1/21/15CELL DIVISION I. CELL CYCLEA. Cells are divided into two groups:1. Sex cells (sperm and ova [eggs])2. Somatic cells (all other cells)B. Cell cycle subdivided into 2 phases:1. Interphase – cell is not dividing (getting ready for cell division) [not resting]=the time between cell divisions when thecell maintains and caries out normal metabolic activitiesa. S-PHASEDNA is replicated during this time2. Mitosis (cell division for somatic cells—division of the nucleus) or Meiosis (cell division for sex cells) II. MITOSIS - Note: DNA was replicated during interphaseA. Prophase1. Chromatin (1/2 DNA and ½ proteins) becomes supercoiled to form chromosomes2. Chromosomes are double-stranded DNA. That is, 2 chromatids (coiled) joined by a centromerea. chromatid (long structure)= one of the duplicated DNA strands 3. Spindle fibers extend from centrioles to the centromere4. Nuclear membrane and nucleolus are dismantled B. Metaphase (“middle”)1. Chromosomes align along center of cellC. Anaphase1. The two chromatids split apart at centromerespindle fibers shortening 2. Each chromatid, a single strand of DNA, is pulled to opposite ends of cellD. Telophase1. Chromosomes uncoil2. Nuclear envelope and nucleolus reforms3. Cleavage furrow develops Cytokinesis = division of cytoplasm (usually occurs). Cells now enter interphaseAlso known as the division of the cell producing two daughter cells III. MEIOSISDef: cell division where gametes (= sex cells: sperm cells or eggs) areformedA. Differences between mitosis and meiosis:1. Mitosis produces 2 cells containing 46 chromosomes 23 pairs of single-strands of DNAa. The two new cells are identical to original cell2. Meiosis produces 4 cells containing only 23 single strands of DNA B. Meiosis: Starts off with one cell that has 23 pairs of chromosomes. (46) - one set of chromosomes came from the MOTHER , the other from the FATHER - During interphase: DNA gets duplicated - Cell now contains 23 pairs of double-stranded chromosomes (total=92 strands of DNA) There are two consecutive meiotic divisions1. Meiosis I: a. Prophase Ii. The process of synapsis allows for the chromosomes line up in groups of four = tetradsii. Crossover occurs : process by which geneticmaterial is exchanged between non-sister chromatids b. Metaphase I, Anaphase I, Telophase I: the cell finishes Meiosis I by separating the tetrads and producing 2 new cells Cell finishes 1st meiotic division produced 2 daughter cells- Daughter cells have 23 double-stranded chromosomes (that is, each chromosome consists of 2 chromatids) - No interphase (DNA will not get replicated because we are not dividing the DNA)2. Meiosis II: Each of the 2 cells produced from Meiosis I divide (NO DNA REPLICATION BEFORE THIS DIVISION):a. Prophase II(don’t have tetrad formation—already occurred), Metaphase II, Anaphase II (centromeres are separated and individual chromatids [single-stranded DNA]are pulled to opposite ends of the cell), Telophase II.b. 4 cells (=gametes) produced, each with 23 single-strands of DNA In which of the following stages of mitosis do the centromeres split and the chromatids begin to separate?a. Prophaseb. Anaphase*****c. Telophased. Metaphasee. None of the above, this only happens in
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