MGD L4.1

Introduction to Nucleic Acids: DNA and RNA

• The Central Dogma of Molecular biology is the flow of information from DNA to RNA to protein in all organisms.
• Genes are specific segments of DNA composed of distinctive sets of nucleotide pairs in a discrete region of a chromosome that encodes a particular protein.
• Alleles are alternative forms of a single gene.
• Nucleic acids are linear polymers of nucleotides that are required for the storage and expression of genetic information.
• There are two chemically distinct types of nucleic acids: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
• Nucleotides are the basic building blocks of DNA and RNA, consisting of three components: a nitrogenous base, a pentose sugar, and a phosphate molecule.
• There are two types of nitrogenous bases: purines (adenine and guanine) and pyrimidines (thymine, cytosine, and uracil).
• The phosphate groups in nucleotides are strongly acidic and are responsible for the acidic nature of DNA and RNA.
• Nucleotides are formed by covalent bonding of the phosphate, base, and sugar.
• Polynucleotide chains are formed by covalently linking nucleotides via 3'→5' phosphodiester bonds. The resulting chain has polarity, with both a 5' end and a 3' end.
• DNA is composed of two polynucleotide chains running in opposite directions, with base pairing between adenine and thymine and between guanine and cytosine.
• The double-stranded structure of DNA offers a molecular explanation for mutation and the complementary nature of the two polynucleotide DNA strands helps explain how DNA is copied.

DNA Structure and Function

• Nucleic acids, DNA and RNA, are linear polymers of nucleotides that store and express genetic information.
• Nucleotides consist of a nitrogenous base, pentose sugar, and phosphate group.
• There are two types of nitrogenous bases: purines (adenine and guanine) and pyrimidines (cytosine, thymine, and uracil).
• Base pairing is highly specific; A pairs with T (or U) and C pairs with G by hydrogen bonds.
• DNA is composed of two antiparallel polynucleotide chains, and base pairing makes the two chains complementary in base composition.
• The double helix structure of DNA is stabilized by hydrogen bonds between base pairs and has a hydrophilic deoxyribose-phosphate backbone.
• The Watson Crick model of DNA explains the molecular basis of genetic information storage and mutation, as well as the mechanisms of transcription and translation.
• The sequence of bases in DNA has a high coding capacity, with 4n combinations for a DNA molecule n base pairs long.
• DNA can be denatured into single strands by disrupting hydrogen bonds between base pairs using acidic, alkaline pH or heating, and can renature under appropriate conditions.
• DNA degradation can occur through hydrolysis of phosphodiester bonds by chemicals or nucleases.
• RNA differs from DNA in its sugar component (ribose instead of deoxyribose) and the presence of uracil instead of thymine.
• The polarity of a nucleic acid chain has two distinct ends: a 5' end with a free phosphate and a 3' end with a free OH-group.