Cell Division and Genetic Material

1. Cell Division and Genetic Material SBI 3U Section 4.1 pp.160- 168

2. Cell Theory • All living things are composed of one or more cells • Cells are the smallest units of living things • New cells come only from pre-existing cells by cell division

3. The Cell Cycle • The cell cycle is the process of growth and division of cells • Three functions of cell division in multicellular organisms: 1. Growth of organism 2. Repair of damaged tissues and organs 3. Replacement of dying or dead cells

4. Stages of the Cell Cycle • Interphase – cell carries out normal functions, grows and makes copies of its genetic material • Mitosis – cell’s nucleus and genetic material divide • Cytokinesis- cell cytoplasm divides and a new cell is created

5. Interphase Occurs before mitosis begins G1 Phase – is a major period of growth for the cell, proteins and enzymes required for DNA replication are synthesized S Phase - Chromosomes are copied (# doubles) and appear as threadlike coils (chromatin). G2 Phase – Cell continues to grow and synthesizes molecules needed for mitosis Cell membrane Nucleus Chromatin cytoplasm

6. Interphase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

7. Prophase(First phase of Mitosis) • Cells chromatin condenses into chromosomes (which contain DNA) • Each chromosome is attached by a centromere to an identical copy (sister chromatid) • Nuclear membrane breaks down and nucleolus disappears • Centrosomes form spindle fibres made from microtubles and move apart to opposite poles of the cell

8. Prophase Plant Cell Animal Cell Spindle fibers Centrioles Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

9. Metaphase • Spindle fibres which attached at the centromere guide the chromosomes to the equator (center line) of the cell

10. Metaphase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

11. Anaphase • Centromeres split apart and sister chromatids separate from each other • Spindle fibres shorted pulling chromosomes to opposite poles of the cell

12. Anaphase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

13. Telophase • Chromosomes have reached opposite poles of cell and begin to unwind • Spindle fibres break down and nuclear membrane forms around new set of chromosomes • Nucleolus reforms

14. Telophase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

15. Cytokinesis • Cytoplasm divides equally between two halves of the cell • Plant Cell: Cell plate forms between two halves of cell, cell walls form on either side of cell plate, two daughter cells separate out • Animal Cell: Indentation forms along equator of the cell, cell is pinched into two daughter cells

16. Animal Cell Plant Cell

17. DNA Structure

18. DNA Structure • DNA consists of two molecules that are arranged into a ladder-like structure called a Double Helix. • A molecule of DNA is made up of millions of tiny subunits called Nucleotides. • Each nucleotide consists of: • Phosphate group • Pentose sugar • Nitrogenous base

19. Nucleotides Phosphate Nitrogenous Base Pentose Sugar

20. Pentose Sugar 5 4 1 • 5 Carbon sugars • Carbons numbered 1 through 5 • RNA – Ribose • DNA – deoxyribose • Difference is the hydroxyl group on #2 carbon 3 2

21. Nucleotides • The phosphate and sugar form the backbone of the DNA molecule, whereas the bases form the “rungs”.

22. Phosphodiester Bonds • The backbone is made up of sugars and phosphates joined by phosphodiester bonds

23. DNA is antiparallel

24. The 4 (5) Nitrogenous Bases Hey!!! Don’t forget about me!!!

25. The 4 Nucleotides A T C Adenine Thymine G Guanine Cytosine

26. Nucleotides • Each base will only bond with one other specific base. • Adenine (A) • Thymine (T) • Cytosine (C) • Guanine (G) Form a base pair. Form a base pair.

27. Base Pairing • Because of this complementary base pairing, the order of the bases in one strand determines the order of the bases in the other strand.

28. A T A A A T T T C C C G G G

29. DNA Replication • When DNA is replicated during interphase, the double helix unwinds and each strand of DNA serves as a template for a new strand

30. Chromosomes • Number of chromosomes each cell contains varies between species • Human somatic cells (cells that form the body of an organism) have 46 chromosome organized into 23 pairs Sex Chromosomes – pair of chromosomes that determine sex of an organism. Human females have 2 paired X chromosomes and human males have paired X and Y chromosomes Autosomes – The remaining 22 pairs of chromosomes Genes – sections of DNA that contain genetic information for the inheritance of specific traits

31. Chromosomes (Continued) Alleles – Different forms of the same gene e.g. the gene for hair colour could include the following alleles: brown, blond, red and black hair Homologous Chromosomes – chromosome pairs of approximately the same length, centromere position and banding pattern with one chromosome inherited from the mother and the other from the father. • Genes that code for the same characteristic are present on the same loci (location) on each chromosome but could contain different alleles of the gene Karyotype– The complete set of chromosomes that an individual has. Humans have 22 autosomes and one pair of sex chromosomes

32. Sexual Reproduction SBI 3U Section 4.2 pp.169-180

33. Reproduction • Mitosis is a form of asexual reproduction that produces exact clones of somatic(body cells) cells within an organism • Humans reproduce through sexual reproduction in which two parents produce a genetically distinct offspring • Two gametes which are Male reproductive cells(sperm) and female reproductive cells(egg) merge to form a zygote in a process called fertilization

34. Gametes are haploid meaning they have half the number of chromosomes (n) that diploid somatic cells have (2n) • In humans the gametes contain n=23 chromosomes and fuse to form a zygote which has 46 chromosomes (n + n = 2n) n Zygote 2n n Haploid

35. Meiosis – Producing Haploid Gametes Meiosis has two key outcomes: • Genetic Reduction – daughter cells are produced with half the number of chromosomes as the parent cell • Genetic Recombination – The products of meiosis have different combinations of alleles giving rise to offspring that are genetically different from each other

36. Stages of Meiosis Interphase diploid germ cell undergoes growth and chromosomes are replicated Prophase 1 Synapsis- homologous chromosomes (one from each parent) each with a sister chromatid attached by a centromere line up side by side held tightly together along their lengths. Nonsisterchromatids exchange pieces of chromosome in a process called crossing over

38. Prophase I (continued) • The centrosomes move to the poles of the cell and the spindle apparatus forms Metaphase I Independent Assortment -Pairs of homologous chromosomes line up along the equator of the cell with the maternal pair facing one pole and the paternal pair facing the other pole in a totally random process. The number of genetically distinct gametes that can be produced is 2n where n is the number of chromosome pairs in the diploid cell • Spindle fibres attach to a site on the centromere of each chromatid pair called the kinetochore

39. Anaphase I • The homologous chromosomes separate and move to opposite poles of the cell • The centromere’s don’t split like in mitosis and the sister chromatids are still held together resulting in a single chromosome made up of 2 sister chromatids • The number of chromosomes is reduced from 2n (diploid) to n (haploid) Telophase I • Homologous chromosomes uncoil and spindle fibres disappear. Cytokinesis occurs creating 2 haploid cells.

40. Meiosis II • The phases of meiosis II are similar to that of mitosis except that the cell that undergoes division is haploid Prophase II- nucleolus and nuclear envelope disapear and centrioles move towards the poles Metaphase II- sister chromatids move to equator Anaphase II- centromeres split and sister chromatids are pulled apart toward opposite poles Telophase II - chromosomes uncoil, spindle disapears and nuclear envelopes reform. Cytokinesis occurs creating 2 haploid cells. • The final result of meiosis is the creation of 4 haploid cells

41. MEIOSIS I: Homologous chromosomes separate INTERPHASE PROPHASE I METAPHASE I ANAPHASE I Centrosomes(withcentriolepairs) Microtubules attached tokinetochore Metaphaseplate Sister chromatidsremain attached Sites of crossing over Spindle Nuclearenvelope Sisterchromatids Tetrad Centromere(with kinetochore) Homologouschromosomes separate Chromatin

42. MEIOSIS II: Sister chromatids separate TELOPHASE IAND CYTOKINESIS TELOPHASE IIAND CYTOKINESIS PROPHASE II METAPHASE II ANAPHASE II Cleavagefurrow Sister chromatidsseparate Haploiddaughter cellsforming

43. Independent Assortment

44. Genetic Variation in Meiosis • Meiosis provides for a vast amount of genetic variation • Crossing over – in prophase I, chromosomes exchange DNA • Independent Assortment – in anaphase I homologs independently separate, in anaphase II sister chromatids independently separate • Additional genetic variation is achieved through mating of non-related individuals

45. Errors Caused by Changes in Chromosome Structure due to crossing over Deletion - A piece of chromosome is deleted Duplication – A section of a chromosome appears two or more times Inversion – A section of a chromosome is inverted Translocation – A segment of one chromosome becomes attached to a different chromosome

47. Errors in Meiosis • Nondisjunction occurs when either:  • homologues fail to separate during anaphase I of meiosis, or  • sister chromatids fail to separate during anaphase II. • Trisomy - one extra chromosome (2n +1) • Monosomy - one missing chromosome (2n - 1)

49. Down syndrome(trisomy 21): The result of an extra copy of chromosome 21. People with Down syndrome are 47, 21+. Down syndrome affects 1:700 children and alters the child's phenotype either moderately or severely: - characteristic facial features, short stature; heart defects - susceptibility to respiratory disease, shorter lifespan - prone to developing early Alzheimer's and leukemia - often sexually underdeveloped and sterile, usually some degree of mental retardation. - Down Syndrome is correlated with age of mother but can also be the result of nondisjunction of the father's chromosome 21.

50. Monosomy X (Turner's syndrome): 1:5000 live births; the only viable monosomy in humans - women with Turner's have only 45 chromosomes!!! XO individuals are genetically female, however, they do not mature sexually during puberty and are sterile. Short stature and normal intelligence. (98% of these fetuses die before birth)