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NOTES: 10.3-10.4
Regulating the Cell Cycle /
Cell Differentiation
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10.3: Regulating the Cell Cycle
Key Concepts:• How is the cell cycle
regulated?
• How are cancer cells different from other cells?
• What causes cancer?
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The Cell Cycle –review of the basics:
• Genetic information is in the form of DNA
• Cell cycle = process of cell division The cell grows;
DNA is copied;
The contents of the nucleus are divided;
Cytoplasm is divided;
Two new cells exactly like the original cell!
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• one of the major characteristics of living things is the ability to GROW
• an adult doesn't have bigger cells, they have more cells
You can grow too many cells!!!
Also, recall…
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An Interesting Fact About Cell Division:
• Not all cells move through the cell cycle at the same rate
– Ex: most muscle cells & nervecells do not divide at all once they have developed
– Ex: skin cells and cells lining our intestines complete the cell cycle every 24-28 hours
– Ex: frog embryo cells take less than one hour!
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• 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 each other, they stop growing
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Controls on Cell Division continued…
• If cells from the center are removed, growth and division will continue until cells are in contact with each other once again
• When have you witnessed this happening with your own body?
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Cell Cycle Regulators
• Several scientists discovered that cells undergoing cell division (mitosis) contained a protein/enzyme
• If this protein was injected into a nondividing cell, the mitotic spindle would start to form– Scientists called this protein CYCLIN
– Scientists have since discovered a family of closely related proteins (cyclins) & dozens of other proteins that help regulate the cell cycle
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Regulatory Proteins:
• The cell cycle is controlled by regulatory proteins, both inside & outside of the cell
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Regulatory Proteins: INTERNAL
• Respond to events occurring inside a cell
• Allow the cell cycle to proceed only when certain events have occurred in the cell itself
• Example: some regulatory proteins make sure a cell does not enter mitosis until its chromosomes have been replicated
• Example: a regulatory protein prevents a cell from entering anaphase until the spindle fibers have attached to all chromosomes.
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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 to slow down or stop their cell cycles…this prevents excessive cell growth & keeps body tissues from disrupting one another.
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Recent studies suggest…
• The portion of interphase just before DNA replication is a key control period in the cell cycle;
• There are several regulatory proteins identified as controlling the cell cycle…
• RECALL: proteins are coded for by DNA! So…
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• A mistake (MUTATION) in the DNA (GENES) that codes for one or more of these control factors/enzymes could lead to a LOSS OF CONTROL OF THE CELL CYCLE.
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• What can happen if the cell cycleis not regulated so carefully?
– CANCER!!
• Cancer cells do not respond to signals that regulate the growth of most cells.
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• The result? They form masses of cells called TUMORS that can damage the surrounding tissues
– Benign vs. malignant
• Cancer cells can also break off and spread throughout the body METASTASIS
BREAST TUMOR
Old Mastectomy
Vs.
New Mastectomy
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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 been replicated properly (without mutations)
– If it isn’t working, damaged DNA can replicate
– The cell may have lost the information it needs to respond to growth control signals
• Cancer is a disease of the cell cycle
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Cancer is the 2nd leading cause of death in the U.S.
• It can affect any tissue, but the most commonly affected are:
lung
colon
breast
prostate
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What causes the loss of growth control?
• Smoking tobacco
• Radiation exposure
• Viral infection
HUMAN LUNG
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Cancer Prevention:● There is a clear link between healthy
lifestyle and reducing the incidence of cancer;
● Diet low in fat and high in fiber;
(fruits, vegetables, & grains)
● Vitamins and minerals;
(A, C, E, & calcium)
● Exercise;
● Wear sunscreen
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● DON’T SMOKE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
(Seriously!! This should be a no-brainer!!)
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Treatments
• surgery (for benign tumors)
• radiation
• chemotherapy
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10.4: Cell Differentiation
Key Concepts:• How do cells become
specialized for different functions?
• What are stem cells?
• What are some possible benefits & issues associated with stem cell research?
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Cell Differentiation:● the process by which cells
become specialized for different functions;
● we all started as an individual fertilized egg cell embryo adult organism
● cell differentiation is controlled by a number of interacting factors in an embryo…many of which we still don’t completely understand!
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STEM CELLS:● how do so many
specialized, differentiated cell types develop from just a single cell?
● such a cell is said to be TOTIPOTENT
● TOTIPOTENT = able to develop into any cell type in the body
● PLURIPOTENT = able to develop into most of the body’s cell types
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STEM CELLS:
● STEM CELLS = the unspecialized cells from which differentiated cells develop
● TYPES of stem cells:
● EMBRYONIC: pluripotent cells found in early embryo stages…mouse embryonic stem cells have been triggered to differentiate into: nerve cells, muscle cells, & even sperm & egg cells!
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STEM CELLS:● TYPES of stem cells:
● ADULT: groups of cells that differentiate to renew & replace cells in the adult body; more limited than embryonic stem cells
● Example: adult stem cells in the bone marrow can develop into several types of blood cells
● Example: adult stem cells in the brain can produce neurons or nerve cells
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STEM CELLS:● BENEFITS of Stem Cell Research:
● stem cells offer excellent prospects to repair cellular damage that is the cause of many human life-threatening conditions:
● Example: heart attacks destroy heart cells
● Example: strokes & spinal cord injuries destroy nerve cells & cause paralysis
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STEM CELLS:● ETHICAL ISSUES:
● adult stem cells can be harvested from willing adult donors
● embryonic stem cells are harvested from early stage embryos…this has led to many ethical discussions involving issues of life and death…
● in the future, technology may help to reduce these ethical concerns (i.e. reprogram an adult stem cell to behave like an embryonic stem cell)
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