What is the difference between a cofactor and a coenzyme?

Answer 1

Coenzymes are proteins that bind to an enzyme to "activate" it, allowing it to do its job. Without its respective coenzyme, an enzyme is called an "apoenzyme." With the coenzyme, it is called a "haloenzyme." Note: most enzymes do not require a coenzyme. Some texts refer to all coenzymes as cofactors but biochemists generally try to separate the two. However, not all cofactors are coenzymes, nor do all cofactors unite with enzymes. While it is true they are often metals, they can be proteins (as in the blood clotting cascade), and can function outside the cell, yet themselves are produced in a cell (with clotting cofactors, produced in hepatocytes, specialized cells of the liver). According to Dorland, a cofactor is "an element or principle, as a coenzyme, with which another must unite in order to function."

Answer 2

Coenzymes are biochemical products of a cell that are required for some process - they are a protein product of DNA transcription.

Cofactors are external products brought into a cell that bind to an enzyme and help it do its job. Cofactors are often metal ions.