Biology Reference
In-Depth Information
DNA
g3
g2
p
i
g1
o
the genes are repressed
A
R
DNA
g3
g2
p
g1
o
the genes are active
B
lactose
R
operon 1
operon 2
DNA
C
regulator protein
F
IGURE
7. The regulation of genes and the genetic programme. A
: In the absence
of lactose, the repressor fixes on the
o
sequence and blocks transcription of the
genes
g
1
,
g
2
and
g
3
.
B
: Lactose binding to the repressor removes this inhibition.
C
: If a gene of an operon codes for a regulator protein, this induces cascade
regulation of several operons (genetic programme).
there is a relationship between the genes which ensures that their
activity is coordinated (Fig. 7C). Consequently, programmes relat-
ing to the overall activity of the genome can be explained by pro-
gressive complexification of the model, involving cascade regulation
of all the genes. How they function is based on the property of
stereospecificity owing to which regulator proteins act like cyber-
netic commands activating or repressing genes. In some cases, these