Cell Cycle and Mitosis http://www.wadsworth.org/bms/SCBlinks/mcewen/Media/fig_1_cell_mitosis.jpg

DNA A cell’s genetic info is contained in the DNA molecules in its nucleus DNA is organized into chromosomes

Chromosomes Every cell contains chromosomes. Before cell division can begin, each chromosome must be copied. Chromosome: A long piece of coiled DNA and proteins Humans have 46 chromosomes per cell, horses have 64, dogs have 78 Can only be seen when the cell divides Once copied it consists of two identical copies called sister chromatids. Each one chromatid is given to each new daughter cell.

Chromatin The form of DNA when the cell is not dividing. Long and stringy substance that is spread out throughout the cell. Condenses into chromosomes at the beginning of cell division.

The Cell Cycle The majority of a cell’s life is spent growing and repairing. A cell can only grow to be a certain size. Once the volume to surface area ratio gets too big the cell can’t function properly. To prevent this, cells divide before they get too big.

Why is the cell cycle important? Healing and tissue repair Cells get damaged and they need to be replaced.   Growth of an organism We all started out as a single cell. From that one cell, through constant division, billions are produced to make up a whole organism. Regeneration Cells get old and die naturally (through apoptosis) and need to be regenerated.

Cell Cycle The repeating cycle of events in the life of a cell Most of it is spent preparing for the cell’s main goal of division. Has two main parts: Interphase (growth and preparation) Cell Division

Interphase Part of the cell cycle where the cell is growing and preparing for division. 90% of the time the cell is in interphase Can be divideded into: Growth 1 phase (organelle replication) Synthesis phase (DNA replication) Growth 2 phase (growth and preparation for division)

Cell Division Can be divided into 2 main parts: Mitosis - the packaging of the genetic material in the nucleus into two equal portions Cytokinesis – the separation of the cytoplasm into two equal portions Involves the separation of genetic material and cytoplasm into two equal parts in order to create 2 new “daughter cells”

G1 interphase M S Cell Division G2

Mitosis There are 4 phases of mitosis: prophase, metaphase, anaphase, and telophase Mitos – comes from the Greek work thread

Prophase Chromatin shorten and thicken The nuclear membrane begins to dissolve The mitotic spindle forms The pair of sister chromatids attaches to the spindle at their centromere In animal cells, a pair of centrioles move to each end of the cell, called the poles of the mitotic spindle. Centriole

Metaphase Each chromosome is now completely condense and has moved toward the equator of the cell The mitotic spindle is not complete and each chromosome now has a tiny tube attached to it that extends from the pole of the cell to the middle of the cell Equator

Anaphase The sister chromatids separate at the centromere and are pulled to opposite poles. Each chromatid is now a separate chromosome

Telophase The single stranded chromosomes have now reached opposite poles A nuclear membrane starts to form around each group of chromosomes at the opposite poles to form two new nuclei The mitotic spindle begins to disappear http://royaleb.files.wordpress.com/2009/04/mitosis_phases1.jpg

Cytokinesis Occurs while telophase is occurring but is technically separate from mitosis The cytoplasm and organelles are divided among the two new cells In animal cells the cell membrane cleaves eventually splitting into two new cells In plant cells, a cell plate forms the cell wall that divides the two new cells.

http://www.youtube.com/watch?v=eFuCE22agyM http://www.youtube.com/watch?v=VlN7K1-9QB0