Question

Suppose an extra base pair is inserted into the coding sequence of a particular gene during replication. Describe how this may affect the translation of the polypeptide chain encoded by the gene.

Answer 1

DNA replication happens before every cell division and it is very important process. DNA replication should happen at high fidelity (no error should happen). But, despite of several repair system some mutations do happen.

Insertion of an extra base pair in coding region of DNA is called frameshift mutation. It mostly happens due to slippage of DNA polymerase.

It can lead to several consequences-

Frameshift mutation can alter the reading frame of codons and therefore, amino acids. frame shift mutation especially becomes dangerous when insertion happens in exon region of DNA,

We know that codons are triplet. If one extra base pair will be added then the reading frame of all the codons and hence, amino acids will be altered and hence. different and faulty amino acids will be added during translation. Such proteins will be functionally altered because of presence of different amino acids

Insertion led frameshift can also create a stop codon prematurely. Therefore, it can lead to either no protein synthesis or production of premature polypeptide (truncated protein). Such truncated proteins have poor or no functional activity.

After frameshift mutation the resulting transcription product (mRNA) may be also degraded by nonsense mediated decay and then again there will be no translation and protein product

Frame shift mutation causes several types of cancer and diseases like Tay sach disease. In case of Tay sach disease there is insertion of 4 base pairs in HEXA gene ( Especially in jewish population). So altered frame produces faulty gene product and hence the disease.