The arrangement of DNA allows for complementary base pairing which is required for the faithful replication of the strands of DNA. The DNA polymerase moves along the strand being replicated and adds bases to the new strand based upon the complementary pairing of bases in the old strand. Adenine always pairs with thymine and cytosine always pairs with guanine. The orientation of the strands is anti-parallel which makes the movement of the DNA polymerase (which can only go in one direction) continuous on the leading strand but discontinuous on the lagging strand.
Some genes are controlled. They can turn on and turn off. Turning genes on is referred to as induction and turning genes off is referred to as repression. Three genes are responsible for controlling gene expression: the I or repressor gene, the O operator gene and the P promoter gene. The I gene produces a repressor protein that binds to the operator gene and prevents RNA polymerase from binding at the promoter site to begin transcription. When the gene is turned on an inducer molecule binds to the repressor and changes its three dimensional shape. This inhibits the binding at the operator site which allows the RNA polymerase to start transcription of the genes.
Proteins develop through three structural phases. The primary structure which is the sequence of amino acids determines the secondary and tertiary structure which give the polypeptide its three dimensional configuration. The primary sequence is coded for by the sequence of DNA which is faithfully transcribed into the proper codons that code for the specific amino acid. Any change in the sequence causes a change in the amino acid sequence which causes the protein to fold incorrectly. Both point and frame shift mutations cause a change in the sequence of DNA that results in a change in the amino acid sequence that cause the protein to fold incorrectly.