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MITOSIS & CYTOKINESIS. MITOSIS : The nucleus of a cell is divided into 2 nuclei with the same number & kinds of chromosomes as parent cell. CYTOKINESIS: The division of the cytoplasm into 2 distinct cells.
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MITOSIS & CYTOKINESIS • MITOSIS: The nucleus of a cell is divided into 2 nuclei with the same number & kinds of chromosomes as parent cell. • CYTOKINESIS: The division of the cytoplasm into 2 distinct cells. • CHROMOSOMES: Contain the genetic information (DNA) passed on to each generation. They differ in number with ea. Specie. • COMPOSITION OF CHROMATIN: Makes up chromosomes. • Condenses between cell division, chromosomes become visible. • Made up of DNA and proteins. The proteins fold the DNA to fit into the nucleus. DNA is 10,000 X the length of chromo. • Don & Ada Olins and Christopher Woodcock discovered that DNA was coiled around histone proteins. • Nucleosomes: Bead-like structures of DNA and histones • These are tightly compacted so they can separate in mitosis.
CHROMOSOMES • CHROMOSOME STRUCTURE • Chromotids: Identical parts contained in chromosomes (2) • Centromere: Located near the center of chromatids (usually) • CELL CYCLE • A cell grows, prepares for division, and divides to form 2 new daughter cells. • Mitosis (M phase) Active cell division, nucleus into 2 new ones • Interphase (G1,G2,& S) Period of non cell division, where other life processes are carried out • Cytokinesis Where the cytoplasm and contents divide • See fig. 8-10 • Cells go through the cycle in different rates: muscles vs. skin
INTERPHASE • http://www.micro.magnet.fsu.edu/micro/gallery.html • INTERPHASE: The period between cell division • G1 (Gap 1): Cellular growth and development takes place • S: (DNA Synthesis): DNA replication takes place, synthesizing of proteins • G2 (Gap 2): Synthesis of organelles and materials required for cell division. Shortest of the phases. • Although this phase seems quiet a lot is going on: • synthesizing of mRNA • making of proteins • DNA is copied • ATP is made and utilized • specialized cells do most of their work: secretion, movement
PROPHASE • Longest of the phases taking between 50-60% of total time. • Chromosomes become visible because of coiling of chromotin • Centrioles separate and go to opposite sides of the cell • Centrioles contain tubulin, a microtubule protein • Chromosomes attach to fibers (spindles) near the centromere. • Spindles help move the chromosomes apart and are developed from the centrioles. • Centrioles are composed of microtubules. • Plant cells do not contain centrioles. • Near the end of the phase coiling becomes tighter, the nucleolus disappears, and the nuclear envelope breaks down.
METAPHASE • The shortest of the phases lasting only a few minutes. • Chromosomes line up across the center (equator) of the cell. • Microtubules connect the centromere of each chromosome to the poles of the spindle. • Because of their starlike arrangement around the poles of the spindle, these microtubules are called ASTERS.
ANAPHASE • Begins when the centromeres that joins the sister chromotids split. • As they separate the spindle grows longer. • The chromosomes move until they have separated into two groups near the poles of the spindles. • Anaphase ends when the movement of the chromosomes stops. • Force that separates the chromosomes isn’t known. • Microtubule cross-bridging • Microtubule assembly/disassembly • Actinmediated force generation • All have been proposed. Problem is that such a small force is needed to move a chromosome that pinpointing the cause is a problem.
TELEPHASE & CYTOKINESIS • Final stage of mitosis • Chromosomes uncoil into a tangle of chromatin in the regions where the nuclei of the daughter cells will form. • The nuclear envelope reforms around the chromatin. • Spindles break apart and nucleolus becomes visible. • We now have two nuclei w/ a duplicate set of chromosomes • CYTOKINESIS • Division of the cytoplasm into two individual cells • Takes place in a number of ways: • In animal cells the cell membrane moves inward until the cytoplasm in pinched into two parts w/ their own nucleus etc. • In plants, a cell plate forms midway between the divided nuclei. It develops into a separate membrane w/ a cell wall.
