Lecture 07 - A primer of cell biology, and a sheep named,...

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Unformatted text preview: A primer of cell biology, and a sheep named, "Dolly" Dolly" Cells are the atoms of life the fundamental organizational units and share a single origin. Cells are exceedingly complex. They have organelles, membranes, and their own little destinies. Ribosomes on the endoplasmic reticulum are where proteins are made. Mitochondria are the cell "batteries". batteries" Mitochondria (and chloroplasts) are degenerate symbionts; they have their symbionts; own circular DNA and two membranes. Extranuclear inheritance is maternal! Markers Transport Plasma membranes are phospholipid bilayers, with proteins and bilayers, carbohydrates stuck in them. Some proteins are for cell recognition, some stimulate reactions in the cell. The protein channels that traverse the cell membrane determine what molecules enter or exit the cell. Receptor 1 Initially, cells are "totipotent", i.e., they can totipotent" grow up to become anything. But cell fates are decided remarkably early in development (1st several divisions). Fates are hierarchical, as you might expect. These decisions result in genes being more or less permanently inactivated in animals... animals... The phenomenon has been most studied in X-chromosomes, which carry 687 Xgenes (color vision, G6PD, etc.) Condensed X's, called "Barr bodies", are X' bodies" found in somatic cells (calico cat ex.). Eutherian mammals have random XXinactivation; marsupials always inactivate the paternal X. More generally, it appears that the methylation of C shuts off gene expression. Cloning is quite simple & dull. In plants, it is trivial. In animals, the nucleus of an egg cell is removed and replaced with a nucleus from a cell of the model individual. Next, cell cycle stages are synchronized via starvation & electric shock. This process is somehow reversed in the formation of gametes and/or zygotes. 2 Is cloning really that easy? Gene inactivation is a well-known wellphenomenon, even though its mechanisms are poorly understood. Reversing the process (only relatively recently recognized as a possibility) is the crux. Most scientists are confident this is the main reason the technique has, and will continue to have, a spectacularly bad success rate. Story #1 from the Washington Post: Is a clone really a "clone"? clone" Not in terms of maternal information, unless you get your eggs from the same mom. This is one reason that Jurassic Park is gibberish, and the use of cloning to revive extinct species or save endangered species is problematic, at the very least. Tuesday, April 8, 2003, Iowa State University: Scientists clone endangered Asian wild cattle A pair of banteng calves born last week were cloned from an animal that died more than 20 years ago, researchers said on Tuesday -adding they hoped to rescue more endangered animals using cloning. cloning. The two bantengs were cloned from the San Diego Zoo's "frozen zoo," a project launched before anyone knew whether cloning would work. ... "Although we started with 16 pregnancies, only two of them went to term." term." ACT did that two years ago with an oxlike animal called a gaur. The little calf died after only a few days. Story #2 from the Washington Post: Wednesday, April 9, 2003, Iowa State University: One of a pair of cloned bantengs, a rare species of Asian cattle, has bantengs, been euthanized because it was abnormally large, its creators said on said Wednesday. The banteng calf was born twice the normal size, a common cause of death in cloned animals, said Dr. Robert Lanza of MassachusettsMassachusettsbased Advanced Cell Technologies. "A banteng should only be 40 pounds (20 kg). The first calf weighed 40 pounds (20 kg) but the second was 80 pounds (36 kg), almost twice what is normal." "It not uncommon at all in cloning. It is called large calf syndrome," syndrome," said Lanza. Lanza. What is the big deal with clones anyway? Clones already walk among us (MZ twins)! 3 Cloning scenario 1: Mad scientist clones army of love slaves. Cloning scenario 2: Eugenics - "The Boys from Brazil". Brazil" Most human traits of interest have so much environmental (& random!) variation as to make this impossible. Verdict: See scenario 1. Verdict: No way. Cloning scenario(s) 4: scenario(s) Cloning scenario 3: "The bereaved parents". parents" Gets a lot of airtime, but... but... 1) the parents will be disappointed, and 2) what kind of demented individuals would really do this to their kid(s)? Verdict: Unlikely (I hope). Verdict: Reasonable. Clones of, e.g., mice, standardize genetic background for drug testing. Clones of, e.g., cattle, provide high resolution quality control of livestock products. Cloned endangered species help restore genetic variation in populations. Cloning scenario 5: Cloning as a fertility technique! Verdict: Inevitable? While human cloning may happen soon, even a viable child is likely to be extremely messed up. The conflation of cloning with stem cell research in the public eye has already generated backlash & collateral damage. Stem cells from early embryos are totipotent, totipotent, and have the full range of tissue fates available to them. We want to use them to find out how to turn back the clock on tissue-specific stem cells. tissue- 4 ...
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This note was uploaded on 04/18/2008 for the course BIOL_SCI 164 taught by Professor Walsh during the Spring '08 term at Northwestern.

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