The Cell Cycle 10-2

The Cell Cycle Process by which a cell grows, prepares for division and divides

The Cell Cycle Four phases G1 (Gap 1) Cell grows, generates organelles, etc. 40% of a cell’s life If a cell’s life were a day it would last from midnight to 9:36 am

The Cell Cycle S (Synthesis) All of a cell’s DNA is copied 39% of a cell’s life If a cell’s life were a day it would last from 9:36 am to 6:47 pm

The Cell Cycle G2 (Gap 2) Final preparation for cell division 19% of a cell’s life If a cell’s life were a day it would last from 6:47 pm to 11:21 pm

The Cell Cycle M (Mitosis) Cell division 2% of a cell’s life If a cell’s life were a day it would last from 11:21 pm to midnight

The Cell Cycle Interphase G1, S and G2 phases “Business as usual” for a cell 98% of a cell’s life Basically the time a cell spends not dividing

Cell Division Ends with two genetically identical daughter cells

Cell Division Before a cell divides: An exact copy of the cell’s DNA is made S phase of the cell cycle

Cell Division DNA condenses into chromosomes Most of the time DNA is in a loose jumbled mess called chromatin Resembles Ramen soup

Cell Division Chromatin cell membrane chromatin nucleus

Cell Division If a cell divided before condensing there is no way to ensure each new cell received equal amounts of DNA

Cell Division Chromosomes Made of two exact copies of the same section of DNA Two copies are attached to one another DNA is very tightly packed

Cell Division Chromosome structure wound around proteins identical strands attach DNA strand DNA condenses

Cell Division Chromosome structure Centromere: attachment point Tightly packed DNA Sister chromatids: two copies of the same DNA

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Cell Division Two Phases: Mitosis: division of the nucleus Cytokinesis: division of the cytoplasm

Cell Division Mitosis Division of the nucleus If something goes wrong here the daughter cells may not function properly or they may die 

Cell Division machinery Chromosomes Spindles: protein fibers that form then pull the chromosomes apart at the end of mitosis Centroles: structures that help organize the spindles

Cell Division 4 Phases: Prophase Metaphase Anaphase Telophase = PMAT

Cell Division Prophase Chromatin (DNA soup) condenses into chromosomes (X-shaped structures) Centrioles move to opposite ends of the cells Spindle begins to form Nuclear envelope breaks down

Cell Division Prophase

Cell Division Metaphase Chromosomes line up down the center of the cell Spindles attach to the chromosomes Nucleus has completely dissolved

Cell Division Metaphase

Cell Division Anaphase Sister chromatids (each half of the X-shaped chromosome) separate Spindles pull sister chromatids apart

Cell Division Anaphase

Cell Division Telophase Chromosomes gather at opposite ends of the cell and begin to unravel into chromatin Two new nuclear envelopes form

Cell Division Telophase

Cell Division Ends with one giant cell with two nuclei

Cell Division Cytokinesis In animal cells: Cell membrane pinches inward between the two nuclei Continues pinching until two nuclei are separated End up with about half the organelles and cytoplasm in each cell

Cell Division In animal cells:

Cell Division In plant cells: A cell plate forms between the two nuclei Cell plate turns into the new cell membrane New cell wall forms around the cell membrane

Cell Division In plant cells: Cell plate

Cell Division Cell division movie

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Control of the Cell Cycle 10-3

Enzymes that Control the Cell Cycle Controlled in large part by a group of enzymes called cyclins Cyclins: levels rise and fall during cycle causing numerous different actions Other enzymes regulate specific phases of the cell cycle Still more enzymes: respond to events outside the cell and adjust the cell cycle

Enzymes that Control the Cell Cycle Production of these enzymes is directed by DNA When DNA is damaged, production of enzymes goes all wrong: Complete lack of production of a enzyme Overproduction of a enzyme Without the proper amount of specific enzymes the cell cycle will either stop (resulting in cell death) or cells will divide uncontrollably (resulting in cancer)

Contact Inhibition Some cells will only divide if they are not in direct contact with one another When skin cells contact one another, cell division slows to rates just fast enough to replace cells that die due to normal wear and tear Skin cells sense contact through chemical signals, which are controlled by DNA Damage to the DNA that controls these signals can also result in cancer

Cancer Cancer: a disease where cells lose the ability to control the cell cycle Caused by changes to the DNA that controls enzymes that regulate the cell cycle Most small changes are fixed by the body, those that are not can become cancer Can begin in any cells of the body and then spread through the body in the bloodstream or lymphatic system (glands)

Cancer A quote from the American Cancer Society website: www.cancer.org “Cancer is the second leading cause of death in the United States. Nearly half of all men and a little over one-third of all women in the US will develop cancer during their lifetimes. Today, millions of people are living with cancer or have had cancer. “The risk of developing most types of cancer can be reduced by changes in a person's lifestyle, for example, by quitting smoking and eating a better diet. The sooner a cancer is found and treatment begins, the better are the chances for living for many years.”

Causes of Cancer The well-known factors that increase risk: Overexposure to UV radiation (THE SUN & SUN LAMPS!!) Smoking Over consumption of alcohol Other forms of radiation Contaminants in water Viruses!

Scare the Girls Slides Cervical Cancer Rates of cervical cancer have risen dramatically in young (16- to 30-year-olds) girls recently Infection with human papilloma virus (HPV) is found in nearly 80% of all cases of cervical cancer There are 3,700 fatalities in the U.S. each year due to cervical cancer HPV is a sexually-transmitted disease!!!

Scare the Girls Slides Cervical Cancer Routine screening (yearly gynecological exam) is the best way to catch the disease early. Vaccines are now available (Gardasil and Cervarix) to protect against HPV but it must be administered before a girl becomes sexually active There is no way to vaccinate or test males (who are carriers) and there is almost no way to tell whether a male is infected

Scare the Guys Slide Testicular Cancer (aka “What Lance Armstrong had”) Testicular cancer is the most common cancer in American men between the ages of 15 and 40 (YOUR AGE GROUP!). 7,600 men receive a diagnosis of testicular cancer each year in the US - 400 men die When diagnosed early, testicular cancer is highly treatable Regular testicular self-examinations can help identify dangerous growths early, when the chance for successful treatment is highest