Download REGULATING GENE EXPRESSION

REGULATING GENE EXPRESSION
13.5
Are all our diploid body cells
genetically identical? Why or why
not?
What makes each different cell type
behave differently?
I.
What is gene expression?
The process by which a gene is
transcribed into mRNA and then
translated into a protein
II.
What is the regulation gene
expression?
involves:
 Activating a gene so that it
can be transcribed and
translated
 Inhibiting a gene so that it
can’t be transcribed and
translated
 When a cell needs to make a
particular protein, the gene
is activated and
transcription and translation
occurs.
 When a cell no longer needs
the protein, the gene is
inactivated and transcription
and translation can’t occur
 Some genes are active in
some cells but not in others.
This allows cells to behave
differently
III. Gene expression in
prokaryotes
A. What is a prokaryote?
 Bacteria
 No nucleus
 No membrane bound
organelles
B. Structure of prokaryotic DNA
 Organized into units called
operons
 Operon = segment of DNA
that contains all of the genes
for a particular pathway
C. The Lac Operon
 Controls the breakdown of
the sugar lactose by
bacteria
1. Components of the lac
operon
 Promoter = region of
operon that binds RNA
polymerase to start
transcription
 Operator = region of the
operon that binds
repressor to prevent
transcription
 Regulator gene = makes
the repressor
 The 3 structural genes =
when transcribed, they
make the 3 enzymes
needed to break down
lactose
2. Regulating the lac operon
 Lac operon off:
o Occurs when glucose
is present and/or
lactose is absent
o Regulator gene makes
repressor
o Repressor sits on
operator
o RNA polymerase can’t
sit on promoter
o No transcription of the
3 structural genes
 Lac operon on:
o When only lactose is
around
o Regulator gene makes
repressor
o Repressor binds with
lactose
o Repressor can’t sit on
operator
o RNA polymerase can
sit on promoter
o Transcription and
translation of the 3
structural genes does
occur
http://www.sumanasinc.com/webcon
tent/animations/content/lacoperon.ht
ml
Why do bacteria want the lac
operon off when glucose is
around?
http://evolution.berkeley.edu/evolibra
ry/news/070401_lactose
IV. Gene Regulation in Eukaryotes
 Prokaryotes have no nucleus
so as a gene is being
transcribed, it can be translated
at the same time
 Eukaryotes do have a nucleus
so transcription and translation
occur at different times
 Eukaryotic gene regulation can
occur at transcription or after
transcription
 Prokaryotic gene regulation
can occur only at transcription
 Eukaryotic gene regulation can
control how much transcription
occurs
 Prokaryotic gene regulation
can only turn transcription on
or off
A. Transcriptional Control of
Gene Expression
1. Controlling how much
transcription occurs
 Eukaryotic genes have
special regions called
enhancers and silencers
 Enhancers = segment of
the gene that can increase
the amount of transcription
 Silencers = segments of
the gene that can decrease
the amount of transcription
 How transcription is
increased:
o Enhancer binds activator
protein
o This increases the
amount of transcription
that RNA polymerase
can do
 How transcription is
decreased:
o Silencer binds repressor
o This decreases the
amount of transcription
RNA polymerase can do
Ex:
2. Controlling whether or not
transcription occurs
 Heterochromatin = highly
condensed chromatin
 Euchromatin = loosely
condensed chromatin
 In a given cell, genes that
are being transcribed are in
euchromatin and genes that
are not being transcribed are
in heterochromatin
B. Posttranscriptional control
Regulating gene expression
AFTER transcription has
occurred
 mRNA storage
the longer the mRNA is
stored in the nucleus, the
less protein will be made
 mRNA halflife
the longer the halflife of the
mRNA the longer it will take
for it to disappear and the
more protein can be made
from it
 rate of translation
the faster the mRNA is
translated, the more protein
will be made
http://highered.mcgrawhill.com/sites/007337797x/student_vi
ew0/chapter13/animation_quiz__control_of_gene_expression_in_eu
karyotes.html