WARM UP #5: Mitosis / Chemotherapy
With selected student responses

QUESTION 1: Each minute, 300 million of your body cells die!!! (Don't worry - these cells are replaced by mitosis, or you would be dead in a very short time!) However, some of the body's cells last for years, and some divide every day. List three types of cells in your body you would think would be replaced frequently. List 2 types of cells you think would be replaced slowly, if at all.

From fakered: Q1 = Replaced frequently are skin cells, cheek cells, red blood cells. Replaced Slowly are brain cells and muscle cells like the heart.

From AS: Q1 = Three types of cells that I think would be replaced frequently are blood cells, stomach cells, and liver cells. Two types of cells that I think that would be replaced slowly are heart cells and brain cells.

From CT: Q1 = Fast replicating cells: red bllod cells,skin cells,and stomach lining cells.Slow replicating cells: nerve cells, brain cells.

From etc: Q1 = Replaced quickly: gametes, cells on the fingers and in the mouth. Slowly replaced cells: neurons and heart cells. I'm a little confused about the question because no where in the reading did I find the answer, so I hope I answered it correctly. Also, isn't there new data to suggest neurons may actually replicate?

Comment from Dr. Marrs: Yes - although neurons do not replicate by themselves in adult tissues, several studies have recently been reported that show that certain growth factors added to brain cells may stimulate neurogenesis, or neuron formation in adult tissues. One such study: Journal of Neuroscience: December 2000

QUESTION 2: A protein called "p53" normally functions to find damaged DNA in the nucleus. p53 prevents cells from going through mitosis until the DNA damage can be repaired. However, smoking cigarettes frequently causes mutations in p53 in lung cells. How do think this might play a factor in the development of lung cancer?

From Lily: Q2 = When p53 is mutated its regulating function is limited or destoyed thus allowing for damaged DNA to continue its journey - damaged cells can then reproduce without control.

From NH: Q2 = By smoking and causing mutations in p53 your cells are losing that protein that detects other forms of mutation that might occur in DNA. This might allow for mutation to to continue in mitosis causing that cell to become more acceptable to cancer.

From Ang: Q2 = If the p53 becomes mutated, then it will not be able to live up to its functions of finding the damaged DNA and therefore those cells which are damaged would be able to proceed to the lung helping in the development of lung cancer.

From DJ: Q2 = I think that it plays a factor in that once the p53 proteins are mutated they will not be able to function their task in monitering the mitosis of DNA. It cells go through mitosis with damaged DNA it could cause problems for example lung cancer. So p53 is very beneficial.

From Sissy: Q2 = A mutation in the p53 could mean that the cell goes through mitosis prematurely when the DNA is still damaged which could play a role in the development of lung cancer.

From Dr. Marrs: Great answers - note in each case the answer mentioned that once p53 is mutated, it cannot do it's normal job in the cell (preventing damaged DNA / cells from replicating). This would allow cells with damaged DNA to replicate, contributing to the development of lung cancer. p53 is a protein also known as "The Guardian of the Genome".

QUESTION 3: Why do you think chemotherapy drugs, which are given to fight cancer, cause a person's hair to fall out?

From pint-size: Q3 = I belive chemotherapy drugs cause a persons hair to fall out because the drugs damage the hair cells and it will not let them replicate themselves until the drugs are out of their body. When the drugs are removed from the body, the hair cells start to replicate and the hair starts to grow back.

From Rachael: Q3 = Hair loss occurs because anticancer drugs can affect normal cells,including the cells responsible for hair growth. This effect, however, is not permanent, and healthy cells grow back normally once chemotherapy is completed. Scalp hairs in the "anagen" or growing phase is susceptible to chemotherapy and radiation. The degree of hair loss depends on the chemotherapy drug, the dosage of chemotherapy or radation, and how it is given.

From Joe Doooooby!: Q3 = They have to kill many cells off just to terminate the cancerous cells. Thus, they cause other cells such as hair cells and sperm to weaken leading to fallout.

From kriket: Q3 = I think chemo kills the cells in our roots of our hair

From Tim: Q3 = ok, I was able to find an answer to this one : ) 'Chemotherapy = treatment of disease with chemicals or drugs; the term most often refers to treatment of cancer. Traditional cancer chemotherapy poisons all body cells to some extent, but particularly targets rapidly dividing cells such as cancer cells. Its effect on other rapidly dividing cells (hair follicles, cells lining the stomach, and red blood cells) accounts for some of the common side effects.'

Comment from Dr. Marrs: Lots of good answers on this questions. The main point is that these drugs generally stop cell division in one stage or another in the cell cycle! They cannot discrimiate between normally dividing cells and cancer cells, so ANY rapidly dividing cells (hair, lining of mouth, blood) are affected. The effects are temporary - but they are given long enough to (hopefully) kill off the cancer cells. Usually people taking chemo drugs are weak and tired (anemic), don't feel like eating, and lose their hair. PS: Many people wanted to know more about this topic...so this week's "Good For" will be on chemo drugs. PPS. There is at least 1 drug on the market, Herceptin (made by Genentech) that specifically looks for and kills breast cancer cells ONLY. A 'magic bullet' if you have that particular type of breast cancer. We will do a Good For on this drug soon!

QUESTION 4: Q4 = ( not related to class) What can I do about the parking? I get to school at 12:30pm and I am generally getting to class 15-30mins late. (any secret spaces?)

[Students: Any tips on this one!!???]

*****************************************************************