The
first phase within interphase, from the end of the previous M phase
until the beginning of DNA synthesis is called G1 (G indicating gap). It
is also called the growth phase. During this phase the bio synthetic
activities of the cell, which had been considerably slowed down during M
phase, resume at a high rate. This phase is marked by the use of 20
amino acids to form millions of proteins and later on enzymes that are
required in S phase, mainly those needed for DNA replication. Duration
of G1 is highly variable, even among different cells of the same
species. It is under the control of the p53 gene.
