1. Chapter 4: Enzymes and Energy. (Review)
Enzymes (and ribozymes) are biological catalysts.
A catalyst is a chemical that:
1. Increases the rate of chemical reactions.
2. Is not itself changed at the end of the reaction.
3. Does not change the nature of the reaction or its final result
(the same reaction would have occurred to the same degree in the
absence of the catalyst, but it would have progressed at a much slower
rate).
Most enzymes are proteins, and their catalytic action results from their complex structure.
The great diversity of protein structure allows different enzymes to be very
specific in the reactions they catalyze.

2. Energy is the ability to do work.
Living organisms require the constant expenditure of energy to maintain their complex structures and processes. Central to life processes are chemical reactions that are coupled, so that the energy released by one reaction is incorporated into the products of another reaction.
Bioenergetics refers to the flow of energy in living systems.