The Cell Cycle 10-2. Process by which a cell grows, prepares for division and divides Process by which a cell grows, prepares for division and divides.

The Cell CycleThe Cell Cycle

10-210-2


Process by which a cell Process by which a cell growsgrows, , prepares for divisionprepares for division and and dividesdivides


Four phasesFour phases1.1. GG11 (Gap 1) (Gap 1)

– Cell grows, Cell grows, generates generates organelles, etc.organelles, etc.

– 40% of a cell’s life40% of a cell’s life– If a cell’s life were a If a cell’s life were a

day it would last day it would last from midnight to from midnight to 9:36 am9:36 am


2.2. S (Synthesis)S (Synthesis)– All of a cell’s DNA All of a cell’s DNA

is copiedis copied– 39% of a cell’s life39% of a cell’s life– If a cell’s life were If a cell’s life were

a day it would last a day it would last from 9:36 am to from 9:36 am to 6:47 pm6:47 pm


3.3. GG22 (Gap 2) (Gap 2)– Final preparation Final preparation

for cell divisionfor cell division– 19% of a cell’s life19% of a cell’s life– If a cell’s life were If a cell’s life were

a day it would last a day it would last from 6:47 pm to from 6:47 pm to 11:21 pm11:21 pm


4.4. M (Mitosis)M (Mitosis)– Cell divisionCell division– 2% of a cell’s life2% of a cell’s life– If a cell’s life were If a cell’s life were

a day it would last a day it would last from 11:21 pm to from 11:21 pm to midnightmidnight


InterphaseInterphase– GG11, S and G, S and G22

phasesphases– ““Business as Business as

usual” for a cellusual” for a cell– 98% of a cell’s life98% of a cell’s life– Basically the time Basically the time

a cell spends a cell spends notnot dividingdividing

Cell DivisionCell Division

Ends with Ends with twotwo genetically genetically identicalidentical daughter cellsdaughter cells


Before a cell divides:Before a cell divides:– An exact copy of the cell’s DNA An exact copy of the cell’s DNA

is madeis made S phase of the cell cycleS phase of the cell cycle


– DNA condenses into DNA condenses into chromosomeschromosomes

Most of the time DNA is in a loose Most of the time DNA is in a loose jumbled mess called jumbled mess called chromatinchromatin– Resembles Ramen soupResembles Ramen soup


ChromatinChromatin

nucleus

cell membrane

chromatin


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


ChromosomesChromosomes– Made of two exact copies of Made of two exact copies of

the same section of DNAthe same section of DNA– Two copies are attached to one Two copies are attached to one

anotheranother– DNA is very tightly packedDNA is very tightly packed


Chromosome structureChromosome structure

DNA strand

wound aroundproteins

identicalstrandsattach

DNAcondenses


Chromosome structureChromosome structureCentromere: attachment point

Tightly packedDNA

Sisterchromatids: two copies of the same DNA

BREAKBREAK


Two Phases:Two Phases:1.1. Mitosis:Mitosis: division of the nucleus division of the nucleus

2.2. Cytokinesis:Cytokinesis: division of the division of the cytoplasmcytoplasm


1.1. MitosisMitosis– Division of the nucleusDivision of the nucleus– If something goes wrong here the If something goes wrong here the

daughter cells may not function daughter cells may not function properly or they may die properly or they may die


machinerymachinery ChromosomesChromosomes Spindles:Spindles: protein fibers that form protein fibers that form

then pull the chromosomes apart at then pull the chromosomes apart at the end of mitosisthe end of mitosis

Centroles:Centroles: structures that help structures that help organize the spindlesorganize the spindles


– 4 Phases:4 Phases: ProphaseProphase MetaphaseMetaphase AnaphaseAnaphase TelophaseTelophase

= PMAT= PMAT


– ProphaseProphase Chromatin (DNA soup) condenses Chromatin (DNA soup) condenses

into chromosomes (X-shaped into chromosomes (X-shaped structures)structures)

Centrioles move to opposite ends Centrioles move to opposite ends of the cellsof the cells

Spindle begins to formSpindle begins to form Nuclear envelope breaks downNuclear envelope breaks down


– ProphaseProphase


– MetaphaseMetaphase Chromosomes line up down the Chromosomes line up down the

center of the cellcenter of the cell Spindles attach to the Spindles attach to the

chromosomeschromosomes Nucleus has completely dissolvedNucleus has completely dissolved


– MetaphaseMetaphase


– AnaphaseAnaphase Sister chromatids (each half of Sister chromatids (each half of

the X-shaped chromosome) the X-shaped chromosome) separateseparate

Spindles pull sister chromatids Spindles pull sister chromatids apartapart


– AnaphaseAnaphase


– TelophaseTelophase Chromosomes gather at opposite Chromosomes gather at opposite

ends of the cell and begin to ends of the cell and begin to unravel into chromatinunravel into chromatin

Two new nuclear envelopes formTwo new nuclear envelopes form


– TelophaseTelophase


– Ends with one giant cell with Ends with one giant cell with two nucleitwo nuclei


2.2. CytokinesisCytokinesis– In animal cells:In animal cells:

Cell membrane pinches inward Cell membrane pinches inward between the two nucleibetween the two nuclei

Continues pinching until two Continues pinching until two nuclei are separatednuclei are separated

End up with about half the End up with about half the organelles and cytoplasm in each organelles and cytoplasm in each cellcell


– In animal cells:In animal cells:


– In plant cells:In plant cells: A cell plate forms between the A cell plate forms between the

two nucleitwo nuclei Cell plate turns into the new cell Cell plate turns into the new cell

membranemembrane New cell wall forms around the New cell wall forms around the

cell membranecell membrane


– In plant cells:In plant cells:

Cell plate


Cell division movieCell division movie

http://www.cellsalive.com/mitosis.htm

BREAKBREAK

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: 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

Can begin in any cells of the body and then spread through the body in the bloodstream or lymphatic system (glands)

Most small changes are fixed by the body, those that are not can become cancer

Cancer

http://www.youtube.com/watch?v=LEpTTolebqo

http://www.youtube.com/watch?v=LEpTTolebqo

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

HPV is a sexually-transmitted disease!!!

There are 3,700 fatalities in the U.S. each year due to cervical cancer

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

The Cell Cycle 10-2. Process by which a cell grows, prepares for division and divides Process by which a cell grows, prepares for division and divides.

Documents

cell slide

cell chromosomes

cell division dna

cell spindles

cell cycle slide

cell membrane slide

cell divides

cell division ends