Understanding DNA: Structure, Function, and Genetics
Understanding DNA: The Building Block of Life
DNA is the fundamental molecule of life. The cell is the basic unit of a living organism, capable of independent function. Despite the diversity in appearance and function among living beings, all cells contain information encoded in DNA molecules. This information guides cellular activity and ensures reproduction and the transmission of traits to offspring (inheritance).
The chemistry of living organisms is largely governed by chemical compounds composed of large molecules, or macromolecules, formed by linking smaller subunits. These chemical compounds enable cells and organisms to grow and reproduce. The primary types of macromolecules include:
- Polysaccharides: Composed of carbohydrate subunits.
- Proteins: Formed from chains of amino acids.
- Nucleic acids: Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), composed of nucleotide subunits.
A DNA nucleotide consists of a deoxyribose sugar molecule, a phosphoric acid molecule, and a nitrogenous base. The nitrogenous base can be a purine (adenine (A) or guanine (G)) or a pyrimidine (thymine (T) or cytosine (C)). In RNA, the sugar is ribose, and uracil (U) replaces thymine.
DNA has a primary structure consisting of a sequence of nucleotides forming long polynucleotide chains. Additionally, it possesses a double-helical secondary structure formed by two antiparallel polynucleotide chains. Before cell division, the genetic material in a eukaryotic cell exists as chromatin. During cell division, chromosomes appear as distinct structures containing DNA and proteins.
Genes and Genetics
The DNA within each chromosome is a single, very long molecule containing functional units called genes. Genetics is the study of individual genes and their effects. A gene is a unit of transmitted information (genetic information) that instructs the parent cell on how to produce proteins. The DNA molecule contains useful biological information that is stably transmitted.
Replication ensures the accurate transfer of genetic information from cell to cell and generation to generation through simple mechanisms for translation of messages. Occasional variations may occur, which, despite seeming contradictory, are essential for organic evolution, leading to new genotypes upon which natural selection can act. The structure of DNA allows for both mutation and recombination.
DNA Structure and Function
The double helix structure of DNA is highly stable, and the unconstrained sequencing of nucleotide bases in its primary structure makes it an excellent informational molecule. The specificity of DNA information lies in the sequence of the four nucleotide bases, expressed as a code based on the order of these bases (e.g., AAGCTTTGCAGGATCC).
The dual structure of DNA allows for accurate replication through the simple separation of the two chains and the synthesis of complementary strands. The string-like structure facilitates sequential reading from end to end in the region of DNA to be translated. Changes in bases, their removal, or the insertion of bases in a given sequence can cause mutation. The exchange of DNA segments between different chromosomes can lead to recombination or the exchange of genetic information.
While DNA carries genetic information and issues instructions for the cell to produce proteins, RNA ensures that these instructions are executed.