Cofactors, Coenzymes And Prosthetic Groups

Question 1

Difference between cofactors and coenzymes

Answer 1

Some enzymes need a non-protein ‘helper’ component in order to carry out their function as a biological catalyst. They may transfer atoms or groups from one reaction to another in a multi-step pathway or they may actually form part of the active site of an enzyme. These components are called cofactors, or if the cofactor is an organic molecule it is called a coenzyme.

Question 2

Cofactors

Answer 2

Inorganic cofactors are obtained via the diet as minerals, like iron calcium chloride and zinc ions. Like enzyme amylase which catalyses the breakdown of starch contains a chloride ion that is necessary for the formation of a correctly shaped active site.

Question 3

Coenzymes

Answer 3

Many coenzymes are derived from vitamins, a class of organic molecule found in the diet. Like vitamin B3 is used to synthesise NAD, a coenzyme responsible for the transfer of hydrogen atoms between molecules involved in respiration. NADP, which plays a similar role in photosynthesis, is also derived from vitamin B3

Another example is vitamin B5, which is used to make coenzyme A. Coenzyme A is essential in the breakdown of fatty acids and carbohydrates in respiration.

Question 4

Prosthetic groups

Answer 4

Are cofactors- they are required by certain enzymes to carry out their catalytic function.while some cofactors are loosely or temporarily bound to the enzyme protein in order to activate them, prosthetic groups are tightly bound and form a permanent feature of the protein. For example zinc ions form an important part of the structure of carbonic anhydrase, an enzyme necessary for the metabolism of carbon dioxide.

Question 5

Precursor activation

Answer 5

Many enzymes are produced in an inactive form, known as inactive precursor enzymes, particularly enzymes that can cause damage within cells producing them or to tissues where they are released, or enzymes whose action needs to be controlled and only activated under certain conditions.

Precursor enzymes often need to undergo a change in shape(tertiary structure), particularly to the active site, to be activated. This can be achieved by the addition of a cofactor. Before the cofactor is added the precursor protein is called an apoenzyme. When the cofactor is added and the enzyme is activated, it is called a holoenzyme.

Sometimes the change in tertiary structure is brought about by the action of another enzyme, such as protease, which cleaves certain bonds in the molecule. In some cases change in conditions, like pH or temp results in change in tertiary structure and activates a precursor enzyme. These types of precursor enzymes are called zymogens or proenzymes.

When inactive pepsinogen is released into the stomach to digest proteins, the acid pH brings about the transformation into the active enzyme pepsin. This adaptation protects the body tissues against digestive action of pepsin.