Q.How are prosthetic groups different from co-factors?

• A co-factor is the general term for any non-protein helper an enzyme needs in order to be catalytically active; without a co-factor, the protein-only part of the enzyme, the apoenzyme, stays inactive.
• Co-factors come in three kinds: prosthetic groups, co-enzymes, and metal ions.
• A prosthetic group is specifically an organic co-factor that is bound very tightly to the apoenzyme, becoming a fixed part of the enzyme's structure, such as the haem group in peroxidase and catalase. …

Many enzymes are not fully active as protein alone. They need an additional, non-protein partner to become catalytically functional, and this partner is called a co-factor in general. The protein portion by itself, without its co-factor, is called the apoenzyme and is inactive; once the co-factor joins it, the complete, working molecule is called the holoenzyme.

Co-factors are not all the same, however - they fall into three distinct kinds:

• Prosthetic groups - organic co-factors bound very tightly to the apoenzyme, effectively becoming a permanent part of the enzyme's structure and often part of its active site; the haem group in peroxidase and catalase is the standard example. …

Method: Contrasting a General Term with Its Specific Subtype

Whenever a question asks how term A differs from term B, and B turns out to be one specific kind of A, the correct approach is to first establish the broader category, then narrow down to what makes the specific subtype distinct within it — never treat the two as simply unrelated, parallel ideas.

Here, start from the fact that an enzyme's protein part alone (the apoenzyme) is often inactive and needs some non-protein helper to work — that helper, in general, is called a co-factor. Once you have that umbrella term fixed, recall that co-factors are not all identical: they come in three flavours — prosthetic groups, co-enzymes, and metal ions — distinguished mainly by how tightly and how permanently they associate with the enzyme protein. A prosthetic group is the tightly, almost permanently bound organic kind; a co-enzyme is organic too but only loosely and transiently associated, usual …