Lecture+5+CHROMOSOME+STRUCTURE - Bio 97 Section D Midterm...

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Unformatted text preview: Bio 97 Section D Midterm Review Wednesday, October 8 6-8 PM Room: ICS 174 Review packets at https://eee.uci.edu/programs/biotutor Free Bio 97 (Lec. A) Peer Tutoring Midterm 1 Review Where: PSCB 120 When: 6-8pm on Thursday, October 9th, 2008 Please check the website below for Review Materials https://eee.uci.edu/programs/biotutor/ Email Dewey or Kevin for any special topic request(s)! Sample exam problem: Chloramphenicol is an antibiotic that inhibits the function of peptidyl transferase, a component of the 50S ribosomal subunit. This means that Chloramphenicol prevents the movement of the tRNA in the A site to the P site. Which of the following statements is TRUE? a) Chloramphenicol will prevent the formation of the initiation complex b) Chloramphenicol will result in Alanine rather than Methionine being the first amino acid in all proteins c) Chloramphenicol will block elongation, but not translation initiation d) Chloramphenicol will cause the ribosome to work backwards and read the mRNA 3' to 5' as translation occurs bidirectionally in prokaryotes e) Chloramphenicol treatment produces the same effects as a "silent" mutation in the DNA Each human cell has 46 linear chromosomes and 6 billion base pairs of DNA . . . How do you fit all that DNA into a cell nucleus??! 5-1 DNA in mammalian cells exists as chromatin Chromatin is a complex of DNA and proteins Chromatin is the material of which chromosomes are composed Chromatin in non-dividing cells is not condensed enough to see by light microscopy 5-2 Chromosomes condense maximally during cell division http://www.nccr-oncology.ch/scripts/page9243.html 5-3 Chromosomes occupy discrete territories in an interphase nucleus INTERPHASE METAPHASE PLoS Biology Vol. 3, No. 5, e157, May 2005 Metaphase (mitotic) chromosome: 5-4 The nature of chromatin: All eukaryotic DNA is associated with numerous protein molecules Histones are the major class of proteins associated with DNA 75-90% of genome is wrapped around histones There are 5 major types of histones in all eukaryotes H1, H2A, H2B, H3 and H4 20-30% of the amino acids in histones are lysine and arginine--DNA has a negative charge 5-5 The core histone particle contains two molecules of H2A, H2B, H3, and H4 The histone "octamer" or core particle 5-6 Nucleosomes look like "beads on a string" http://cmgm.stanford.edu/biochem201/Slides/Chromatin%20Structure/ 15%20EM%20of%20Chromatin%20Solenoid.JPG http://www.people.virginia.edu/~zs9q/zsfig/chromatin.html Stryer's Biochemistry Fig. 31-15 5-7 Histone placement affects gene expression: The Histone Code Position of histones affect ability of other proteins to access the DNA Histone placement is determined by DNA sequence and by accessory proteins Histones are removed from areas of active transcription Transcriptional start sites tend to have low levels of histones 5-8 Why have so many nucleosomes with so little DNA wrapped around them? vs. 5-9 Nucleosomes are compacted into a 30 nm fiber Molec. And Cellular Biology Fig. 9-31 5-10 Histone H1 is not a part of the octamer core Developmental Biology, Fig. 5-1 Molec. Biol. of the Cell, Fig. 4-31 5-11 Electronmicrograph of the 30 nm fiber formed from nucleosomes 30 nm fiber nucleosomes 5-12 30 nm fibers form loops and coils Fig. 4-55 Molec. Biol. of the Cell 5-13 30 nm fiber loops extending from a protein scaffold http://cmgm.stanford.edu/biochem201/Slides/Chromatin%20Structure/ 5-14 Chromatin is "decondensed" in areas of active gene expression 5-15 5-16 5-17 Condensed metaphase chromosome 1400 nm wide (1.4 m) http://cmgm.stanford.edu/biochem201/Slides/Chromatin%20Structure/01%20Human%20Chromosome.JPG 5-18 Structure of a centromere The centromere consists of several types of repeated DNA sequences A variety of kinetochore proteins bind to the centromere and form the kinetochore 5-19 Things to remember about centromeres Centromeres are visible only in condensed chromosomes The centromere is composed of DNA repeats and kinetochore proteins Spindle fibers attach to the centromere to pull the chromosomes to opposite poles during mitosis 5-20 The lagging strand is synthesized discontinuously and cannot be copied all the way to the end 5' 3' 5' 5' 3' 5' 3' 3' 5' 3' = RNA primer 5-21 The lagging strand is synthesized discontinuously and cannot be copied all the way to the end 5-22 Eukaryotes deal with this problem by placing telomeres at the 3' ends of chromosomes TELOMERES Human telomeres are composed of many repeats of this sequence 5-23 Telomerase adds repeats to the chromosome ends to prevent the chromosomes from shortening with each round of DNA replication 5-24 Telomerase and DNA polymerase work together to build telomeres 5-25 Telomeres are double-stranded sequences with a short single stranded overhang at the 3' end 5' 5' 3' 3' D-loop t-loop 5-26 T-loops form at the ends of mammalian chromosomes The single stranded 3' end of the chromosome folds back and forms a loop This loop is stabilized by proteins The loop structure protects the single stranded DNA from nucleases The loops look different from the ends of damaged DNA that needs to be repaired 5-27 Loss of telomeres can produce end-to-end chromosome fusions http://www.med.nus.edu.sg/phys/Projects_Telomere_Prakash.htm 5-28 Telomere length limits how many times human cells can divide in culture 5-29 Disruption of telomere structure can cause end-to-end chromosomal fusions Telomeres are stained RED Cell 126:49 (2006) http://pa-dev.wustl.edu/news-info/news/page/normal/6635.html 5-30 Mice have active telomerase and longer telomeres than humans http://www.med.nus.edu.sg/phys/Projects_Telomere_Prakash.htm 5-31 Things to remember about telomeres Telomeres are found at the ends of chromosomes and are important for chromosome stability Because DNA polymerase cannot replicate the very 3' end of the template DNA strand, chromosomes would shorten with each cell division Telomerase is a complex of proteins and an RNA template that adds DNA repeats to chromosomes and prevents shortening Telomeres can serve as a cellular "clock" 5-32 Most genes are found in euchromatin (in the middle of the chromosome arms) Heterochromatin is seen as the darkly staining regions 5-33 ...
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This note was uploaded on 10/05/2008 for the course BIO SCI 05300 taught by Professor Edinger during the Fall '08 term at UC Irvine.

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