AS Biology - Cell division

AS Biology - Cell division
Covering:
Mutation (cancer),
Mitosis,
Meiosis

Transcript

1. Cell Division
2. Cell cycle The sequence of events which takes place between one cell division and another
3. DNA mutations • Length of cell cycle is controlled by genes that ensure mitosis happens where and when it should • When organism is growing or when something needs repairing • Specific gene sequences can alter the timing of cell division • A gene is a section of DNA that codes for a particular polypeptide
4. Mutated genes Tumour suppressor genes prevent rapid replication, if these genes are mutated then a tumour can form Proto-oncogenes are genes that have the potential to become mutated and become oncogenes Oncogenes are genes with the potential to cause cancer
5. Causes of mutation Radiation (UV and/or ionising) Certain chemicals Some viruses
6. Cancers • Cancers are the result of uncontrolled mitosis • Cancerous cells can divide repeatedly and out of control with the formation of a tumour • A tumour is a irregular mass of cells
7. Treating cancer • Some chemicals inhibit the cell cycle to fight cancer • These are highly toxic and risk damaging normal cells as well as cancerous ones • Methotrexate is incorporated into DNA and prevents DNA replication • Doxorubicin targets enzymes essential for the cell cycle • Vinblastine and Vincristine prevent spindle formation
8. Mitosis
9. Interphase • Cell is not dividing yet but is still carrying out what ever function it has • Chromatids are not visible • DNA and centrioles replicate • Cell organelles (Mitochondria) replicate because they have their own DNA • All other organelles duplicate
10. Prophase • Chromosomes condense and become visible • 2 chromatids are joined by a centromere to form 1 chromosome • Centrioles make their way to opposite poles of the cell • Spindles (microfibres) begin to form from centrioles • Nucleus and nuclear membrane disappear
11. Metaphase • Chromosomes align across the equator of the cell • Spindle fibres connect the centrioles to the centromere of a chromosome
12. Anaphase • Chromatids move to opposite poles • Pulled by their centromere, pulled by the spindle
13. Telophase • Spindle fibres break down • Chromosomes uncoil and lengthen • Nucleus and nuclear membrane reform • Cytokinesis – The two new cells move apart from one another
14. Mitosis animation
15. Meiosis
16. Interphase • Cell is not dividing yet but is still carrying out what ever function it has • Chromatids are not visible • DNA and centrioles replicate • Cell organelles (Mitochondria) replicate because they have their own DNA • All other organelles duplicate
17. Prophase I • Homologous chromosomes join in their bivalents • Section of DNA from one chromatid may be exchanged with the equivalent from the homologous chromosome Chiasmata – Crossing over section of DNA
18. Metaphase I • Pairs of chromosomes line up along the equator of the cell • Centrioles move to the poles • Spindles attach centromeres to centrioles
19. Anaphase I The chromosomes in each bivalent are pulled to separate poles by their centromeres being pulled by the spindles getting shorter
20. Telophase I • Sometimes the nuclear envelope will reappear during cytokinesis • Sometimes the chromosomes will stay in their condensed form until Prophase II
21. Prophase II • Centrioles separate • New spindle is organised at a right angle to that used in the first division
22. Metaphase II • Chromosomes line up along the equator • Each centromere attaches to a centriole by a spindle
23. Anaphase II • Chromatids are pulled to opposite poles by their centromeres being pulled by shortening spindles
24. Telophase II • Spindles disintegrate • Chromatids lengthen and are no longer visible • Nucleus and nuclear envelope reappear • Cytokinesis pulls the four new cells away from one another
25. Meiosis animation
26. Mitosis Meiosis Number of divisions 1 2 Number of daughter cells 2 4 Chromosome number in each daughter cell Same as parent Half of parent Ploidy of daughter cells of diploid parent cells Diploid Haploid Chiasmata Absent Present Genetic crossing over None Prophase I Independent assortment None Metaphase I and Metaphase II Genetic composition Genetically identical Genetically different