DNa nitrogenous bases

DNA Strand Orientation

Always 5’ to 3’

5’ End

Free phosphate group

3’ End

Free hydroxyl (OH) group

Phosphodiester Bond

Covalent bond between phosphate and sugar in DNA backbone

Glycosidic Bond

Covalent bond between sugar and nitrogenous base

A-T Base Pairing

Two hydrogen bonds between adenine and thymine

G-C Base Pairing

Three hydrogen bonds between guanine and cytosine

Nucleoside

Sugar and nitrogenous base (no phosphate)

Nucleotide

Sugar, base, and one or more phosphate groups

Monophosphate

One phosphate group

Diphosphate

Two phosphate groups

Triphosphate

Three phosphate groups

Phosphate Group

Provides a negative charge to the nucleotide

Nitrogenous Bases
Purines

Double-ring structure includes adenine and guanine

Pyrimidines

Single-ring structure includes cytosine, thymine, and uracil

Adenine

Purine base with NH₂ group at top

Guanine

Purine base with NH₂ and O groups

Cytosine

Pyrimidine base with NH₂ group

Thymine

Pyrimidine base with CH₃ group

Uracil

Pyrimidine base lacking CH₃ group (in RNA)

Chemical Bonds and Reactions
Ionic Bond

Bond formed by electron transfer between atoms

Covalent Bond

Bond formed by sharing electrons between atoms

Hydrogen Bond

Weak bond between polar molecules

Peptide Bond

Covalent bond between amino acids (C–N bond)

Phosphodiester Bond

Covalent bond between phosphate and sugar in DNA/RNA

Phosphoanhydride Bond

Bond between phosphate groups in ATP

Hydrolysis

Reaction that breaks bonds by adding water

Condensation Reaction

Reaction that forms bonds by removing water