Cell Growth and Reproduction Mitosis Cell Growth and Reproduction

Essential Question How is mitosis the key to life and death?

Nucleus- Organelle that directs the activities of the cell.

Chromosomes: Threadlike material made of DNA Chromosomes: Threadlike material made of DNA. The chromosomes carry strands of DNA that determine an organisms characteristics. Characteristics are things like: hair color, eye color, skin tone,and many others.

A human cell has 46 chromosomes A mouse has 40 chromosomes A horse cell has 60 chromosomes A corn cell has 20 chromosomes Among the approximately 23,000 genes found in human DNA, scientists currently estimate that there may be as few as 50 to 100 that have no counterparts in other species.

What is mitosis? Mitosis is the process by which a cell reproduces. When a cell divides, two new cells are created. Each new cell has a nucleus (which contains genetic information) and a complete set of organelles. Most cells in the body are capable of cell division. A cell is capable of dividing many times during a lifespan.

Why is mitosis important Why is mitosis important? Mitosis is important because it allows organisms to grow, and replace worn out or damaged cells

Which cells reproduce? All cells in an organism start off being the same. These cells are called stem cells. Stem cells are cells that can specialize or turn into other cells (like muscle cells, or nerve cells, or bone marrow.) Stem cells are only present in the early stages of development (embryo). Adults do not have stem cells.

After a cell specializes, they will continue to reproduce After a cell specializes, they will continue to reproduce. Some will reproduce throughout a persons lifetime. These cells, among others, reproduce throughout your lifespan: Skin Cells, Hair Cells, Bone Cells, and Blood Cells. These cells continue reproducing but slow down after several years, Nerve cells and Muscle cells.

Cell Division in Cancer Cells When it comes to cell division, cancer cells break just about all the rules! Cancer cells can divide without appropriate external signals. This is analogous to a car moving without having pressure applied to the gas pedal. An example would be the growth of a breast cancer cell without the need for estrogen, a normal growth factor. Some breast cancer cells actually lose the ability to respond to estrogen by turning off expression of the receptor for estrogen within the cell. These cells can still reproduce by bypassing the need for the external growth signal.

Mitosis Notes Cell division occurs in a series of stages, or phases.

Mitosis Notes Chromosomes are copied (# doubles) • Chromosomes appear as threadlike coils (chromatin) at the start, but each chromosome and its copy (sister chromosome) change to sister chromatids at end of this phase 1st: INTERPHASE Centromere

Mitosis Notes • Mitosis begins (cell begins to divide) • Centrioles (or poles) appear and begin to move to opposite ends of cell • Spindle fibers form between the poles 2nd: PROPHASE

Mitosis Notes • Chromatids (or pairs of chromosomes) attach to the 3rd: METAPHASE • Chromatids (or pairs of chromosomes) attach to the spindle fibers

Mitosis Notes • Chromatids (or pairs of chromosomes) separate and 4th: ANAPHASE • Chromatids (or pairs of chromosomes) separate and begin to move to opposite ends of the cell.

Mitosis Notes • Two new nuclei form 5th: TELOPHASE • Two new nuclei form • Chromosomes appear as chromatin (threads rather than rods) • Mitosis ends

Mitosis Notes Cell membrane moves inward to create two daughter 6th: CYTOKINESIS Cell membrane moves inward to create two daughter cells - each with its own nucleus with identical chromosomes

1st: INTERPHASE 2nd: PROPHASE 4th: ANAPHASE 3rd: METAPHASE 6th: CYTOKINESIS 5th: TELOPHASE