Structure and Properties of DNA
diphosphate (ADP or dADP)
- Adenosine triphosphate or -
triphosphate (ATP or dATP)
Ribose (X = OH)
Deoxyribose (X = H)
Structure of the nucleotide in DNA and RNA. The base adenine is used as an example. See Table 27-1 for a complete
nomenclature of nucleosides and nucleotides.
A base linked to a sugar is called a
base linked to a sugar linked to a phosphate is called a
or a nucleoside phosphate. The nucleotides in
nucleic acids are joined to one another by a second phos-
phodiester bond that joins the 5'-phosphate of one nu-
cleotide to the 3'-OH group of the adjacent nucleotide.
Such a doubly esterified phosphate is called a
Base Pairing and Base Composition
The molar content of the four bases in DNA (called the
base composition) always satisfies the equalities [A] =
[T] and [G] = [C] where [ ] denotes molar concentration.
These equalities arise because of the base pairing rules in
Structure of a phosphodiester group. The vertical arrows show the bonds in
the phosphodiester group that are free to rotate. The horizontal arrows
show the N-glycosidic bond about which the base can rotate freely. A
polynucleotide consists of many nucleotides linked together by