#tertiary structure

The overall three-dimensional structure of a protein molecule. It is the result of interactions between the R groups of different amino acids in parts of the protein molecule such as:

hydrogen bonding between R groups

formation of disulfide bridges between 2 cysteine amino acids

hydrophobic interactions (hydrophobic R groups tend to associate together in the middle of the molecule away from the aqueous environment)

hydrophilic interactions (hydrophilic R groups tend to associate with water  molecules in the cell and so become arranged on the outside of the molecule)

Enzymes are biological catalysts*. This means their job is to lower the activation energy of chemical reactions. Lowering the activation energy* means the rate of reaction* will be faster as less energy is needed to make this reaction happen. They are not 'used up' as part of the reaction. Metabolic reactions require enzymes to occur. Enzymes are useful industrially as it is specific to one substrate and doesn't produce unwanted by-products. However, it is slower than inorganic catalysts.

Enzymes are globular proteins so they have a 3D 'ball' structure. The hydrophobic (water-hating) amino acid R-groups are found in the centre of the 'ball' and the hydrophilic (water-loving) amino acid R-groups are found on the outside of the 'ball'.

-Yellow part: hydrophobic -Red part: hydrophilic 

The hydrophilic R-groups on the outside of the 'ball' is what makes enzymes soluble in water. 

Enzymes are specific so only one type of enzyme will catalyse a reaction of one particular substrate*. This is because each type of enzyme has a different sequence of amino acids. This sequence of amino acids controls the tertiary structure of the enzyme, which in turn controls the shape of the active site on the enzyme. The active site is an area on the enzyme where a substrate binds to. We say the substrate is complementary to the active site of the enzyme (INCLUDE THIS IN YOUR EXAM ANSWER, IT WILL HELP YOU!!!!). If you changed the amino acid sequence, the tertiary structure would change. This means the active site would also change and a different type of substrate would fit into the active site instead.

Enzyme activity is affected by temperature and pH (I will explain this in a later post).

*Definitions:

Activation energy: the amount of energy needed for a reaction to take place.

Rate of reaction: how fast or slow a reaction is.

Substrate: the substance that is used up in an enzyme-controlled reaction.