Maurice Wilkins all played pivotal roles in elucidating the structure of DNA.ĭNA is coiled into chromosomes and tightly packed in the nucleus of our cells. Both the replication of DNA and the synthesis of proteins in our cells are dependent on the double-helix shape of DNA.The twisting of DNA is the result of both hydrophilic and hydrophobic interactions between the molecules that comprise DNA and water in a cell.This double helix shape is often visualized as a spiral staircase. Its double helix consists of two spiral chains of DNA. Double helix is the biological term that describes the overall structure of DNA.The nitrogen (blue atoms) containing bases are inside, stacking perpendicular to the helix axis.Īll contents copyright © 1997. The sugar-phosphate backbone is on the outside of the helix where the polar phosphate groups (red and yellow atoms) can interact with the polar environment. The helix axis is most apparent from a view directly down the axis. dA-dT and dG-dC base pairs can occur in any order within DNA molecules DNA Helix Axis Therefore the DNA molecule has a uniform diameter. dA-dT and dG-dC base pairs are the same length, and occupy the same space within a DNA double helix. Within the DNA double helix, A forms 2 hydrogen bonds with T on the opposite strand, and G forms 3 hyrdorgen bonds with C on the opposite strand. The bases of the individual nucleotides are on the inside of the helix, stacked on top of each other like the steps of a spiral staircase.The sugar-phosphate backbones of the two DNA strands wind around the helix axis like the railing of a sprial staircase.The two polynucleotide chains run in opposite directions.Two DNA strands form a helical spiral, winding around a helix axis in a right-handed spiral.Two polynucleotide chains, held together by weak thermodynamic forces, form a DNA molecule. DNA Double HelixĭNA is a normally double stranded macromolecule. The deoxyribose sugars are joined at both the 3'-hydroxyl and 5'-hydroxyl groups to phosphate groups in ester links, also known as 'phosphodiester' bonds. The DNA backbone is a polymer with an alternating sugar-phosphate sequence. A nucleotide is a nucleoside with one or more phosphate groups covalently attached to the 3'- and/or 5'-hydroxyl group(s). The four different nucleosides of DNA are deoxyadenosine (dA), deoxyguanosine (dG), deoxycytosine (dC), and (deoxy)thymidine (dT, or T).In dA and dG, there is an 'N-glycoside' bond between the sugar C1' and N9 of the purine. Nucleosides differ from nucleotides in that they lack phosphate groups. The sugar in deoxynucleosides is 2'-deoxyribose. Nucleosides and NucleotidesĪ nucleoside is one of the four DNA bases covalently attached to the C1' position of a sugar. Deoxyribose lacks an hydroxyl group at the 2'-position when compared to ribose, the sugar component of RNA. The hydroxyl groups on the 5'- and 3'- carbons link to thephosphate groups to form the DNA backbone. The carbonatoms are numbered 1', 2', 3', 4', and 5' to distinguish from the numbering of theatoms of the purine and pyrmidine rings. The deoxyribose sugar of the DNA backbone has 5 carbons and 3 oxygens. Like purines, all pyrimidine ring atoms lie in the same plane. The 6 atoms (4 carbon, 2 nitrogen) arenumbered 1-6. The 9 atoms that make up the fused rings (5 carbon, 4 nitrogen) are numbered 1-9. Purines are the larger of the two types of bases found in DNA. The four nucleotides are given one letter abbreviations asshorthand for the four bases.Īdenine and guanine are purines.

There are four different types of nucleotides found in DNA, differingonly in the nitrogenous base. The monomer units of DNA are nucleotides, and the polymer is known as a 'polynucleotide.' Each nucleotide consistsof a 5-carbon sugar (deoxyribose), a nitrogen containing base attached to the sugar, anda phosphate group. DNA Structure DNA Structure Activity Problem 10: Review of the Features of the Watson-Crick Model for DNA Structure Components of DNAĭNA is a polymer.

Dna sugar phosphate backbone