Final answer:
The G1 phase is marked by a cell's growth and production of proteins, preparing it for the upcoming S phase where DNA replication occurs. It does not involve DNA replication or mitosis and cytokinesis; these occur later in the S phase and M phase respectively.
Step-by-step explanation:
G1 Phase of the Cell Cycle
During the G1 phase of the cell cycle, the primary focus is on the cell's growth in size and content. This growth encompasses an increase in cell size and the production of proteins necessary for the upcoming phases of the cell cycle. Importantly, DNA replication does not occur during the G1 phase; rather, it takes place during the S phase (synthesis phase). In contrast, the event of mitosis and cytokinesis happens during the M phase, which is separate from the G1 phase.
Summarily, G1 phase is characterized by cell growth and activities preparing for DNA replication. Proteins produced in this phase include those required for the DNA replication process in the subsequent S phase. The cell also performs its normal metabolic functions during this time.