Asexual Reproduction, The Cell Cycle and Mitosis

1. Name________KEY_______________________ Asexual Reproduction, The Cell Cycle and Mitosis General Biology

2. Reproduction • All Cells come from other cells (Remember the cell theory?) • Asexual – Organisms formed by only one parent; offspring are identical; fast; fine for environments that don’t change frequently since each organism is a clone • Sexual – Organisms formed by two parents; offspring are not identical; helpful in environments that change frequently since each offspring is unique

3. Cell Size • Most cells are small . • Why do you think that is? • Most cells range from about 1 to 1000 m (Most are less than 1mm in diameter). • Prokaryotic Cells are usually smaller than Eukaryotic cells.

4. http://www.southtexascollege.edu/nilsson/Scanned_download_f_Fall2010_f/04_F4_2_CellSize.jpghttp://www.southtexascollege.edu/nilsson/Scanned_download_f_Fall2010_f/04_F4_2_CellSize.jpg

5. Surface Area to Volume Ratio • Surface Area = area of the cell membrane • Should be high so the cell has many opportunities to exchange materials with the environment by active and/or passive transport • Volume = the amount of space the “insides” take up • Should be low compared to the surface area so the cell’s needs/demands are reasonable for what the surface area can handle

6. Cell Surface Area & Volume CLICK • As a cell grows, its volume increases at a faster rate than its surface area. • A cell will function best with a HIGH surface area to volume ratio. (SA ÷ Vol = SA to Vol Ratio)

7. Muscle Cells: Nerve Cell: • Notice that both the muscle cells and nerve cell have a large volume. Therefore they both have elongated shapes to maximize their surface areaand give a HIGH SA/Vol ratio for maximum efficiency.

9. Divide or else!… • When a cell’s volume starts to become so great that the surface area is insufficient to serve the needs of the cell, it must divide. • The cell divides into two identical smaller cells which now each have a very HIGH surface area to volume ratio again. • The cycle repeats.

10. When/Why do Cells Divide? • In Unicellular Organisms: • Cells divide for reproduction. • 1 cell (organism) divides into 2 cells (organisms) which are identical. • In Multicellular Organisms: • Growth (more cells = bigger organism) • Replace/repair lost or damaged cells to maintain the body’s tissues and organs.

11. How often do cells divide and how fast does Cell Division occur? • Some cells reproduce rapidly, others slowly • Cell division takes place rapidly in fetuses, embryos, young organisms • Average Cell division times for normal, healthy cells: • Fly embryo 8 mins • Bacteria 20 mins • Yeast 2 hours • Human skin cells 20-24 hours • Human sperm cells about 64 days • Human liver cells 1 year or more • Human nerve cells – never, once mature Source:://www.wisegeek.org/how-long-does-it-take-for-cells-to-divide.htm

12. DNA Replication • When/why does DNA replicate? 1) _______ Two Identical Copies of the original DNA 2) _______ Original DNA 3) _______ The DNA unzips 4)_______ New DNA ends with one parent strand and one daughter strand. 5)_______ DNA Polymerase enzyme pairs complimentary nucleotides to the parent strands

13. Chromatin vs. Chromosome #1, 2, 3 – DNA double helix winds around histones. This form is CHROMATIN. #4, 5 – After the DNA copies it condenses more tightly and stays attached to its replica. This form is a DOUBLE ARMED CHROMOSOME made of two identical SISTER CHROMATIDS.

14. Chromatin vs. Chromosome • CHROMATIN (long and thin) • “working” form of DNA; loosely coiled • DNA is in this form most of the time • Codes can be used for protein synthesis • Can be copied • CHROMOSOME (move your home) • Tightly coiled/condensed form of DNA • Only during cell division • Already copied • Codes inaccessible; cannot be used for protein synthesis

16. Chromatin DNA is very long and stringy – see picture at left which shows only a small part of the DNA of a single human chromosome. (human body cells contain 46 chromosomes each!!) http://www.ultranet.com/~jkimball/BiologyPages/M/Mitosis.html (provided by J. R. Paulson and U. C. Laemmli)

18. The Cell Cycle • = Life cycle of the cell • In general, a cell will undergo growth for a while then it will copy its DNA and divide into two identical “daughter” cells. • Each step must be complete before the next one can begin. • The DNA gets “proofread” and there are several “checkpoints” during the cell cycle to help make sure the cell goes through the stages properly

19. The Cell Cycle Click here for animation!

20. The Cell Cycle • INTERPHASE – period between cell divisions • G1: Growth, normal cell functioning • S:DNA replication • G2: Further Growth to prepare for cell division • CELLDIVISION • Mitosis – Separate the Chromosomes • Prophase, Metaphase, Anaphase, Telophase • Cytokinesis – Divide into two genetically identical cells

21. Can you name the parts of the cell cycle? • A. • B. • C. • D. • E. • F. • G. • H. • I.

22. MITOSIS • Definition: • The part of eukaryotic cell division during which the cell nucleus divides. • Condense the replicated DNA into chromosomes, divide it into two identical sets so that the cells can then be split. • Don’t forget – Interphase comes before Mitosis, and Cytokinesis comes after mitosis. • NOTE: Remember I-P-M-A-T-C • Not used to make sex cells (that is meiosis, which we will discuss later).

23. What cell parts are involved in mitosis? • Typical animal cell: • Surrounded by cell membrane • Most material inside called cytoplasm • Contains a nucleus • Nuclear membrane surrounds nucleus • Chromosomes are found inside nucleus • Centrioles present in the cytoplasm. (cytoplasm) (nucleus) (nuclear membr.) (cell membrane) http://www.accessexcellence.org/AB/GG/ membranes.html

24. Steps of MITOSIS • PROPHASE • METAPHASE • ANAPHASE • TELOPHASE Click here for animation!

25. Imagine a cell with just 4 chromosomes… • An important step takes place in the nucleus of every cell before mitosis begins (during “Interphase”). • EACH CHROMOSOME BECOMES DOUBLED. • The two strands of each doubled chromosome are held together at one point. • The two strands of a chromosome after it becomes doubled are called sister chromatids. • Each chromatid is an exact copy of the original chromosome. • The centrioles also double just before mitosis begins.

26. INTERPHASE • Cells not undergoing division stay in this phase. (But a cell is never truly at “rest”!) • If a cell is going to undergo mitosis, it is during the “S” phase of interphase that its chromosomes become doubled. Although the chromosomes have doubled, you would not be able to see them with a light microscope at this stage. They are still too fine and stringy.

27. Steps of Mitosis • Step 1: Prophase • Sister chromatids begin to shorten and thicken. In fact, they can be seen using a light microscope at this stage. • The nuclear membrane begins to break down. • The centrioles move away from each other • Fibers form between the centrioles. These fibers make up a spindle made of strands of protein that stretch between the two ends of the cell http://clab.cecil.cc.md.us/faculty/biology1 /mitosis.htm http://www.uoguelph.ca/zoology/devobio /210labs/mitosis1.html

28. Steps of Mitosis • Step 2: Metaphase • The centrioles move to opposite ends of the cell. • The fibers (spindle) stretch between the 2 ends of the cell. • The doubled chromosomes attach to the fibers at the point where the 2 sister chromatids are attached to each other. • The doubled chromosomes (pairs of sister chromatids) become lined up along the center of the cell (the “equator”). http://clab.cecil.cc. md.us/faculty/ biology1/mitosis.htm http://www.uoguelph.ca /zoology/devobio/ 210labs/mitosis1.html

29. Steps of Mitosis • Step 3: Anaphase 1. The two sister chromatids of each doubled chromosome are pulled apart by the fibers. • The fibers pull each chromatid toward the centrioles at the opposite ends of the cell. Remember that each chromatid is an exact copy of one original chromosome. http://www.uoguelph.ca /zoology/devobio/210labs /mitosis1.html http://clab.cecil.cc.md.us/ faculty/biology1/mitosis.htm

30. Steps of Mitosis • Step 4: Telophase • Each end of the cell now has a complete set of chromosomes. The number of chromosomes will equal the number seen in the starting cell from Step 1. • The spindle fibers begin to disappear. • The nuclear membrane begins to reform. • The cell membrane pinches in until the cytoplasm is divided into 2 new cells. The cells are identical to each other and to the original cell that started Step 1. http://www.uoguelph.ca/zoology/devobio/210labs/mitosis1.html http://clab.cecil.cc.md.us/faculty/biology1/mitosis.htm

31. How is Mitosis different in Plant Cells? • The process proceeds in basically the same steps, but there are two major differences in plant cells: • 1. Plant cells form the spindle fibers without using centrioles. • 2. A cell plate helps form new cell wall at the end of telophase to separate the 2 new cells. http://www.microscopy-uk.org.uk/mag/artaug99/mitosis.html Notice in the root tip cells seen above, you can see many different plant cells in various stages of mitosis.

34. Can you Identify the Stages of Mitosis shown?

35. Can you identify the stages of mitosis in this sketch?

36. Changes in the Rate of Mitosis • Even in healthy cells, the rate of mitosis is different for different types of cells. • The rate of mitosis can speed up or slow down. • Aging involves mitosis slowing down. • Cancer involves rapid, uncontrolled mitosis.

37. Aging • The process of becoming older. • You are born with a certain number of muscle cells. As you become older, the muscle cells wear out, and no new ones replace them. So, for example, the heart weakens. • Some of the common signs of aging (loss of hair, wrinkled skin, loss of calcium in bones, fingernail growth slowing down) may be due to an overall slowing (or stopping) of mitosis in various body tissues.

38. American Cancer Society Website http://www.cancer.org Cancer • Healthy cells reproduce at a regular, predictable rate. • Canceris a disease of the cell cycle in which body cells reproduce at an abnormally fast rate. • Cancer results from mutations in genes which control the cell cycle. Follow the changes in lung tissue as the outer layer of cells become rapidly multiplying cancer cells.

39. Click here for Cancer Biology video What causes cancer? • Three well-known causes of cancer: • chemicals (carcinogens) • toxic wastes, asbestos, tobacco products • radiation • nuclear radiation, UV radiation from sun, high levels of Xrays • certain viruses • cells multiply out of control to form a mass of abnormal cells, called a tumor. Tumors can crowd out normal tissue and affect the functioning of organs. If pieces of a tumor break off and spread to other parts of the body, the tumor is referred to as malignant. If the tumor stays in one place, it is called benign.

40. How is cancer treated? • Generally treatment involves some combination of the following steps: • surgery to remove as much of the tumor as possible • chemotherapy – treatment with drugs which kill any cells which are rapidly multiplying • radiation – targeted to kill the cancerous cells • The best strategy is to reduce your cancer risk in the first place!! • Proper Diet, Exercise, Avoid known cancer risks