Cell Division (aka Mitosis)

Cell Division (aka Mitosis)

Cell Growth and Division Cell division is needed to Grow most organisms grow by producing more cells Repair wounds and damaged cells

Develop and change Why do cells divide? (aka, why are cells small?) Two main reasons why cells cant grow indefinitely: A larger cell places more demands on its DNA (more things to control and not enough DNA) Surface-to-volume ratio decreases as size increases

Thus, before the cell becomes too large, it divides When do cells divide (or stop)? When cells crowd each other, they stop dividing When internal factors signal the cell to start or stop dividing e.g., p53 gene makes sure the cell doesnt divide until chromosomes have doubled; cyclin enzymes start/stop the

cell cycle When external chemical or physical signals (growth regulators) stimulate or inhibit growth and division (Cancer is an example of uncontrolled cell growth.we will discuss cancer later in the unit) Cells divide at different rates

The rate of cell division varies with the need for the type of cell What is the cell cycle? The series of phases that cells go through as they grow and divide. A continuous process, but we divide it into 3 stages: 1. Interphase 2. Mitosis

3. Cytokinesis http://images1.clinicaltools.com/images/gene/celldivision/cellcycle.jpg Stage 1: Interphase

Cell life between divisions The longest stage! Nucleus is still present Phases: Gap 0 (G0) grows and functions Gap 1 (G1) duplicates organelles and molecules

needed for cell division Synthesis (S) duplicates DNA (in chromotin form) Gap 2 (G2 ) checks for errors Stage 2: Mitosis Duplication and division of the cell nucleus Phases:

1. 2. 3. 4. Prophase Metaphase Anaphase Telophase

Stage 3: Cytokinesis Pinching off of the cytoplasm (Often grouped as part of mitosis) Mitosis + cytokinesis result in two identical daughter cells! YouTube: Mitosis

Now!, Lets look at your Mitosis Flipbook and compare (Review) Interphase Nucleus is still intact and the nucleolus is visible.

DNA is in chromatin form Includes G1, S, and G2 Mitosis step 1: Prophase Centrioles separate and produce spindle fibers Chromatin condenses to form chromosomes Nuclear envelope and nucleolus break down prophase pro (#1!)

Chromatin? Chromosomes? Chromatin = DNA unwound (looks like spaghetti) Chromosome = DNA condensed and organized; looks like this: 2 chromosomes

Sister chromatids = a duplicated chromosome Centromere = the place where chromotids are connected Some useful DNA vocabulary! To recap During prophase, chromatin condense into chromosomes which have duplicated into sister chromatids, attached to each

other at their centromeres. Mitosis step 1: Prophase Centrioles separate and produce spindle fibers Chromatin condenses to form chromosomes Nuclear envelope and nucleolus break down prophase pro (#1!) Mitosis step 2: Metaphase

Chromosomes line up at the middle of the cell A spindle fiber attaches to each sister chromatid at the centromere metaphase middle Mitosis step 3: Anaphase Spindle fibers contract and pull apart the chromosomes to opposite ends of the cell anaphase apart

Mitosis step 4: Telophase Chromosomes return to chromatin form Nuclear membranes and nucleolus reform

Spindle fibers disappear Nuclear division is complete telophase telephone After mitosisStage 3: Cytokinesis Pinching of the cytoplasm, resulting in two

identical daughter cells. The cell cycle: IPMATC I Passed My Algebra

Test with a C YouTube: Mitosis Video Mitosis Review Mitosis in plants Plants dont have centrioles

Cell plate forms during telophase During cytokinesis, cell plate separates the daughter cells and becomes the new cell wall Blood lily mitosis Mitosis in real cellsPMAT

Where doesnt mitosis happen? Nerve and blood cells are different Sex cells (gametes) undergo a different division process Your summary

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