Structure of the Nucleic Acids

• The central dogma of molecular biology is that DNA is transcribed to RNA, which is translated to protein.
• Nucleotides, consisting of a nitrogenous base, a five-carbon sugar, and phosphate, are the monomeric unit of the nucleic acids DNA and RNA (see Chapter 3).
• DNA contains the sugar 2′-deoxyribose; RNA contains ribose.
• DNA and RNA contain the purine bases adenine (A) and guanine (G).
• DNA contains the pyrimidine bases cytosine (C) and thymine (T), whereas RNA contains C and uracil (U).
• DNA and RNA are linear sequences of nucleotides linked by phosphodiester bonds between the 3′ sugar of one nucleotide and the 5′ sugar of the next nucleotide.
• Genetic information is encoded by the sequence of the nucleotide bases in DNA.
• DNA is double stranded; one strand runs in the 5′ to 3′ direction, while the other is antiparallel and runs in the 3′ to 5′ direction.
• The two strands of DNA wrap about each other to form a double helix and are held together by hydrogen bonding between bases in each strand.
• A hydrogen bonds to T, while C hydrogen bonds to G.
• Transcription of a gene generates a single-stranded RNA; the three major types of RNA are messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA).
• Eukaryotic mRNA is modified at both the 5′ and 3′ ends. In between it contains a coding region for the synthesis of a protein.
• Codons within the coding region dictate the sequence of amino acids in a protein. Each codon is three nucleotides long.
• rRNA and tRNA are required for protein synthesis.
• rRNA is complexed with proteins to form ribonucleoprotein particles called ribosomes, which bind mRNA and tRNAs during translation.
  The tRNA contains an anticodon which binds to a complementary codon on mRNA, ensuring insertion of the correct amino acid into the protein being synthesized.