Is a enzyme a protein that acts as a catalyst in a chemical reaction that takes place in a living thing?

Answer 1

An enzyme is a protein.

If you are asking if an enzyme could be considered to be an independent living organism... generally no. However, a bit of artistic interpretation of the seven "signs of life" (listed below) could lead one to interpret some enzymes as independent living organisms. The prions associated with mad cow disease would be an interesting example of a protein which has the ability to reproduce itself without direct usage of a nucleic acid, as they find proteins which are similar in structure to themselves, and using catalytic action, tweak the structure of the substrate protein to function as a new prion. Thus "reproducing."

A more interesting question: Can a reproducing catalytic RNA be considered 'alive'?

1) living things have highly organized, complex structures; 2) living things maintain a chemical composition that is quite different from their surroundings; 3) living things have the capacity to take in, transform, and use energy from the environment; 4) living things can respond to stimuli; 5) living things have the capacity to reproduce themselves; 6) living things grow and develop; and 7) living things are well-suited to their environment.

Answer 2

True.