CELL DIVISION

Two Types

Mitosis Used for growth, repair, and asexual

reproduction Results in 2 exact copies of the original

cell Meiosis (next chapter)

Used in sexual reproduction Results in cells with ½ the number of

chromosomes of the original cells More on this later.

Mitosis

Starts with 1 cell, results in 2 cells that are exact copies of the original.

Four phases: Prophase Metaphase Anaphase Telophase

Prophase Chromatin coils to

form chromosomes Nucleolus and

Nuclear membrane breaks down

Centrioles move away from each other toward the poles (animals only).

Spindle fibers form

Metaphase

Chromosomes are moved to the equator by spindle fibers.

Anaphase

Sister chromatids separate.

Separated chromatids (now called daughter chromosomes) move toward the poles.

Telophase

Spindle fibers break down.

Chromosomes unwind to form of chromatin.

Nuclear membrane and nucleolus reform.

Which phase?

Metaphase

Which phase?

Telophase

Which phase?

Anaphase

Which phase?

Prophase

Animations

http://www.cellsalive.com/mitosis.htm

Cytokinesis

The physical division of the cytoplasm.

Animals pinch their cell membrane inward until 2 cells are formed.

Plants form a “cell plate” to form a new cell.

Control of the cell cycle

Control of the Cell Cycle

Not all cells follow the cell cycle at the same rate.

Skin cells Liver cells Nerve cells

Control of the Cell Cycle

Normal cells: Divide until they come in contact with

one another, then stop when they become too crowded.

Only grow when connected to something.

Respond to internal and external signals Many molecules control the cell cycle from

inside the cell and from outside the cell. “Cyclins” and Growth Factors are two

examples of these molecules (they act like stop and go signals).

Control of the Cell Cycle

Cancer Cells: Have lost control of the cell cycle. Do not respond the system of chemical

signals Do not stop dividing when in contact

with other cells. Can move from one place in the body to

another. Interrupts normal tissue activity.

Cancer Terms

Tumor – a mass or lump of cells resulting from uncontrolled cell division. Benign tumor – tumor that does not

spread to other areas. Malignant tumor – invades surrounding

tissues Apoptosis – programmed cell death

(normal) Cancer cells do not respond to this.

Causes of cancer

Caused by anything that changes the DNA responsible for controlling the cell cycle. Tobacco Radiation Sunlight Viral infections Random mutation

Treatments

Remove tumor by surgery if possible. Radiation treatment Chemotherapy

Cell Differentiation Zygote – a

fertilized egg

Differentiation – process in which cells become specialized.

Stem cells

Undifferentiated cells The zygote and the first few cells

that arise from it can become any type of cell. Totipotent cell – a cell that can become

any type of cell The zygote develops into a

blastocyst. Pluripotent cell – a cell that can become

most, but not all types of cells.Undifferentiated cells

Stem Cells continued

Embryonic stem cells are the cells found in the early embryo Are pluripotent

Stem cells continued Adult stem cells are

cells that replace certain types of cells in our bodies when needed. Multipotent cell – has

a limited potential to develop into many types of cells

Ex. Adult stem cells in the bone marrow can develop into any type of blood cell (red, white, or platelets.

Stem cells continued

Benefits of stem cell research? Ethical issues?