4.4 - Cofactors, Coenzymes, and Prosthetic Groups Flashcards
What are cofactors and why are they needed by some enzymes?
Cofactors are non-protein helper components that enzymes need to carry out their functions. They may transfer atoms or groups in multi-step reactions or form part of the enzyme’s active site.
What is the difference between a cofactor and a coenzyme?
A cofactor is a non-protein molecule required by some enzymes for activity. If the cofactor is an organic molecule, it is called a coenzyme.
What are inorganic cofactors and where are they obtained?
Inorganic cofactors are minerals such as iron, calcium, chloride, and zinc ions, typically obtained from the diet. For example, amylase requires a chloride ion to form a correctly shaped active site.
How are coenzymes related to vitamins?
Many coenzymes are derived from vitamins. For example, vitamin B3 is used to synthesize NAD and NADP, which transfer hydrogen atoms in respiration and photosynthesis, respectively. Vitamin B5 is used to make coenzyme A, essential for fatty acid and carbohydrate breakdown in respiration.
What are prosthetic groups and how do they differ from other cofactors?
Prosthetic groups are co-factors that are tightly and permanently bound to the enzyme, unlike other cofactors which may be loosely or temporarily attached.
Can you provide an example of a prosthetic group?
One example is the iron ion in hemoglobin, which is a prosthetic group that helps the protein function. Another example is the zinc ion (Zn²⁺) in carbonic anhydrase, which is important for carbon dioxide metabolism.
What is the function of prosthetic groups in enzymes?
Prosthetic groups are necessary for enzymes to carry out their catalytic functions, forming a permanent part of the enzyme’s structure.
What is a precursor enzyme?
A precursor enzyme is an inactive enzyme that is produced in a form that can be activated under certain conditions, often to prevent damage to the cells or tissues where it is produced.
What is the difference between an apoenzyme and a holoenzyme?
An apoenzyme is an inactive precursor enzyme that requires a cofactor to become active. Once the cofactor binds, the enzyme is activated and is called a holoenzyme.
How can precursor enzymes be activated?
Precursor enzymes can be activated through several mechanisms, including the addition of a cofactor, a change in tertiary structure (sometimes by another enzyme like a protease), or changes in environmental conditions such as pH or temperature.
What are zymogens (or proenzymes)?
Zymogens (or proenzymes) are precursor enzymes that are activated by a change in their tertiary structure, often due to conditions like pH changes or the action of another enzyme.
How does the activation of pepsinogen illustrate precursor activation?
Pepsinogen is an inactive precursor enzyme (zymogen) released in the stomach. The acidic pH activates it by converting it into the active enzyme pepsin, which is responsible for digesting proteins. This prevents pepsin from damaging the tissues in which it is produced.
What is blood clotting (coagulation)?
Blood clotting is a biological process that begins when platelets aggregate at the site of tissue damage. This leads to the release of clotting factors, which are crucial in forming a blood clot.
What role does Factor X play in blood clotting?
Factor X is an important enzyme in the blood clotting process. It is activated by vitamin K and, once activated, it catalyzes the conversion of prothrombin into thrombin, which is essential for clot formation.
How is Factor X activated?
Factor X is activated by the cofactor vitamin K. Once activated, it catalyzes the conversion of prothrombin into thrombin by cleaving certain bonds in the prothrombin molecule, altering its tertiary structure.
