week01 - Biochemistry 442 Spring 2007 Week 1 Quiz Questions...

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Biochemistry 442, Spring 2007: Week 1 Quiz Questions 1. A) Protein A is rich in Ser. As we know, 6 codons can be translated to be Ser, which are AGC, AGU, UCA, UCC, UCG and UCU. Unfortunately, all 6 codons exist in the mRNA encoding protein A. Obviously, there’s no such tRNA that could translate all 6 codons by itself. Thus, to produce this protein, we need a set of tRNAs instead of just one tRNA. How many sets are possible? Please list all the sets. B) Arg encoded by codons AGA and AGG are also found in mRNA of protein A. (Don’t consider other 4 codons) When you obtain the protein sequence for the translated product, you find that several Arg (not all) are replaced by amino acid Ser in protein A. Could you explain why? (Don’t consider mutation) 2. A transfer RNA attached to methionine walks into a bar full of ribosomes and messenger RNA. The name of the bar is Five Prime and their motto: Always write RNA sequences 5’ to 3’ . a. This transfer RNA feels very confident because it knows it can initiate translation. What is the three nucleotide sequence of its anticodon ? __ __ __ It orders a drink and the bartender says, “since you’re with methionine, no charge.” It then notices one particularly attractive mRNA sequence: RNA: 5’G A A U G G G A U G U A G U A A C U A G U C 3’ So it asks the bartender if he knows where that mRNA is from. The bartender says, “Of course I do, anyone who knows the central dogma of molecular biology can answer that. It came from DNA.” And the transfer RNA says, “OK wise guy, but what was the sequence of that DNA? b. Write the DNA sequence here: DNA:5’_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 3’ It approaches the strand of messenger RNA with the intent to initiate some translation; it wants a reading frame that will enable it to make a polypeptide . c. Circle a codon in the mRNA sequence below where it could start: RNA:5’G A A U G G G A U G U A G U A A C U A G U C 3’ d. Circle a codon in the mRNA sequence below where it could stop: RNA:5’G A A U G G G A U G U A G U A A C U A G U C 3’ Just before it starts to go for the P-site, with other transfer RNAs gathering around, waiting to take a shot at the A-site, a gang of antibiotics bursts into the bar. Everything stops. No more translocating. No more A-site binding. You can’t even hear a single peptidyl transferase reaction.
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