![]() ![]() When nucleotides are incorporated into DNA, adjacent nucleotides are linked by a phosphodiester bond: a covalent bond is formed between the 5’ phosphate group of one nucleotide and the 3’-OH group of another (see below). In DNA, however, it loses two of these phosphate groups, so that only one phosphate is incorporated into a strand of DNA. In an aqueous environment, like inside the cell, the phosphate groups are negatively charged, as drawn in the figure above.Ī free, unincorporated nucleotide usually exists in a triphosphate form that is, it contains a chain of three phosphates. The second principle feature of a nucleotide is the triphosphate group attached to the 5’ carbon of the ribose group. Because the -OH group on the 2’ carbon is missing in the form of ribose found in DNA, the sugar in DNA is called 2’-deoxyribose. Each carbon of ribose is numbered as shown. The sugar found in DNA is a variant of the five-carbon sugar called ribose. Note that in the figures drawn in this unit, each unlabeled vertex of a structure represents a carbon atom. A single nucleotide is composed of three functional groups: a sugar, a triphosphate, and a nitrogenous (nitrogen-containing) base, as shown below. Other examples of a helix include yarn, a phone cord, or a spiral staircase.Įach chain of the double helix is made up of repeating units called nucleotides. Note that there are two strands: one shown in blue, one in yellow. The image in the center shows the structure of DNA. In the image above, a corkscrew is shown on the left, with the helical region labeled. A helix is a winding structure like a corkscrew DNA is known as a double helix because there are two intertwined strands within each molecule of DNA. In 1953, using data obtained by Rosalind Franklin, James Watson and Francis Crick determined that DNA exists in a form known as the double helix. In this unit, the molecular structure of DNA and its packaging within cells will be examined. DNA provides the instructions to build, maintain, and regulate cells and organisms and is passed on when cells divide and when organisms reproduce. ![]() Life Sciences Cyberbridge Nucleotides and the double helixĭNA, or deoxyribonucleic acid, is the heritable material found in all cells. ![]()
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