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2.1.2 Biological Molecules (Water and Sugars) (Disaccarides (α glucose + α…
2.1.2 Biological Molecules (Water and Sugars)
Water
Hydrogen Bonding
helps stabilise structure of molecules
liquid
Cohesion and Surface Tension
e.g. pond skaters on water; xylem pulls water from roots
molecules stick together; surface of water contracts to resist force
High Latent Heat of Vaporisation
lot of energy needed for water to evaporate due to hydrogen bonds holding molecule together, so is a coolant
e.g. sweating in humans
High Specific Heat Capacity
lot of energy needed for water to change temperature by 1°C
e.g. living organisms need stable temperature for enzyme reactions; fish need stable temperature in water to live
Polar
Ice less dense than water
ice forms lattice structure due to polar nature, so ice floats at the top
e.g. fish can still live in water under ice and not be frozen; ponds insulated against cold by ice layer at top
Solvent
polar nature attracts positive and negative parts of a solute, so solute bonds with H+ and OH- ions and can dissolve
e.g. substances in cytoplasm can dissolve and react and move
Transport Medium
substances dissolve in polar water so can move around in water
e.g. molecules and ions in erythrocytes; sucrose and water in phloem can be trasnported
Hydrolysis
one molecule splits in two and water is added
Condensation
two molecules join and a water molecule is lost
Monosaccarides
Hexose Sugars
β glucose
α glucose
Pentose Sugars
ribose
deoxyribose
Disaccarides
α glucose + α glucose --> maltose
α glucose + fructose --> sucrose
α glucose + β galactose --> lactose
β glucose + β glucose --> cellobiose
1-4 glycosidic bonds: bond between carbon 1 of one molecule and carbon 4 of the other
1-6 glycosidic bonds: bond between carbon 1 of one molecule and carbon 6 of the other
Polysaccarides
Storage Molecules (Starch and Glycogen)
Compact: don't occupy a lot of space; form dense granules in cell
Chains: glucose can be easily snipped off from terminal ends
Branched: more compact and more terminal ends
Less soluble in water; water potential of cells is not disturbed; OH groups on inside of spiral so don't form hydrogen bonds
Cellulose
straight chain of α and β glucose
unbranched
hydrogen bonds between chains to stop spiralling
α 1-4 glycosidic bonds
β 1-4 glucosidic bonds
Plant cell walls
cellulose chains --> microfibrils --> macrofibrils --> cell wall
micro and macro fibrils have high tensile strength due to H bonds
each cell needs to have strength to support whole plant because of lack of skeleton
Amylopectin (Starch)
branched spiral of α glucose molecules
held in place by hydrogen bonds
1-4 glycosidic bonds (straight)
1-6 glycosidic bonds (branched)
tendency to coil
Plant energy store
Amylose (Starch)
spiralled chain of α glucose molecules
unbranched
may form double helix
spiral held in place by hydrogen bonds
1-4 glycosidic bonds
Plant energy store
Glycogen
branched spiral of α glucose molecules
branched (more than amylopectin): more terminal ends; glucose can be taken off from more places; animals need it for respiration
held in place by hydrogen bonds
1-4 glycosidic bonds (straight)
1-6 glycosidic bonds (branched)
less tendency to coil
Animal energy store
Sammer Sheikh