This exercise is designed to help you understand better how DNA exists as a doub

Question

This exercise is designed to help you understand better how DNA exists as a double strand and how it can code for a protein and the consequences of variation (mutation) of the DNA on the protein that it codes for. If you are unsure how to do this exercise you should look to your transcription and translation lectures for guidance. The DNA sequence I is the anti-sense strand (template), the other 4 sequences are the sense (non template) strands. Do the following exercise: 1. Write out the sense DNA strand for sequence 1 and indicate polarity 1-Template 3-TAC TCG AAC TCC CGC CCT GGG ACG TAC ATT-5, 2. Complete the following exercises: a. Transcribe each DNA (lI-V) sequence into RNA and write out the RNA sequence b. Translate each RNA sequence generated in section (a) into a (string of amino acids) using the genetic code attached in page 2. out the protein sequence (The arrangement/spacing of the sequence indicates how the codons should be read). protein Write Look at the DNA sequences of II and III and compare the DNAs. Look at the proteins sequences that they code for. What do you notice about the DNA sequences? What do you notice about the protein sequences? Is it interesting? Why is this interesting? c. d. Compare DNA sequence II to sequence IV, how are they different? Do the same thing with sequence II and sequence V. Wha of the differences in the DNA sequences. Why is it interesting if you compare it to the answer to question 2c? t are the consequences 11 sense 5,-ATG TCA CTA CGC GCA GGC CCA TGT ATG TAG-3, III sense 5'- ATG AGC TTG AGA GCT GGT CCT TGC ATG TAG-3 iv sense 5,-ATG TGA CTA CGC GCA GGC CCA TGT ATG TAG -3, v sense5- ATG CTC ACT ACG CGC AGG CCC ATG TAT GTA -3'

Explanation / Answer

A) The following are the RNA transcripts for each of the DNA sequence

B) The following is the translation of the RNA transcripts

Met Ser Leu Arg Ala Gly Pro Cys Met stop

Met Ser Leu Arg Ala Gly Pro Cys Met stop

Met stop

Met Leu Thr Thr Arg Arg Pro Met Tyr Val

C) Although the DNA sequnece of II and III are competely different, the protein sequence that are encoded by them is the same. This is because many different codons are know to code for the same aminoacid. The given example, is the perfect representation of this phenomenon. Such mutations are called as non-sense mutations.

D) on comapring the DNA sequences of II and IV, we can see that a mutation of C to a G at position 5 has occured in the sequence IV. Due to this mutation, the second in the sequence IV now encodes a stop codon and hence the protein is not synthesised in this case. Such mutations are called as point mutations.

On comapring the DNA sequences of II and V, we can see that an extra nucleotide C was inserted at postion 4. Due to this addintion in sequence V, the complete protein sequence changes from that observed in sequence II. This inserted nucleotide causes a shift in the frame of the DNA and hence is called as a frame shift mutation.

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