Notes 4-3 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.Interphase 2.Mitosis 3.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.Growing 2.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.Prophase 2.Metaphase 3.Anaphase 4.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!!!)