NOTES for Cell Cycle & Mitosis Biology 2016 Johnson
I. The Cell Cycle II. http://www.youtube.com/watch?v=q6uckwiifmg (2:15-4:25) III. http://www.cellsalive.com/mitosis.htm A. Limits to Cell Size 1. As an organism grows, it gets MORE cells, NOT bigger cells! 2. Two things allow a cell to get only so big: a. Materials Movement *nutrients and wastes need to get into and out of the cell, and they only move so fast. b. DNA overload *the single copy of DNA in a cell s nucleus can only control so many organelles!
B. When a cell gets too big, it divides. 1. Two daughter cells are more efficient than a single, big cell. 2. Average life spans of some human cells before they divide: a. lining of small intestine = 1-2 days b. lining of esophagus = 2-3 days c. lining of large intestine = 6 days d. red blood cells = 120 days e. white blood cells = 10 hours decades f. heart & nerve cells = never (irreplaceable) C. Two main parts of a cell s life: Interphase & Mitosis (again, here s what we re talking about: http://www.cellsalive.com/mitosis.htm )
1. Interphase = when a cell is NOT dividing. a. Most of a cell s life. b. Normal cell activities. c. Three phases in Interphase: Step1: G 1 = Cell growth Step 2: S = DNA is doubled so both new daughter cells can have a copy after it divides. Step 3: G 2 = All organelles are doubled so cell is ready for division.
2. Mitosis = cell division a. Also called M-phase. b. Very short part of a cell s life (about 2%) compared to Interphase. c. How you got from 1 cell to trillions of cells. d. Divided into 5 steps: Prophase Metaphase Anaphase Telophase Cytokinesis
IV. Events in each phase of Mitosis: A. Prophase = first step in mitosis 1. DNA wraps around proteins (called histones ) to form chromosomes. 2. Nuclear membrane breaks down. 3. Spindle fibers form. B. Metaphase Chromosomes (made of two identical sister chromatids joined at the centromere) attach to spindle fibers along middle of cell. C. Anaphase Sister chromatids split into daughter chromosomes and begin to move along spindle fibers to opposite ends of cell. D. Telophase New nuclear membrane forms around chromosomes. Spindle fibers disappear. E. Cytokinesis Cell pinches off to make two new daughter cells. Chromosomes unravel back into chromatin. Each daughter cell enters G 1
V. Events in each phase of Mitosis: A. Prophase = first step in mitosis 4. DNA wraps around proteins (called histones ) to form chromosomes. 5. Nuclear membrane breaks down. 6. Spindle fibers form. F. Metaphase Chromosomes (made of two identical sister chromatids joined at the centromere) attach to spindle fibers along middle of cell. G. Anaphase Sister chromatids split into daughter chromosomes and begin to move along spindle fibers to opposite ends of cell. H. Telophase New nuclear membrane forms around chromosomes. Spindle fibers disappear. I. Cytokinesis Cell pinches off to make two new daughter cells. Chromosomes unravel back into chromatin. Each daughter cell enters G 1
Loose DNA: chromatin Changes to DNA during the Cell Cycle 1. G 1 -Interphase: DNA is a long thread called chromatin. 2. S-Interphase: chromatin copies itself to get ready for cell division. 3. Prophase: chromatin wraps around proteins called histones to form chromosomes. a. To organize the 6 feet of DNA in the nucleus. b. The paired identical chromosomes are called sister chromatids which are joined at a point called the centromere. 4. Metaphase: still sister chromatids. 5. Anaphase: sister chromatids separate into daughter chromosomes. 6. Cytokinesis: chromosomes unravel back into loose chromatin.
II. Cell Cycle Controls A. Two things control when a cell divides: 1. Chemicals called cyclins build up in a cell and trigger mitosis when they reach a certain level. These cyclins are produced by a single gene on a cell s chromosome. 2. Contact Inhibition (when cells touch each other) also regulate when a cell divides. *especially important in wound healing B. If that gene that produces cyclin gets messed up, cells may divide uncontrollably. This occurrence is called cancer. (3:00-6:25)
1. Cancer (Tumor) Characteristics: a. invade and destroy healthy tissues. b. use up more nutrients than normal cells and grow their own blood vessels. c. may break loose and move to other parts of the body in a process called metastasis. d. One out of four people in the US will get cancer at some time in their life
2. Cancer Causes a. Genetic (many forms run in families) b. Carcinogens - things in the environment 1) radiation -sunlight, nuclear, etc. 2) tobacco - 30% of ALL cancers 3) pollution 3. Cancer Treatments a. Surgery remove an accessible, isolated tumor. b. Radiation shoot inaccessible, isolated tumors c. Chemotherapy harsh chemicals used to kill off widespread cancerous cells. 4. Cancer Prognosis-depends on the type a. pancreatic cancer = 3% survival b. testicular cancer = 91% survival