NOTES: 10.3-10.4Regulating the Cell Cycle /Cell Differentiation
10.3: Regulating the Cell Cycle
Key Concepts:
•How is the cell cycleregulated?
•How are cancer cellsdifferent from othercells?
•What causescancer?
The Cell Cycle –review of the basics:
•Genetic information is in theform of DNA
•Cell cycle = process of celldivision
The cell grows;
DNA is copied;
The contents of the nucleus aredivided;
Cytoplasm is divided;
Two new cells exactly like theoriginal cell!
•one of the major characteristics of livingthings is the ability to GROW
•an adult doesn't have bigger cells, they havemore cells
You can grow too many cells!!!
Also, recall…
An Interesting Fact About Cell Division:
•Not all cells move through thecell cycle at the same rate
–Ex: most muscle cells & nervecells do not divide at all oncethey have developed
–Ex: skin cells and cells liningour intestines complete thecell cycle every 24-28 hours
–Ex: frog embryo cells take lessthan one hour!
•Controls can be observed in a lab
–Cells in a petri dish containing nutrient broth(food) will grow and divide forming a thin layer
–When the cells come into contact with eachother, they stop growing
Controls on Cell Division continued…
• If cells from the centerare removed, growth anddivision will continueuntil cells are in contactwith each other onceagain
• When have youwitnessed this happeningwith your own body?
Cell Cycle Regulators
•Several scientists discovered that cellsundergoing cell division (mitosis)contained a protein/enzyme
•If this protein was injected into anondividing cell, the mitotic spindlewould start to form
–Scientists called this protein CYCLIN
–Scientists have since discovered a family ofclosely related proteins (cyclins) & dozensof other proteins that help regulate the cellcycle
Regulatory Proteins:
•The cell cycleis controlledby regulatoryproteins, bothinside &outside of thecell
Regulatory Proteins: INTERNAL
•Respond to events occurring inside a cell
•Allow the cell cycle to proceed onlywhen certain events have occurred inthe cell itself
•Example: some regulatory proteinsmake sure a cell does not enter mitosisuntil its chromosomes have beenreplicated
•Example: a regulatory protein preventsa cell from entering anaphase until thespindle fibers have attached to allchromosomes.
Regulatory Proteins: EXTERNAL
•Respond to events occurring outside the cell
•GROWTH FACTORS: stimulate growth &division of cells
-important during embryo development &wound healing
•Other external regulators cause cells toslow down or stop their cell cycles…thisprevents excessive cell growth & keepsbody tissues from disrupting one another.
Recent studies suggest…
•The portion of interphasejust before DNAreplication is a key controlperiod in the cell cycle;
•There are severalregulatory proteinsidentified as controllingthe cell cycle…
•RECALL: proteins arecoded for by DNA! So…
•A mistake (MUTATION) in the DNA(GENES) that codes for one or more ofthese control factors/enzymes couldlead to a LOSS OF CONTROL OF THECELL CYCLE.
•What can happen if thecell cycleis not regulatedso carefully?
–CANCER!!
•Cancer cells do notrespond to signals thatregulate the growth ofmost cells.
•The result? They formmasses of cells calledTUMORS that can damagethe surrounding tissues
–Benign vs. malignant
•Cancer cells can also breakoff and spread throughoutthe body METASTASIS
BREAST TUMOR
Old Mastectomy
Vs.
New Mastectomy
Recent Research
•Many cancer cells have a defect in a
gene called p53
–The protein made from this gene normally
halts the cell cycle until all chromosomes have beenreplicated properly (without mutations)
–If it isn’t working, damaged DNA can replicate
–The cell may have lost the information it needs torespond to growth control signals
•Cancer is a disease of the cell cycle
Cancer is the 2nd leading cause ofdeath in the U.S.
•It can affect any tissue,but the most commonlyaffected are:
lung
colon
breast
prostate
What causes the loss of growthcontrol?
•Smoking tobacco
•Radiation exposure
•Viral infection
HUMAN LUNG
Cancer Prevention:
● There is a clear link between healthylifestyle and reducing the incidence ofcancer;
● Diet low in fat and high in fiber;
(fruits, vegetables, & grains)
● Vitamins and minerals;
(A, C, E, & calcium)
● Exercise;
● Wear sunscreen
● DON’T SMOKE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
(Seriously!! This should be a no-brainer!!)
Treatments
•surgery (for benign tumors)
•radiation
•chemotherapy
10.4: Cell Differentiation
Key Concepts:
•How do cells becomespecialized fordifferent functions?
•What are stem cells?
•What are somepossible benefits &issues associatedwith stem cellresearch?
Cell Differentiation:
● the process by which cellsbecome specialized fordifferent functions;
● we all started as anindividual fertilized egg cell embryo adultorganism
● cell differentiation iscontrolled by a number ofinteracting factors in anembryo…many of which westill don’t completelyunderstand!
STEM CELLS:
● how do so manyspecialized,differentiated cell typesdevelop from just asingle cell?
● such a cell is said to beTOTIPOTENT
● TOTIPOTENT = able todevelop into any cell type inthe body
● PLURIPOTENT = able todevelop into most of thebody’s cell types
STEM CELLS:
● STEM CELLS = theunspecialized cells fromwhich differentiated cellsdevelop
● TYPES of stem cells:
● EMBRYONIC: pluripotentcells found in early embryostages…mouse embryonicstem cells have beentriggered to differentiate into:nerve cells, muscle cells, &even sperm & egg cells!
STEM CELLS:
● TYPES of stem cells:
● ADULT: groups of cells that differentiateto renew & replace cells in the adultbody; more limited than embryonic stemcells
● Example: adult stem cells in the bonemarrow can develop into several typesof blood cells
● Example: adult stem cells in the braincan produce neurons or nerve cells
STEM CELLS:
● BENEFITS of Stem Cell Research:
● stem cells offer excellent prospects torepair cellular damage that is the causeof many human life-threateningconditions:
● Example: heart attacks destroy heartcells
● Example: strokes & spinal cord injuriesdestroy nerve cells & cause paralysis
STEM CELLS:
● ETHICAL ISSUES:
● adult stem cells can be harvested fromwilling adult donors
● embryonic stem cells are harvested fromearly stage embryos…this has led tomany ethical discussions involvingissues of life and death…
● in the future, technology may help toreduce these ethical concerns (i.e.reprogram an adult stem cell to behavelike an embryonic stem cell)
