What would happen if a cell lacked a key enzyme?

Answer 1

Generally, key enzymes are involved in a large pathway with lots of other enzymes and molecules. If the enzyme was involved in metabolism/catabolism, then there will be a build-up of the intermediate molecule it acts upon, this can sometimes be toxic to the cell and end up in it apoptosing (dying). If the enzyme is involved in cell division or creating proteins/DNA, then it tends to fail passing the regulations within the cell that allow it to divide by mitosis, it will then die in the same way by apoptosis. So I would say that generally, if it lacks a key enzyme, it will probably not be functional and enter programmed cell death (PCD) by apoptosis, they do not always die however. In a genetic disease called phenylketonuria, cells cannot produce the functional enzyme phenylalanine hydroxylase and although it can be detrimental, babies can develop to be completely normal adults if they are put on a specialised diet. In this case it is because without the enzyme, a toxic intermediate molecule builds up which impairs brain development and so reduce the intake of that molecule in your diet and your brain develops fine.

I hope this is OK, as a summary, most cells would die, some would be OK but it is likely to result in other problems.