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 CellsHow Often Cells Divide Embryo Cells30 minutes Intestinal Cells3 days Blood Cells3 months Nerve CellsNever / 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 membrane clearly 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