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BIOL 207 (09/11/13) - Chromosomes During Cell Cycle (con't) & Human Chromosomes

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Biology (Biological Sciences)
Course Code
Mike Harrington

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BIOL 207 (September 11, 2013) Chromosomes during the Cell Cycle (con’t) & Human Chromosomes Replication of Linear Pieces of DNA Problem: The ‘end replication problem’  Near the end of replication, an after the removal of the RNA primers, the lagging strand is a bit shorter than the parent strand.  Normally, Okazaki fragments can patch back up the gap created by the removal of primers, but in this case, the Okazaki fragments are too big to fit! o If nothing were done about this, this would result in shorter and shorter daughter molecules  Why can’t DNA polymerase fill this gap up with nucleotides? Because DNA polymerase only works from 3’ to 5’ direction and not the other way around… Solution:  Telomerase is able to extend the parental (longer strand) so that Okazaki fragments CAN attach the complimentary bases  Telomerase is an exception to the ‘DNA is replicated using an ssDNA template’ nucleic acid rule  The ends of chromosomes are covered by telomeres for protection  DNA + histone proteins = nucleosome o Histone proteins aid in the condensation of genetic material  When the chromosomes of a cell are getting ready to condense (prophase), they actually separate within the nucleus into chromosome territories. Each chromosome has it’s own territory. o This arrangement results in no overlapping and makes it easier for the chromosomes to condense Cohesin and Condensin  Cohesion holds sister chromatids together o Composition: Smc2 + Smc3  Condensin compacts paired sister chromatids o Composition: Smc2 + Smc4 + Bm1 HUMAN CHROMOSOMES (LECTURE 3) Naming Our Chromosomes A. Occurrence a. if 2 copies are present in a somatic cell then the chromosome is an autosome b. if the chromosome is not present in two copies for both males and females then these particular chromosomes are called sex chromosomes B. Length a. The longest autosome is called Chr 1 (Length = 250Mb) b. The higher the chromosome number, the shorter the c
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