Nucleic Acids: DNA and RNA Structure

Nucleotides and Bonding

• The phosphate group of a nucleotide forms a covalent phosphodiester bond with the 3' hydroxyl group of another nucleotide.
• Nucleotides are polymerized through phosphodiester bonds, creating a long chain of nucleic acids.

RNA Function

• Most RNA in cells plays a crucial role in protein synthesis and acts as a messenger (mRNA), transfer RNA (tRNA), or ribosomal RNA (rRNA).

Nucleotide Structure

• Purines, which include adenine and guanine, are the bases that have a double ring structure in nucleotides.
• In DNA, the nitrogenous bases are attached to a deoxyribose sugar molecule.

DNA Polarity and Arrangement

• DNA is a polymer with polarity, characterized by a 5' end and a 3' end, allowing directional synthesis.
• The polynucleotide strands in the Watson-Crick Model of DNA are arranged in an antiparallel configuration.

Base Pairing and Stability

• Hydrogen bonds form between nucleotide bases during base pairing; specifically, three hydrogen bonds occur between cytosine (C) and guanine (G) base pairs.
• The feature of DNA's structure that allows for precise base pairing is its complementary base pairing mechanism.

Watson and Crick Contribution

• James Watson and Francis Crick published their model of the DNA double helix in the journal Nature in 1953.

Additional Features

• The double helix of DNA has a major and minor groove, with the double helix stabilized by hydrophobic interactions and hydrogen bonds.
• At one end of the DNA double helix, a phosphate group (5' end) is found, while the other end has a hydroxyl group (3' end).
• For proper base pairing in DNA to occur, it is necessary for one base to be oriented 'upside down' relative to the other, maintaining the antiparallel orientation of the strands.