Explain how certain molecules or ions increase the activity of enzymes.

Cofactors and coenzymes bind to an enzyme's allosteric site. This causes interactions between hydrogen bonds in the tertiary structure of the protein to change- altering its structure.The change of structure therefore induces a change in the shape of the active site, making it a 'better fit' or a more complementary shape to its substrate. This allows for the enzyme-substrate complex to be formed more easily, hence increasing the activity of the enzyme.