2009 Group 3 Project
- 1 Cell Division
- 1.1 Introduction
- 1.2 Types of Cell Division
- 1.3 History of Cell Division Research
- 1.4 Mechanisms of Cell Division
- 1.5 Mitosis
- 1.6 Meiosis
- 1.7 Cytokinesis
- 1.8 proteins of cell division
- 1.9 errors of cell division
- 1.10 Current Research on Cell Division
- 1.11 Glossary of terms
- 1.12 References
- 1.13 2009 Group Projects
Types of Cell Division
Cell Theory states that cells are derived from pre existing cells, and in understanding this, and cell division clearly illustrates this. Cell division is the process by which a cell can replicate itself. There are essentially three different modes of cell division. The different types of division are present due to the different types of organisms, or the purpose of the cell. The three main differing types of Cell Division are Binary fission, Mitosis, and Meiosis.
Binary Fission is the mode of cell division whereby prokaryotes(e.g, amoeba) duplicate themselves. It is a known type of asexual reproduction where the cell is divided in a way such that the product is equal to/almost equal to that of the original. The division of the cell includes the genetic material as well, however there is often a high mutation rate. Thus the high mutation rate enables bacteria to develop resistance to antibiotics and other drugs/chemicals.
Mitosis is a process of cell replication where the parent cell duplicates the DNA and then divides into two daughter cells which are almost or are equal to each other. It is replicated such that it remains a diploid cell. To summarise quickly mitosis consists of the stages, prophase, metaphase and anaphase. After interphase occurs, where the genetic material is replicated, the 2 sets of chromosomes/ 4 sister chromatids then become condensed and the nuclear envelope is then broken down and the sister chromatids are attached to the spindle and lined up in the centre. The chromatids are then pulled towards the poles and the nuclear envelopes reform and thus two identical daughter cells are the result.
Meiosis is a process of cell division, which is associated with gametogenesis. Gametogenesis is the formation of gametes by process of meiosis, whereby cells which are replicated, and diploid cells become haplpoid.It can described in two phases, reduction and division. Similar to mitosis, it follows a similar sequence of prophase, metaphase and then anaphase, and cytokinesis. Meiosis is similar to mitosis in that the DNA replicates and the sister chromatids are condensed, and the nuclear envelope is broken, however, the chromatids do not line up in the middle and are not attached to the spindle, but instead are sent to either poles, where crossover may occur. The act of crossing over of chromatids, this allows for genetic variation. Two daughter cells are then produced with single sets of chromosomes, and the resulting daughter cells are now haploid, as opposed to the end products of mitosis which are two diploid cells that are identical to each other.
History of Cell Division Research
- 1902 – Theodore Boveri made discoveries on mitotic spindle division through the study of fertilised sea urchin eggs.
- 1951 - Gunnar Östergren published a ‘theory of co-orientation by pulling’, explaining the unique interaction between paired chromosomes in meiosis.
- 1953 – James Watson and Francis Crick discovered the double-helical structure of the DNA, explaining the mechanism of DNA replication.
- 1968 – Taylor and colleagues identified tubulin as the protein subunit of microtubules.
- 1970 – Lee Hartwell identified the existence of a set of cell division cycle genes that function to control mechanisms of cell division at specific stages of the cell cycle. Rao and Johnson also published a series of experiments indicating that the sequential and unidirectional phases of the cell cycle are controlled by a series of chemical signals that can diffuse freely between the nucleus and cytoplasm.
- 1971 – Yoshio Masui and Clement Markert identified the maturation-promoting factor (MPF), which controls the progression of cell division during mitosis and meiosis.
- 1974 – Arthur Pardee showed that cells re-enter the cell cycle at a particular point, which he called the restriction point.
- 1975 – Paul Nurse began to investigate the mechanisms that control cdc2 regulation.
- 1980 – Louise Clarke and John Carbon found a way to isolate a functional centromere, thus allowing them to study important features of chromosomes.
Mechanisms of Cell Division
Mechanics of cell division
Mitosis is the process of creating genetically identical daughter cells from a parent cell. This allows for accurate replication of DNA which is important in any organism. The DNA replicates and only divides once splitting into two daughter cells, unlike meiosis which replicates twice which creates 4 cells. The daughter cells produced by mitosis are called diploid as they contain 46 chromosomes whilst the haploid cells produced by meiosis only have 23 chromosomes and are gametes. There are several proteins which are involved in cell division, some controlling the entire cell cycle which controls the timeline of when things are to occur, while others allow cohesion of the chromatids, the breakdown of cohesion, and the motors that allow the mitotic spindle to draw the replicated chromosomes to opposite poles of the cell, and finally the protein that initiates cytokinesis. The main proteins involved in cell division are CDK-1, Cyclin B, Cyclin D, Cdk4, Cohesin, and Seperase. These proteins are crucial to the successful process of cell division.
- there are 3 phases for mitosis
- Is marked by the disappearance of the nuclear envelope, chromosomes start to move towards the poles. ‘The chromosomes are still being held along the equatorial line by the mitotic spindle and cohesion holding the centromeres of the pairing of chromatids together’ (Purves, Sadava, Orians, Heller, 2004. pg 172).
- Is the condensing of the DNA and attached to the poles of the cell. ‘once all of the chromatids are attached to the poles by the mitotic spindle, seperase is used to catalyse cohesion breakdown’ (Purves at al, 2004. pg 173) allowing the chromatids to separate and move towards the opposite poles.
- The separation of the sister chromatids to opposite poles is the beginning of the anaphase process. ‘The chromatids are now referred to as the daughter chromosomes’ (Purves et al, 2004, pg 173)
- Cytokinesis is the last process of cell division. Cytokinesis is the process of microfilaments causing a furrow on the cell, which tightens until the cell membrane comes together, fuses causing two identical daughter cells. This process is different in plant cells as they have a cell wall, the idea is the same, but a ‘ell plate is created in the middle of the cell which elongates until the membrane reaches the cell wall and fuses, thus separating the cells’ (Purves et al, 2004, pg 174).
Meiosis is the process of reducing the number of chromosomes in a cell, which allows for diversity. Meiosis has 2 nuclear divisions that reduce the number chromosomes from diploid to haploid in preparation for sexual reproduction, the cells involved in meiosis are called gametes. In meiosis, the chromatids are allowed to diversify. When the chromatids synapse along the equatorial line, certain parts of the homologous chromatid will crossover with the pair homologous chromatid creating recombiant chromatids, crossover allows the diversification of the DNA. ‘The result of meiosis is 4 nuclei, each nucleus is haploid and has a single set of unreplicated chromosomes that differs from other sets in its genetic composition’ (Purves et al, 2004, pg 180). There are only 2 phases in the meiotic process, phase 1 is the synapse of the homolog chromatids along the equatorial line. Phase 2 is the separation of the homolog chromatids.
proteins of cell division
- Cell division cycle 2(CDK1) induces entry into M phase and is found in all eukaryotes
- Cyclin B
- Cyclin B forms part of the Mitosis Promoting Factor (MPF)and is crucial to nuclear translocation
- Cyclin D
- Cyclin D provides a DNA binding site
- Cdk4 is pivotal in controlling cell proliferation in the G1 phase
- This protein holds the chromatids together in both mitosis and meiosis. It allows for the replication of DNA to occur as accurately as possible.
- This protein, also known as Anaphase promoting complex (APC), acts after the DNA has been accurately replicated and allows the daughter chromosomes to separate and move to the opposite poles of the cell. Seperase works by catalysing the cohesin, degrading it, thus separating the sister chromatids. APC also degrades other mitotic CDK complexes rsulting in the completion of the mitotic process. http://www.ncbi.nlm.nih.gov/books/bookres.fcgi/mcb/ch24anim1.mov
- regulate the microtubule attachment at the kinetochores and also the tension between sister kinetochores. Also activation of the spindle assembly checkpoint(SAC) to delay the mitotic process when either of these is absent.
errors of cell division
- There are 2 main types of errors in cell division. They are:
- Error in the division process
- Is a ‘condition in which one of the chromosomes are either lacking or present in excess’ (Purves et al, 2004, pg 182), one of the reasons could be the cohesin protein being absent or in excess. Anaeuploidy can be found in both the mitotic and meiotic processes.
- In meiotic process where the crossing over does not occur in an equal manner, causing one chromatid to become longer or smaller than its pair, this usually occurs because one part of a chromatid has broken off and attached to another chromatid.
Current Research on Cell Division
Glossary of terms
- Centromere - The region where sister chromatids join.
- Chromatid -
- Chromosome -
- Cytokinesis -
- Eukaryote -
- Kinetochore - The protein struture found on chromosomes which is the site of attachment of the mitotic spindles (microtubules) allowing the separation of chromosomes to occur.
- Meiosis -
- Mitosis - A type of cell division in which a single cell divides into two; each resulting cell has the same amount of chromosomes and genetic content as the original cell.
- Prokaryote -
Ratogi, C.S.,(2003) Cell and Moelcular Biology, New Age International.
Erich A. Nigg, 2001, Mitotic kinases as regulators of cell division and its checkpoints, Nature Reviews Molecular Cell Biology 2, 21-32 (January 2001) | doi:10.1038/35048096
Purves W.K, Sadava D, Orians G.H, Heller H.C (2004) Life: The Science of Biology 7th edition. Sinauer associates and VHPS/W.H. Frreman & Co.
2009 Group Projects
--Mark Hill 14:02, 19 March 2009 (EST) Please leave these links to all group projects at the bottom of your project page.
Group 1 Meiosis | Group 2 Cell Death - Apoptosis | Group 3 Cell Division | Group 4 Trk Receptors | Group 5 The Cell Cycle | Group 6 Golgi Apparatus | Group 7 Mitochondria | Group 8 Cell Death - Necrosis | Group 9 Nucleus | Group 10 Cell Shape