The Cell Cycle

1. The Cell Cycle Mitosis

2. Introduction Cell division is part of a life cycle for cells called the cell cycle. Cell division has 3 main functions: growth, reproduction, and repair. central to the development of a multicellular organism that begins as a fertilized egg or zygote. 2 trillion cells produced every day by humans, that is 25 million cells per second.

3. DNA and Chromosomes Before a cell can divide it must copy and distribute its genes equally in the dividing cell.

4. Cont�. cell�s genetic information, packaged as DNA, is called its genome, containing genes that code for proteins that control many aspects of life. To get 2 copies of our DNA 1 for each new daughter cell, the cell must copy 3m of DNA 6 billion nucleotides long. It accomplishes it in a matter of hours. Our DNA first gets condensed from an unwound form into tight packages called chromosomes Somatic cells = 46 2n or diploid: Sex Cells or gametes = 23 n or haploid

5. Cont�. Each chromosome has hundreds or thousands of genes When DNA is unwound it is called Chromatin, the chromatin winds around histones which then condense together. SEE PG 153 At the most condensed state is the chromosome. The X shape of chromosomes comes from sister chromatids pairing up. 2 chromatids are attached to each other at a point called a centromere. chromatids are separated during cell division and placed into each new cell ensuring that each new cell will have the same genetic information as the original.

6. Chromosome

7. Chromosome # Mosquito 6 Chimp 48 Human 46 Adders Tongue Fern 1,262 Potato 48 Plum 48 Dog 78 Myrmecia Australian Ant 1 Size: 500 chromosomes lined up end to end would fit across the thickness of a nickel.

8. Cell cycle 5 basic phases of a cells life; G1, S, G2, Mitosis, and cytokinesis cell spends 90% of its life in interphase, a collection of G1, S, and G2 phases. G1 Phase- The first Growth phase. During this phase a cell grows rapidly and carries out its routine functions. Cells not dividing remain in this phase. Most muscle and nerve cells never divide so they remain in this phase. If they die they can not be replaced. S phase- Known as the synthesis phase. DNA is copied in this phase. At the end of this phase each chromosome is now 2 chromatids attached at the centromere.

9. Cell Cycle Cont� G2- Second growth phase. Preparations are made for the nucleus to divide. Microtubules, or hollow protein fibers, are assembled and will be used to move the chromosome around and eventually separate them. Mitosis- Nucleus is divided into 2 nuclei each with the same # of chromosomes as the original. Has 5 steps. Cytokinesis- Is cell division in which the cytoplasm divides Mitosis and cytokinesis produce new cells identical to the original RBC lives for 120 days. Our bone marrow produces 2 million new RBC�s per second.

10. Cell Cycle

11. Control of Cell Cycle The cell cycle has checkpoints where feedback information from the cell can trigger the next phase Proteins are responsible for the control through bonding to signal receptors. 3 checkpoints: G1 checkpoint- makes the decision as to whether the cell will divide. If conditions are favorable. Like the cell is healthy and large enough proteins will stimulate the cell to start the S Phase. The cell cycle can also be stopped or sent to a resting point, Ex. Muscle and nerve cells, at this checkpoint.

12. Control Cont.. G2 checkpoint- DNA replication is checked hear by DNA repair enzymes. If the DNA is copied correctly with no errors proteins then signal mitosis phase. Mitosis Checkpoint- Triggers the exit from mitosis phase.

13. Loss of Control (Cancer) Cancer cells divide excessively and invade other tissues since they are free from our body�s control mechanisms. Cancer cells do not stop dividing when growth factors are depleted either because they manufacture their own Cancer cell may divide as long as you live if they have a continual supply of nutrients nearly all mammalian cells divide 20 to 50 times under culture conditions before they stop, age, and die. Cancer cells may be �immortal�??? Cells from a tumor removed from a woman (Henrietta Lacks) in 1951 are still reproducing in culture.

14. Cancer CANCER- certain genes called oncogenes contain the information needed to make the proteins that regulate cell growth and division. If one of these genes gets damaged in may not work correctly and disrupt cell growth and division. So cancer is a disorder of cell division. Cancer results from damage to a small set of genes that limits the ability of cells to divide normally. There are many causes of this damage like cigarettes, pollutants, and radiation just to name a few. The thing all of these have in common is the are all powerful DNA mutagens. The fact that cancer is caused by a mutation of cell DNA is widely accepted. Research indicated that only a few gene need to be mutated to cause cancer. A cell divides when it receives a signal, in the form of a chemical, to do so.

15. Cont.. The chemical substance is then bound to a receptor protein on the cell surface. This binding activates a second protein, second messenger, on the inside . Then a family of proteins relay the signal from protein to protein to the nucleus like a relay race in track. The genes that make these signal carrying proteins are called oncogenes and if they are changed by a mutation that makes them speed up cancer results. An increase in the activity of these proteins amplifies the divide signal and causes the cell to divide more often. However, our nucleus has breaks that can stop over division call tumor suppressor genes. In cancer theses genes are damaged and do not work properly. Cells have 3 kinds of TSG�s and all must be disabled for cancer to occur.

17. Cell Division (Mitosis) prophase,prometaphase,metaphase,anaphase, and telophase. 1. Prophase: chromosomes are tightly coiled, with sister chromatids joined together, nuclear envelope degrades, mitotic spindle begins to form

18. Prometaphase nuclear envelope fragments and microtubules from the spindle interact with the chromosomes attaching at the kinetochores, special regions of the centromere, where the microtubules attach

19. Metaphase Chromosomes are pushed to the middle of the cell where they line up along the metaphase plate an imaginary line in the middle of the cell

20. Anaphase the centromeres divide, separating the sister chromatids. Chromatids are pulled toward the pole to which it is attached by spindle fibers. By the end, the two poles have equal numbers of chromosomes

21. Telophase Two nuclei begin for form Chromosomes start to unwind Cytokinesis, division of the cytoplasm, begins.

24. Chromosome Movement

25. Cytokinesis

26. Plant Cell Division

27. Final View

28. References Jack Brown M.S. Biology Starr and Taggart: The Unity and Diversity of Life 10th edition: 2004: Thomson Brookes/Cole Campbell and Reece: Biology 6th edition. : 2002: Benjamin Cummings. Microsoft Encarta Encyclopedia 2004 Raven and Johnson: Holt Biology: 2004: Holt, Rinehart and Winston.