The Cell Cycle

Phases of The Cell Cycle

• The cell cycle is like the lifecycle of a cell – from the beginning of a new cell, through growth, and finally division.
• Some cells are capable of dividing many times, while others are not.
• In order to divide, a cell must go through its "stages of life". In this time, the following things will happen:
• The cell will grow;
• It will replicate its DNA;
• It will produce new organelles;
• As it nears cell division, it will sort the DNA so that each daughter cell receives one copy of each chromosome;
• Split into two cells (twin daughter cells).

• Interphase: Cell growth and DNA replication.
• G1 phase (1st gap)
• S phase (Synthesis)
• G2 phase (2nd gap)
• Mitotic (M) Phase: Replicated DNA and cell contents are separated.
• Mitosis
• Cytokinesis (partitioning of the cytoplasm)

Interphase

1. G1 phase: Gap phase 1.
2. The cell is stocking up on nucleotides, proteins and energy to replicate its DNA. That is, it increases abundance of molecules involved in replication.
3. S phase: Synthesis phase.
4. The cell replicates its DNA to form sister chromatids, and replicates the microtubules organizing center called the centrosome.
5. DNA remains in semi-condensed chromatin form.
6. G2 phase: Gap phase 2.
7. The cell may grow in size and increases abundance of proteins involved in mitosis (i.e. chromosome movement and manipulation).
8. It also replenishes energy stores and some organelles are duplicated.

• There may also be a G0 phase, in which the cells exist in a quiescent state (quiet) and they are not in the process of dividing or preparing to divide. This can sometimes be seen as an extended G1 phase.
• May be temporary (e.g. due to lack of nutrients);
• May be permanent (e.g. adult heart cells usually do not divide).