The Cell Cycle

1. The Cell Cycle

2. The Cycle of Life Unicellular Offspring Unicellular You Mitosis Multicellular You Meiosis

3. Why Must Cells Divide? • Cells must be small • As cells grow bigger, problems develop • DNA Overload • Same amount of DNA must serve larger and larger areas • Surface Area/Volume Ratio • Cytoplasm increases faster than cell membrane • Cell can’t exchange enough material • Material can’t reach center fast enough

4. Surface Area/ Volume Ratios • Surface Area (cube) = 6 x width2 • Volume (cube) = width3 • Surface Area/ Volume

5. Comparing Organisms • Unicellular • Single cell will go through cycle • When cell gets too large, it will divide • Produces two new cell, each one is its own organism • Form of asexual reproduction called binary fission • Each “offspring” is identical to the parent cell • Multicellular • Beginning Cell- Zygote • Cell(s) go through cell cycle to form parts of organism • Cell division continues through development, growth, repair, and wear and tear • Each division creates 2 new cells identical to the parent cell • In some species, can be used for asexual reproduction such as budding and fragmentation

6. DNA Review • Chromatin- • Form of DNA during interphase • Chromosome • Form of DNA during cell division • Centromere • center point holding two sister chromatids together • Sister chromatids • two copies of a chromosome held together by a centromere

7. Diploid • Diploid (2n) • Cells have 2 sets of chromosomes • one inherited from mom and one from dad • Found in somatic cells (all cells except sex cells) • Different number in different organisms • Humans diploid # is 46 • Homologous chromosomes- name of the 2 alike chromosomes from each set

8. Haploid • Haploid (n) • Cells have 1 set of chromosomes • Found in gametes (sex cells) • Diploid # / 2 • Human # is 23 (46 / 2) • When fertilization occurs, the organisms will have the diploid number again

9. Somatic Cells • All cells in a multicellular organism except sex cells • Beginning cell- zygote (fertilized egg) • Totipotent- able to divide and create all the cell types needed in the body • Starts dividing to form early embryo (at 5 days is called a blastocyst) • Pluripotent- able to divide and create many of the cell types needed in the body • Continues to divide to form the all the structures • Adult stem cells- found in various parts of the body • Multipotent- able to divide and create some of the cell types needed in the body

10. Cell Specialization • Also called cell differentiation • Many different cell types • Each has identical copies of DNA • Each type has a unique shape and function

11. The Cell Cycle

12. Interphase

13. Interphase

14. G1 • Gap phase • Cell grows and carries out normal functions

15. S Phase

16. G2 • Gap phase • Cell grows and carries out normal functions • Other organelles replicate

17. G0 • Some cells will never leave interphase or will stay in interphase for a very long time • Phase looks like G1 • These cells will not divide

18. Cell Division

19. Mitosis • Division of the nucleus of somatic cells • One division with 4 phases • Cell divides into two identical daughter cells • Cells start diploid and end diploid

20. Prophase

21. Prometaphase

22. Metaphase

23. Anaphase

24. Telophase

25. Cytokinesis

26. Animal vs Plant Cytokinesis • Animal • Cell membrane pinches together to form two cells • Plant • Cell plate forms • Will become cell wall to form two new cells

27. Controlling Cell Division • External Controls • Growth Factors and Hormones- stimulate cell division • Crowding- inhibits cell division • Internal Controls • Cyclins- proteins whose levels rise and fall during the cell cycle; must reach a certain amount and interact with kinases to create cell division • Checkpoints- check that cell cycle is proceeding correctly • S phase- checks if all DNA has been copied correctly • Metaphase- checks if all chromosomes are on spindle fiber

28. Cancer • Uncontrolled cell division • Usually results from mutations to • Oncogenes- accelerate the cell cycle • Genes that stop the cell cycle • p53 gene- normally stops cell division from occurring until all chromosomes are replicated • Cells are undifferentiated and don’t do their job • Benign tumors- stay clustered together • Malignant spread into other area creating problems (metastisize)

30. Asexual Reproduction • Occurs in • Unicellular prokaryotes • Unicellular eukaryotes • Some multicellular eukaryotes • Done by mitosis or processes similar to mitosis • Examples • Binary fission • Budding • Fragmentation

31. Sexual Reproduction • Combines genetic information from two parents • Creates a unique offspring • Parents create gametes (sex cells) using meiosis • In humans, egg and sperm

32. Meiosis

33. Characteristics • Meiosis • Occurs in games (sex cells) • 2 divisions with 4 phases each (8 phases total) creating 4 unique cells • Cells start out diploid and end haploid

34. Prophase I

35. Prometaphase I

36. Metaphase I

37. Anaphase I

38. Telophase I

39. Cytokinesis I

40. Meiosis II • Similar to mitosis • Two haploid cells created by Meiosis I both divide • Creates four haploid cells

41. Spermatogenesis • Formation of sperm • Starts at puberty • Forms 4 sperm during each meiosis • Men will make 5 to 200 million sperm/day

42. Oogenesis • Formation of the egg • Meiosis starts inside the womb, continues is some during every cycle after puberty • 1 egg and 3 polar bodies created after every meiosis • Egg must contain lots of cytoplasm to support the developing embryo after fertilization