Explain why a single base deletion could be potentially more damaging to protein synthesis than a deletion of three consecutive bases confined to one triplet?
A single base deletion in the DNA sequence can have a more severe impact on protein synthesis compared to a deletion of three consecutive bases confined to one triplet. To understand why, let's first explore the process of protein synthesis.
Protein synthesis occurs in two main stages: transcription and translation. During transcription, the DNA sequence is first transcribed into a messenger RNA (mRNA) molecule. This mRNA molecule carries the instructions for protein synthesis. Then, during translation, the mRNA is read by ribosomes, and amino acids are joined together to form a protein.
Now, let's consider the consequences of a single base deletion versus a deletion of three consecutive bases.
1. Single Base Deletion:
If a single base is deleted in the DNA sequence, it leads to a frameshift mutation during transcription. A frameshift mutation occurs when the reading frame of the mRNA is shifted, meaning the grouping of bases into triplets is altered. As a result, all subsequent codons and, consequently, the corresponding amino acids in the protein sequence will be incorrect from that point on.
For example, let's assume we have the DNA sequence: ATG ACT GAC TGA. The corresponding mRNA sequence would be AUG ACU GAC UGA. If we delete the "G" in the second codon (AUG ACU _AC UGA), all the following codons will be altered, leading to a completely different amino acid sequence. This disruption can result in a nonfunctional protein or a protein with impaired function.
2. Deletion of Three Consecutive Bases Confined to One Triplet:
If three consecutive bases are deleted within one triplet, the deletion will remove an entire codon from the sequence. Since the genetic code is redundant, meaning multiple codons can code for the same amino acid, the deletion of one codon may not have as severe consequences as a frameshift mutation.
For example, let's consider the DNA sequence: ATG ACT GAC TGA. If we delete "ACT" (ATG AC _GAC TGA), the remaining codons can still code for the same amino acids as before, and the overall protein structure may remain relatively intact.
In summary, a single base deletion causes a frameshift mutation, altering the entire reading frame of the mRNA. This, in turn, disrupts the subsequent codons and leads to an incorrect amino acid sequence. On the other hand, a deletion of three consecutive bases confined to one triplet may only remove one codon, and since the genetic code is redundant, the impact on the overall protein structure may be less severe.