Science, Tech, Math › Science DNA Definition: Shape, Replication, and Mutation Share Flipboard Email Print Andrey Prokhorov/E+/Getty Images Science Biology Genetics Basics Cell Biology Organisms Anatomy Physiology Botany Ecology Chemistry Physics Geology Astronomy Weather & Climate By Regina Bailey Biology Expert B.A., Biology, Emory University A.S., Nursing, Chattahoochee Technical College Regina Bailey is a board-certified registered nurse, science writer and educator. Her work has been featured in "Kaplan AP Biology" and "The Internet for Cellular and Molecular Biologists." our editorial process Regina Bailey Updated January 20, 2019 DNA (deoxyribonucleic acid) is a type of macromolecule known as a nucleic acid. It is shaped like a twisted double helix and is composed of long strands of alternating sugars and phosphate groups, along with nitrogenous bases (adenine, thymine, guanine, and cytosine). DNA is organized into structures called chromosomes and housed within the nucleus of our cells. DNA is also found in cell mitochondria. DNA contains the genetic information necessary for the production of cell components, organelles, and for the reproduction of life. Protein production is a vital cell process that is dependent upon DNA. Information contained within the genetic code is passed from DNA to RNA to the resulting proteins during protein synthesis. Shape DNA is composed of a sugar-phosphate backbone and nitrogenous bases. In double-stranded DNA, the nitrogenous bases pair up. Adenine pairs with thymine (A-T) and guanine pairs with cytosine (G-C). The shape of DNA resembles that of a spiral staircase. In this double helical shape, the sides of the staircase are formed by strands of deoxyribose sugar and phosphate molecules. The stair steps are formed by the nitrogenous bases. The twisted double helix shape of DNA helps to make this biological molecule more compact. DNA is further compressed into structures called chromatin so that it can fit within the nucleus. Chromatin is composed of DNA that is wrapped around small proteins known as histones. Histones help to organize DNA into structures called nucleosomes, which form chromatin fibers. Chromatin fibers are further coiled and condensed into chromosomes. Replication The double helix shape of DNA makes DNA replication possible. In replication, DNA makes a copy of itself in order to pass genetic information on to newly formed daughter cells. In order for replication to take place, the DNA must unwind to allow cell replication machinery to copy each strand. Each replicated molecule is composed of a strand from the original DNA molecule and a newly formed strand. Replication produces genetically identical DNA molecules. DNA replication occurs in interphase, a stage prior to the start of the division processes of mitosis and meiosis. Translation DNA translation is the process for the synthesis of proteins. Segments of DNA called genes contain genetic sequences or codes for the production of specific proteins. In order for translation to occur, the DNA must first unwind and allow DNA transcription to take place. In transcription, the DNA is copied and an RNA version of the DNA code (RNA transcript) is produced. With the help of cell ribosomes and transfer RNA, the RNA transcript undergoes translation and proteins synthesis. Mutation Any change in the sequence of nucleotides in DNA is known as a gene mutation. These changes can affect a single nucleotide pair or larger gene segments of a chromosome. Gene mutations are caused by mutagens such as chemicals or radiation, and can also result from errors made during cell division.