PSE2 2018

All answers must be typed and in bold font so we can distinguish your answers from the questions. If you use more than one page they must be stapler together or points will be deducted. 1. a) Complete the table below. Assume that reading is from left to right and that the columns represent transcriptional and translational alignments. Label the 5’ and 3’ ends of DNA and RNA and carboxyl and amino acid ends of protein. (You may fill in this chart by hand writing- no typing necessary here.) b) Is the top or bottom DNA strand the template strand? The bottom DNA strand is the template strand. 2. In a eukaryotic cell, four general types of RNA molecules are involved in gene expression. a) What are these four types of RNA? mRNA, tRNA, rRNA, hnRNA b) Which is not involved in gene expression in prokaryotic cells? Why not? hnRNA is not involved in gene expression in prokaryotic cells. This is because hnRNA is involved in splicing out introns and joining together exons. In prokaryotes, there is not introns or exons, there for hnRNA would not be used. 3. A double mutant produced by uneven crossing-over contains two single nucleotide mutations that result in frame shifts and are separated by about 20 base pairs. The first is an insertion, while the second is a deletion. The amino acid sequences of the wildtype and mutant polypeptide in this region of the protein are as follows: Wildtype: Lys – Lys – Tyr – His – Gln – Trp – Thr – Cys – Asn Double Mutant: Lys – Gln – Ile – Pro – Pro – Val – Asp – Met – Asn a) What are the original and double mutant mRNA sequences. You may find it useful to use the conventional symbols Y for pyrimidine, R for purine, N for any nucleotide, and H for A,C, or T. Wild Type 5’AAN CAN AUA CCA CCA GUG GAU AUG AAU3’ Double Mutant 5’AAN CAN AUH CCN CCN GUN GAY AUY AAU3’ b) Which nucleotide was inserted? N c) Which nucleotide was deleted? U 4. In a particular region of the genome of a certain bacterium, one DNA strand is transcribed to give rise to an mRNA for protein A and the other DNA strand is transcribed to give rise to an mRNA for protein B. a) Would there be any problem in expressing the two genes? Yes, there would be a problem because you would be transcribing two different sequences. DNA strands are complementary base paired, they are not identical. For example 5’ATCGACT 3’ 3’TAGCTGA5’ If you were to transcribe the top strand you would get a different set of proteins then you would if you transcribed the bottoms strand. There is always one template strand of DNA and never are both stands of DNA transcribed. b) If a mutation occurred to affect the structure of protein A, what would you observe in the structure of protein B? There are two possibilities, one being the original mutation on the DNA affected both strands, which would result in a both protein A and B being affected by the mutation. The second possibility is the mutation only affected one the two complementary DNA strands which means only protein A would be affected and that protein B is not necessarily affected.