Proteins (I)

Elements C H O and N sometimes S Textbook p98-99

Testing for proteins Biuret test (pale blue colour containing sodium hydroxide and copper sulfate) The chemicals react with the peptide bonds found in protein, which results in a colour change to lilac. Does not require any heating

What are proteins made from? Acid group What are proteins made from? Amino group Amino acids 20 different types Each amino acid has an amino group at one end and an acid group at the other.

R groups Can be Big Postively charged Negatively charged Acidic Basic Hydrophobic Hydrophilic Include Sulphur Ring structures Such properties will influence the higher level structures of the protein – more of this later Textbook p98-99

Plants Animals Manufacture the amino acids they need Nitrate – used to form amino groups which are then bonded to organic groups. Animals Must take amino acids in as part of their diet. 8-10 of the 20 amino acids are essential amino acids (meat and soya) Can’t store excess amino acids – amino group makes them toxic Deamination

Forming peptide bonds Condensation reaction Peptide bond formed. This can be broken by a hydrolysis reaction.

Proteins from amino acids Dipeptides Polypeptides (10 or more amino acids) and proteins Amino acids in proteins are known as residues (due to loss of the water molecule and therefore part of the amino acid structure) Draw four amino acids joined together with peptide bonds (use general structure with the R group)

Making polypeptides and proteins On ribosome (protein synthesis) Uses mRNA According to the code on the mRNA the amino acids are assembled in the right order and then joined by a peptide bond.

Primary structure of proteins What is it? Consider a protein chain that is four amino acids long.... It has 20 x 20 x 20 x 20 possibilities = 160,000! The primary structure of a protein is given by the specific sequence of amino acids that make up the protein What codes for each of the proteins primary structures?

Breaking down proteins Enzymes involved... Protease enzymes Looking at two examples: Hormone regulation Ageing

Answers to Q8 from booklet