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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 5, The Cell Surface and Cytoskeleton - Signal
Transduction, pg. 82-83
Chapter 9, The Cell Cycle - Starving a Tumor, pg. 145 -
Cell Cycle Control and Cancer, pg. 153--1561
Chapter 13, DNA Structure and Function - Transcription
Factors,
pgs 241
Chapter 33, The Endocrine System - Hormones pg 657-661
The "Reviewing Concepts" boxes are valuable summaries of the
main
ideas in these sections of the text.
You have open access (no log-in or password needed) to
instructional
materials on the Text web site. Select the "Resources" link at the
top left of the web page. Then select the text chapter you want and
use the links to the e-learning modules or other available materials.
Web Crossing
You may also ask questions and see answers to your classmates'
questions in Web Crossing in the "Talk to Jim 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:
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Explain the concept of gene expression by the process of
protein
synthesis.
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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.
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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.
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Compare mechanisms of the control of gene expression
involving RNA
processing, translation, and protein structure.
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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.
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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
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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.).
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We start our lives as a fertilized egg cell. All the
resulting cells
are the product of mitosis.
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All the cells have the same genetic information. (With
the exception
of random mutations that are not repaired.)
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Cells develop different structures and functions because
different
genes are "turned on" or "turned off" in different parts of your
body.
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Cells produce different types and quantities of proteins
(gene
products).
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Genes must be turned on or off in the correct sequence
during
development
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Control proper embryo developmental sequence: homeotic
genes --
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 Lewis chapter 40, Human Reproduction and
Development.
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Homeotic Genes
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Body changes are induced by hormones during puberty
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Organisms respond to the environmental changes by turning
on (or
off) specific genes or groups of genes.
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Practical applications:
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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?)
A gene consists of two main parts:
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The Protein Encoding (structural) Region - This is
the
section of DNA that is transcribed to produce the mRNA that is then
processed (introns cut out and exons spliced together) and translated
at
the ribosome to produce a protein molecule.
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The Promoter Region - This is a section of DNA at
the
beginning of the gene that acts as an on/off switch for the protein
encoding region.
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The role of the Promoter Region in Gene Expression
(see Lewis, pg 241, fig. 13.20)
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Transcription factors - Proteins that bind to
specific base
sequences on the Promoter Region of a gene.
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RNA Polymerase - the enzyme that constructs
the
RNA from the base sequence in the protein encoding region of the Gene.
(Image from the
Advanced Light Source.
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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.
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RNA Polymerase and Transcription Factors from the
Transcription animation from
DNA Interactive.
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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.
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Chose "Copying the Code" toward the bottom of the
screen
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then select "puting it together" from the top of the
next screen.
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Then choose the "Transcription animation"
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Note that the transcription factors and the RNA polymerase
are also
proteins and thus, the products of the expression of other genes.
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If a transcription factor gene is mutated the proper
transcription
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
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
Easily pass through the phospho-lipid bilayer of the cell
membrane of
all cells.
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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.
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Fat soluble hormone, like estrogen interacting
with
a hormone receptor protein. (Lewis, et. al. text, pg 660, fig 34.3)
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The Hormone-Receptor Protein Complex in some way
interacts
with Transcription Factors.
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Depending on the gene involved, the transcription factor
gains or
looses the ability to bind to the DNA of the promoter region of the
gene
Water-Soluble Hormones
Can't pass through the cell membrane.
Environmental Signals
May be chemical substances or in some cases energy in
the form of
light.
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Transcription Factor Proteins are affected
directly or
indirectly, through Receptor Molecules on the cell surface or
within the cell, by interactions with these Environmental
Signals.
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The three dimensional shape and/or the chemical
properties of the
transcription factor protein are changed by the presence of the
environmental signal.
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The Transcription factor may loose its ability to bind
to the DNA of
the promoter region and TURN OFF the gene.
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The transcription factor may gain the ability to bind
to the DNA of
the promoter region and TURN ON the gene.
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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.
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Information on Common Drugs of Abuse From the
National Institute on Drug Abuse.
Light as an Environmental Signal
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