Proteins are made up of chains of amino acids that determine their shape and function. There are structural, hormone, carrier, and enzyme proteins. Enzymes speed up chemical reactions by fitting substrates into their active sites like keys in locks. Each enzyme only works on a specific substrate. Enzymes function best at an optimal temperature and pH, as extremes can denature the enzyme and change its shape. Mutations can occur spontaneously or due to radiation/chemicals and may lead to different proteins by changing the DNA code and amino acid order, with effects that can be harmful, neutral, or advantageous.

1. C3: Proteins and mutations
All proteins are made up of long chains of amino acids joined together.
Functions of proteins:
-structural proteins used to build up cells and tissues e.g. collagen
-hormones, which carry messages to control a reaction for example insulin controls blood
sugar levels
-carrier proteins e.g. haemoglobin carries oxygen
-enzymes
Each protein has its own order of amino acids (much like DNA base codes). This makes
each type of protein molecule a different shape and gives it a different function.

2. Enzymes
Enzymes are biological catalysts, they speed up reactions in the body.
They catalyse chemical reactions occurring in respiration, photosynthesis and protein
syntheses of living cells
The substrate molecule fits into the active site like
a key fitting into a lock or like a piece of a jig-saw.
This explains why each enzyme can only work on
a particular substrate
Enzymes work best at an optimum
temperature and pH:
-At a low temperature the molecules move
more slowly so the enzymes active site is less
likely to collide with the substrate
-At a high temperature (or pH), the enzymes
active site ‘denatures’, which means it
changes shape. This results in the substrate
not fitting in the active site.

3. Mutations
Mutations can occur spontaneously but it is often due to radiation or chemicals.
When they occur, mutations:
-may lead to the production of different proteins because they change the base code of
the DNA usually made, so it changes the order of the amino acids in the protein.
-often harmful but can have no effect.
-may give the individual an advantage.