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The Cell Cycle

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  1. The Cell Cycle Chapter 12 VIEW SLIDES> TAKE NOTES TO ORGANIZE AND LEARN THE INFORMATION  ALL SLIDES, INFO FROM VIDEOS and question topics will be on exam #3 COMPLETE QUESTIONS FOR EACH SECTION.  SEND THE COMPLETED QUESTIONS by Monday Nov 7 to work submitted must be in the students own words


  3. The Key Roles of Cell Division • cell division =reproduction of cells • All cells come from pre-existing cells Thought question (do not turn in) What pre-existing cells did your cells come from?

  4. Unicellular organisms  division of 1 cell reproduces organism • Binary fission • ASSIGNMENT: View video on binary fission • QUESTION 1: • How frequently do some bacteria divide? • How does this explain their ability to expand their numbers quickly?

  5. Multicellular organisms Example: embryo adult Example: stomach lining is continually replaced Example: repair of burn • Why cells reproduce • Development/Growth • Replacement • Repair

  6. Watch the video • • Sea stars can reproduce cells in a way that humans cannot – view and understand.

  7. FYI • Three Hundred Million Cells Die In Your Body Every Minute • It does sounds like a lot but this is actually less than 0.0001% of the amount of cells being replaced in your body every day. (about 10-50 trillion cells are replaced in your body every day)

  8. Cellular Organization of Genetic Material • chromosome = strand of DNA • 2 sets of 23 chromosomes in humans = 46 • genome = All DNA in a single cell • single chromosome (prokaryotes) • many chromosomes (eukaryotes) Assignment: View the data on the website Explore the number of chromosomes in each type of organism’s cells. Question 2: • Is there a correlation between chromosome number and intelligence? Provide evidence to support your claim. 20 µm

  9. This is an electron micrograph of the 46 chromosomes in a human cell.

  10. chromatincomplex of DNA and protein Chromatin normally looks diffuse - hard to see individual chromosomes 20 µm

  11. Terms needed to continue • Haploid – a cell with one set of chromosomes • Diploid – a cell with two sets of chromosomes • Assignment. Visit the website • Question 3 • Look carefully at the list – are these diploid, or haploid chromosome numbers? • How many chromosomes are in the sperm of a fruit fly? • Which organisms have genome sizes similar to humans (Mb size is multiplied by 1 million for total size)

  12. Mitosis – cell division process to replicate cells • Ex. Skin cells do this • Meiosis – cell division process to generate unique haploid cells • Ex. Spermatogenesis, oogenesis

  13. BE ABLE TO DISTINGUISH BETWEEN MITOSIS AND MEIOSIS • Somatic cells= body cells (2 trillion in adult) • two sets of chromosomes (pairs= diploid) • Produced by mitosis - 1 diploid cell  2 identical diploid cells • Skin cells produced by mitosis  • Gametes sperm and eggs • have one set = haploid • Produced by meiosis – 1 diploid cell  4 unique cells • Occurs only in ovaries, testes Egg cell (oocyte) is a gamete produced by  meiosis

  14. Identical cells Unique cells Diploid Haploid

  15. Assignment: Read the textbook and study the previous slides to answer the following QUESTION 4 • A fruit fly sperm contains 4 chromosomes. How many chromosomes . Which of the cells below are diploid? (there are 6) - fruit fly wing cell - monkey liver cell - haploid cell - plant pollen (contains sperm) - gamete from a fern plant - fish somatic cell - fertilized whale egg - human embryo cell - cell produced by meiosis - cell with 2 sets of chromosomes - sperm of frog - unfertilized bird egg b. Which of the following terms are associated with mitosis (there are 6) - sperm - somatic - genetically identical - diploid - ovary - 2n - unique cells - liver cell - 46 chromosomes - 1 set of chromosomes - 4 daughter cells - gametes

  16. Cell Division also includes: • Nuclear division= division of the nucleus • Cytokinesis = division of cytoplasm View the video to compare • When both have occurred, there are 2 new cells, each identical to the “parent” cell

  17. The cell cycle = time from new cell to when it divides Interphase ~ 90% of a cell’s time cell is doing its normal activity during this time Mitosis - ~ 4o min cell is involved in replicating to make 2 new cells INTERPHASE S (DNA synthesis) G1 G2 MITOTIC (M) PHASE A cartoon showing the time cell spends in interphase and mitosis. Note that mitosis is short

  18. Now, we will examine the individual steps in the cell cycle. Give yourself enough time to understand each step before proceeding.

  19. INTERPHASE (~90% of the cell’s time in the cell cycle, not part of mitosis) • G1 phase – cell grows, gets ready • S phase – DNA replicates • G2 phase – cell grows, gets ready Watch the cell cycle video S (DNA synthesis) G1 G2 MITOTIC (M) PHASE

  20. Signs of interphase? • Note the distinct nuclear membrane • Note that the chromosomes inside the nucleus are not visible (they are too thread-like at this stage to see) Cell membrane Photo of a fish cell

  21. S phase of Interphase • Chromosomes replicate to form: • Sister chromatids = 2 for each chromosome, they are attached at thecentromere (constricted region) This is one chromosome that has replicated into a pair of sister chromatids

  22. All 46 chromosomes in a human cell have been replicated to form sister chromatids held together at the centromeres

  23. Assignment: review the textbook and notes Question 5 • Number of chromosomes in a human sperm or egg cell • Number of chromosomes in a human fertilized egg • Total number of sister chromatids in a human cell after S phase of Interphase (not sister chromatid pairs, individual sister chromatids)

  24. PHASES OF MITOSIS • Prophase • Metaphase • Anaphase • Telophase • Cytokinesis (division of cytoplasm) by late telophase

  25. I. Prophase of Mitosis A. Chromosomes condense = they become thicker and shorter B. Nuclear membrane breaks apart C. Mitotic spindle forms from centrioles WATCH THE PROPHASE VIDEO

  26. A chromosome in prophase= 2 identical sister chromatids held together at centromere

  27. Note the absence of a nuclear membrane in the cell that has entered prophase The nuclear membrane is breaking up A fish cell

  28. Prophase of mitosis This is a slide of onion cells with chromosomes stained red View: condensed chromosomes in prophase and absence of nuclear membrane Cannot see the mitotic spindle in this photo

  29. The mitotic spindle in prophase • Remember the centrioles • They have replicated and moved to opposite sides (poles) of the cell • AND, microtubules have grown from them – the red lines – they attach to the centromeres of the sister chromatid pairs • The microtubles are called spindle fibers

  30. • Scitable is a website that contains information on many aspects of biology and genetics. The components of the mitotic spindle are covered here. • You may need to register, its free. If you do not have a textbook, the definitions on Scitable will be useful to you.

  31. Assignment: Read the text and study the slides. Question 6 • Are the two sister chromatids that compose a chromosome in prophase identical? • To what structure do the mitotic spindle microtubules attach on the chromosomes? • What are the components of the mitotic spindle? • What are centrioles composed of? • What is meant by “chromosomes condense” ? WATCH THE PROPHASE VIDEO

  32. II. Metaphase of mitosis • chromosomes (still in sister chromatid pairs) line up at the metaphase plate • midway between spindle’s two poles Centrioles with spindle fibers Chromosomes are lined up Fish cell

  33. Metaphase plate Centriole with spindle fibers The chromosomes here do not look as neat – but their centromeres are in a line on the metaphase plate

  34. Assignment: Watch the metaphase video Question 7 • How can you determine visually that a cell is in metaphase? • About how long in minutes or hours is metaphase? • Is the spindle apparatus (mitotic spindle) obvious during metaphase? • Are the sister chromatids still attached at the centromere during metaphase?

  35. III. Anaphase • sister chromatids separate ! They split into individual chromosomes. • Mitotic spindle shortens –to move newly separated chromosomes toward opposite ends of cell • This is tightly controlled – need a full set of chromosomes moving to each side! Plant cell chromosomes in red

  36. Fish cell – note that a set of chromosomes, is moving to each end of the cell. The cell also is huge

  37. Assignment: Watch the anaphase video • Question 8 a. Once sister chromatids have split, what are they referred to as? b. About how long does anaphase of mitosis take? c. Does each side of the cell have a full set of chromosomes at the end of anaphase? d. What happens to the mitotic spindle?

  38. IV. Telophase of mitosis • Identical nuclear membranes form around each set of chromosomes • Chromosomes start to decondense

  39. Cytokinesis • Division of cytoplasm • animal cells • cleavage furrow • plant cells • cell plate

  40. Cleavage furrow in dividing cell 100 µm Cleavage furrow Daughter cells Contractile ring of microfilaments (a) Cleavage of an animal cell (SEM)

  41. Cell plate in plant cell Vesicles forming cell plate Wall of parent cell 1 µm Cell plate New cell wall Daughter cells (b) Cell plate formation in a plant cell (TEM)

  42. Assignment: Read textbook and study slides • Question 9 • Identify the phase in A – D of this photo • List one feature that tells you the cell in in that particular phase of mitosis C A B D

  43. A plant cell in interphase Nucleus Chromatin condensing Nucleolus 1 Prophase

  44. prophase Chromosomes 2 Prometaphase

  45. metaphase 3 Metaphase

  46. anaphase 4 Anaphase

  47. Telophase and cytokinesis with cell plate 10 µm Cell plate Cell plate 5 Telophase

  48. Onion cells in various stages of the cell cycle

  49. Assignment – read textbook and study slides Question 10 Fill in the appropriate phase of mitosis or interphase: • DNA synthesis occurs : ____ • Interphase consists of subphases: ____ ____ ____ • Sister chromatids form : ____ • Stage that involves a cleavage furrow ____ • Beginning of cell cycle ____ • Sister chromatids separate ____ • The nuclear membrane is visible ____ • Chromosomes condense ____ • Centromeres line up ____ • 1 cell divides into two cells ____ • A distinct nuclear membrane is visible____ VIDEOS TO ASSIST YOU next page

  50. sumanas • ms stokes bio • pisgahscience • Kyrk