Unsolved Problems in Cell Biology Biology 446 October 28, 2015 Albert Harris
(Questions that might be on the final exam)
What parts of the following statements (all of which are quotes from web pages) would you disagree with? Please argue pro and con. Change them to be more accurate. Figure out what possible evidence would prove or disprove each statement.
1) "Telomeres have been compared with the plastic tips on shoelaces, keep chromosome ends from fraying and sticking to each other."
2) "... telomeres also have been compared with a bomb fuse."
3) Telomeres are made of repeating sequences of TTAGGG on one strand paired with AATCCC on the other.... In white blood cells, the length of telomeres ranges from 8,000 base pairs in newborns to 3,000 base pairs in adults and... 1,500 in elderly people.... Each time it divides, an average cell loses 30 to 200 base pairs from the ends of its telomeres. Cells normally can divide only about 50 to 70 times, with telomeres getting progressively shorter until the cells become senescent or die."
4) "Telomeres do not shorten in tissues where cells do not continually divide, such as heart muscle."
5) "During chromosome replication, the enzymes that duplicate DNA cannot continue their duplication all the way to the end of a chromosome." (What property of DNA polymerase causes this inability?)
*6) Invent one or more alternative molecular mechanisms that could serve the function of telomeres (for example in bacteria). Hint: Why are so many bacterial and viral chromosomes circles?
7) "The popular press has persisted in using the term "The Hayflick Limit" to promote the scientifically naïve idea that the human lifespan is determined by a limited number of cell divisions, although the relevance of finite divisions by fibroblasts in culture to lifespan in an organism, e.g. a person, is highly questionable."
8) "Hayflick and his associates have vehemently condemned 'anti-aging medicine' and criticized organizations such as the American Academy of Anti-Aging Medicine. Hayflick has written numerous articles criticizing both the feasibility and desirability of human life extension."
9) "The force of natural selection weakens with increasing age - even in a theoretically immortal population..."
10) "..the force of selection against late-acting deleterious mutations, which affect only these few older individuals, is very weak. The mutations may not be selected against, therefore, and may spread over evolutionary time into the population."
11) "More individuals survive to later ages, so the force of selection against late-acting deleterious mutations is stronger. Fewer late-acting deleterious mutations equates to slower aging and therefore a longer lifespan. Birds are also warm-blooded and are similar in size to many small mammals, yet often live 5-10 times as long. Seabirds live longest".
12) "Stochastic theories blame environmental impacts on living organisms that induce cumulative damage....as the cause of aging, examples of which ranging from damage to DNA, damage to tissues and cells by oxygen radicals (...widely known as free radicals countered by ... antioxidants), and cross-linking."
13) "...there are over 700 genes associated with aging in model organisms: 555 in Caenorhabditis elegans.."
14) "...aging is seen as a progressive failure...of homeostasis,"
15) "the Gompertz function, named after actuary Benjamin Gompertz, 1779-1865) proposed an exponential increase in death rates with age. ..accurately from 30 to 80 years of age doubling of mortality every .69/.085 = 8 years"
*#6 is a question to think about; not a quotation
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