Answer: A change to the DNA sequence may or may not change the functionality of the protein, make an inactive protein, or prevent production of the protein.
Explanation: NO SEQUENCE SHOWN, but generally
A gene codes for a protein. A change in one nucleotide (single nucleotide polymorphism - SNP) can have several different consequences. The deletion or insertion of a nucleotide also has consequences
The protein-making part of the gene is organised into codons - groups of three nucleotides who sequences make up the genetic code. Changes may have any of these consequences for the protein:
1. No consequence: there are redundancies in the code and an SNP may not change the meaning of the codon, especially if it is the third nucleotide
Example: CGT --> CGA these both code for serine, so no change
2. No consequence: an SNP may change the amino acid, but if this is not at a critical part of the protein and/or the amino acids have similar properties it will not affect the end product
Example: ACT --> CCT = isoleucine --> leucine
3. An SNP affects protein folding or the active site. This can alter or prevent protein function
Example: GAG --> GTG = glutamic acid --> valine
leads to sickle cell anaemia if both alleles affected
4. An SNP may prevent completion of the protein. STOP codons tell the reading mechanism the process is complete. If this happens during the process, the incomplete fragment is removed. If the revers occurs, reading will continue until another STOP codon adding additional structure thar will interfere withprotein function.
Example: TAT --> TAG = thyrosine --> STOP codon
5. Insertions and deletions can also disrupt protein formation, by changing the reading frame. The transcription process relies on having a start point, so that codons are read from that point (the reading frame). Adding or removing alters the reading frame so that codons are read incorrectly
Example (start)TTCATCGAGTATCGTACA...codes for phe-ile-glu-tyr-arg-thr
suppose the second C is deleted
the reading frame becomes (start)TTCATGAGTATCGTACA.
which reads as phe-met-ser-ile-val- , a very different sequence.
