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Gene Regulation
Expression of certain genes in any
given cell
Mechanisms That Regulate Gene
Expression

Amount of mRNA transcribed

Rate of translation

Activity of protein product
Bacterial Gene Regulation

Transcription-level control is most efficient

Constitutive genes are constantly transcribed

Genes that are needed only under certain
conditions are arranged in operons
Operons

Groups of structural genes with related
functions + DNA responsible for controlling
them:


Promoter – site for RNA polymerase to bind
Operator – switch that controls transcription
The lac Operon

Produces enzymes for lactose digestion

Only needed when no glucose present but
lactose is

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pter18/animations.html#
Gene Regulation in Eukaryotes

Transcriptional controls

Posttranscriptional controls

Posttranslational modification
Eukaryotic Transcriptional Controls

Heterochromatin –


tightly coiled
cannot be transcribed

DNA methylation – adding methyl groups
to cytosine nucleotides – no transcription

Multiple copies of genes – tandem repeats

Selective gene amplification – certain cells

TATA box required for transcription to
begin



Promoter 25-35 bp upstream from gene
RNA polymerase binds
Upstream promoter elements



100-200 bp upstream from RNA polymerase
binding site
Regulatory proteins bind to UPEs
# of UPEs affects expression

Enhancers



Help to initiate transcription
May be located far from gene
Transcription factors

Proteins that bind to DNA (enhancers and
UPEs)
Posttranscriptional controls

Addition of poly-A tail




5’ cap


May prevent degradation
Intitiates translation
Longer tail, more efficient translation
Prevents degradation
Differential mRNA processing
Posttranslational control

Allosteric enzymes regulated through
feedback inhibition

Proteolytic processing


Proteins made as inactive precursors
Chemical modification

Ex. Kinases add phosphate groups