Bell Ringer 1/18 on pg.5 Each minute, 300 million of your body cells die!!! (Don’t worry—these cells are replaced by cell division, 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. Answer yesterday’s bell ringer too!!

Why Do Cells Divide? Grow? Maintain workable surface area to volume - too big-can ’ t work!! Replace damaged cells

A C ELL ’ S L IFE Humans have trillion cells. Cells have varying life spans… Stomach cells - 2 days Sperm cells – 2-3 days Skin cells – days Immune cells - 6 weeks Red blood cells -120 days Pancreatic cells - one year Bone cells – years Brain cells – lifetime o When damaged or infected, cells will self- destruct by a process called apoptosis. o The longest cells in the body are the motor neurons (up to 4.5 feet long) o An average of about billion of your cells die and are replaced each day. Yea for cell division!

W ARM U P 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 you think this might play a role in the development of lung cancer?

W ARM U P Why do you think chemotherapy drugs, which are given to fight cancer, cause a person’s hair to fall out?