
The cell and its basic mechanisms 15
FIGURE 2.7: The DNA materia l in the nucleus is tightly packed in a com-
plex way. The very long double-stranded DNA that co ntains the genes is some-
times compared with a string. From place to pla c e along this string , there are
cylindrical structures called histones. The scale is such that if the DNA is
compared with a s tring, the his tones could be compared with some be ads on
this string, only that instead of the string going through each bead, the string
is wrapped around each bead. The double-stranded DNA wrapped around a
histone forms a nucleosom e. The “bea ds on a string”structure ca n be further
folded ...