Textbook Question
Consider the sequence 3'-ACGCTACGTC-5'.
What is the total number of noncovalent bonds joining the nucleotides of the complementary strands?
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7. DNA and Chromosome Structure
DNA Structure
1:38 minutesProblem 11
Textbook Question
How are the carbon and nitrogen atoms of the sugars, purines, and pyrimidines numbered?
Verified step by step guidance1
Understand that the numbering of carbon and nitrogen atoms in sugars, purines, and pyrimidines follows specific conventions to ensure consistency in molecular biology and genetics.
For sugars (like ribose and deoxyribose), the carbon atoms are numbered starting from the carbon attached to the nitrogenous base. This carbon is labeled as C1', and the numbering continues clockwise around the sugar ring (C2', C3', C4', and C5'). The prime (') symbol distinguishes sugar carbons from those in the nitrogenous bases.
For purines (adenine and guanine), the numbering starts at the nitrogen atom in the six-membered ring that is closest to the five-membered ring. The numbering proceeds counterclockwise around the six-membered ring and then continues into the five-membered ring.
For pyrimidines (cytosine, thymine, and uracil), the numbering starts at the nitrogen atom in the six-membered ring that is bonded to the sugar. The numbering proceeds clockwise around the ring.
Remember that these numbering conventions are critical for identifying the positions of functional groups, such as phosphate groups or hydroxyl groups, and for understanding the structure and function of nucleotides and nucleic acids.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Nucleotide Structure
Nucleotides are the building blocks of nucleic acids, consisting of a sugar, a phosphate group, and a nitrogenous base. The sugar can be ribose or deoxyribose, and the nitrogenous bases are categorized into purines (adenine and guanine) and pyrimidines (cytosine, thymine, and uracil). Understanding the structure of nucleotides is essential for grasping how carbon and nitrogen atoms are numbered in these molecules.
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Carbon Numbering in Sugars
In sugars, carbon atoms are numbered starting from the carbon adjacent to the oxygen in the ring structure. For ribose and deoxyribose, the numbering continues around the ring, with the first carbon being part of the base attachment. This systematic numbering is crucial for identifying the positions of functional groups and understanding the sugar's role in nucleotides.
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Nitrogenous Base Structure
Purines and pyrimidines have distinct structures that influence how their nitrogen atoms are numbered. In purines, the numbering starts from the nitrogen in the base's fused ring system, while in pyrimidines, it begins from the nitrogen in the single ring. This numbering is vital for understanding base pairing and the overall structure of nucleic acids.
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