Cell Division: Understanding the Process and Significance

1. CELL DIVISION Before it divides? What causes it to divide? What controls the division? Cell Cycle Determines whether or not a cell undergoes cell division Replace dead cells/damaged cells

2. Cell Cycle Growth phase protein Synthesis of : New cytoplasmic organelle Cell continues to grow mitochondria chloroplast Cell metabolically active Synthesis of DNA High metabolic rate Cell accumulates energy DNA undergoes replication Chromosomes-threadlike str Cell completes preparations for next stage of cell division Chromatin Each chromosome consists of 2 identical chromatids

3. Types of cell division Mitosis Meiosis

4. Number of chromosomes What is chromosome? An organized structure of DNA and protein that is found in cells A single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences

5. Number of chromosomes in an organism Human = 46 Monkey = 48 Fruit fly = 4 Pig= 38 23 pairs 24 pairs 2 pairs 19 pairs Where do these creatures come from? MOTHER

6. Father has 46 chromosomes Mother has 46 chromosomes A type of cell division occurs to produce gametes which halve the number of chromosomes from the father and the mother The division only occurs in reproductive organs; ovary and testes (in this case) Producing ovum and sperm with 23 chromosomes each MEIOSIS

7. Genetic Variation as many as 223

8. + 23 23 23 + 23 = 46 To maintain the diploid number of chromosomes from one generation to the next

9. Occurs to some organisms ; -ameoba -planaria Occurs all somatic cells ; -skin cells -liver cells -intestinal cells After fertlisation, zygote divides from 1 cell  2  4  8 blablabla. Cell divides, differentiate into heart cells, muscle cells, nerve cells, skin cells hair cells etc. Those cells divide and increase their numbers. Until a complete human is formed. Cells produced(daughter cells) through this type of division have the same number of chromosome as their parent cell. Usually occurs ; -to replace dead or damaged cells -for growth Mitosis Cells produced, daughter cells will carry out function same as their parent cell

10. MEIOSIS Chromatid Prophase I How many chromosomes are there in the nucleus? Centromere Sister chromatids The chromosomes begin to condense, become shorter and thicker Synapsis occurs ; the homologous chromosomes pair up/synapse to form bivalents Each bivalent consists of 4 part structure called tetrad

11. Homologous chromosomes Bivalents Tetrad A tetrad consists of 2 non-sister chromatids Crossing over takes place : Non-sister chromatids exchange segments of DNA Chiasma Chiasma Crossing over occurs at chiasma/chiasmata- site where 1 chromatid overlapped on the other chromatid Exchange of genetic material, resulting a new combination of genes on a chromosome

12. Centrioles Nuclear membrane Nucleolus Nucleolus and nuclear membrane dissapear Cenrtioles migrate to the opposite poles

13. Prophase I The chromosomes begin to condense, become shorter and thicker Synapsis occurs ; the homologous chromosomes pair up/synapse to form bivalents Each bivalent consists of 4 part structure called tetrad Crossing over takes place : Non-sister chromatids exchange segments of DNA Crossing over occurs at chiasma/chiasmata- site where 1 chromatid overlapped on the other chromatid Exchange of genetic material, resulting a new combination of genes on a chromosome Nucleolus and nuclear membrane dissapear Cenrtioles migrate to the opposite poles

14. Centrioles Nucleolus Nuclear membrane Homologous chromosomes Tetrad Prophase I

15. Metaphase I Spindle fibre The chromosomes line up side by side as tetrads on the metaphase plane One chromosome of each pair is attached to the spindle fibre from one pole while its homologue is attached to the fibre from the opposite pole The centromeres do not divide

16. Anaphase I Anaphase is responsible to halve the number of chromosomes The spindle fibres pull the homologous chromosomes apart and move them to the opposite poles Each chromosome still consists of two sister chromatids which move as a single unit Only two chromosomes move towards to the opposite pole

17. Telophase I Cleavage furrow Each pole has a haploid daughter nucleus The chromosomes arrive at the poles The nuclear membrane reformed The spindle fibresdissapear The nucleolus reappears

18. Cytokinesis

19. Prophase II The nuclear membrane disintegrate Two haploid daughter cells Nucleolus dissapear Centrioles migrate to the opposite poles The spindle fibres reformed

20. Metaphase II The chromosomes, each still made up of sister chromatids, are positioned randomly on the metaphase plate Each sister chromatid is attached to the spindle fibres at the centromere

21. Anaphase II The centromere of the sister chromatid divide The spindle fibres pull the sister chromatids apart to the opposite poles

22. Telophase II The nucleolus and nuclear membrane reformed Cytokinesis follows 4 haploid daughter cells are formed

23. Through meiosis 4 haploid daughter cells Produced from 1 diploid parent cell

24. Mitosis Vegetative in potato Ameoba, Planaria Skin loss replacement

25. Prophase Chromosomes shorten and thickened Each chromosomes consists of 2 sister chromatids joined together at a centromere Spindle fibres begin to form Nucleolus disappears Nuclear membrane disintegrates

26. Metaphase Spindle fibres are fully formed Chromosomes line up on the metaphase plane 2 sister chromatids are attached to one another at the centromere Centromeres divide

27. Anaphase The 2 sister chromatids are separated to the opposite poles by the shortening of the spindle fibres

28. Telophase 2 sets of chromosomes at the opposite site of the cell Chromosomes uncoil and called chromatin Nucleolus reappears Spindle fibresdissappear Nuclear membrane reformed

29. Cytokinesis Actin filaments in the cytoplasm contracts In animal cell The ring of the plasma membrane is pulled inwards forming cleavage furrow The cleavage furrow pinches at the equator Cleavage furrow Constriction It deepens progressively The cell is separated into 2 daughter cells

30. Cytokinesis In animal cell cell plate MEV Membrane enclosed vesicles (MEV) gather at the equator between the 2 nuclei The vesicles fuse to form a cell plate The cell plate grows outward until its edges fuse with the plasma membrane of the parent cell New cell walls and plasma are formed from the contents of the cell plate Finally the cell is divided into 2 daughter cells At the end of cytokinesis, cellulose fibres are produced by the cells to strengthen the new cell walls

31. The significance of mitosis Number of chromosomes can be maintained from parent cell to daughter cells in somatic cells Organisms have diploid (2n) number of chromosomes. 1 set (n) is inherited from father and another 1 (n) set is from mother 1 set is inherited from father and another 1 set is from mother making 2 sets. (n + n=2n) Glory to Allah, Who created in pairs all things that the earth produces, as well as their own (human) kind and (other) things of which they have no knowledge

32. The new cells produced can carry out the same functions as the parent cell Each daughter cell carries genetic material inherited from the parent cell Each DNA molecule contains genes which encode information for the synthesis of proteins such as enzymes which are needed by the cell The 2 daughter cells produced by mitosis are genetically identical to each other and to the parent cell. Double the number of cells without changing the genetic content of the chromosomes To replace dead or damaged cells Vegetative reproduction Growth

33. The significance of meiosis Number of chromosomes can be maintained from one generation to the next Meiosis produces haploid gametes For species which reproduces sexually, meiosis ensures that the diploid number of chromosomes is maintained Meiosis leads to genetic variation Variation occurs through genetic recombination. 1. During prophase I, crossing over resulting in the exchange of genetic materials between non-sister chromatids of a bivalent 2. During metaphase I, each pair of homologous chromosomes is arranged independently and randomly at the metaphase plate.(independent assortment)

34. 3. Random fertilisation of ovum by a sperm Crossing over Independent assortment

35. Random fertilisation

36. The importance of controlled mitosis Divide in controlled and orderly manner To distribute an exact copy of chromosomes to new cells For the proper functioning of the organism Normal growth, development and maintenance Rate and time must be in correct manner Skin cells divide through out life Nerve cells, muscle cells and liver cells do not divide at all once they mature

37. Uncontrolled mitosis Factor Mutagen Chemical Physical X-rays, Gamma radiation Benzene, formaldehyde, tar in tobacco smoke Too much exposure to UV rays in the sunlight-damage the DNA molecule Specific proteins that trigger the replication of chromatin are not present Cell fails to divide Cell divide repeatedly

38. Cell divide repeatedly Due to severe disruption to the mechanism which controls the cell cycle Uncontrolled mitotic cell division can produce cancer cells Cancererous cells divide freely and uncontrollably without heeding the cell cycle control system These cells compete with the surrounding normal cells to obtain enough nutrients and energy for their own growth A cancerous cell divide uncontrollably to form a tumour Cancer cells can intrude on and spread to other tissues This lead to the malfunction of tissues and ultimately death

39. Comparison between mitosis and meiosis Similarity DNA is replicated once only before the start of mitosis and meiosis Differences Mitosis Meiosis Occurs in the cells of the reproductive organs Occurs in all somatic cells Produces new cells for growth and repair Produces gametes for sexual reproduction Synapsis occurs during prophase I to form bivalents Synapsis does not occur Crossing over between non-sister chromatids does not occur during prophase Crossing over between non-sister chromatids occurs during prophase I

40. Differences Mitosis Meiosis Chromosomes are arranged randomly at the metaphase plate during metaphase Homologous chromosomes line up side by side at the metaphase plate during metaphase I Sister chromatids are separate to move to the opposite poles during anaphase Homologous chromosomes are separated to move to the opposite poles during anaphase I Involves 2 times cell division; meiosis I and meiosis II Involves one time cell division 2 daughter cells are formed at the end of division 4 daughter cells(gametes) are formed at the end of division Daughter cells are diploid(2n) and have the same number of chromosomes as the parent cell Daughter cells are haploid(n) and have half number of chromosomes as the parent cell Daughter cells are genetically identical to the parent cell Daughter cells are genetically different to the parent cell

41. Appreciating the movement of chromosomes during mitosis and meiosis Flaws in the division Stage : Metaphase If the centromere does not divide, then sister chromatids are not separated. Predict the features of daughter cells produced after this cell division.

42. Stage : Anaphase Stage : Telophase

43. 1 daughter cell has 4 chromosomes and the other one has 3 chromosomes. The second daughter cell is abnormal Conclusion : The movement of chromosomes during mitosis and meiosis must occur in an orderly manner

44. Flaws in the division Stage : Metaphase I Stage : Anaphase I

45. Daughter cells produced after Meiosis I Undergo meiosis II

46. If the parent cell has 4 chromosomes, daughter cells must have 2 chromosomes at the end of meiosis 4 abnormal gamete cells are produced

47. Ovum If any of these abnormal sperms fertilises with a normal ovum, an abnormal zygote will be formed

48. Examples : Down’s syndrome 24 + 23 = 47 chromosomes Trisomy on chromosomes 21 Slanted eyes Normal Short stature Mental retardation

49. Turner’s syndrome 23 + 22 = 45 chromosomes One of X (sex chromosomes)chromosomes is missing Occurs in female Non-working ovaries, amenorrhea(absent of menstrual cycle), sterility, Congenital heart disease, hypothyroidism, (reduced hormone secretion by the thyroid), diabetes, vision problems, hearing concerns, autoimmune diseases. difficulties in visuospatial, mathematic, and memory areas Normal

50. Klinefelter’s syndrome 23 + 24 = 47 chromosomes In boys and men Extra one X chromosome in the sex chromosomes The male sperm fuses with the female egg, the fetal cells have at least one extra X chromosome A normal person, whether male or female, has a total of 46 chromosomes in the nucleus Of those 46 chromosomes, 44 are grouped in a total of 22 pairs and are called autosomes, the name given to the non-sex determining chromosomes that determine other characteristics In addition there are normally two sex chromosomes, females having two X chromosomes and males having one X and one Y The Y chromosome contains the male determining gene A normal male would have 44 autosomes and the X and Y sex chromosomes, making a total of 46 This is expressed as 46,XY and is known as that individual's karyotype The most common number of chromosomes found in KS is 47, that is 44 autosomes and 3 sex chromosomes giving a karyotype of 47,XXY