NOTES: 10.3-10.4

Regulating the Cell Cycle /

Cell Differentiation

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?

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!

• 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…

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!

• 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

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?

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

Regulatory Proteins:

• The cell cycle is controlled by regulatory proteins, both inside & outside of the cell

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.

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.

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…

• 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.

• 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.

• 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

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

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

What causes the loss of growth control?

• Smoking tobacco

• Radiation exposure

• Viral infection

HUMAN LUNG

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

● 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 become

specialized for different functions?

• What are stem cells?

• What are some possible benefits & issues associated with stem cell research?

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!

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

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!

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

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

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)