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.

·         Metabolic

o   Water takes part as a reactant in some chemical processes.

o   Hydrolysis reactions & photosynthesis.

·         Incompressibility

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.

Amino acids

·         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.

·         α-helix.

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).

Haemoglobin

·         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.

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