test3(mona) - .~,.~. \ . GENETICS (BFO 3 25) F mL2m5 Sample...

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.~ ., ~. \ . -. GENETICS (BFO 325) FmL2m5 kiE y Sample q@diBtions -111 Exam 1. A DNA fragment containing a specific gene is isolated hm a eukaryotic organism. This DNA fragment is mixed with the carresponding mRNA isolated from the organism and allowed to hybridize following denaturation and annealing of the nucleic acids. The DN&KNA hybrid formed is observed by electron microscopy. The following figure shows the DNA-RNA hybrid. (a) How many introns does this gene contain? Six (b) How many exons does this gene contain? Seven (c) In the figure, the looped out region corresponds to DNAIRNA (circle the correct answer) DNA 2. Since introns are largely genetic 'junk,' they do not have to be removed precisely from the primary transcript during RNA splicing. Answer if this statement is true or false. False @) Explain your answer. The RNA will not be translated properiy if the introns are not removed precisely. Addition or deletion of bases due to imprecise splicing will most likely result in change in the reading frame; consequently, the protein product may be shorter, longer, or have changes in the amino acid sequence. 3. Self-splicing introns use two distinct strategies to accomplish splicing. Group I 1
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introns bind a guanosine hm so&ioa, activating it for attack on the 5'- splice site. Group I1 introns activak apwticularly reactive A nucleotide within the intron sequence and use it to &&the S- splice site. For both types of intron the next step joins the two exons, releasing the 3' end of the intron. (a) Which mechanism (Groupl or Group 11) most closely resembles pre- mRNA splicing catalyzdby the spliceosome? (b) What is the structure (li0ex ,axr lariat) of the excised intron following splicing mediated by the spliceosome? (a) Group (b) Lariat 4. Indicate whether the following statements are true or false. (a) Binding to the promoter orients WA polymerase so that it transcribes the adjacent gene; however, the choice of template strand is dictated by additional protein factors. In any one region of the DNA double helix, only one DNA strand is usually used as a template. (c) Bacterial mRNAs are processed before they are translated. (d) Introns are the coding regions within eucaryotic genes. fe) RNA polymerases require both a template and a primer before they can initiate RNA synthesis. (a) False (b) True () False (d) False (e) False 5. What is the sequence of amino acids in polypeptide chains produced by the polymer (GU)n (for example, GUGUGUGUGUGUGUG) in a protein- synthesizing system that does not need the AUG start codon? (Use the Genetic code) Alternating valine and cysteine residues (Val-Cys-Val-Cys-Val --- or Cys-Val-Cys-Val----). (i) What are the two common secondary structures found in proteins? a-helix and p-sheet (pleated sheet) (ii) Explain your understanding of "colinearity of gene and protein" and briefly describe the experiment that was used to demonstrate colinearity.
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test3(mona) - .~,.~. \ . GENETICS (BFO 3 25) F mL2m5 Sample...

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