Cell Cycle:

The cell cycle is the series of events from the time a cell is produced until it completes mitosis and produces new cells.

Main phases of the cell cycle:

The cell cycle consists of two major phases

1. interphase
2. mitotic phase (M phase)

The mitotic phase is a relatively short period of the cell cycle. It alternates with the much longer interphase, where the cell prepares itself for division. Interphase is the time when a cell's metabolic activity is very high, as it performs its various functions.

Phases of interphase:

It is divided into three phases.

1. G1 (first gap), 2. S (synthesis), 3. G2 (second gap).

G1 phase:

After its production, a cell starts its cell cycle in the G1 phase. During this phase, the cell increases its supply of proteins, increases the number of many of its organelles (such as mitochondria, and ribosomes), and grows in size. This phase is also marked by the synthesis of various enzymes that are required in the next phase i.e. S phase for DNA replication.

Cells that have temporarily or permanently stopped dividing are said to have entered a state of quiescence called the GO phase.

S phase:

In this phase, the cell duplicates its chromosomes. The DNA molecule of each chromosome is copied, and new protein molecules are attached. The result is that each chromosome consists of two sister chromatids, which contain identical genes.

G2 phase:

In the G2 phase, the cell prepares proteins that are essential for mitosis mainly for the production of spindle fibers. After the G2 phase of interphase, the cell enters the division phase le. M phase. It is characterized by mitosis, in which the cell divides into the two daughter cells.

G0 phase:

In multicellular eukaryotes, cells enter the G0 state from G1 and may remain quiescent for long periods, possibly indefinitely (as is often the case for neurons). Some cell types in mature organisms, such as some cells of the liver and kidney, enter the G0 phase semi-permanently and can only be induced to begin dividing again under very specific circumstances. Other cells, such as epithelial cells, do not enter G0 and continue to divide throughout an organism's life.