The Cell Cycle and Cell Division Mitosis The Cell Cycle and Cell Division

Let’s Review All living things are made of tiny cells. These cells work dividing in order to replace cells that are old, damaged, or dead. These new cells allow us to grow, and they allow scrapes and wounds to heal! This process of cell growth, replicating and dividing is called a cell cycle.

Notice that Mitosis is only a very small portion of the cell cycle. The cell cycle of your cells and the cells of all other living things is divided into two phases: a growth phase (called Interphase) and a cell division phase (called Mitosis). Notice that Mitosis is only a very small portion of the cell cycle. The Life of a Cell Interphase Mitosis

Interphase is divided into three parts: G1: cells grow and prepare for DNA replication S: a copy of the cell’s DNA is made G2: DNA molecules begin to coil The Cell Cycle

The DNA coils into Chromosomes, chromsomes: Pass GENETIC information from one generation of cells to the next Found in the nucleus of a cell Are made of DNA & PROTEINS Different cells types have different NUMBERS of chromosomes Are ONLY visible during division

Chromosomes Consist of 2 identical “sister” CHROMATIDS Attached at the centromere Human body cells have 46 chromosomes centromere

The cell division phase has two parts: mitosis and cytokinesis. Mitosis is divided into four phases. Look at the next few slides to see what happens in each of the four phases.

1st Phase (PACK) DNA and proteins condense (PACK) into chromosomes

1st Phase: DNA PACKS into Chromosomes

2nd Phase (MIDDLE) Chromosomes line up across the center (middle) of the cell Chromosomes attach to the spindle fiber at its centromere

2nd Phase: Chromosomes line up in the MIDDLE of the cell

3rd Phase (APART) Sister chromatids separate (move apart) into individual chromosomes Spindle fibers pull the chromosomes to opposite sides of the cell

3rd Phase: Chromosomes are pulled APART to opposite ends of the cell

4th Phase: (TWO) Chromosomes gather at opposite ends of the cell and lose their shape Two new nuclear membranes form

4th Phase: TWO new cells are formed (still attached)

Cytokinesis Occurs with Telophase The RESULT: Two new IDENTICAL cells are formed.

What happens when cells do not divide or divide too much?....CANCER - Cells have internal & external regulators that control cell division - Cancer cells do not respond to the regulators so they have uncontrolled cell growth and form tumors * benign tumors * malignant tumors