Describe how hydrogen bonding occurs between water molecules & relate this & other properties of water to roles in living organisms.
· Hydrogen bond is a weak interaction
o Occurs between slightly negatively charged oxygen atom bonded to slightly positively charged oxygen atom bonded to slightly positively charged hydrogen.
Covalent bonds - electrons shared between them.
· Good solvent
o Water molecules are attracted to ions & polar molecules e.g. glucose.
o Transport in blood, xylem & phloem.
o Good solvent for both charged & uncharged substances.
· High specific heat capacity
o 4.2 kJ to increase the temperature of 1kg of water.
o Thermal energy absorbed & used to break hydrogen bonds.
o Helps prevent changes in body temperature.
· High latent heat of vaporisation
o Thermal energy used to cause water molecules to turn to vapour.
o During transpiration in plants.
o During sweating & panting in animals.
o Small amount of water absorbs much thermal energy.
· High cohesion
o Hydrogen bonds "stick" water molecules together.
o Helps draw water up the xylem.
o Water takes part as a reactant in some chemical processes.
o Hydrolysis reactions & photosynthesis.
o Outside pressure cannot force water in smaller.
o Hydrostatic skeleton for some animals i.e. earthworm.
o Provides turgidity in plants.
Describe the structure of an amino acid.
· Monomers of proteins.
· Anime group.
· Carboxylic group.
· R group.
o Each R group is different therefore have different properties.
o Determine the shape of the active site.
Describe the formation & breakage of peptide bonds in synthesis & hydrolysis of dipeptides & polypeptides.
· Formed by condensation reaction.
Broken by hydrolysis reaction.
Explain the term primary structure.
· Primary structure of a polypeptide is the amino acid sequence determined by the gene that codes for a polypeptide.
Explain the term secondary structure.
· Folding of a polypeptide.
o Right handed helix.
· β-pleated sheet.
o Flat sheet.
o Polypeptide folds back on itself.
Explain the term tertiary structure.
· Further folding of polypeptide to give complex 3D shape.
· Precise & specific shape to function of polypeptide.
o Hydrogen between polar groups.
o Hydrophilic / hydrophobic non polar R groups.
o Disulfide bonds between S - containing R groups.
o Ionic interactions.
Explain the term quaternary structure.
· Protein structure where protein has more than one polypeptide chain.
e.g. Haemoglobin (globular protein).
· 4 polypeptides.
o 2 x α
o 2 x β
· Held in place by interactions between R groups on adjacent polypeptides.
· Haem group (prosthetic group) contains Fe 2+ ion.