Chapter
18
Animations
Art
Unit 3: Genetics
Regulation of Gene Expression
Review
Regulation of protein production can occur by
inhibition or by
control, as illustrated in the
E. coli
operon.
The
trp
operon is a
system
that is turned
unless
repressed
by the repressor.
Repressible enzymes usually function in
pathways.
The
E. coli
lac
operon is an
system
that is turned
unless
induced
by the inducer.
Inducible enzymes usually function in
pathways.
Expression of the
lac
operon is also subject to positive control: the
operon
is
by the catabolite-activating
protein
(CAP), together with Cyclic adenosine monophosphate (
cAMP
) when
is absent.
In eukaryotes, gene regulation controls cell specialization and
.
Eukaryotic gene expression can be regulated at many
stages,
from the
to the
.
Chromatin modification:
acetylation
of
"tails" loosens the configuration of chromatin and enhances
by making DNA more accessible to enzymes.
Transcription control: many genes contain control
elements
such as
and
that can stimulate transcription.
RNA processing: different
molecules can be produced from the same primary
transcript,
in a process called alternative RNA
.
mRNA degradation: single-stranded
(miRNAs) can lead to
degradation
of an mRNA, thus limiting its life span.
Protein processing and degradation: protein
complexes
called
degrade proteins by binding to proteins tagged by
and digesting them.
Multicellular organisms develop from a single-celled
to cells of many different types through
cell
,
cell
, and
morphogenesis.
Differential distribution of
determinants
in the egg can lead to
subsequent
of
embryonic
cells.
Expression of genes for tissue-specific proteins result in cell
, and leads to
observable
.
Cancer results from genetic changes that affect cell
control.
Mutations in
-
oncogenes
can turn them into cancer-causing
that lead to abnormal cell growth.
Tumor-
genes regulate cell growth;
mutations
in these genes can lead to uncontrolled cell growth and cancer.
mutations are generally needed for full-fledged cancer; at least one active
and accumulation of several mutant tumor-
genes characterize
most
cancers.
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