Unit Three Cell Proliferation and Genetics Mitosis Prokaryotic

Unit Three “Cell Proliferation and Genetics” “Mitosis”

Prokaryotic Cell Cycle § Prokaryotic cell division occurs in two stages, which together comprise a “Simple Cell Cycle” – A) DNA Replication – B) Cell divides in process known as “Binary Fission” *** Each new cell contains one chromosome and is a complete prokaryotic organism

Eukaryotic Cell Cycle § The eukaryotic cell cycle is much more complex than that of prokaryotes due to the following factors: – 1. cells are larger – 2. many more organelles – 3. much more DNA arranged in linear segments known as “Chromosomes” – 4. cell division is more complex due to above factors

Eukaryotic Cell Cycle

Eukaryotic Cell Division § Division of nonreproductive cells is called “Mitosis” § Nonreproductive cells are referred to as “Somatic Cells” § Mitosis involves the even division of chromosomes and organelles between two cells that are not part of the reproductive system § The parent cell undergoing Mitosis has a Diploid number (2 n) of chromosomes § The two daughter cells that result from Mitosis have a Diploid number(2 n) of chromosomes

Eukaryotic Cell Division § Division of reproductive cells is called “Meiosis” § Reproductive cells are referred to as “Germ Cells”, and upon completion of Meiosis those cells are called “Gametes” § Meiosis is often referred to as “Reduction Division” because the number of chromosomes is reduced from the Diploid number (2 n) to the Haploid number (n) § One parent cell with a Diploid number results in four daughter cells with a Haploid number

Chromosomes § First observed by German Embryologist Walther Fleming 1882 § What he saw under his primitive microscope were thread-like structures of salamander larval cells appearing to separate lengthwise § He called the division “Mitosis” based on the Greek word “Mitos”, meaning thread § Number of chromosomes vary greatly by species: Humans (46), House Cat (18), Plants (100’s)

Chromosomes § In Somatic Cells, Chromosomes group together in pairs based on size and genetic information; they are called “Homologous Chromosomes” or “Homologues” § Before cell division, each Homologous Chromosome replicates resulting in two identical copies called “Sister Chromatids” § The “Sister Chromatids” remain joined after duplication and prior to cell division at the center or their structures; this area is called the “Centromere”

Chromatin § During Interphase, the macromolecular complex of DNA and Protein is referred to as “Chromatin”, as stated previously § Chromatin is 40% DNA and 60% Protein § The reason there is a large proportion of protein associated with the DNA structure is chemical in nature § The proteins allow the DNA to thicken and coil in preparation for cell division; if there were no proteins present, this would not happen

Chromosomes § Often in discussion, the long strands of DNA are called “Chromosomes” § However, DNA strands are actually referred to as “Chromosomes” only during cell division (whether it is mitosis or meiosis) § The above is the case because it is just prior to cell division that the DNA strands thicken and coil taking on a unique appearance, that of a “Chromosome” § Throughout the majority of the cell cycle (Interphase), the DNA strands are called “Chromatin”

Cell Division § Cell Division takes approximately 1 hour of the 24 hour Cell Cycle § Cell Division has four distinct phases § Some scientists further subdivide those phases into five or more § The four phases in order are: – A) Prophase – B) Metaphase – C) Anaphase – D) Telophase

Prophase § 1. Chromosomes begin to migrate to the center of the cell § 2. Chromosomes also pair up with their homologue § 3. The Nuclear membrane degrades § 4. The Centrioles appear, migrate to opposite ends of the cell, and project their Spindle Fibers outward toward the Centromeres of the Chromosomes

Prophase

Metaphase § 1. The Chromosomes are lined up in the middle of the cell § 2. The Nuclear Membrane has completely disintegrated § 3. The Centrioles’ Spindle Fibers attach to the centers of the Chromosomes, the Centromeres, in preparation to pull the Chromosomes apart

Metaphase

Anaphase § 1. Spindle Fibers from the Centrioles pull the Chromosomes apart toward opposite ends of the cell § 2. Once the Chromosomes separate they are referred to as “Sister Chromatids”

Anaphase

Telophase § 1. Each set of Sister Chromatids has been pulled to opposite ends of the parent cell § 2. The Nuclear Membrane begins to reform around two new nuclei (the locations of the sister chromatids) § 3. The Sister Chromatids begin to uncoil and loosen, and now are designated as Chromosomes § 4. The Plasma Membrane of the parent cell begins to “pinch off” into two new membranes via “Cytokinesis” § 5. The Centrioles deactivate and “disappear” into the cytoplasm

Telophase

Miscellaneous Cell Cycle Information § Cytokinesis – the division of the cytoplasm at the end of cellular division § Cleavage Furrow – the physical action of the parent cell’s cytoplasm being pinched apart during Cytokinesis § Mitosis is sometimes referred to as “Karyokinesis” § Plant cells use a “Cell Plate” (wall in the center of the parent cell) to divide the cytoplasm instead of a “Cleavage Furrow” § It is important to understand that a cell does not necessarily divide every 24 hours: it can enter a “stasis” until environmental conditions are more favorable

Cancer § Old/malfunctioning cells do not die and continue to reproduce improperly functioning cells § Bundles of cells that are malformed are called “Tumors” § Some of the cells in the tumor can then migrate to other parts of the body, thereby enabling the proliferation of more cancerous cells/tumors in other locations: “Metastases”

Cancer Treatment § The conventional approach to treating, and hopefully curing cancer, is Chemotherapy and Radiation § Chemotherapy – a chemical that is delivered to the person usually intravenously; the drug targets and kills cancer cells § Radiation – high frequency energy delivered to a person’s body via a machine in an effort to target and kill cancer cells § There are many forms of cancer each with a unique set of treatment options