The Cell Cycle

Interphase and Mitosis

All living things..

..begin life as a single fertilized cell.

Humans begin as a fertilized OVUM or human egg cell.

The egg cell …

• ….then begins to divide into exact duplicate “stem cells”.

• these first cells will be the basis for all future cells in the human body.

• ---->note the ovum has divided into 8 stem cells

This little batch of cells…

• …will not stay the same. Cells specialize and take on different jobs.

• ---------->at 5-6 weeks the embyro has animal-like features including a fully functional heart.

When Cells Divide

Type of Cells How Often Cells Divide

Embryo Cells 30 minutes

Intestinal Cells 3 days

Blood Cells 3 months

Nerve Cells Never / Very Rare

Nerve cells…

• …remain in INTERPHASE for long periods of time.

• They go through mitosis about once every 75 years.

Cancer cells…

• …behave much differently than nerve cells.

• …spend very little time in interphase and go through mitosis uncontrollably.

• Approx. 1/10,000 of your cells are cancerous-the good news-your defense cells usually kill them fast

How does this work?

• Let’s go back to the little batch of 8…

• We will now look at cells when they are dividing…and when they aren’t!

Interphase

• The time between cell division

• Cell is doing its job• DNA duplicates-

chromosomes make exact copies of themselves

Genetic material is all strung out as chromatin – can’t see chromosomes

Nuclear membraneclearly in place

Mitosis

• (division of the nucleus)

• There are four different stages– Prophase– Metaphase– Anaphase– Telophase

Prophase

• DNA condenses to form distinct DOUBLE chromosomes (2 copies of each)

• Nuclear membrane disappears

Metaphase• Copied chromosomes

line up in the middle (equator) of the cell

• Spindle fibers attach to chromosomes

Anaphase

• Copies of chromosomes separate and move toward opposite ends of the cell (poles)

Telophase

• Single chromosomes reach the poles

• New nuclear membrane forms around each set

• Chromosomes unwind to become thread-like chromatin again

Cytokinesis (End of Telophase)

• The cytoplasm is evenly divided

• New cell membrane forms in animal cells

• New cell wall is built across for plant cells