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Dna backbone9/19/2023 ![]() Professional Application in Service Learning I (LDR-461).Art History I OR ART102 Art History II (ART101).Child and Adolescent Psychology (PSY-355).The United States Supreme Court (POLUA333).Nutrition and Exercise Physiology (NEP 1034).Early Childhood Foundations and the Teaching Profession (ECE-120).Methods of Structured English Immersion for Elementary Education (ESL-440N).Introduction to Environmental Sciences (ENVS 1301).Strategic Decision Making and Management (BUS 5117).Intro to Professional Nursing (NURSING 202).Health-Illness Concepts Across the Lifespan I (NUR 1460C).(Remember that the strands run antiparallel, so the 5’ end of one strand must be able to pair with the 3’ end of the other.) These strands are called complementary. In this way, if one strand of DNA is known to have the sequence 5’-ATGGCT-3’, the other strand must have the sequence 3’-TACCGA-5’. Therefore, if the sequence of one strand of DNA is known, the sequence of the other strand can be determined as well. More information on polarity can be found in the tutorial on bonding.īecause of the specificity of hydrogen bonding, in the context of DNA A always pairs with T, and G with C. The cellular environment is aqueous and therefore polar, so surrounding the non-polar bases with charged phosphates maximizes the solubility of DNA under physiological conditions. Second, the non-polar, uncharged bases are hidden in the center of the helix. The double-helix structure, with negatively charged phosphates on the outside edges, allows the phosphates to be as far apart as possible. First, remember that like charges repel each other. This structure places the non-polar bases of DNA in the center of the double-stranded molecule, surrounded by the charged phosphate groups. The strands of DNA run anti-parallel, or in opposite directions: the 5’ end of one strand is paired with the 3’ end of the other. The width of each “step” is approximately the same size, since a base pair always consists of one pyrimidine and one purine. If DNA were thought of as a spiral staircase, the base pairs would be the steps. This occurs via hydrogen bonds, which are shown with dotted lines in the figure above. These interactions are specific: A base pairs with T, and C base pairs with G. Hydrogen-bond interactions between the bases allow two strands of DNA to form the double helix. In the structure below, each nucleotide is drawn in a different color, for clarity. The backbone has a 5’ end (with a free phosphate) and a 3’ end (with a free OH group). In this manner, each strand of DNA has a “backbone” of phosphate-sugar-phosphate-sugar-phosphate. 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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