Each "rung" of the ladder is a pair of nitrogenous bases, one purine and one pyrimidine extending into the center of the molecule. The pairing of these bases is always adenine with thymine A - T and guanine with cytosine G - C. The sugar-phosphate backbones of the two polynucleotide chains coil around one another making the "ladder" into a spiral "staircase". This superstructure is known as a "double helix".
DNA acts as the store of genetic information. The sequence of bases along its length are the "language" of the cell and code for all its proteins. DNA is also the molecule of heredity. Do you want to LearnCast this session? This article has been posted to your Facebook page via Scitable LearnCast.
Change LearnCast Settings. Scitable Chat. Note that two pairs of bases have similar structures. A and G both have two carbon-nitrogen rings and are known as purines. In contrast, C and T have a single carbon-nitrogen ring and belong to a class of molecules called pyrimidines.
Hydrogen-bond interactions between the bases allow two strands of DNA to form the double helix. These interactions are specific: A base pairs with T, and C base pairs with G. This occurs via hydrogen bonds, which are shown with dotted lines in the figure above.
If DNA were thought of as a spiral staircase, the base pairs would be the steps. This is illustrated in the figure below. Possible Answers: A nitrogenous base and a phosphate. A nitrogenous base, a ribose or deoxyribose sugar, and a phosphate group. A nitrogenous base and a ribose or deoxyribose sugar. Correct answer: A nitrogenous base and a ribose or deoxyribose sugar.
Explanation : This question is mostly about the differentiations between a nucleoside and a nucleotide. Possible Answers: A covalent bond is formed. Correct answer: Maximized number of hydrogen bonds. Explanation : Cytosine and guanine, when base paired, have three hydrogen bonds between them. Chargaff is credited with which of the following discoveries about DNA base pairs? Possible Answers: The ratio of adenine to guanine is close to and the ratio of cytosine to thymine is close to.
Correct answer: The ratio of adenine to thymine is close to and the ratio of guanine to cytosine is close to. Explanation : Due to DNA's double-helical structure, the nucleotide bases are paired. Copyright Notice. View AP Biology Tutors. Parker Certified Tutor. Julia Certified Tutor. Auburn University, Doctor of Education, Vocational Mikhail Certified Tutor. Report an issue with this question If you've found an issue with this question, please let us know.
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