problem set 6 answers

problem set 6 answers - Problem 1. The genetic code a) Look...

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Problem 1. The genetic code a) Look at the structure in your book or on the handout b) 3’ AUU 5’; 3’ GUG 5’; 3’ CGG 5’ these would normally be written in the opposite direction (5’ 3’) c) Stop codon, His, Ala d) While there are 61 codons that code for amino acids, there are actually fewer types of tRNA. This means that one type of tRNA can recognize MORE THAN ONE codon. In many cases, the third base of a given codon can vary, and the codon will still code for the same amino acid. Thus, the third base in a codon is said to "wobble." For example, take a look at all the codons that encode Valine. They all start with GU, but it doesn't matter what the third base of the codon is. : U, C, A, and or G in the third position will all encode for Valine. e) Check your sheet—there are 6! (I will give you the codon chart on the final) f) No, one codon codes for only 1 AA PROBLEM 2. You are studying a protein with the following primary sequence: MetAlaValAsnArgGlyTrp (a) How many different open reading frames can code for exactly this peptide? A lot!!! For those of you who really want to know its: 1 x 4 x 4 x 2 x 6 x 4 x 1 = 768. Just multiply how ever many codons can encode for each amino acid. (b) Write out one possible double-stranded DNA coding region that can encode this little peptide. Include the start codon and a stop codon. Indicate the 5’ and 3’ direction of the DNA. The mRNA strand is read: 5’AUG GCU GUU AAU AGA GGU UGG UAA -STOP 3’ THEREFORE, THE DNA strand must be 3’TAC CGA CAA TTA TCT CCA ACC ATT -STOP 5’ 5’ATG GCT GTT AAT AGA GGT TGG TAA -STOP 3’ (c) Which strand is the antisense strand for this peptide, and which is the sense strand? The antisense strand for this peptide is the DNA strand that the mRNA complements. Thus it is the TOP DNA strand in part b. The sense strand is the BOTTOM DNA strand (the strand that is not used for the transcription of mRNA) and is the same sequence as the mRNA strand, using thymine instead of uracil. (d) Write out the segment of amino acid sequence encoded by the corresponding portion of the antisense strand. Write out the encoded peptides from N to C terminus. (there should be 3) The antisense strand is 3’TAC CGA CAA TTA TCT CCA ACC ATT- 5’ Written 5’-3’ the sequence is: 5’-TTA CCA ACC TCT ATT AAC AGC CAT-3’ The amino acid sequence for open reading frame(ORF) #1: N-LEU PRO THR SER ILE ASN SER HIS-C The Sequence for ORF#2 is: 5’-T TAC CAA CCT CTA TTA ACA GCC AT-3’ The amino acid sequence is N-TYR GLN PRO LEU LEU THR ALA-C The sequence for ORF#3 is 5’-TT ACC AAC CTC TAT TAA CAG CCA T-3’
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The amino acid sequence is N-THR ASN LEU TYR STOP-C (e) Do the same exercise for the sense strand. How many potential proteins could be encoded by this piece of dsDNA? The sequence for ORF#1 is
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This note was uploaded on 04/28/2008 for the course BILD BILD 1 taught by Professor Bever during the Winter '08 term at UCSD.

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problem set 6 answers - Problem 1. The genetic code a) Look...

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