Experimental Model Systems Used for Molecular Studies- Purpose of use of model organisms is to define genes and components involved incell growth and division, development, behavior, and disease- E. colio Prokaryotic bacteria used for studies; one cell division around every 10-15minutes in ideal conditionso About 5000 genes- Bacteria phageo Virus that attach to bacteria and use bacteria cell machinery to reproduce o Used to determine the method of replication of DNAo 10-15 genes- Yeast o Eukaryotic cellso Easy to grow; divide every few hourso Can put yeast genes into humans and will still function and vice versa- SV40 virus (Simeon virus 40)o Used to study mechanisms in eukaryotic cellso 10 geneso Can infect human and mouse cells, but not yeast cellso Used as an early model for cancer Infecting mouse cells with SV40 causes cells to become cancerous- Dictyosteliumo Used to understand cellular differentiationo Live in the soil differentiate from a single-celled organism to a multicellular organism- Arabidopsiso Only plant model organismo Every two weeks, new weed; seed  plant in two weekso Used to study plant and flower development; plant structure- Drosophilao Fruit flyo Used for over 100 years in researcho 17,000 geneso Used to study organ development, environmental affect on gene expression, behavioro Mutant antennapedia – mutation in one protein caused antennas near the eyes to become legs Shows pathway for turning one body part into another still exists inthe genomeo Mutant ultrabiothorax Normally, drosophila has 2 wings, but single gene mutation causedsmall balance organs (haltere) to become 2 additional wings- C. Elegans (soil worm)o Digestive, reproductive, and nervous systemo Completely transparent skin, which allows researcher to see all cells; can use lasers to knockout certain cells - Zebra fisho Common vertebrate model organism - Lab mouseo Share 95% of our genome with miceo Transgenic models common- Human cells in cultureo Tissue sample  add protease  leads to single cells  put cells into petri dish  add tissue culture media into the dish Media contains amino acids, vitamins, salts, metals, glucose, 10% animal serum (most often from cows) Normal cells may grow, but only for a short period of timeo Hayflick limit – noticed normal human cells can only go through around 50 generations; some internal counting mechanism that stops them from growing after that (role of telomeres in internal clock discovered in 2010) As cells divide, telomeres get shorter; in cancer cells, telomeres elongated so “clock” is messed up Only cancer cells and stem cells can bypass the Hayflick limit; cancer cells do it by mutations that bypass the limit mechanism- HeLa cells in 1953- Mouse cells in cultureo Strain grows for around 25 generations and then begins to die off like human cells; however, at transition point, the cell population becomes immortal and begins to grow again- Stem cells – adult stem cells, embryonic stem cells, and induced stem cells (iPS)o Human embryonic stem cells not used;  5-day old embryo (blastocyst) has inner cell mass of about 100 cells that will eventually become all of the cells in the body; if removed and grown in culture, can differentiate and become any other cell (totipotent)o Adult stem cells can come from bone marrow, skin, etc.; dividing cells throughout the body that eventually stop dividing and become mature cells; for example, bone marrow stem cells can only differentiate into adult bone marrow cells- Induced pluripotent cells (iPS) – normal cells are induced to become stem cells byforcing expression of 4-6 genes; can then be differentiated into different cell types; problem: some of these genes also involved in causing cancer, so can’t really be used for therapy- In vivo, cells exist in 4 stateso Dividing/cycling cells – stem cells in hair, stomach, places where cells have to be renewed constantlyo Non-dividing/existing – immune system, skin, liver; resting currently but can be triggered to divide againo Permanent non-dividing – cells of the CNSo Apoptotic cells – cells that are dying through a normal cellular process- Cell cycleo G0 phase is resting phaseo