Download GENE EXPRESSION CHAPTER 11

GENE EXPRESSION
CONSTITUTIVE GENE PRODUCTS ARE NEEDED BY
THE BODY AT ALL TIMES
TUMOR SUPRESSOR
PROTEINS
ENZYMES THAT
CONTROL CELLULAR
RESPIRATION
ADAPTIVE GENE PRODUCTS ARE ONLY
REQUIRED UNDER CERTAIN CONDITIONS
GENES FOR PROTEIN DIGESTION ARE TURNED
OFF WHEN THERE IS NO PROTEIN AVAILABLE.
THE LAC OPERON
Transcription in bacteria is an easy process. Transcription is initiated when RNA
polymerase binds to the promoter. This occurs when there is an inducer present in the
bacteria (activation). If there is no inducer, the process is physically unable to occur
(repression).
EX: Bacteria use the sugar lactose for energy. They break down lactose with the aide of
the enzyme lactase. Lactase will only be made if necessary. This will save the bacteria
energy. If lactose, the inducer, is not present, than transcription of the mRNA that is
translated into lactase is not made.
Once enough mRNA is produced, it is immediately translated, even if the entire mRNA
strand is not completed.
 3 parts to an operon



Promoter – site where RNA polymerase binds to start transcription
Operator – on/off switch
Structural gene(s) – codes for the protein
 Repression – no inducer is present.



Bacteria have regulatory genes that control their expression. This gene produces the
repressor protein.
If there is no inducer, the repressor protein latches onto the operator and turns the
operon “off” by physically blocking RNA polymerase from performing transcription.
No mRNA is made. Therefore, no protein.
 Activation – inducer is present



The repressor protein is latched on to the operator. The inducer comes and attaches
to the repressor protein, causing it to change it shape and let go of the operator.
The operon is now “on” and RNA polymerase can move through and transcribe the
gene.
mRNA is made. The protein is made.
 Activation will lead to repression once all of the inducer is broken down by the
protein, as there will be none left to grab onto the repressor protein.
EUKARYOTIC GENE
EXPRESSION
• ONLY EUCHROMATIN CAN BE TRANSCRIBED
• TRANSCRIPTION IS SPATIALLY AND TEMPORALLY SEPARATED
FROM TRANSLATION
• DNA IS MORE COMPLEX BECAUSE A GREATER NUMBER OF
GENE PRODUCTS ARE NEEDED FOR SPECIALIZED FUNCTIONS.
EUKARYOTIC PROMOTERS (1)
 Promoters are the binding site of RNA polymerase
 TATA box: an 8-base pair repeating sequence of
TATATATA in the promoter that helps RNA
polymerase bind
 CCAAT box: another sequence in the promoter DNA
that helps RNA polymerase bind.
 Both are located in front of the genes that will be
transcribed.
ENHANCERS: Non-coding control sequences in
Eukaryotic DNA located in front of the promoter.
Enhancers must be activated for a gene to be
expressed.
.
Transcription Factors:
.Transcription factors are substances that activate
enhancers and cause protein production
THE STEROID
TESTOSTERONE IS ALSO
A TRANSCRIPTION
FACTOR. MANY
STEROIDS AND
HORMONES ARE
TRANSCRIPTION
FACTORS AND HELP TO
REGULATE GENE
EXPRESSION.
ANABOLIC STEROIDS:
known commonly for their illegal use by athletes,
anabolic steroids are used medically to treat
growth abnormalities, anemia, leukemia, kidney
failure, and other medical problems.
Transcription produces a molecule called premRNA, which is made in the nucleus. Then it is
edited and spliced together to form mRNA. The
mRNA goes to the cytoplasm. (2)
Pre-mRNA is very similar for all vertebrates.
Splicing is done per organism to make us
unique.
From a
gene on a
chromosom
e to a
sequence
of amino
acids to a
protein.
THINK ABOUT IT . . .
Our structural genes contain
information to make products
from all organisms, amoeba
to zebra. We transcribe it all.
We translate only selected
exons.
IN MOST MAMMAL CELLS, ONLY
1% OF DNA IS COPIED INTO
FUNCTIONAL RNA
Over our existence on the planet, “junk” DNA has been
added to our DNA. Junk DNA is DNA that seems to
have no purpose. One theory is that junk DNA is made
of viral sequences inserted into our genome.
Control of gene expression (3, 4, &5):