Why do cells divide?

1. Why do cells divide?

2. Why might a unicellular organism need to divide?

3. Why might a multicellular organism need cell division?

4. Cells use cellular transport to get material into and out of cells – what makes a cell more efficient at this?

5. In summary – we want cells with… • Large Surface Area • Small Volume • Large Surface Area/Volume Ratio

6. Some cells that have mastered this ideal…

7. Caution! • Rates of diffusion don’t change depending on the cell size!!!

8. Different types of Reproduction…

9. Sexual Reproduction Asexual Reproduction

10. DNA comes in various forms and genomes depending on the type of organism:

11. What does DNA look like in prokaryotes?

12. In eukaryotes – what is different?

13. In this unit, we will focus on the division of DNA in eukaryotic organisms: • The form of DNA in eukaryotic cells depends upon whether the cell is dividing or non-dividing: • 1) chromatin-unwound DNA + proteins • in non-dividing cells • 2) chromosomes-condensed DNA + proteins • in dividing cells

14. Why would it be an advantage to have the DNA in the form of chromatin in a non-dividing cell? • Why does the DNA condense into chromosomes before cell division?

15. From DNA to Chromosomes (a review)

16. What is a gene? ( a review) • A gene codes directly for the production of what? • This translates to what we see as …. • All the genes that make up the DNA of an organism are called….

17. Anatomy of Double Arm Chromosomes

18. Make a prediction… • Each double arm chromosome carries two identical copies of the genes – do you need both copies? • What do you think is going to happen to the chromosomes during cell division?

19. Cell Cycles and Mitosis

20. The Cell Cycle in Eukaryotes

21. So are my cells dividing….right now? At this exact moment, what phase of the cell cycle would most of your body cells be in? Interphase Some cells constantly divide to form new cells EXAMPLE: skin cells, stomach cells, stem cells, and cells in a developing embryo). Other cells don’t divide at all after the organism matures EXAMPLE: nerve and muscle cells.

22. Try to think of a helpful acronym to remember the phases correctly I nterphase P rophase M etaphase A naphase Telophase C ytokinesis I P lay M usic A t T he C lub

23. How often do cells divide??? • Nerve Cells • Most cannot divide (possible 30-50 years) • Muscle Cells • CANT! • Interferes with their function • Skin Cells • Every 20 days • Red Blood Cells • Every 120 days • Stomach Lining Cells • Every 2 days

24. Summary of Events in the Process of Mitosis and Cell Division Begin with: DNA Replication: Condense DNA: Split chromatids: End with: 46 (or 23 pairs) of double arm chromosomes 46 pieces of replicated chromatin 92 single arm chromosomes 46 pieces of chromatin per cell 46 pieces of chromatin in humans

25. PHASES OF THE CELL CYCLE

26. Interphase Period of cell growth and DNA replication. What types of processes might be taking place in a cell during interphase? Production of organelles, photosynthesis, Most of the cells’ metabolism occurs here. Is the cell shown below an animal or plant cell? Animal How can you tell? It has centrioles but not a cell wall

27. Interphase A. G1 phase—Period of Cell Growth Synthesis of proteins and cell organelles occurs in preparation for division. B. S phase—DNA Replication! C. G2 phase—Continued growth and preparations for cell division. Centrioles in animal cell divide.

28. MITOSIS: Prophase 1. Replicated DNA condenses into double-arm chromosomes. 2. Nuclear membrane breaks down and nucleoli disappear. 3. Spindle fibers form at ends of the cell. 4. Centrioles in animal cells move to opposite ends of the cell.

29. MITOSIS: Metaphase 1. Double-arm chromosomes line up on the middle or “equator” of the cell. 2. Spindle fibers attach to chromatids at the centromere. Equator Pole Pole

30. MITOSIS: Anaphase 1. Spindle fibers contract, causing centromeres to split and identical chromatids to separate. 2. Single-arm chromosomes move to opposite ends or “poles” of the cell.

31. MITOSIS: Telophase 1. Chromosomes unravel into chromatin. 2. Nuclear membrane reforms and nucleolus reforms. 3. Spindle fibers break down. 4. Furrow in animal cell forms (or cell plate in plant cells) as the cytoplasm begins to divide.

32. CYTOKINESIS A. Cytoplasm divides B. Furrow or cell plate is completed. C. Two, identical “daughter” cells are formed.

33. Differences Between Animal and Plant Mitosis and Cytokinesis • Centrioles organelles that aid in cell division that are only found in animal cells • Cytokinesis 1) Furrow-in animal cells indentations in the cell membranes 2) Cell platein plant cells- formation of the cell membrane from vesicles budding off the golgi apparatus-a new cell wall then grows from the formation of cellulose.

36. Frequency and length of time for the cell cycle depends on… • Type of cell- Skin, stomach, embryonic cells frequently divide Mature nerve, blood and muscle cells do not divide. • Size of cell (SA/V ratio) • Nutrients available • Density of cells. • Age of Cells- the ends of chromosomes (called telomeres) shorten each time a cell divides. After a certain number of divisions (about 50) the cell stops dividing. • Regulation of the cell cycle by proteins and external stimuli

37. Cancer A disease of the cell cycle

38. Uncontrolled Cell Growth = Cancer • Cancer = disorder, body cells lose the ability to control growth • Result when cell cycle regulation breaks down • the genes whose protein products that control the cell cycle are damaged • Some- will not respond to external growth regulators • Others- fail to produce internal regulators that ensure orderly growth • Result- Divide uncontrollably and form masses of cells called tumors

39. What are some causes of Cancer? • Tobacco • Radiation Exposure • Air Pollutants • Carcinogens (chemicals) • Virus • Cause mutations in genes • Inheritance