amino acids

• amino acids are composed of carbon, hydrogen, oxygen and nitrogen
• there are 20 amino acids
• all amino acids have an amino group, a carboxyl group and a functional side chain
• side chains can be charged, polar and hydrophilic or non polar and hydrophobic
• charged side chains are usually exposed on the surface
• non polar side chains are buried in the hydrophobic interior of proteins, out of contact with water
• proteins need at least one of each amino acid to function
• errors in amino acid sequence or protein folding can lead to dysfunctional proteins and disease states
• the primary structure of a protein is the amino acid sequence, determined by the genetic code
• in the primary structure, amino acids are joined together by dehydration synthesis forming covalent peptide bonds
• the left over amino and carboxyl group, after the peptide bonds will join for the secondary structure
• the secondary structure is determined by the arrangement of the polypeptide backbone from H bonding of the O of the carboxyl group and the H of the amino group
• the secondary structure can either form alpha helices or beta pleated sheets
• alpha helices are a coiled structure stabilised by H bonds between the amino acids, they link AA that are about 3-4 places apart
• both alpha helices and beta pleated sheets are very stable due to the hydrogen bonds
• beta pleated sheets are linked by hydrogen bonds of different parts of the same chain
• the tertiary structure is determined by the spatial relationship of different secondary structures in a polypeptide chain and how they fold into a 3D product
• the quaternary structure is for multi-subunit proteins that are made up of multiple polypeptide chains, all bound together by weak R group interactions
• changes in ph alter proteins as acids and bases disrupt the ionic charge between side chains. eg. protein digestion in the stomach
• changes in temperature can denature proteins as heat imparts energy to the protein which breaks weak bonds, causing unfolding. eg. sterilise medical instruments with heat to break down bacterial cell walls
• solvents caused denaturing as they disrupt side chain bonding. eg. alcohol disinfectant on skin penetrates bacterial cell wall
• oxidation is a form of chemical modification that can denature proteins
• ways to denature proteins are changing pH, temperature, solvents or chemical modifications
• chaperone molecules help proteins to fold correctly
• R groups determine the electrical charge of a molecule
• primary structure is broken by hydrolysis
• connecting loops are pieces of the chain that connect secondary structure together
• R group interactions

  ionic bonding, van der Walls forces, hydrogen, hydrophobic interactions, disulphide bonds
• haemoglobin has 4 polypeptide chains and 4 non-protein haeme group