These control cell reactions.
Enzymes need to be at their optimum temperature to work best.
If the temp. is too high, then the enzymes denature.
Examples of reactions caused by enzymes;
These are used to transport smaller molecules.
Haemoglobin binds to oxygen molecules and transports them around the body.
Hormones are used to carry messages around the body.
Insulin is a hormone.
It is released into the blood stream by the pancreas, and regulates blood sugar levels.
These are physically strong proteins.
Collagen is a structural protein.
It strengthens connective tissues - so things like cartilage and ligaments.