 A single nucleotide difference within DNA can cause a change in the amino acid sequence of a protein . Because protein structures are the result of their amino acid sequences , some changes can dramatically change the properties of a protein by destabilizing the structure or changing the surface of the protein in a way that changes its interaction with other proteins and molecules . For example , sickle @-@ cell anemia is a human genetic disease that results from a single base difference within the coding region for the β @-@ <unk> section of hemoglobin , causing a single amino acid change that changes hemoglobin 's physical properties . Sickle @-@ cell versions of hemoglobin stick to themselves , stacking to form fibers that distort the shape of red blood cells carrying the protein . These sickle @-@ shaped cells no longer flow smoothly through blood vessels , having a tendency to clog or degrade , causing the medical problems associated with this disease . 
