Biological Sciences 101 – General Biology
Lecture One: The Cell Cycle
Chapter 12, pg. 228-243
- All living organisms are comprised of cells. (Approximately 2 x 10 cells = 200
- All cells are derived from pre-existing cells.
- Organisms may be single-celled organisms (Amoeba/Bacteria) or multiple cells.
3) Reproduce (Cell Division).
4) Cell Cycle.
Fig. 6.8: Animal Cell.
The Role of Cell Division:
1) For reproduction – to produce new cells.
2) Growth and development of organisms.
3) For repair of any damaged cells.
Cell division must give rise to genetically identical
“daughter” cells, through division of nucleus.
Division of nucleus -> Mitosis -> Cytokineses
(Division of cytoplasm).
Simplest form of cell division is in bacteria (binary
Fig. 12.12: Chromosome Replication of E. coli Cell. Multicellular Organisms and Components of the Cell Cycle:
Cell Cycle: The two-phase cycle during which a cell replicates its DNA, divides, and
then goes through the processes necessary to replicate DNA, etc.
- Cell cycles can vary in duration from 8 minutes to 1 year, though the general
duration is around 24 hours for fast dividing mammal cells.
- The two phases of the cell cycle are interphase and mitosis.
Fig. 12.16: The Cell Cycle.
G1 Phase = First gap phase (cell
S Phase = Synthesis (DNA replication)
- Approximately 2 metres of DNA.
G2 Phase = Second gap phase (cell
M Phase = Mitosis and Cytokineses.
The cell cycle is the recurring sequence of events that includes the duplication of a
cell’s contents and its subsequent division.
The cell cycle is an essential process for all living organisms.
- In single-cell organisms, each round of the cell cycle leads to the production of an
entirely new organism.
- Other organisms require multiple rounds of cell division to create a new individual.
- In humans and other higher-order animals, cell death and growth are constant
processes and the cell cycle is necessary for maintaining appropriate cellular
- It is a control point where stop and go-ahead signals can
regulate the cell cycle.
- The signals are transmitted within the cell by the kinds of
signal transduction pathways.
G1 checkpoint = “Restriction Point” where the cells gets the go-
ahead to either continue on to G1, S, G2 and M phases and
divide or does not get the go-ahead and exits the cycle,
switching into a non-dividing state of G0. Interphase and Mitosis:
1) Prophase: Chromosomes features appear, with sister chromatid.
- Structure called Mitotic Spindle (microtubules) forms in cytoplasm.
2) Prometaphase: Nuclear envelope breaks down.
- Microtubules organize at poles of cell.
- Kinetochore forms at centromere; this is where the microtubules attach.
3) Metaphase: Chromosomes begin to migrate to the centre of the cell and align
themselves according to the centromeres.
- Spindle apparatus is complete.
4) Anaphase: Chromosome separate and migrate to poles of cell.
5) Telophase: Two nuclei-formed, cytokinesis occurs, 2 genetically identical cells
- Nuclear envelope forms.