21:14 $0 0.00 vo KB/S LTED 496 Microsoft Word - Assignment Ol.docx Assignment 01 1. The gene encoding the E. coli. enzyme ß-galactosidase begins with the sequence ATGACCATGATTACG. What is the sequence of the RNA transcript specified by this part of gene? 2. If the splicing of mRNA in a vertebrate cell is blocked, the rRNA modification reactions are also blocked. Suggest a reason for this. Original TTGACAT 15 to 17 bp TATAAT Mutant TATAAT 15 to 17 bp TTGACAT 3. A researcher was mutating prokaryotic cells by inserting segments of DNA. In this way, she made the following mutation: A. What does this sequence represent? B. What do you predict will be the effect of such a mutation? Explain. 4. What is the primary function of the sigma factor? Is there a protein in eukaryotes analogous to the sigma factor? 5. The human ß-globin polypeptide is 146 amino acids long. How long is the coding portion of the human ß-globin mRNA? 6. An E. coli gene has been isolated and shown to be 68 nm long. What is the maximum number of amino acids that this gene could encode? 7. For several decades, the dogma in biology has been that molecular reactions in living cells are catalyzed by enzymes composed of polypeptides. We now know that the introns of some precursor RNA molecules such as the rRNA precursors in Tetrahymena are removed auto catalytically (“self-spliced”) with no involvement of any catalytic protein. What does the demonstration of auto- catalytic splicing indicate about the dogma that biological reactions are always catalyzed by proteinaceous enzymes? 8. List three ways in which the mRNAs of eukaryotes differ from the mRNAs of prokaryotes. 9. The primary transcript or pre-mRNA of a nuclear gene in a chimpanzee has the sequence: 5' -G-exon 1-AGGUAAGC-intron-CAGUC-exon 2-A-3' After the intron has been excised, what is the most likely sequence of the mRNA? 10. A human B-globin gene has been purified and inserted into a linear bacteriophage lambda chromosome, producing the following DNA molecule: 21:14 +4G KB/S LTED 41 96 09.00 Vo Microsoft Word - Assignment 02.docx Assignment 02 1. Groups of alleles associated with the lactose operon are as follows (in order of dominance for each allelic series): repressor, IS (superrepressor), I *(inducible), and I "(constitutive); operator, OC (constitutive, cis dominant) and 0+ (inducible, cis- dominant); structural, Z and Y. (a) Which of the following genotypes will produce B-galactosidase and B-galactoside permease if lactose is present: (1) 1*0* Z* Y*, (2) 1 *OCZ+ Y+, (3) OCZ+ Y+, (4) IS O+ Z+ Y+, and (5) 10+ Z+Y+? (b) Which of the above genotypes will produce ß-galactosidase and ß-galactoside permease if lactose is absent? Why? 2. By what mechanism does the presence of tryptophan in the medium in which E. coli cells are growing result in premature termination or attenuation of transcription of the trp operon? 3. Suppose that you used site-specific mutagenesis to modify the trpL sequence such that the two UGG Trp codons at positions 54-56 and 57-60 in the mRNA leader sequence were changed to GGG Gly codons. Will attenuation of the trp operon still be regulated by the presence or absence of tryptophan in the medium in which the E. coli cells are growing? 4. Would attenuation of the type that regulates the level of trp transcripts in E. coli be likely to occur in eukaryotic organisms? 5. Is the CAP-CAMP effect on the transcription of the lac operon an example of positive or negative regulation? Why? 6. Would it be possible to isolate E. coli mutants in which the transcription of the lac operon is not sensitive to catabolite repression? If so, in what genes might the mutations be located?