Chapters 12 and 13

1. Chapters 12 and 13 • Objectives • Describe binary fission in bacteria • Describe the structures that play roles in the mitotic phase of the cell cycle: the centrioles, spindle microtubules and chromosomes • Outline the phases of the cell cycle • Describe the factors that control cell growth and how cancer results from a breakdown of this control • Outline the general progression and overall results of meiosis, contrasting them with mitosis

2. Explain how meiosis provides possibilities for genetic recombination

3. Introduction Ch12/13 • Life cycle is sequence of life forms from one generation to next • Sexual reproduction involves passing traits from two parents to next generation • Asexual reproduction involves passing traits from one parent to next generation • Cell division is basis of all processes that link phases of life cycle

4. Cellular Basis of Reproduction and Inheritance Chapter 12 and 13

5. Like beget like (more or less) • True only for organisms that reproduce asexually • single-celled organisms reproduce asexually by dividing in two • called binary fission • daughter cells receive identical copy of parent’s genes

6. offspring of multi-cellular organisms not genetically identical to parents • unique combination of parents traits • breeders of domestic plants and animals manipulate sexual reproduction by selecting offspring that exhibit desired traits

7. Cells arise from preexisting cells • cell reproduction called cell division • two roles • enables fertilized egg to develop through various stages to adult organism • ensures continuity from generation to generation

8. Binary Fission • Bacterial chromosomes • genes carried on single circular DNA molecule • up to 500x cell length • minimal packaging • complexed with few proteins and attached to plasma membrane at one point

9. Binary fission • prior to cell division, genome copied • copies attached to adjacent parts of membrane • cell elongation and new plasma membrane separates two genomes • plasma membrane pinches through cell

11. Eukaryotic Cell Division • Eukaryotes have large, complex, multiple chromosomes • human cells contain about 30,000-35,000 genes • organized into separate, linear chromosomes • DNA complexed with proteins • Just prior to division, chromosomes become visible • remain visible during division process

12. Somatic Cells • Somatic cells are body cells (not sex cells) • Ex. Hair cells These cells need to contain the full set of chromosomes so that all the directions for functions and activities of the cell can be carried out. Normally you inherit 23 chromosomes from each of your parents • This complete set of chromosomes (46) is known as the Diploid Number in Humans

13. Sex Cells (Gametes) • Sex cells are known as gametes • These cells have half of the number of chromosomes that a body cell would have. • In humans this number is 23

14. Sooooo..Somatic (body) cells contain the diploid number of chromosomes compared to sex cells (haploid number) • human cells: • somatic cells-46 chromosomes (2n=46) • sex cells-23 chromosomes (n=23)

15. What is a chromosome?????? • Prior to cell division, chromosomes are duplicated • visible chromosomes consist of two identical sister chromatids attached at centromere • sister chromatids are able to be separated… • Once sister chromatids separate they are again called chromosomes • I know you are all thinking: WHAAAAAAATTTTTT????????

17. Lets tie it all together • Humans have 23 pairs of chromosomes • They get numbers 1-23 from Mom and 1-23 from Dad = 46 • These 46 chromosomes are found in somatic cells • Sex cells ( gametes) have only 23 • Each species has a specific diploid number

18. Cell Cycle • The cell cycle is like a “ alarm clock” that tells the cell when it is time to do some essential activities and when to divide. • It is regulated by many chemicals inside the cell.

19. Cell Cycle • Cell cycle results in cell division • many cells in an organism divide on regular basis • dividing cells undergo cycle: sequence of steps repeated during each division

21. Cell Cycle Cont. • Cell cycle divided into several steps (phases) • interphase represents 90% or more of cycle time • G1-cell increases in size and increases supply of proteins and organelles • S-DNA synthesis occurs • G2-cell prepares for division, increases supply of proteins necessary for division, checks for DNA damage • G0 – cell stops progressing through cycle- will not divide

22. Cell Cycle • G0 = This is a very important phase of cellular activity • The cell has the opportunity to stop progressing towards division, or DNA synthesis • Why would this be important for a cell?????? • Cells can phase into and out of G0 from several other cell cycle phases, its like an escape hatch

23. Cell Cycle Cont. • Different cells are in various phases of cycle even in same tissue • Also Different Tissues May Regulate Cycle Differently • Ex. Hair Divides Constantly • Nerve Tissue Never Divides In Adults • Adult Liver Tissue Does Not Divide, Except For Repair

24. Cell Cycle cont. • How does a cell progress through the cell cycle? • Many biochemicals stimulate the transition • One of them is a Kinase • A Kinase is an enzyme that catalyzes the transfer of a phosphate group from ATP to another molecule.

25. How does a Kinase work ? • It works a bit like turning on a light switch…. • A PO4 is taken off ATP: • AT-PO4 - PO4 - PO4  AT-PO4 - PO4 + PO4 • The PO4 is placed onto an enzyme, which activates the enzyme • The enzyme ( and many other chemicals) now tell the cell to move to the next phase of its cell cycle

26. Soooooooooooooooooooooooooooo • If you are thinking…. Who cares???? • How is this relevant to my life????? • Get ready to write down the ways!

27. Cyclins • Cyclins are special chemicals that make the cell cycle go around • There are many different types

28. Cell Cycle cont. • A Cdk is a cyclin dependent kinase • MPF is a co- chemical that is attached to Cdk • These chemicals stimulate the transition to cell division. When they are HIGH, the cell will divide • Why do we care about this? • BECAUSE CYCLIN AND CDK LEVELS ARE ALTERED IN CANCER CELLS……..

30. Mitosis: Somatic Cell Division • mitotic (division) phase divided into two steps: • mitosis-nuclear division • cytokinesis-cytoplasmic division • result is two daughter cells with identical chromosmes

31. Mitosis • Somatic cells in humans have 46 chromosomes • At the end of mitosis will they be diploid or haploid and why?????

32. Mitosis • Interphase: not part of division; Cell does other work • Prophase (division beginning): mitotic spindle forms from MTOC’s; ends when chromatin coiled into chromosomes; nucleoli and nuclear membrane dissolved

34. Metaphase: spindle formed; chromosomes aligned single file with centromeres on metaphase plate; MAD • Anaphase: sister chromatids separate; migrate to poles • Telophase: reverse of prophase • Cytokinesis: division of cytoplasm • movement of chromosomes driven by addition or subtraction of protein subunits to kinetochore end of spindle microtubules

38. Cytokinesis differs in plants and animals • in animals, ring of microfilaments contracts around periphery of cell • forms cleavage furrow that eventually divides cytoplasm

40. in plants, vesicles containing cell wall material collect on spindle equator • vesicles fuse from inside out forming cell plate • cell plate gradually develops into new cell wall between new cells • membranes surrounding vesicles fuse to form new parts of plasma membranes

42. In Normal Cells • In mitotic normal mammal cells division only occurs 20-50 times prior to cell death. • Telomeres are the “cell clocks” that govern cell longevity • Telomeres shorten with each division; after about fifty times they reach a critical length and a division cessation signal is given

43. Factors Affecting Cell Division • Control of cell division important for proper growth, development and repair of organisms • growth factors regulate cell division • product of dividing cell • most plant and animal cells will not divide unless in contact with solid surface-anchorage dependence

44. Density Dependent Inhibition • division usually stops when single layer of cells formed and cells touch= density-dependent inhibition • due to depletion of growth factor proteins in cell mass

47. Three Cell Cycle Checkpoints • Three major check points in cell cycle • G1 of interphase • G2 of interphase • M phase • Release of growth factor/ chemical signals at each of these checkpoints allows cell cycle to continue • The cell will ultimately divide if not halted at a checkpoint