NUCLEIC ACIDS 53
A, B, and Z DNA structure are found in Table 2.3 as adapted from Table 1.10
of reference 15 and the Jena image library at http://www.imb-jena.de/IMAGE_
DNA_MODELS.html.
In the nucleus of eukaryotic cells, a compacted DNA is formed by winding
in a shallow, left - handed superhelix around a group of eight histone proteins
to form nucleosome core particles. The core particles are further organized
into chromatin through interaction with additional histone proteins. Chroma-
tin is anchored to a scaffold of proteins within the chromosomes. In order for
replication, transcription, or translation to take place, supercoiled DNA must
unravel and the DNA strands separate, at least temporarily. It is thought that
the unraveling process, or some version of it, may be necessary before plati-
num antitumor agents such ascis - dichlorodiammineplatinum(II), cisDDP, can
bind to DNA, their major target in vitro and in vivo. Much more about the
platinum - containing drugs is found in Chapter 7 of the fi rst edition of Bioin-
organic Chemistry: A Short Course.
2.3.3 Transmission of Genetic Information,
Three major components in the transmission of genetic information are deoxy-
ribonucleic acids (DNA), ribonucleic acids (RNA), and proteins. The genetic
code expressed through DNA ultimately determines which proteins a cell will
produce. Coiled and supercoiled DNA molecules contain numerous sequences
of nucleotides that may be transcribed as RNAs and translated to many dif-
ferent proteins. DNA molecules also contain long sequences of nucleotides
not coding for protein and whose purpose is not completely understood. A
gene is a specifi c sequence of DNA that encodes a sequence of messenger
TABLE 2.3 Some Properties of A DNA, B DNA, and Z DNA
Property A DNA B DNA
Z DNA (the repeat unit
is the dimer – G C – )
Helix handedness Right Right Left
Sugar pucker C 3 ′ - endo C 2 ′ - endo C 3 ′ - endo
Number of nucleotides per
pitch or base pairs per turn
11 10.4 12
Turn angle per nucleotide or
twist angle ( t , ° )
32.7 34.6 30
Helical rise ( h , Å ) 2.56 3.38 3.7
Pitch ( P , Å ) 24.6 34.0 45.6
Diameter ( Å ) 25.5 23.7 18.4
Conformation of gylcosidic
bond
Anti Anti Anti at C
Syn at G
Major (minor) groove width
( Å )
2.7(11.0) 11.7(5.7)
Major (minor) groove depth
( Å )
13.5(2.8) 8.5(7.5)
