MIkey-1 - LS3 MIDTERM I INSTR L JOHNSON NAME(last(first I.D...

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1 LS3 MIDTERM I INSTR: L. JOHNSON Thursday, Oct. 23, 2008 NAME:_________________________________ (last) (first) I.D. #__________________________________ TA ___________________________________ INSTRUCTIONS 1. This exam is 8 pages long. Page Value Score Before starting make sure you have all the pages. 2 15 2. WRITE YOUR NAME ON EVERY PAGE. 3 14 3. No credit will be given for an 4 12 illegible answer. 5 23 4. WRITE ONLY IN THE SPACE PROVIDED. NO OTHER ANSWER WILL BE GRADED. 6 14 7 12 8 10 Total 100 NAME:_________________________________ ID __________________________
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2 (last) (first) (6 pts) 1. In the table below, list similarities and differences between the DNA double helix and the protein α -helix. (+1 for each valid similarity or difference with max of 6) Similarities Differences Both right handed helix protein single strand, DNA double strand Both held together by H-bonds H-bonds parallel to axis in proteins, Both form independent of sequence H-bonds perpendicular to axis in DNA R groups stick out from helix in proteins Bases stick into helix in DNA α -helix is rigid, double helix is flexible (9 pts) 2. DNA in the cell is found associated with proteins. a. Describe the composition of the eukaryotic nucleosome. (4 pts) DNA 2xH2A 2xH2B 2xH3 2xH4 b. What types of post-translational modifications can be found on these nucleosomal proteins? (3 pts) methylation, acetylation, phosphorylation (optional ubiquitination, adenylation) c. What is one purpose of these modifications? (2 pts for either answer) Provide binding site for proteins Modulate how tightly DNA binds to histones NAME:_________________________________ ID __________________________ (last) (first)
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3 (9 pts) 3. RNA structure is important for many different processes. a. What are the three fundamental differences between RNA and DNA? (3 pts for any three of the following) ribose instead of deoxyribose uracil instead of thymine single stranded instead of double stranded complex secondary structure b. Describe in detail one example of how RNA folding can affect gene expression. (4 pts for one of the two examples) Attenuator: Two alternative stem-loops can form in the leader region, one of these is a rho-independent terminator. Which structure forms is dependent on translation of a leader peptide which contains two or more codons for the amino acid that the genes in the operon are responsible for synthesizing. When the amino acid is plentiful, the ribosome doesn’t pause and the terminator stem loop forms causing early termination. When the amino acid is in low supply, the ribosome pauses at the aa codons allowing the
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MIkey-1 - LS3 MIDTERM I INSTR L JOHNSON NAME(last(first I.D...

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