The Cell Cycle & Mitosis

2 Reasons why cells divide 1) Growth 2) Replace worn out or damaged cells http://www.adc.state.az.us/images/Off-Library.JPG

Cell Division in Eukaryotes Called Mitosis Cell Grows & copies its DNA before it can divide

The series of events that cells go through as they grow & divide ~ The Cell Cycle

2 Phases of the Cell Cycle Interphase “M” Phase Includes Mitosis & Cytokinesis

The Cell Cycle: G1 S G2 Prophase Metaphase Anaphase Telophase Interphase Mitosis

M G2 G1 S

Interphase: a growth period G1 (Growth/Gap 1) – Cell grows in size, makes new organelles performs assigned function DNA is relaxed in chromatin and is not visible

Interphase: a growth period S phase (Synthesis) – duplicates DNA to prepare for mitosis G2 (Growth/Gap 2) – cell prepares for mitosis

Talk to a partner: Explain the phases of Interphase

Chromosomes condense and become visible at the start of mitosis

Chromatin DNA is relaxed; DNA appears as chromatin during interphase Chromosome visible DNA during mitosis

Mitosis occurs in 4 phases Prophase Metaphase Anaphase Telophase

Vocab Terms Sister chromatidsidentical halves of the duplicated parent chromosome Centromerecell structure that joins the two sister chromatids of a chromosome

Prophase DNA organizes Nuclear membrane & nucleolus disappear. Chromosomes are paired with their identical copies (sister chromatids held together by the centromere) chromatin condense into visible chromosomes. Nuclear membrane & nucleolus disappear. Spindle fibers form between the centrioles, located at opposite ends of the cell Prophase

Metaphase Chromosomes line up in the middle of the cell. Each chromatid is attached to a separate spindle fiber by its centromere.

Anaphase Sister chromatids are pulled apart to opposite poles of the cell.

Telophase 2 identical daughter cells are formed. Cytokinesis occurs (the division of the cytoplasm) as the plasma membrane pinches in along the equator. Nucleolus and nuclear membrane reappear, chromosomes begin to uncoil & relax back into chromatin

In plants… Because plant cells have a cell wall, the plasma membrane does not pinch in. Rather a structure known as the cell plate forms across the cell’s equator.

Plant in cytokinesis It’s hard to see, but there is a cell plate forming in the middle of the cell, next to the arrow.

Finally… After mitosis is complete, each new daughter cell is an identical copy of the parent cell. Both cells enter interphase to carry out their assigned function until they are ready to divide.

All together now…

Talk to a partner: Explain the phases of Mitosis

Cell Cycle practice

What happens when the cell is not growing or dividing? Cell is resting

Cell enters G0 phase, where cell is resting and carrying out its normal function

When cells are damaged and need repair or need to be replaced, cell will reenter the cell cycle

Controlling Cell Growth Through Gene Regulation Cell division stops when cells touch Can resume if space is available (injury)

Talk to a Partner: Do Cells Grow Indefinitely? Section 10-3 If center cells are removed, cells near the space will start to grow again. SHOWS: Cell division genes can be turned on and off Cells grow until they touch other cells

What happens when the genes that control cell division become damaged? Some cells do not respond to the signals that regulate the growth Result ~ uncontrolled cell growth: cancer Causes of cancer: cigarette & tobacco use radiation exposure (X-ray & UV light) genetics some viruses

Cancer Video

Stem Cells Stem cells - unspecialized cells Through cell differentiation – stem cells become specialized in structure and function Two Types: Embryonic and Adult Stem Cells

Cornell Summary