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Announcements
&
Assignments
Lecture
Objectives
Web
Resources
Overview of
Control of
Gene Expression
The Gene
Revisited
External
Control
of Gene Expression
Fat Soluble
Hormones
Water
Soluble
Hormones
External
Environmental
Signals
Other Levels
of Control
Lecture
Syllabus
IB
100/101 Home
Page
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Announcements
Text Readings
in Lewis |
Chapter 4
Signal Transduction, pg. 76-77
Chapter 8
Starving a Tumor, pg. 137-138
Control of Cell Cycle, pg. 145--154
Chapter 13
Transcription Factors, pgs 245-246
Chapter 33
Hormones Are Chemical Messengers and Regulators,
peptide and steroid hormones, pg 657-659 |
The "Mastering Concepts" boxes are valuable summaries of
the main
ideas in these sections of the text.
Answers to many of these questions can be found at the Text On-Line Learning Center
You may also ask questions and see answers to your
classmates'
questions in Web Crossing in the "Talk to Carl and Ed" discussion.
Objectives:
The content of today's lecture will help you
answer question #1 on
this assignment:
After studying this material you should be able
to:
- Explain the concept of gene expression by the process
of protein
synthesis.
- Explain how it has been possible for the somatic
cells in all the
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 gene,
transcription factors, and RNA polymerase in the expression of a
gene.
c. Describe the interactions of water soluble and
fat soluble
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
involving RNA
processing, translation, and protein structure.
- Explain how mutation might result in a change in
protein structure
and function resulting in the loss of control of the expression of a
gene.
- List some examples of responses to changes in the
environment that
involve control of gene expression. (One of the qualities shared by all
living organisms from Lecture #1.)
Web Resources:
Overview of the Control of Gene
Expression
Gene = a cell's manual for making a specific protein
Our cells all have the same genetic information
Why we need to understand control of gene expression:
- Most of the living cells in our body have the same
genetic
information, BUT are able to develop very different structures and
perform unique functions (skin, nerves, muscles, bone, fat, kidney,
etc.).
- We start our lives as a fertilized egg cell. All
the resulting cells
are the product of MANY rounds of mitosis.
- mitosis starts with one cell and produces 2
cells genetically identical to the starting cell
- all of our cells were produced when the
fertilized egg was duplicated through mitosis, producing cells that
also got duplicated by mitosis
- all of our cells are genetically identical to
the fertilized egg we started out as
- All of the cells in your body have the same genetic
information,
except:
- cells with random mutations that are not
repaired
- sperm or egg cells produced by meiosis
- Our cells are genetically identical, but they
develop different structures and perform
different functions
depending on which proteins they make. The proteins they make are
determined by which genes are "turned on" or "turned off".
- genes are "turned on" when the cell uses them to
make a protein
- genes are "turned off" when the cell is not
using them to make a protein
- Cells are different (skin vs. muscle cells) because
they produce different types and quantities of
proteins (gene
products).
- As an embryo develops, genes must be turned on or
off in the correct
sequence.
- During embryo development, genes need to be
expressed in a particular
sequence within particular groups of cells.
- Homeotic genes = A gene that turns other genes on
and off. It cause other genes to turn on or
off in the right sequence, so that the embryo develops normally.
A mutation in a homeotic gene will disrupt the function in many genes,
resulting in radical changes of structure and function. See
Lewis chapter 41 Human Reproduction and
Development.
- Homeotic Genes
- Body changes are induced by hormones during puberty
- hormones travel through the blood stream to
their target cell (a cell producing the receptor protein)
- a hormone bind to its corresponding hormone
receptor on the target cell
- the binding results in a change in gene
expression within the target cell
- Organisms respond to the environmental changes by
turning on (or
off) specific genes or groups of genes.
- Practical applications:
- For a more detailed look:
Review of Gene Expression
DNA---------->RNA---------->PROTEIN
The Gene Revisited - Promoter and Protein Encoding
(structural)
Regions
(It had to be more complicated, didn't it?)
The 2 Main Parts of a Gene:
Protein Encoding Region = Describes how to make a
protein
Only some of our genes are used at any given moment
A gene is turned on when it starts to be transcribed
A gene is turned off when it stops being transcribed
Key Players in Transcriptional Control of Gene
Expression
A gene consists of two main parts:
- RNA
Polymerase - the enzyme that constructs the RNA
from the base
sequence in the protein encoding region of the Gene. (Image from
the University of Munich Gene
Center.
- RNA Polymerase will not bind to the DNA and
initiate transcription
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
DNA Interactive.
- Animation 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
screen
- then select "puting it together" from the top
of
the next screen.
- Then choose the "Transcription animation"
- Note that the transcription factors and the RNA
polymerase are also
proteins and thus, the products of the expression of other genes.
- If a transcription factor gene is mutated, a mutant
transcription
factor protein will be produced. It won't bind to the promoter region
properly, causing abnormal expression of the genes it's supposed to
control.
External Control of Gene
Expression (External to a cell)
Gene Expression can be turned on or turned off by
signals from
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 factors to
either activate or inactivate the transcription of a gene by RNA
Polymerase.
Fat-Soluble Hormones
Regulates gene expression by affecting the
transcription factors ability to promote transcription
Easily pass through the phospholipid bilayer of the
cell membrane of
all cells
Binds to receptors within the cell
- If the proper Receptor Protein
is present in a cell the Hormone will combine with
it and turn
on
or turn off genes in
that cell (ex., estrogen recepter with estrogen)
- Fat soluble hormone, like estrogen
interacting with
a hormone receptor protein.
- The Hormone-Receptor Protein Complex
in some way interacts
with Transcription Factors.
- Depending on the gene involved, the transcription
factor gains or
loses the ability to bind to the DNA of the promoter region of the
gene
Water-Soluble Hormones
Regulates gene expression by affecting the
transcription factors' ability to promote transcription.
Cannot pass through the phospholipid bilayer of the
cell membrane of
all cells.
Binds to receptors in the cell membrane from the
outside.
- Hormone Molecules interact
with
specific Receptor
Proteins embedded in the surface of the cell membrane
- Different types of cells have different
receptors (either in their membranes or inside the cell).
- A hormone only has effects on cells that have
its receptor protein.
- Water soluble hormone (like CCK hormone)
interacting
with a hormone receptor protein
- The Receptor Proteins are
changed by binding with the Hormone and transmit a
chemical signal
inside the cell.
- The chemical signal is passed through a series of Relay
Proteins in the cytoplasm which eventually interact with Transcription
Factors in the nucleus.
- The transcription factors gain or lose the
ability
to bind to the
DNA of the promoter region(s) of one or several genes.
- When the transcription factor gains the ability
to bind to a promoter, the corresponding gene will be turned on and a
protein will be produced.
- When the transcription factor loses its ability
to bind to a promoter, the corresponding gene will be turned off and no
protein is produced.
- Pancreas cells and insulin hormone
production
- Insulin Signaling Pathway From the
Sigma-Aldrich
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Environmental Signals
May be chemical substances or in some
cases
energy in the form of
light.
Causes a change in gene expression by
interacting with its corresponding
receptor protein
Then, the receptor protein affects the
ability of
a
transcription factor to bind to the promoter, affecting gene expression.
- Transcription Factor Proteins
are affected directly or
indirectly by Receptor Molecules that have
interacted with Environmental
Signals. The receptor molecules may be on the cell
surface or
within the cell.
- The three dimensional shape and/or the chemical
properties of the
transcription factor protein are changed by the presence of the
environmental signal.
- The transcription factor may lose 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.
- The Addicted Brain form Scientific
American
How drugs interfere with transcription factors and the control of gene
expression to induce the production of proteins that enhance the
craving
for a drug, cause addiction, and increase the chance of repeated drug
abuse.
- Information on Common Drugs of Abuse
From the
National Institute on Drug Abuse.
-
Light as an Environmental Signal
-
Environmental Estrogens (EEs)
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