Chapter 8 Cell Reproduction R. LeBlanc, MS MPHS Modified: 10/’11
Chromosome Structure • Chromosomes are rod-shaped structures made of DNA and protein. Chromatin uncoils to make RNA and replicate itself.
Most of cell’s life, chromosomes exist as chromatin (short strands of DNA wrapped around protein). • Before cell division chromatin threads coil (shorten and thicken) forming tightly packed chromosomes.
Chromosome Numbers of Various Organisms Each species has a characteristic number of chromosomes in each cell.
Sex Chromosomes and Autosomes • Sex chromosomes are chromosomes that determine the sex of an organism. • All of the other chromosomes in an organism are autosomes.
Chromosome Numbers • Diploid and Haploid Cells • Cells having two sets of chromosomes arediploid (2n). • Haploid cells (1n) have only one set of chromosomes.
Cell Reproduction • Cells divide so organisms can grow and replace damaged or worn out cells. • Binary fission is the process of cell division in prokaryotes.
Cell Division in Eukaryotes • Cell Cycle • The cell cycle is the repeating set of events in the life of a cell. • The cell cycle consists of cell division and interphase. • Cell division in eukaryotes includes nuclear division, called mitosis, and the division of cytoplasm, called cytokinesis.
Cell Cycle Introduction What are the three parts of the cell cycle? Interphase Mitosis Cytokinesis
Cell Cycle Sequence of growth and division of a cell: • 1. Growth: (Interphase) Most of a cell’s life • 2. Division: (Mitosis) Nucleus and cytoplasm divide to form 2 “daughter cells” identical to “parent cell”. • 3. Cytokinesis: The division of the cytoplasm equally into both new cells. Animal cells will develop a cleavage furrow which pinches in an eventually develops into 2 cells.
Comparing Cell Division in Plants and Animals • During cytokinesis in animal cells, a cleavagefurrow pinches in and eventually separates the dividing cell into two cells. • In plant cells, a cell plate separates the dividing cell into two cells.
Control of the Cell Cycle • When Control is Lost: Cancer • Cancer may result if cells do not respond to control mechanisms.
In the final stage of cancer, cells enter the circulatory system and spread throughout the body forming other tumors that disrupt normal functions. • Cancer - 2nd leading cause of death in U.S. (Heart disease = #1) • Cancerous cells take up space and deprive normal cells of nutrients.
Lung, Colon, Breast and Prostate cancers kill the most people in the U.S. • Both genetic and environmental factors are involved. • Environmental factors - Smoke, Air and Water pollution, Exposure to U.V. Radiation from sun, and some viruses. • Ex. Cancer patterns follow the country in which a person lives not their country of origin.
Interphase • “Resting Phase” - Nucleus is visible but chromosomes are not (thin chromatin). • G1: Protein production (normal cell growth). • S: DNA synthesis (replicates its chromosomes). • G2: Organelles are duplicated; the cell is preparing for cell division (mitosis).
Mitosis 4 phases • Prophase, Metaphase, Anaphase & Telophase
Prophase (Packed) • Chromatin coils into chromosomes (visible near center of cell). • Copies of chromosomes called sister chromatids held together by a centromere. • 2 centriolesmigrate to poles. • Nucleus disappears. • Nucleolus and nuclear envelope disintegrate. • Spindle fibers form between centrioles.
Metaphase (Middle) • Chromosomes attached to spindle fibers at centromeres. • Chromosomes line up at equator.
Anaphase (Away, Apart) • Sister chromatids separate at centromeres. • Spindle fibers “pull”chromatids to opposite poles.
Telophase (Two) • Chromatids are at opposite ends of cell. • Chromosomes uncoil into chromatin • Spindles break down. • Nucleolus and Nuclear membrane reappear. • Will result in formation of 2 “daughter cells”.
Section 3 Meiosis Chapter 8 Sexual Reproduction • Sexual reproductionis the formation of offspring through meiosis and the union of a sperm and an egg. • Offspring produced by sexual reproduction are genetically different from the parents (because of a process called crossing-over of genetic information).