The Cell Cycle & Mitosis Biology The Cell Cycle & Mitosis

Cell Cycle Dividing cells follow something called the cell cycle. Only 10% of the cell cycle is devoted to cell division (mitosis). The other 90% is devoted to cell growth, DNA replication and preparation for cell division.

Cell Cycle cont’d 4. Cell division 3. Cell prepares to divide 1.Cell Growth 2. Synthesis: DNA replicates

Interphase The longest stage of the cell cycle. During Interphase, the cell carries out all life functions except division. They include Growth Cellular respiration Other special functions. At this stage, the genetic material (DNA), is in very long invisible strands inside the nucleus (chromatin). When the cell prepares for division, the DNA is replicated and more organelles are formed.

Chromatin Centrioles: “Barrel” shaped organelles used in division.

DNA Stands for Deoxyribonucleic Acid. Contains all the genetic material for a living organism. Humans have 23 pairs of chromosomes for a total of 46: 23 from mom, 23 from dad The entire DNA molecule contains all genetic material in a single undivided form.

Cell Division Occurs in two stages: Mitosis: The division of contents of the nucleus. 4 steps: Prophase Metaphase Anaphase Telophase Cytokinesis: The division of the rest of the cell including: Cytoplasm, organelles and cell membrane. Each division produces two identical daughter cells.

Prophase Long strands of DNA condense into a compact form called chromosomes. Chromosome contains a portion of DNA. Since DNA was copied during interphase, each chromosome contains a pair of identical strands called sister chromatids. The chromatids are held together by centromeres. Nuclear membrane dissolves during this time. Centrioles (organelles used in pulling cells apart) migrate to opposite sides of cell. Spindle fibres are released by the centrioles to attach to chromosomes.

Nuclear Membrane Centromere Spindle Fibres Sister Chromatids

Metaphase Chromosomes line up in the middle of the cell. Spindle fibres from centriole attach to centromeres of each chromosome. All must be in line for mitosis to continue.

Attached spindle fibres Sister chromatids lined up

Anaphase Centromere splits and the sister chromatids separate. They are now called daughter chromosomes. They are pulled by spindle fibres to opposite sides of the cell.

Daughter chromosomes

Telophase Final stage of mitosis. Daughter chromosomes stretch out, become thinner, and are no longer visible. Turn back into chromatin. A new nuclear membrane forms around each area of chromatin. Cell appears to have two nuclei.

Daughter chromosomes stretching out

Cytokinesis The final stage of cell division. Cytoplasm divides producing two genetically identical daughter cells. Different for each type of cell: Animal cell: Cytoplasm pinches in half. Plant cell: Plate between two cells turn into a cell wall.

Chromatin Two daughter cells

Checkpoints in Cell Cycle Cell division is a very complicated and closely monitored process by the cell. Specialized proteins in the cell monitor progress. The cell will not divide if: Cell not growing properly. DNA has not been replicated DNA is damaged If the DNA is damaged, cell may either repair it or destroy itself via the lysosome (“suicide sac”).

References Edupic Graphical Resource: Cells http://www.edupic.net/cells.htm

Homework P.44 #1-7