Chapter 4- 4.4- Cofactors, coenzymes, and prosthetic groups Flashcards
What is the difference between cofactors and coenzymes?
Some enzymes need a non-protein “helper” component in order to carry out their function as biological catalysts. 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 re called cofactors, or if the cofactor is an organic molecule is called a coenzyme.
How are inorganic cofactors obtained?
Inorganic cofactors are obtained via the diet as mineral, including iron, calcium, chloride, and zinc ions. For example, the enzyme amylase, which catalyses the break down of starch contains a chloride ion that is necessary for the formation of a correctly shaped active site.
Where are many enzymes derived from?
What is the definition of a vitamin?
What are 2 examples of these vitamins?
Many enzymes are derived from vitamins, a class of organic molecules found in the diet. For example vitamin B3 is used to synthesise NAD (nicotinamide adenine dinucleotide), 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 B5, which is used to make coenzyme A. Coenzyme A is essential in the breakdown of fatty acids and carbohydrates in respiration.
What is the difference between a prosthetic group and a cofactor?
Prosthetic groups are similar to cofactors in that they are required by certain enzymes to carry out their catalytic function. But while cofactors bind loosely to proteins 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.
The prosthetic group for the globular protein haemoglobin is iron.
Why are many enzyme produced in an inactive form?
Many enzymes are produced in an inactive form, known as inactive precursor enzymes, particularly enzymes that can cause damage within the cells producing them or to tissues where they are released, or enzymes whose action needs to be controlled and only activated under certain conditions.
How are precursor enzymes activated?
Precursor enzymes often 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 a protease, which cleaves certain bonds in the molecule. In some cases a change in conditions, such as pH or temperature, results in a 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 the digestive action of pepsin.
