（3A最后一部分）

The Physical Roots of the Biochemical World

We can now summarize the various principles of the molecular logic of life:

A living cell is a self-contained, self-assembling, self-adjusting, self-perpetuating isothermal system of molecules that extracts free energy and raw materials from its environment.

The cell carries out many consecutive reactions promoted by specific catalysts, called enzymes, which it produces itself.

The cell maintains itself in a dynamic steady state, far from equilibrium with its surroundings. There is great economy of parts and processes, achieved by regulation of the catalytic activity of key enzymes.

Self-replication through many generations is ensured by the self-repairing, linear information-coding system. Genetic information encoded as sequences of nucleotide subunits in DNA and RNA specifies the sequence of amine acids in each distinct protein, which ultimately determines the three-dimensional structure and function of each protein.

Many weak (noncovalent)interactions, acting cooperatively, stabilize the three-dimensional structures of biomolecules and supramolecular complexes.