1.6 Cell division

Mitosis is the division of the nucleus of eukaryotic cells into two genetically identical daughter nuclei. Mitosis occurs during embryonic development, growth, tissue repair and asexual reproduction. Four phases of mitosis: prophase, metaphase, anaphase and telophase.

Interphase, a very active phase of the cell cycle with many processes occurring in the nucleus and cytoplasm, is the period before mitosis begins. During interphase:DNA is replicated in the nucleus in the S phase, and protein synthesis occurs in the cytoplasm; each part of a duplicated chromosome is called a sister chromatid (joined at the centromere)

the number of mitochondria (and chloroplasts in plant and algae cells) increasesplant cells synthesize cellulose and use vesicles to add it to their cell walls

Sequence of events during mitosis See BCC pg. 53-54

Prophase

two parts of the chromosome are called sister chromatidschromosomes condense (shorten and thicken) by supercoilingnucleolus breaks downmicrotubules originating from centrosomes or MTOC form the spindle apparatusat the end of prophase the nuclear membrane breaks down

Metaphase

microtubules attach to the centromeres of each chromosomechromosomes align on the metaphase plate equator of the cell

Anaphaseeach centromere divides, allowing the sister chromatids to separate, forming individual structures once again called chromosomesspindle microtubules pull the chromosomes to opposite poles of the cell

Telophase

chromosomes reach the poles and are pulled together in a tight group near the centrosomenuclear membrane forms around each groupchromosomes uncoilnucleolus formsdivision of cytoplasm begins

 

Cytokinesis occurs after mitosis and is different in animal and plant cells. In animal cells:plasma membrane is pulled inward by contractile proteins to form a cleavage furrow at the equatorcell is pinched apart into 2 genetically identical daughter cells

In plant cells:vesicles move to the equator and fuse to form tubular structures across the equatoreventually the tubular structures merge to form 2 layers of membrane across the equator, which develops into the plasma membranes of the daughter cellspectins, cellulose and other substances are brought by vesicles to the equator and are deposited by exocytosis to form new cell walls for each daughter cell