The Cell Cycle Summary
Why a Summary of the Cell Cycle in Animals?
This hub is designed to act as revision material for students of any biology course who will no doubt need to learn and remember the outline of the cell cycle.
Below are the stages and main functions of each phase starting with Interphase and ending with Cytokinesis.
There is also a 'What you MUST know' section.
Remember: Prophase to Telophase is what is known as Mitosis.
The phase in which the cell performs its functions. Splits into three stages:
Gap 1 (G1)
- Amino acids
- DNA is replicated (doubled)
Gap 2 (G2) -
- Production of microtubules
- Checking for errors of DNA synthesis
- Chromosomes condense into pairs of chromatids.
- Centrioles double up and separate themselves equally between opposite poles of the cell.
- Nuclear envelope breaks down.
- Nucleolus disappears (not 'breaks down').
- Spindle begins to form.
- Chromosomes (pairs of chromatids) line up in the centre of the cell along the metaphase plate.
- Spindle fibres attach at the centromeres of the chromatid pairs.
- Centrioles separate the chromatid pairs, contracting to pull one of two chromatids to one side of the cell and the other chromatid to the other side of the cell.
- Spindle fibres pull at the centromere which then drags the chromatids along behind it.
- Chromosomes become visible again by decondensing.
- The nuclear envelope reforms.
- The nucleolus reappears (not rebuilds/reforms).
- The spindle breaks down.
Telophase and Cytokenesis
In an Animal
- Nuclei separate into two different sides of the cell
- Contractile fibres in the middle of the cell conract and create a 'cleavage furrow' (see diagram above). The fibres then proceed to 'pinch off' at the centre so that the cell is split into two from the middle.
- Two new functional identical cells are left -> interphase.
In a Plant
Cytokinesis in plants
- Instead of a cleavage furrow, acellulose wall begins to form from the inside of the cell outwards away from it.
- The cellulose wall begins as golgi vessicles (all containing the basic structure of the cell wall) which join to make large vacuoles which in turn fuse together and make a cell plate - joining the small basic structures of the cell wall into a large cell wall.
- This cell plate has then becomes acellulose wall and is surrounded bycell surface membrane. A small indent is known to be present in the cell wall known as the middle lamella.
- Small gaps between the vesicles create the larger gap known as theplasmodesma.
What you MUST know:
- You must know that the order of the cell cycle is: interphase Prophase Metaphase Anaphase Telophase Cytokensis (IPMATC)
- You must know what a centromere is.
- You must know what a centriole is.
- You must know about the cell cycle of plants and its difference to that of animals, namely:
- Plants have no centrioles but still use a spindle, the fibres of which are formed in the cytoplasm and not by a centriole.
- Only meristems in plants are capable of mitosis and cytokinesis whereas all animal cells can complete the whole cell cycle.
- You must know how to recognise any stage of the cell cycle from an electron photograph.
- The middle lamella is the gap between cell walls at the sides of plant cells (see diagram).