1. Cell Reproduction

2. Reproduction of Prokaryotes Prokaryotes reproduce through a process called binary fission The single, circular chromosome (which is attached to the plasma membrane) replicates The cell grows & elongates, separating the two chromosomes The plasma membrane and cell wall pinch inward, eventually forming two daughter cells

4. Eukaryotic Chromosomes and Cell Division Almost all of a eukaryotic cell’s genes are found in the cell’s nucleus, and are grouped into multiple chromosomes Chromosomes are only visible when a cell is in the process of dividing The rest of the time, the DNA + protein threads exist as a diffuse mass called chromatin

5. Before dividing, the eukaryotic cell replicates its chromosomes The two copies of the chromosome are called chromatids, and they are connected to each other at a region called the centromere The pair of chromatids is still only one chromosome, and the chromatids are not considered chromosomes until they separate from one another

7. The Eukaryotic Cell Cycle A eukaryotic cell spends most of its time in interphase, the period of time between cell divisions During interphase, metabolic activity is high; the cell grows, produces cell parts, and in the middle of interphase the cell’s chromosomes duplicate Interphase accounts for 90% of the total time required for the cell cycle

8. Interphase Interphase may be divided into three subphases The first subphase is called G 1 (the G is for gap); the cell is producing proteins and organelles The second subphase is the S phase, which is when DNA synthesis occurs The third subphase is called G 2, which is a time of metabolic activity; proteins needed for cell division are produced

9. Mitotic Phase (M Phase) Consists of two processes: mitosis and cytokinesis During mitosis, the chromosomes divide and are distributed into two daughter nuclei During cytokinesis, the cytoplasm is divided into two These two processes result in the production of two genetically identical daughter cells

11. Phases of Mitosis - Prophase Chromatin fibers condense Nucleoli disappear Each chromosome has two chromatids joined at the centromere The spindle begins to form; microtubules grow out of the centrosomes, which contain centrioles The nuclear envelope fragments

12. Microtubules grow until they can reach the chromosomes Each chromatid has a special region at the centromere, called the kinetichore, where the spindle will attach Spindles that don’t attach to kinetichores extend toward the opposite side of the cell The chromosomes begin moving toward the center of the cell

13. Phases of Mitosis - Metaphase The spindle is fully formed All of the centromeres of the chromosomes are lined up at the metaphase plate (the middle of the cell) The kinetichores of the chromatids face opposite sides of the cell

14. Phases of Mitosis - Anaphase The centromeres of the chromosome come apart and the sister chromatids separate (they are now considered daughter chromosomes) Motor proteins on the kinetichores walk the chromosomes toward opposite sides of the cell Kinetichore microtubules shorten and non- kinetichore microtubules lengthen (the cell elongates)

15. Phases of Mitosis - Telophase Basically the reverse of prophase Cell elongation that began in anaphase continues Daughter nuclei appear-nuclear envelope appears Chromatin fibers uncoil Nucleoli reappear Spindle disappears

16. Cytokinesis Occurs along with telophase In animal cells, cytokinesis involves a cleavage furrow, which pinches the cell in two In plants, cytokinesis involves a cell plate, which grows outward and accumulates cell wall material

25. The Cell Cycle & Cancer Cancer is a disease of the cell cycle Systems that control the cell cycle do not work in cancer cells As a result, cancer cells divide excessively and can invade other body tissues The excessive growth can result in an abnormal mass called a tumor

26. Tumors Benign tumor-abnormal mass of normal cells; can cause problems if they grow in an organ; remain in their original site; can usually be completely removed by surgery Malignant tumor-cancerous; capable of spreading to other body areas; displaces normal tissue; can form new tumors by breaking apart and spreading through the circulatory system (called metastasis)

27. Types of Cancers Carcinomas-originate in the external or internal coverings of the body (skin) Sarcomas-originate in tissues that support the body (bone and muscle) Leukemias and Lymphomas-cancers of blood forming tissues (bone marrow, spleen, and lymph nodes)

28. Treatments for Cancer Radiation- parts of the body with cancerous tumors are exposed to high energy radiation, which disrupts cell division (damage to ovaries or testes may cause sterility) Chemotherapy-administration of drugs that disrupt cell division; some interfere with the formation or functioning of the spindle

29. Meiosis Essential for the formation of gametes (ova and sperm) that will be used for sexual reproduction Occurs in two consecutive cell divisions Reduces the chromosome number by ½ (for humans, this means creating gametes that have 23 chromosomes)

30. Human Chromosomes Occur in pairs (there are 23 pairs) in somatic cells (typical body cells); these are called diploid cells (di=2) Occur unpaired (a single set of 23) in the gametes; these are called haploid cells The paired chromosomes in somatic cells are called homologous chromosomes, because they have genes for the same traits

32. Human Chromosomes 22 of the chromosome pairs are called autosomes The 23 rd pair consists of the sex chromosomes Human females have a pair of sex chromosomes called X chromosomes (XX) Human males have one X chromosome and one Y chromosome (XY)

33. Inheritance of Human Chromosomes One chromosome from each pair is inherited from our mothers, and the other chromosome in the pair is inherited from our fathers At the time of fertilization, the two haploid gametes (sperm and ovum) unite to form a diploid cell called the zygote Fertilization results in the formation of a diploid cell, thus restoring the normal diploid number of human chromosomes

34. Meiosis Produces Gametes Meiosis occurs in the reproductive organs