Some different proteins will be produced from the gene.
When one of the nitrogen bases of a DNA is replaced by another, the phenomenon is called a point mutation. This condition actually is a mutation because, a gene translates into a protein through the mRNA. Now the DNA transcribes into a mRNA. If one of the nitrogen bases are changed in DNA, it will lead to change in the corresponding base of mRNA too. So the codon of which the changed nitrogen base is a part of, also changes which now codes for a different amino acid. So the protein structure also changes.
This condition is actually seen in sickle cell anaemia, where the 6th amino acid of haemoglobin changes from glutamic acid to valine, and the RBC structure becomes sickle celled owing to a hydrogen bond between valine and other amino acids.
