of Gene Expression
IB 100/101 Home
Chapter 3, - Signal Transduction, pg. 56-57
Chapter 8, - Cell Cycle Control and Cancer, pg. 165-170
Chapter 12, - Transcription Factors, pgs 245-246
Chapter 27, Starving a Tumor, pg. 565
Chapter 30, The Endocrine System - Hormones pg. 616-620
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The content of today's lecture will help you answer
question #1 on
After studying this material you should be able to:
Explain the concept of gene expression by the process of
Explain how it has been possible for the somatic cells in
different parts of your body, given their genetic similarity (give or
take a few mutations, of course!), to have developed such different
characteristics and functions.
Transcriptional Control of Gene Expression:
a. Contrast the roles of the promoter and protein encoding
(structural) portions of a gene.
b. Describe the interactions of the promoter region of a
transcription factors, and RNA polymerase in the expression of a
c. Describe the interactions of water soluble and fat
hormones and other extra cellular signals with receptor molecules and
transcription factors that "turn on" or "turn off" the expression of a
particular gene in a cell.
Compare mechanisms of the control of gene expression
processing, translation, and protein structure.
Explain how mutation might result in a change in protein
and function resulting in the loss of control of the expression of a
List some examples of responses to changes in the
involve control of gene expression. (One of the qualities shared by all
living organisms from Lecture #1.)
Overview of the Control of Gene Expression
All of the living cells in our body have the same genetic
information, BUT are able to develop very different structures and
functions (skin, nerves, muscles, bone, fat, kidney, etc.).
We start our lives as a fertilized egg cell. All the
are the product of mitosis.
All the cells have the same genetic information. (With
of random mutations that are not repaired.)
Cells develop different structures and functions because
genes are "turned on" or "turned off" in different parts of your
Cells produce different types and quantities of proteins
Genes must be turned on or off in the correct sequence
Control proper embryo developmental sequence: homeotic
during embryo development, genes need to be expressed in a particular
sequence within particular groups of cells. One way to accomplish this
is to have "master genes" whose products "turn on" a sequence of
coordinated events. See Hoefnagels chapter 37, Human Reproduction and
Body changes are induced by hormones during puberty
Organisms respond to the environmental changes by turning
off) specific genes or groups of genes.
For a more detailed look:
Review of Gene Expression
The Gene Revisited - Promoter and Protein Encoding
(It had to be more complicated, didn't it?)
A gene consists of two main parts:
The Protein Encoding (structural) Region - This is
section of DNA that is transcribed to produce the mRNA that is then
processed (introns cut out and exons spliced together) and translated
the ribosome to produce a protein molecule.
The Promoter Region - This is a section of DNA at
beginning of the gene that acts as an on/off switch for the protein
The role of the Promoter Region in Gene Expression
(see Hoefnagels, pg 246, fig. 12.11)
Transcription factors - Proteins that bind to
sequences on the Promoter Region of a gene.
RNA Polymerase - the enzyme that constructs
RNA from the base sequence in the protein encoding region of the Gene.
(Image from the
Advanced Light Source.
RNA Polymerase will not bind to the DNA and initiate
until all the required Transcription Factors are properly bound to the
Promoter Region of the gene or the RNA Polymerase itself.
RNA Polymerase and Transcription Factors from the
Transcription animation from
of Transcription Factors - DNA -->
RNA from DNA Interactive
The "bundle of factors assembling at
the start of
a gene" in the video are the TATA binding protein and other
transcription factors that provide the starting point for the RNA
polymerase to begin transcription.
Chose "Copying the Code" toward the bottom of the
then select "puting it together" from the top of the
Then choose the "Transcription animation"
Note that the transcription factors and the RNA polymerase
proteins and thus, the products of the expression of other genes.
If a transcription factor gene is mutated the proper
factor protein will not be produced and the gene that the transcription
factor helps turn on or off will not function properly.
External Control of Gene Expression (External to a
Gene Expression can be turned on or turned off by signals
outside a cell coming from some other part of the body or even from the
environment outside the organism.
External signals in some way interact with transcription
either activate or inactivate the transcription of a gene by RNA
Easily pass through the phospho-lipid bilayer of the cell
If the proper Receptor Protein is present in a
cell the Hormone will combine with it and turn on or turn off
Fat soluble hormone, like estrogen interacting
a hormone receptor protein. (Hoefnagels text, pg 619, fig 30.4b)
The Hormone-Receptor Protein Complex in some way
with Transcription Factors.
Depending on the gene involved, the transcription factor
looses the ability to bind to the DNA of the promoter region of the
Can't pass through the cell membrane.
May be chemical substances or in some cases energy in
the form of
Transcription Factor Proteins are affected
indirectly, through Receptor Molecules on the cell surface or
within the cell, by interactions with these Environmental
The three dimensional shape and/or the chemical
properties of the
transcription factor protein are changed by the presence of the
The Transcription factor may loose its ability to bind
to the DNA of
the promoter region and TURN OFF the gene.
The transcription factor may gain the ability to bind
to the DNA of
the promoter region and TURN ON the gene.
Long-Term Effects of Drugs On the Brain from National Institutes of Health
Information on Common Drugs of Abuse From the
National Institute on Drug Abuse.
Light as an Environmental Signal