4.4 Cofactors, Coenzymes, & Prosthetic Groups Flashcards
What are cofactors
Non protein helper component that helps enzymes carry out their function as biological catalysts. May transfer atoms or groups from one reaction to another in a multi step reaction pathway or may actually form part of the active site of an enzyme
What is a coenzyme
Organic molecule cofactor
How are inorganic cofactors obtained
The diet as minerals, including iron, calcium, chloride, and zinc ions e.g. amylase catalyses breakdown of starch. It contains a chloride ion that is necessary for formation of correctly shaped active site
How are coenzymes obtained
Vitamins, class of organic molecule found in the diet.
Vitamin B3 used to synthesise NAD, coenzyme responsible for transfer of H atoms between molecules involved in respiration.
NADP plays similar role in photosynthesis (also derived from B3)
Vitamin B5 is used to make coenzyme A. Enzyme is essential in break down of fatty acids and carbohydrates in respiration.
What are prosthetic groups
Cofactors that are required by certain enzymes to carry out their catalytic function.
What makes prosthetic groups different
They are tightly bound and form a permanent feature of the protein whilst others are loosely or temporarily bound
Example of a prosthetic group
Zinc ions form an important part of carbonic anhydrase - enzyme necessary for metabolism of carbon dioxide
Why are precursor enzymes necessary
Enzymes are produced in an inactive form as they may cause damage within the cells that produce them or to tissues where they are released or their actions may need to be controlled and only activated under certain conditions
How are inactive precursor enzymes activated
Need to change the tertiary structure, particularly the active site.
Precursor activation through a cofactor
Addition of a cofactor can change the tertiary structure of the enzyme.
Precursor protein before and after cofactor addition
Before - apoenzyme
After - holoenzyme
Other ways change in tertiary structure is caused
Action of another enzyme which cleaves certain bonds in the molecule
Change in conditions (pH, temperature)
Name of precursor enzymes that are activated by other enzymes or a change in conditions
Zymogens, proenzymes
Example of change in conditions activating precursor enzyme
When inactive pepsinogen is released into the stomach to digest proteins, pH brings transformation into active site of enzyme pepsin. Adaptation protects body tissues against digestive action of pepsin,
