Mitosis

Cell Growth and Reproduction

Nucleus- Organelle that directs the activities of the cell.

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 chromosomesAmong 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 cap[able of dividing many times during a lifespan.

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. 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 CellsWhen 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 atend of this phase

1st: INTERPHASE

Centromere

Mitosis Notes

• Mitosis begins (cell begins to divide)• Centrioles (or poles) appear and begin to move toopposite ends of cell• Spindle fibers form between the poles

2nd: PROPHASE

Mitosis Notes

• Chromatids (or pairs of chromosomes) attach to thespindle fibers

3rd: METAPHASE

Mitosis Notes

• Chromatids (or pairs of chromosomes) separate andbegin to move to opposite ends of the cell.

4th: ANAPHASE

Mitosis Notes

• Two new nuclei form• Chromosomes appear as chromatin (threads ratherthan rods)• Mitosis ends

5th: TELOPHASE

Mitosis Notes

Cell membrane moves inward to create two daughtercells - each with its own nucleus with identicalchromosomes

6th: CYTOKINESIS

1st: INTERPHASE 2nd: PROPHASE

3rd: METAPHASE 4th: ANAPHASE

5th: TELOPHASE 6th: CYTOKINESIS