Sunday, August 18, 2013

Phases of the Cell Cycle, Interphase and Mitosis

Phases of the Cell Cycle
The Cell Cycle; credit: wikimedia

The cell cycle encompasses the series of events that culminate in the creation of two daughter cells, known as cell division. This process is a key feature for life as we know it, allowing organisms to reproduce or repair as is the case for multicellular life. The cycle itself can be broken into interphase and the mitotic phase.


The bulk of the cell cycle actually consists of interphase which itself can be broken into several subphases.
G1: During this phase the cell grows in size, creating more organelles such as mitochondria and gathering materials for DNA replication.
G0: Some cells actually don't go past the G1 phase and onto division. Once an organism reaches maturity certain cells will only divide in order to repair and they typically enter what's known as G0, where they just perform normal cell functions but do not move on to the S phase.
S: This stands for synthesis and appropriately during this stage DNA is replicated resulting in two sister chromatids.
G2: The final stage of interphase, during G2 proteins required for cell division are synthesized.

Phases of Mitosis


In comparison to interphase the M phase is much shorter, but this is when cell division actually occurs. This includes division of the nucleus, or mitosis and division of the cytoplasm, or cytokinesis.

Mitosis: Actually consisting of five distinct phases as well, during mitosis the two sets of previously duplicated chromosomes are separated, each into a new nucleus.
  1. Prophase: Chromosomes are condensing, and are held together at a centromere. The mitotic spindle starts forming and centrosomes move away from each other as microtubules lengthen.
  2. Prometaphase: Nuclear envelope breaks down and the nucleolus disappears. Microtubules from the centrosomes now invade the nuclear area. Chromosomes now have a specialized protein, called a kinetochore, located at the centromere.
  3. Metaphase: The longest stage, centrosomes are now at opposite poles of the cell, the chromosomes arrange themselves midway between them along the metaphase plate.
  4. Anaphase: The sister chromatid part after cohesin proteins are cleaved, officially becoming chromosome. They move to opposite ends of the cell as kinetochore microtubules shorten.
  5. Telophase: The cell now has two daughter nuclei and nuclear envelopes start to form. Chromosomes become less condensed and mitosis ends.
Cytokinesis: Towards the end of telophase division of the cytoplasm was already underway. During this final stage a cleavage furrow forms as the cell appears to be pinched in two.

No comments:

Post a Comment