MITOSIS AND MEIOSIS Chapter 10 and 11-4

WHAT IS MITOSIS?  For growth and to replace old, worn out or damaged cells.  Occurs in body cells therefore forms body cells.  Results in 2 identical cells of the original parent cell.  Maintains chromosome number  Creates diploid cells (2N) – has two sets of chromosomes  One division of the nucleus  Also known as binary fission  In single-celled organisms, cell division is a form of asexual reproduction.

CELL GROWTH  There are limits to cell growth 1. DNA “information” overload: The bigger the cell, the greater the demand on the DNA.  Compare a cell to a growing town. The town library has a limited number of books. As the town grows, these limited number of books are in greater demand, which limits access.  A growing cell makes greater demands on its genetic “library.” If the cell gets too big, the DNA would not be able to serve the needs of the growing cell.

2. Exchange materials: The bigger the cell, the harder it is to move materials and wastes in and out of the cell. - Small cells maintain more efficient transport systems. - Imagine a cell shaped like a cube. As length of the sides increases, its volume increases faster than its surface area, decreasing the ratio of surface area to volume. - If a cell gets too large, the surface area of the cell is not large enough to get enough oxygen and nutrients in and waste out. CELL GROWTH

WHAT IS THE SOLUTION? The Cell Cycle: Interphase + Cell division Interphase = cell growth (preparation to divide) Cell division = dividing the cell Cell Division = Mitosis + Cytokinesis Mitosis – the division of the nucleus Cytokinesis – the division of the cytoplasm

G1 Phase: The cell grows in size and develops duplicate organelles. S Phase: DNA # is doubled. G2 Phase: gets ready for mitosis. Finishes all growth. Checkpoint 1 *Has 2 complete sets of DNA Checkpoint 2 6

CELL DIVISION – 3 MAJOR STEPS 1. Interphase is the phase in which cells spend 90% of their time getting ready to divide. Has 3 parts: 1. G1 2. S 3. G2

 G1 phase – The first period of cell growth (size), when the cell grows its organelles.  S phase – The period when DNA is duplicated, replicated or copied.  Chromosomes Chromosomes  Why is this stage so important?  G2 phase – The period when a cell finishes all growth and prepares for mitosis. CELL DIVISION – 3 MAJOR STEPS

Chromosomes = DNA and Histones(protein) Chromosome Chromatid Duplicated Chromosome Sister Chromatids Centromere Where they join

2. Mitosis (Cell Division) 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase 3. Cytokinesis (Splitting of the cytoplasm) Results in 2 new identical daughter cells. CELL DIVISION – 3 STEPS

Centriole copies are made (G1) INTERPHASE Cell Organelles are being replicated. More Cytoplasm is being made. The cell is getting ready for MITOSIS (G2) DNA is replicating (S)

X X X X 4. Nuclear Membrane begins breaking down 1. Centrioles start moving apart. 2. Spindle fibers form 3. Chromosomes shorten and thicken into visible chromosomes. MITOSIS – PROPHASE

XX XX NOTE: THE NUCLEAR MEMBRANE IS NO LONGER PRESENT NOTE: THE NUCLEAR MEMBRANE IS NO LONGER PRESENT 1.Centrioles are at opposite poles. And move toward the middle of the cell. MITOSIS – METAPHASE (STEP 2) 2.Spindles attach to the chromosomes

> > > > > > > > MITOSIS – ANAPHASE (STEP 3) 1.Centrioles begin to pull sister chromatids to opposite sides of the cell.

1.Chromosomes continue to be pulled toward the centrioles. >> > > > > > > MITOSIS – TELOPHASE (STEP 4) 2.Cell Membrane begins to separate into two cells 3.Nuclear Membranes begin to reappear. 4. Spindles disappear. 3.Nuclear Membranes begin to reappear. 4. Spindles disappear.

CYTOKINESIS Cytoplasm splits between the two identical cells

THE STAGES OF THE CELL CYCLE

The process is VERY SIMILAR in each type of cell. There are only 2 differences: 1.Plant cells do not have centrioles 2.The cell membrane cannot pinch because of the cell wall. 3.Instead a cell plate forms between the 2 nuclei division. 18

REGULATING THE CELL CYCLE  Contact inhibition: stop dividing when crowded  Cyclins: Protein regulators  Checkpoints  Internal Regulators (timing)  External Regulators (growth factors) Uncontrolled Cell Growth Cancer: can form masses called tumors Unresponsive to internal and external regulators. Deprive healthy cells from nutrients. Results in uncontrolled cell growth.

CANCER CANCER  Tumor: uncontrolled cell division  Benign (cysts, warts) = not too harmful  Malignant = Cancer = harmful  Metastasis: cancer cells break off & spread  Kinds  Carcinomas: skin & organ linings (breast & lung CA)  Sarcomas: bone & muscle  Lymphomas: tissues that make blood cells  Leukemia: uncontrolled production WBC  Cancer Effects on Cell Cycle  Healthy cells stop dividing when crowded  Cancer cells keep dividing & steal blood supply

cancer cell bloodstream normal cell 21

_______________________ 22

MITOSIS VS. MEIOSIS  For growth and to replace old, worn out or damaged cells.  Occurs in body cells therefore forms body cells.  Results in 2 identical cells from the original parent cell.  Maintains chromosome number  Creates diploid cells (2N)  One division of the nucleus To make sperm and eggs. Occurs in sex cells therefore forms sex cells or gametes. Results in 4 genetically different cells from the original parent cell. Cuts chromosome number in half Creates haploid cells (1N) Two divisions of the nucleus

Spermatogenesis Oogenesis In males: These cells develop into 4 individual sperm. In oogenesis: These cells would have developed into three small polar bodies and only one large egg. THE POLAR BODIES ASSIST WITH EQUAL CHROMOSOMAL DIVISION, HOWEVER THE POLAR BODIES DIE Uneven division of cytoplasm

Fertilization: Union of sperm and Egg - Zygote- cell resulting from fertilization of egg by sperm (full number of chromosomes) Re-establishes the full number (diploid) of chromosomes in an organism 2 chromosomes 4 chromosomes

PURPOSE OF MEIOSIS  Also known as reduction division  To produce sex cells or gametes with half the number of chromosomes.  Called haploid cells  Sex Cells – Reproductive cells produced by sex organs  Sperm and ova  In meiosis the cell divides twice.

 Meiosis involves 2 cell divisions.  Meiosis I  Prophase I  Metaphase I  Anaphase I  Telophase I  Cytokinesis  Meiosis II  Prophase II  Metaphase II  Anaphase II  Telophase II  Cytokinesis

STEPS OF MEIOSIS  Prophase I (Step one) - Identical steps to Mitosis prophase  EXCEPT  (a) Homologous (matching) chromosomes pair up, also known as tetrads  (b) crossing over occurs – exchange genetic material  Metaphase I - Identical steps to Mitosis Metaphase  EXCEPT  (a) Spindle fibers move homologous pairs of chromosomes to the center of the cell

STEPS OF MEIOSIS  Anaphase I – identical steps to Mitosis Anaphase  EXCEPT  (a) Spindle fibers move Homologous chromosomes apart  Telophase I – identical steps to Mitosis Telophase  EXCEPT  (a) These 2 new cells now enter Meiosis II.

MEIOSIS II – THE STEPS ARE IDENTICAL TO THE STEPS OF MITOSIS.  Prophase II  Metaphase II  Anaphase II  Telophase II  4 cells with half the number of original chromosomes

31