Transcript Gene Regulation

GENE REGULATION
HOW DOES A CELL KNOW?
which gene to EXPRESS
&
which gene should stay
SILENT?
GENE REGULATION
When a gene is EXPRESSED, it
is transcribed into mRNA.

When a gene is SILEN T, it is
NOT transcribed.

EXPRESSED GENE = TRANSCRIBED
SILENT GENE = NOT TRANSCRIBED
GENE REGULATION
Why would a cell NOT want
to express a gene?

– Wastes energy & materials
ATP
GENE REGULATION

Cells regulate what genes are
expressed based on what protein
the cell NEEDS.
GENE REGULATION
Where does regulation
occur? At what step?
 Most regulation occurs
at the DNA to RNA
step—transcription!
 Why?
 Conserves the most
energy!

GENE REGULATION—HOW?

Expression is regulated by:
Promoters
 Start & Stop Base Pair Sequences
 Regulatory Sites called Operators

GENE REGULATION--PROMOTERS

What is a promoter?


Specific DNA base pair sequence that
provides a binding site for RNA polymerase.
“Promotes” or allows transcription to occur
GENE REGULATION-START AND
STOP BASE PAIR SEQUENCES

What do they do?

Control where transcription starts and stops.

If changed (mutated), transcription is altered.
AUG
UAA
UAG
UGA
GENE REGULATION-OPERATORS

What is an operator?
 Like an on/off switch.

Proteins bind to the operator to regulate
transcription.
GENE REGULATION-REPRESSORS

What is a repressor protein?

Binds to the operator to physically
blocks the RNA polymerase from the
promoter site.
BINDS
HERE
BLOCKS THE
PROMOTER
GENE REGULATION-ENHANCERS

What is an enhancer protein?

BINDS
HERE
Binds to the operator to enhance
binding of the RNA polymerase to the
promoter site.
ENHANCES
BINDING TO
THE PROMOTER
GENE REGULATION IS DIFFERENT IN
PROKARYOTES AND EUKARYOTES, WHY?

Discuss with the person next to you.

Prokaryotic DNA
Eukaryotic DNA
PROKARYOTIC GENE REGULATION


In prokaryotes, genes are organized into
operons.
What is an operon?
A group of genes that code for the same function, and
are regulated by the same promoter and operator.
 One promoter/operator controls the expression of
multiple genes.

EUKARYOTIC GENE REGULATION

Eukaryotic DNA has exons and introns.

What are exons?


The coding regions of DNA that are expressed into
proteins.
What are introns?

Non-coding regions of the DNA.
EUKARYOTIC GENE REGULATION
EUKARYOTIC GENE REGULATION
CELL DIFFERENTIATION
CELL DIFFERENTIATION
One chromosome may have several genes.
Not all the genes will be transcribed and
translated.
The genes that are transcribed and
translated determine the type of cell.
CELL DIFFERENTIATION
So these cells all have the exact
same DNA, but each cell uses
different segments of the DNA
during transcription.