Genetics Basic Concepts
DNA strand with its nitrogenous bases
DNA, which stands for deoxyribonucleic acid, is a molecule found in all living beings. It carries the genetic information needed for the organism to develop and function.
A DNA molecule is shaped like a long twisted ladder, which is why it is often referred to as a double helix. The sides of the ladder are made of alternating sugar (deoxyribose) and phosphate molecules. The rungs of the ladder, which bond to the sugar molecules on each side, are formed by pairs of nitrogenous bases facing one another. They are the building blocks of the DNA molecule. There are four different nitrogenous bases: adenine (A), thymine (T), cytosine (C) and guanine (G). When forming the rungs, A always pairs with T and C always pairs with G. The order of the nitrogenous bases (ACCATTCGCT...) is what determines DNA’s instruction, also known as the genetic code.
DNA is associated with different proteins (histones) and found in the nucleus of the cell.
Some DNA fragments are non-coding; in other words, they do not seem to be useful or they serve to regulate the use of DNA by the cell. For example, promoters are DNA sequences that can initiate the expression of information embedded elsewhere in DNA. Enhancers are DNA sequences that can increase or decrease the intensity of DNA expression. There are additional non-coding regions that play an essential role in the production of proteins using the information in DNA.