Cell DivisionPages 55-62 “C” in book

Cells go through a cycle. During this cycle, the cells make a copy of their DNA and a new cell is

created. This process is what allows a huge pumpkin to grow from a tiny seed and become larger and larger! The cells duplicate over and over and over again and so the pumpkin gets

larger.

Be sure you only take notes on the bold and underlined sections.

• You will have an assignment at the end of the power point presentation and you will get your notes and pictures from your book also.

The new cells are called daughter cells.

• This cell cycle has a regular sequence of growth and division. Each of the daughter cells will begin the cell cycle again.

• There are three main stages: interphase, mitosis, and cytokinesis.

Think of it as the phases or stages you go through in your life:

• 1. Infant 2.Toddler

3. Adolescence 4. Adult 5. Old age

What does the cell cycle look like?

• See page 58 & 59 “C”• in your textbook.• 1 & 2 Interphase• 3. Prophase• 4. Metaphase• 5. Anaphase• 6. Telophase• 7. Cytokinesis

Stage 1-Interphase

• 1st stage of cell cycle. This is the period before cell division. Some call it “resting stage” ------it is not!

• What happens during interphase? The cell grows, makes a copy of its DNA, and prepares to divide into two cells. There are also two structures called centrioles that are also copied.

Stage 2 is Mitosis

• Mitosis is actually divided into smaller stages that are quite easy to see. The chromosomes are in different positions for each of the stages in mitosis. The stages within mitosis are:

• A. Prophase• B. Metaphase• C. Anaphase• D. Telophase.• Let’s look at each one separately.

Prophase

• The chromatin (nucleic acid – DNA & RNA) in the nucleus condenses and forms chromosomes.

What else occurs during prophase?

• The pairs of centrioles move to the opposite sides of the nucleus and spindle fibers form a bridge between the ends of the cell. The nuclear envelope breaks down and then it disappears.

Next stage = Metaphase

• During metaphase the chromosomes line up across the center of the cell. Each chromosome attaches to a spindle fiber at its centromere.

• Metaphase

Next comes Anaphase

• What happens—the centromeres split. The two chromatids separate. One chromatid is drawn by its spindle fiber to one end of the cell. The other moves to the opposite ends of the cell. The cell stretches out.

Now we are at telophase

• The chromosomes begin to stretch out and lose their rod-like appearance. A new nuclear envelope forms around each region of chromosomes.

Last thing to occur is Cytokinesis

• The cell membrane pinches in around the middle of the cell. The cell splits in two. Each daughter cell ends up with an identical set of chromosomes and about half the organelles.

During cytokinesis remember:

• The cytoplasm divides, the organelles are distributed into each of the two new cells.

• Cytokinesis begins about the same time as telophase so they often look alike. The two daughter cells have the same number of chromosomes as the parent cell.

•The cell then goes into - - - - - - - - - - ?

The cell cycle then goes back to the Interphase stage

• Then it “rests” –but remember it is not really resting but getting ready for the stages to begin again.

Is there a difference between animal and plant cells? Of course!!

• In animal cells during cytokinesis, the cell membrane squeezes together around the middle of the cell. The cytoplasm pinches into two cells and each daughter cell gets about half of the organelles.

So, what about the plant cell?

• It is different because plants cannot squeeze due to their rigid cell walls. Instead a cell plate forms across the middle of the cell. The cell plate gradually develops into a new cell wall. A new cell membrane develops between the two new daughter cells and the cell walls form.

OK Review time---

• Cell cycle:

Are you ready to see what you can recognize?

• This is the __________________stage

• What happens here?

It’s Anaphase

• I think of it as little A’s being pulled towards the ends of the cell’s poles. The sister chromatids are actually separated and pulled to opposite poles of the cell

Now this---name the stage

• What is happening?

Interphase!!!

• Did you get it right?• Remember this is when the cell grows to its

mature size, makes a copy of its DNA and prepares to divide into two cells. The centrioles are also are copied.

How about this one?

• Remember that• this one looks like another one that follows it and

they actually happen almost at the same time.

Telophase!!

• The chromosomes stretch out and lose their rod-like appearance and a new nuclear envelope forms around each region of the chromosomes---then finally…….

•Cytokinensis

Now for your assignment:

• Using your journal and a textbook—turn to a new page in the journal and use today’s date and the topic of “The Cell Cycle”

• Turn to page 58-59 C in your book-using ½ page each drawing-draw the stages and write what is happening from your pages for each phases of the stages. Basically you are copying what you see into 3 pages of your journal. Get to work—Be sure to draw them in order and color (Easier to see what is going on).

Again---get to work!!!!