1. Notes 4-3 Cell Division

2. 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

3. The cell cycle • The cell cycle is divided into 3 stages: • Interphase • Mitosis • Cytokinesis *Notice how long interphase is, then mitosis is short, and cytokinesis is VERY short!

4. Stage 1: Interphase • Longest phase of the cell cycle • The cell is doing 3 major things: • Growing • Copying its DNA (process known as replication) • 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.

5. 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: • Prophase • Metaphase • Anaphase • Telophase Let’s look at each phase!

6. 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

7. Metaphase • Chromosomes attach to the spindle fibers and move to the middle of the cell • Metaphase = middle!

8. 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

9. 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

10. 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

11. 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

12. 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

13. Plant cell

14. The Cell Cycle

15. 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!!!) 