What is Mitosis? Mitosis is when the cell’s nucleus divides into two new nuclei and one copy of the DNA is distributed into each daughter cell. New cells formed are called daughter cells.

Why Do Cells Need to Divide? Cells want to divide for several reasons: 1) Large cells can’t control their functions as well as small cells-- as a cell gets bigger, it still the same amount of DNA to do the same jobs 2) Large cells can’t exchange materials as well-- the ratio of surface area (cell membrane) to cell volume decreases as a cell gets bigger, making it harder for food to get in and wastes to go out 3) As cells age, they aren’t as efficient

The Cell Cycle Cells aren’t constantly dividing; instead, cells grow, live their lives and then divide when necessary. Cell cycle -- this process of growth and division is known as the The cell cycle consists of three parts: Interphase -- interphase is further divided into three parts Mitosis -- mitosis is also divided into four parts called prophase, metaphase, anaphase, and telophase Cytokinesis -- Completes the process of cell division

Image of the Cell Cycle

Interphase The cell cycle begins when a new daughter cell is formed and immediately begins interphase. During interphase, the cell undergoes the following life “phases” 1. Cells grow to their mature size 2. Cells replicate their DNA so that they have a copy for each new daughter cell. 3. Cells also manufacture new proteins and organelles preparing to divide into two cells. ONCE THIS HAPPENS MITOSIS IS READY TO BEGIN!!

About Chromosomes Chromosomes are only visible when mitosis is about to begin and during mitosis. Chromosomes consist of a chromatid (a strand of DNA) with a condensed area called the centromere. Centromeres are near the middle of a chromatid. DNA (and therefore chromosomes) are replicated during the interphase, so each chromosome actually consists of two “sister” chromatids. Humans have 23 matching pairs of chromosomes, for a grand total of 46 chromosomes

Image of a Chromosome

Mitosis Biologists usually consider the first four parts to be actual “mitosis”, The parts of mitosis are: -- prophase -- metaphase -- anaphase -- telophase The final part of the cell cycle, cytokinesis, happens later.

Prophase Prophase is the longest phase of mitosis During prophase: -- the centrioles line up on opposite sides of the nucleus 1. Chromatin condenses into visible chromosomes 2. Structures called spindle fibers form a bridge between each end of the cell. 3. Nucleolus disappears and nuclear membrane breaks down

Metaphase Metaphase only last for a few minutes During metaphase: 1. Chromosomes line up across the center of the cell 2. Chromosome attach to the spindle fibers at the centromere

Anaphase During anaphase: 1. Centromeres that join sister chromatids separate and the chromatids become individual chromosomes 2. Chromosomes move apart until they reach the centrioles near the end of the spindle 3. Cell becomes stretched out as the opposite ends pull apart. Anaphase ends when the centrioles stop moving

Telophase During telophase: 1. Chromosomes begin to tangle back into chromatin and lose their rod-like appearance 2. Nuclear membrane begins to re-form around each set of chromosomes 3. Spindle fibers break 4. Nuceloli become visible in each new nucleus END OF MITOSIS

Cytokinesis Although cells have split up their genetic material and formed new nuclei, the cells are not split. Cytokinesis is the process by which cells split their cytoplasm into two new daughter cells In animals, cytokinesis happens when the cell membrane is drawn in and the cell divides into two new cells In plants, a structure made of wall-building vesicles, called a cell plate forms between the two new nuclei, and eventually becomes a dividing membrane

Full Diagram of Mitosis