Notes 4-3

Cell Division

Cell Division

• How do you get bigger?• Your cells grow and divide into 2 cells over and

over again.• This is known as the cell cycle.• The 2 new cells made are known as daughter

cells

The cell cycle

• The cell cycle is divided into 3 stages:

1. Interphase2. Mitosis3. Cytokinesis

*Notice how long interphase is, then mitosis is short, and cytokinesis is VERY short!

Stage 1: Interphase• Longest phase of the cell

cycle• The cell is doing 3 major

things:1. Growing2. Copying its DNA (process

known as replication)3. Preparing for cell division

(preparing for stage 2: mitosis)

• Why do you think the cell must copy its DNA before it divides?

After cell division, you end up with 2 new cells. Each of these cells must have its own copy of DNA in order to carry out functions.

Stage 2: Mitosis

• The cells nucleus divides, each containing a copy of DNA

• This way, each of the 2 daughter cells made gets a copy of DNA

• Mitosis is divided into four parts:

1. Prophase2. Metaphase3. Anaphase4. Telophase

Let’s look at each phase!

Prophase

• Chromatin (DNA) in the nucleus condenses into X-like structures called chromosomes

• Each part of the “X” of the chomosome is an identical copy of DNA and is called a “sister chromatid”

• The nuclear envelope begins to disappear

• A spindle begins to form

Metaphase

• Chromosomes attach to the spindle fibers and move to the middle of the cell

• Metaphase = middle!

Anaphase

• Each chromosomes are pulled apart• Spindle fibers move each sister chromatid to

opposite sides of the cell• Each chromatid is now called a chromosome

Telophase

• The cell begins to pinch off in the middle• 2 Nuclear envelopes reform around each set

of chromosomes• By now, the nucleus has successfully divided

into 2 distinct nuclei

Stage 3: Cytokinesis

• The cell membrane continues to pinch off until the cell splits into 2 daughter cells

• Each daughter cell has an identical and complete copy of DNA

• After cytokinesis, each daughter cell will then immediately enter interphase, and restart the cell cycle

• The process is endless

• This slide shows you telophase again at the top (1 cell but 2 nuclei), and then cytokinesis (2 cells, each with 1 nucleus)

• This is an animal cell

Cytokinesis in plant cells

• Since plant cells have rigid cell walls, the cytoplasm cannot pinch off like in animal cells

• Instead, a cell plate forms across the middle of the cell

• The cell plate eventually turns into new cell membranes between the 2 daughter cells, and then the cell walls form around the new cell membranes

Plant cell

The Cell Cycle

How to remember the steps…

• I-P-MAT, then cytokinesis

• This represents the order of all the parts of the cell cycle… a teacher told me this silly riddle once and I never forgot it!

• I-P-MAT (Don’t pee on your mat!!!)