Carbohydrates
- Created by: Jenny Le
- Created on: 08-04-14 18:06
What is a Carbohydrate?
- Most abundant organic molecule on the planet!
- Simple carbohydrates: (C.H20)n where n>=3
- Can also contain N, S or P
- Monosaccharide = 1 sugar unit
- Can link with other sugar units with glycosidic bonds
- Disaccharide = 2 units
- Oligosaccharide = app. 2-10 units
- Polysaccharides = >=10 units
Function of Carbohydrates - Metabolism
SOURCE AND STORAGE OF ENERGY
Energy is trapped in photosynthesis as carbohydrates
Carbohydrate is main metabolic fuel
Polysaccharides such as starch and glycogen store energy
STARTING POINT FOR BIOSINTHESIS OF OTHER MACROMOLECULES
Carbon skeleton for macromolecules.
Function of Carbohydrates - Structure
CELL ORGANELLES
Plant cell walls - cellulose
Bacterial cell walls - murein
Insect exoskeletons - chitin
Extracellular matrix - mucopolysaccharides
CELL-CELL RECOGNITION AND SIGNALLING
Glycoproteins and glycoplipids
IMMUNE SYSTEM
Key for recognition as foreign
Stereoisomerism
Asymmetric carbon: has 4 different groups bound
Chrial: 4 different groups that can be organised to create mirror images
Enantiomers: stereoisomers that are mirror images of each other
Diastereoisomers: stereoisomers that are not mirror images (more than one chiral centre) and have different physical and chemical properties
Epimer: diastereoisomers that differ in configuration around 1 carbon only
Oligo- and Poly- saccharides
Oligosaccharide: 2-10 monosaccharides joined by glycosidic bonds
Polysaccharide: More than 10 monosaccharides
Homo-polysaccharide: longer chains of all the SAME type of monosaccharide units
Hetero-polysaccharide: longer chains built up from MORE THAN ONE TYPE of monosaccharide unit
Storage polysaccharide: storage of chemical energy, e.g. starch and glycogen
Structural polysaccharide: role in structure of the cell, e.g. cellulose in plant cell walls
Storage polysaccharides
Glucose cannot be stored as a monomer due to osmotic pressure.
Properties of storage molecules:
- easily made and broken down
- compact
Animals use glycogen
Plants use starch. Starch consists of two glucose polymers:
- Amylopectin
- Amylose
Amylopectin
Homopolymer of glucose with a glycosidic link between alpha(1-4) and alpha(1-6)
Branches every 24-30 glucose molecules
Very large molecule - 10^6 glucose molecules
Helix and branched structures - compact
Branches - lots of sites for degradation
Glycogen
Homopolymer of glycose with glycosidic link between alpha(1-4) and alpha(1-6)
Branches every 8-12 glucose molecules
Highly branched - easily broken down by glycogen phosphorylase to give glucose-1-PO4
Debranching enzyme for alpha(1-6) branch points
Liver glycogen maintains blood glucose levels (~100g)
Muscle glycogen used in strenuous activity (~400g)
Structural polysaccharides
Properties:
- Insoluble
- Strong
- Rigid
CELLULOSE
- Homopolymer of glucose with beta(1-4) links
- Up to 15000 glucose units
- Found in all plants and fungi
- Forms long straight chains
- Every other glucose residue flipped 180 degrees
- Extended chain
- Parallel chains closely packed
- Intra- and intechain H-bonding gives strength
- Bundles of chains stack to form large rigid fibres
Chitin - homopolysaccharide
Major structural component of insect and crustacea exoskeletons.
Cell walls of fungi and algae
Linear polymer of N-acetyl glucasamine with beta(1-4) links
Glycosaminoglycans (mucopolysaccharides)
Long unbranched chains of repeating disaccharide units.
One sugar is N-acetyl glucosamine or N-acetyl galactosamine
Many carboxyl and sulphate groups - many negative charges
Chain extended, highly hydrated - very viscous, slimy mucous like consistency, elastic
Found in:
- Ground substance of extracellular spaces
- Synovial fluid of joints
- Vitreous humor of the eye
Hyaluronic acid
Ground substance of connective tissue and synovial fluid
Repeating disaccharide unit
D-glucuronate B(1-4) n-acetyl-glycosamine
High negative charge
Highly hydrated
Viscosity changes with shear force - shock absorber
Glycoproteins
Found:
- On the cell surface
- In exported proteins e.g. extracellular matrix and blood
Distinguish between N-linked (N-X-S/T) and O-linked (S/T)
Involved in folding, signalling, recognition, increasing solubility
Proteoglycan: Bottlebrush Model
Cartilage network of collagen fibres linked to mucopolysaccharide
Collagen provides strength and proteoglycans give resistance to compression
As cartilage compressed:
- Water squeezed out
- Negative charges exposed
- Repel each other and resist further compression
Glycosylation
Key in folding exported proteins
Possible outcomes of glycosylations:
- Protein is ready for use
- Protein needs folding
- Protein is terminally misfolded
Related discussions on The Student Room
- Do I need to know how to draw structures for carbohydrates? (AQA A Level Bio) »
- Could carbohydrates be used as antidepressants »
- How to answer 6-mark questions in A-Level Biology? »
- Mark my AS level bio essay pls »
- how to lose weight healthily??? »
- What kind of effects would it have if an underweight person has fizzy drink every day »
- I really need help!!!!!!!! *Biology* »
- What should we do and eat on the day of the exam »
- How to lose face fat? »
- Science help (carbonate and sulfate tests) »
Comments
No comments have yet been made