carbohydrates (d,e,f,g) Flashcards
what is a monosaccharide?
single sugar e.g. glucose, fructose, ribose
what is a disaccharide?
two monosaccharides e.g. lactose, sucrose
what is a polysaccharide?
2 or more monosaccharides linked to form a polymer e.g. glycogen, cellulose, starch
what is a glucose an example of?
a hexose monosaccharide - composed of 6 carbons
difference between alpha and beta glucose
- alpha = H and OH same on both sides
- beta = H and OH alternate on either side
properties of glucose
- polar and soluble in water - due to hydrogen bonds that form between the hydroxyl groups + water molecules
- solubility - dissolved in the cytosol of the cell - easily transported
- its chemical bonds contain lots of energy
what is ribose an example of?
a pentose monosaccharide - composed of 5 carbon atoms
synthesis of disaccharides and polysaccharides
- monosaccharides are joined together by glycosidic bonds
- condensation reaction - a hydrogen atom on one monosaccharide bonds to a hydroxyl group on the other, releasing a molecule of water
breakdown of disaccharides and polysaccharides
- the reverse of the condensation reaction is hydrolysis
- a molecule of water reacts with the glycosidic bond, breaking it
describe maltose
- 2 alpha glucose molecules joined together by a 1,4 glycosidic bond
- disaccharide
describe sucrose
- alpha glucose + fructose joined together
- disaccharide formed from 2 hexose monosaccharides
describe lactose
- galactose + either alpha or beta glucose
- disaccharide formed from 2 hexose monosaccharides
what is starch and describe its structure
- a chemical energy store - main store in plants
- Starch is a mixture of 2 polysaccharides of alpha-glucose - amylose and amylopectin
Describe the structure of amylose
- long unbranched chain of alpha-glucose
- joined by 1,4 glycosidic bonds only
- angles of bond mean the long chain of glucose twists to form a helix which is further stabilised by hydrogen bonding within the molecule
describe the structure of amylopectin
- a long branched chain of alpha-glucose
- made of 1,4 glycosidic bonds and 1,6 glycosidic bonds on 2 glucose molecules (once every 25 subunits)
how does the structure of amylose relate to the function of starch?
- it is compact - good for storage
- much less soluble than glucose - does not cause water to enter the cells by osmosis which would make them swell
how does the structure of amylopectin relate to the function of starch?
- its side branches allow the enzymes that break down the molecule to get at the glycosidic bonds easily - thus glucose can be released quickly
what is glycogen?
- a chemical energy store - the main store in animals and fungi
- animals store excess glucose as glycogen - insoluble
describe the structure of glycogen
- polysaccharide of alpha-glucose
- similar to amylopectin but more branches so less space needed to store it
how does the structure of glycogen relate to its function?
- compact - important for the mobility of animals
- branching means many free ends where glucose molecules can be added or removed, which speeds up the processes of storing or releasing glucose molecules required by the cell - important for energy release in cells
what is cellulose?
A major component of cell walls in plants
describe the structure of cellulose
- long unbranched chains of beta-glucose
- beta-glucose molecules bond to form straight chains (alternate beta molecules are turned upside down)
how are fibres made?
- cellulose molecules make hydrogen bonds with each other to from microfibrils
- these join together to form macrofibrils, which join together to form fibres
how does the structure of cellulose and fibres relate to its function?
- fibres are strong and insoluble, providing structural support for cells
- important in a diet - necessary for a healthy digestive system
