3. What type of mutation would be caused if two bases are deleted from the origi

Question

3. What type of mutation would be caused if two bases are deleted from the original DNA strand? What would happen to the protein? What type of mutation would be caused if three bases were deleted from the original DNA strand? Would this cause an amino acid to be lost? Explain why changing the sequence of nucleotides in the original DNA strand does not always result in a different amino acid sequence. Show examples with two specific codons. Use the real Genetic Code in your textbook for this; not the Genetic Code for this simulation.

Explanation / Answer

Ans. #3. It is a frameshift mutation. Frameshift mutation is the insertion or deletion of on ‘n’ residues in the reading frame of DNA, where n is NOT divisible by 3. It thus changes the reading frame of mRNA because the reading frame is shifted by a number not equal to 3 or its multiple – which is the basic unit (triplet codon) of translation.

Change in the reading frame leads to the largest extent of changes in the amino acid sequence depending on the position of mutation (closer is the mutation to 5’end of mRNA, greater would be change in amino acids sequence).

It leads to loss and structural and functional integrity of the protein.  

#4. It is a deletion mutation – the mutation causing deletion of one or more nucleotides from reading frame DNA. It may cause following effects-

I. If the 3 deleted nucleotides constituted a single codon, only that codon would be lost. In such case, only one amino acid would be lost from protein. The rest amino acid sequence in mutated protein remains the same as that of original protein.

II. If the 3 deleted nucleotides were part of 2 adjacent codons, it would lead to a frameshift mutation. This type of deletion would change the amino acid sequence to largest extent simultaneously with loss of on amino acid.

#5. The point mutation that does not change amino acid sequence is called a Silent Mutation. Silent point mutation arise due to substitution of one base with another base AND the mutated codon codes the same amino acid as wild type. It does not affect the amino acid sequence of resultant proteins. For example-

            CCU, CCC, CCA and CCG all encode for the same amino acid.

So, a mutation that changes the last letter of the codon does not change amino acid sequence.

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