nucleic acids

Question 36

Why are polysaccharides better than monosaccharides for energy storage

Answer 36

- compact granule | - binding means less osmotic pull so little water associated with it

Question 37

What’s the key similarity between starch and glycogen

Answer 37

Both homopolymers of a-d-galactose (a 1-4 linkages)

Question 38

Describe starch

Answer 38

``` Unbranched = amylose Branched = amylopectin (a 1-6 linkage every 30 residues) ```

Question 39

Describe glycogen

Answer 39

Branched a 1-6 linkage every 10 residues

Question 40

Describe cellulose

Answer 40

Used for cell wall structure in plants Unbranched polymer of glucose residues joined by b1-4 linkages. The b configuration allows formation of long straight chains. Parallel chains can interact by hydrogen bonding forming Fibrils. These fibres have high tensile strength.

Question 41

Describe chitin

Answer 41

Used for cell wall structure of insects (exoskeleton) Linear homopolymer composed of N-acetylglucosamine linked by b1-4 glycosidic bonds Differs form cellulose by replacement of the C2 hydroxyl group with an acetylated amino group Parallel chains interact by hydrogen bonding leading to high tensile strength

Question 42

Describe bacteria cell walls

Answer 42

Sugar rich coating outside Plasma membrane. Gram-positive bacteria retain a dye-iodine complex, washed out of Gram-negative bacteria. Gram-positive bacteria- cross-linked multilayered proteoglycans, whereas gram negative- only a single layer.

Question 43

Describe proteoglycans

Answer 43

Polysaccharides with protein associated to it Proteoglycans chains are called glycosaminocans (GAG). Are anionic chains made from repeating disaccharide units: Monosaccharide + amino sugar = N-acetylglucosamine or N-acetylgalactosamine.

Question 44

Proteoglycans in connective tissue

Answer 44

Glycosaminoglycans attached to Core Protein These units can attach to long filament of Hyaluronan to form enormous assemblies These can interact with fibrous matrix protein e.g collagen Forms cross-linked meshwork giving strength and resilience

Question 45

Describe a sugar fingerprint

Answer 45

Sugar residues of our cell surfaces unique to us- recognise self from non- self. Sugars allow more variety of structure than proteins Very important for tissue typing. Define blood groupings. Mount immune response.

Question 46

Describe oligosaccharides and blood typing

Answer 46

Oligosaccharides are synthesised by Glycosyltransferases and are specific to sugars being linked In Blood ABO groups – carbohydrates attached to proteins and lipids on cell surface A and B antigens differ by 1 monosaccharide – N-acetylgalactose (A) or Galactose (B) linked a1,3 to O antigen Type A and B glycosyltransferase add specific sugars they differ by 4aa out of 354aa O phenotype is result of mutation resulting in no active glycosyltransferases

Question 47

Describe lectins

Answer 47

proteins that recognise and bind specific carbohydrate structures. Help with cell-cell recognition and adhesion processes. Recognise old erythrocytes and remove them. Eryth surface changes and lectins recognise and and take away when too old. Microbial/viral pathogens utilise lectins for adhesion/toxin entry

Question 48

Role played by lectins in influenza virus

Answer 48

Hemagglutinin (lectin) recognises sialic acid residues on host surface glycoproteins. After penetrating the membrane neuramidase (sialidase) breaks glycosidic bond to release the virus Without neuramidase, virus non invasive. Tamiflu and Relenza inhibit the enzyme.