between them. This joining does not happen spontaneously but only
under specific catalytic conditions found within the ribosomes of
cells. Ribosomes are structures inside cells that are built from proteins
and nucleic acids. They are the sites of protein synthesis within cells,
with enzymatic activity of the ribosome facilitating, or catalyzing, the
formation of covalent bonds between amino acids. The diagram above
shows that an -H and an -OH are removed in the formation of a pep-
tide bond. They will produce one molecule of water, HzO, which floats
away. You can also see that the two ends of the resulting polypeptide
structure have an amine group and an acid group available to form
additional peptide bonds. Thus, it is possible to form very long chains
of amino acids, covalently linked by peptide bonds. Ribosomes pro-
vide the conditions for this to take place.
H Ho Ho
N-G-C-N-G-C.
H oR, HR, OH
Amino acids forming a dipeptideWhen a bunch of amino acids link together to form a polypeptide
chain, they fold around and form a shape. Similar to water flowing
downhill, the polypeptide chain folds in such a way so as to arrive at
a lowest-energy configuration, determined by the myriad attractions
and repulsions among the component atoms. Thus, the chain of
amino acids develops a unique three-dimensional shape, and it is this
shape that will help determine how it functions in the cell. Any chain