The Cell Cycle: Mitosis Notes

Facts * Somatic cells – “soma” means body * Body cells each contain the same number of chromosomes *How many chromosomes do human body cells have? Facts * Somatic cells – “soma” means body * Body cells each contain the same number of chromosomes *How many chromosomes do human body cells have?

Chromosome = cell structure that contains the genetic material in the form of DNA. This is located inside the nucleus.

Centromere = cell structure that joins two chromatids together to form a sister chromatid. Chromatid = one copy of the original chromosome.

Sister chromatid = identical halves of the duplicated parent (original) chromosome formed during interphase.

Interphase The time between the formation of the cell and the next mitosis The longest part of the cell cycle Divided into three parts

G1 phase (1 st Growth Phase) ~cell grows rapidly ~cell carries out normal functions ~organelles duplicate ~this phase occupies most of the cell’s life

S Phase (Synthesis) ~ S Phase (Synthesis) ~DNA is replicated (copied) ~At the end, each individual chromosome consists of two chromatids attached at the centromere.

G2 Phase (2 nd Growth phase) ~ G2 Phase (2 nd Growth phase) ~ cell is getting ready to divide ~ organelles are duplicating ~ microtubules are assembled to move the chromosomes during mitosis

Phases of Mitosis

Prophase – this is the first step of mitosis and it lasts the longest. Usually 60% of the total time for mitosis. ~ Chromosomes coil up into short rods ~ Nucleolus and nuclear membrane disappear Prophase – this is the first step of mitosis and it lasts the longest. Usually 60% of the total time for mitosis. ~ Chromosomes coil up into short rods ~ Nucleolus and nuclear membrane disappear

~ Spindle fibers form between centrioles ~ Centrioles move to opposite ends of the cell

Metaphase – second phase of mitosis ~ Meta = middle ~ Centromeres of chromosomes attach to spindle fibers

~ Chromosomes align along the middle of the cell (equator)

Anaphase – third phase of mitosis ~ Centromeres separate ~ Chromatids separate and become separate chromosomes again

~Spindle fibers pull chromosomes apart to opposite ends of the cell ~Cell membrane begins to pinch in the middle

Telophase – final stage of mitosis ~ Nuclear membrane forms around each set of chromosomes ~ Nucleolus reappears ~ Chromosomes return to threadlike form

Cytokinesis – the division of the cytoplasm Animal cells – cell membrane pinches in at the end of telophase and two new identical daughter cells are produced.

Plant cells – since plant cells have a rigid cell wall, the cell membrane can’t just pinch in. So, a cell plate forms across the middle of the cell to divide the two cells into two separate cells.