Question

Long Answer

1. You perform a Nirenberg and Ochoa type experiment in which synthetic RNAs are made by incubating polynucleotide polymerase with CDP and UDP (80% CDP to 20% UDP ratio). What ratios of each of the eight possible codons do you expect?

2. What percentages of radioactivity would you expect for each of the 20 amino acids when a cell free translation assay is run 20 times in which each time a different radioactive amino acid is included with the 19 other non-radioactive amino acids?

3. You perform a Khorana type experiment with three different co-polymer RNAs made from 5’-UA-3’, 5’-AAU-3’, and 5’-UACA-3’polymers. After running 20 cell-free translations assays on these different copolymers what would you be able to conclude regarding codon usage? I don’t want you to tell me what the amino acids for each codon are but rather what Khorana would have concluded regarding codon usage. Hint: you will need to determine the codons present in each co-polymer and the expected amino acids that would be incorporated given the genetic code. Then, use the results to determine which amino acids could be definitively assigned to a codon and which could not be definitively assigned.   

Answer 1

1) Using two types of nucleotides CDP, UDP The 8 posible codans are CCC, UUU, CUU, CUC, CCU,UCC, UCU and UUC.

2)cell free translation assay used for in vitro expression of proteins that means protein synthesis out of cells. If the adioctive amino acids are replaced for all amino acids in step wise manar than the whole protein product will be radioactive. Hence the radioactivity is hundred percent.

3) 5'UA3' Co polymer gives UAU AUA...repeating polymer which yields tyr-ile peptide polymer.

5' AAU3' polymer gives AAU AAU repeating RNA which yield poly peptide with asp repeating units.

5'UACA3' polymer gives 'UAC AUA CAU ACA repeating RNA which yield poly peptide with tyr- ile-his-thr amino acid repeating unit.

Together they utilise tyr,ile,asp,his,thr amino acids in reaction tube.