Biology Chapter: Nucleic Acids and Nucleotides

Nucleotides and Nucleic Acids

• DNA and RNA are nucleic acids and are composed of chains of nucleotides.
• A nucleotide consists of a nitrogenous base, a five-carbon sugar, and a phosphate group.
• The nitrogenous bases found in DNA are adenine (A), cytosine (C), guanine (G), and thymine (T).
• RNA contains uracil (U) instead of thymine (T).
• The sugar-phosphate backbone is formed by the phosphate and sugar components of nucleotides.

DNA Structure

• DNA is a double helix, where the sugar-phosphate backbone is on the outside and the nitrogenous bases are paired in the interior.
• Nitrogenous bases pair in a specific manner: A pairs with T, forming two hydrogen bonds, and G pairs with C, forming three hydrogen bonds.
• The specific pairing of bases gives the helix a uniform shape.

RNA Structure

• RNA codons consist of three nitrogenous bases.
• The sequence of RNA codons determines the sequence of amino acids in proteins.
• There are 64 possible RNA codons, each specifying one of the 20 amino acids or a stop signal.

Comparison of DNA and RNA Nucleotides

• DNA nucleotides contain the sugar deoxyribose, while RNA nucleotides contain the sugar ribose.
• DNA contains the nitrogenous base thymine (T), while RNA contains uracil (U).
• A cell should contain at least 4 types of nucleotides to build all the DNA and RNA molecules.

Watson-Crick Model

• James Watson and Francis Crick proposed the double-helix DNA model in 1953.
• They, along with Maurice Wilkins, were awarded the 1962 Nobel Prize in Physiology and Medicine for their discoveries on the structure of DNA and its significance in inheritance.