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 Cells go through the cycle in different rates: muscles vs. skin

INTERPHASE 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

INTERPHASE

PROPHASE

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.

ANAPHASE

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.

TELOPHASE

CYTOKINESIS