Cofactors | Coenzymes | Holoenzyme | Apoenzyme

Summary

This video explains cofactors and coenzymes, essential non-protein components required for some enzymes to function. It differentiates between a holoenzyme (enzyme with its cofactor) and an apoenzyme (enzyme without its cofactor, usually inactive). Cofactors can be inorganic, like metal ions (e.g., magnesium for DNA polymerase or zinc for carbonic anhydrase), or organic. Organic cofactors tightly bound to enzymes are called prosthetic groups, while those released after catalysis are coenzymes. Most coenzymes are derived from vitamins and are crucial for enzyme activity, such as NADH, NADP, and FAD.

Takeaways

• 🔬 Some enzymes need non-protein components to perform biological reactions; these components are called cofactors.
• ⚙️ An enzyme combined with its cofactor is called a holoenzyme, and without its cofactor, it's referred to as an apoenzyme, which is usually inactive.
• 🧬 DNA polymerase requires magnesium ions as a cofactor, and when combined with these ions, it becomes a holoenzyme.
• 🧬 Similarly, RNA polymerase requires the Sigma factor to function, and the combination is called a holoenzyme, while RNA polymerase alone is an apoenzyme.
• 🧲 Cofactors can be either inorganic or organic molecules; inorganic cofactors are usually metal ions.
• 🔗 An example of an enzyme with an inorganic cofactor is carbonic anhydrase, which uses a zinc ion at its active site.
• 🧪 Organic cofactors are either tightly bound to enzymes (prosthetic groups) or released after the reaction (coenzymes).
• 🍀 Most coenzymes are derived from vitamins and cannot be synthesized by the body.
• 💊 Examples of coenzymes include NADH, NADP, FAD, and others.
• 🔗 Prosthetic groups remain tightly bound to the enzyme, while coenzymes are released after the catalytic process.

Q & A

What are cofactors in relation to enzymes?

Cofactors are non-protein components that are necessary for some enzymes to carry out biological reactions.

What is a holoenzyme?

A holoenzyme is an enzyme that is bound to its cofactor and is in its active form.

What is a proenzyme or apoenzyme?

A proenzyme, also known as an apoenzyme, is an enzyme that has lost its cofactor and is therefore inactive.

Can you give an example of a holoenzyme and a proenzyme?

DNA polymerase with magnesium ions is a holoenzyme, while DNA polymerase without magnesium ions is a proenzyme.

How do cofactors contribute to the function of enzymes?

Cofactors assist enzymes in carrying out their biological functions. Without the appropriate cofactor, the enzyme remains inactive.

What are some examples of enzymes that require cofactors?

Examples include DNA polymerase, which requires magnesium ions, and RNA polymerase, which requires the Sigma factor.

What is the difference between inorganic and organic cofactors?

Inorganic cofactors are usually metal ions, like zinc in carbonic anhydrase, while organic cofactors can be tightly bound prosthetic groups or free-moving coenzymes after catalysis.

What are prosthetic groups and how do they differ from coenzymes?

Prosthetic groups are tightly bound organic cofactors that remain attached to the enzyme, whereas coenzymes are organic molecules that can be released after catalysis.

What are some examples of coenzymes?

Examples of coenzymes include NADH, NADP, and FAD, which are often derived from vitamins and are essential for enzyme functions.

Can the human body synthesize coenzymes?

Most coenzymes cannot be synthesized by the body and must be obtained from external sources, such as vitamins in the diet.