Biology 100/101
Lecture 16
Control of Gene Expression
(Print Version)

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

Text readings in Hoefnagels

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

You have open access (no log-in or password needed) to instructional materials on the Text web site. Select "Resources" from the upper left of the page and select the text chapter you want.

Moodle

You may also ask questions and see answers to your classmates' questions in Moodle in the "Talk to Ed" forum.

Objectives:

The content of today's lecture will help you answer question #1 on this assignment:

Take-home Assignment #7, Control of Gene Expression & Biotechnology due at Lecture Tuesday April 13.

After studying this material you should be able to:

1. Explain the concept of gene expression by the process of protein synthesis.

2. 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.

3. 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.

4. Compare mechanisms of the control of gene expression involving RNA processing, translation, and protein structure.

5. 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.

6. 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:

• Interactive Chromosome/Gene Poster from Gene Gateway - Exploring Genes and Genetic Disorders

• The Inner Life of the Cell Watch a jaw-dropping animation of the inside of a human white blood cell fighting an infection.

  Select "All Media" from the left hand menu.

  Then select one of the first three "Inner Life: View the Animation" links, depending on the speed of your internet connection, and Watch David Bolinski talk about Truth and Beauty and the production of the "Inner Life" animation.

• DNA Interactive

• DNA Replication (Making sister chromatids during the S phase of the cell cycle)

• 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"

• Transcription DNA --> RNA

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"

• Translation mRNA --> Protein

• Chose "Reading the Code" toward the bottom of the screen

• then select "puting it together" from the top of the next screen.

• Then choose the "Translation animation"

• Animation of a complex series of steps that illustrate the reaction of liver cells to the extracellular hormone, epinephrine from sumanasinc.com.
  Select "Extracellular Signaling".
  Just watch the animation to get the "gist" of how a water soluble hormone interacts with a cell surface receptor protein to turn on genes in the nucleus.

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 resulting cells are the product of mitosis.

• All the cells have the same genetic information. (With the exception of random mutations that are not repaired.)

• Cells develop different structures and functions because different genes are "turned on" or "turned off" in different parts of your body.

• Cells produce different types and quantities of proteins (gene products).

• Genes must be turned on or off in the correct sequence during development

• 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 Hoefnagels chapter 37, Human Reproduction and Development.

• Homeotic Genes

• Body changes are induced by hormones during puberty

• Organisms respond to the environmental changes by turning on (or off) specific genes or groups of genes.

• Practical applications:

• Stem Cell Information from the National Institutes of Health.

• How Theraputic Cloning Works
  Select "The Basics - How it Works"

• Cancer and angiogenesis signals Life by Lewis, et. al. "Starving a Tumor" Pg 145 (Not included in new textbook)
  

• See the NOVA program "Cancer Warrier" to learn more about how a cancer tumor triggers the development of blood vessels to feed itself.

• For a more detailed look:

• Theraputic cloning methods from Scientific American

• Woman receives windpipe built from her stem cells

• Lab-grown bladders 'a milestone'

• Organ Printing

Review of Gene Expression

DNA---------->RNA---------->PROTEIN

• Protein Synthesis "Your Friend"

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:

• 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.

• 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.

• The role of the Promoter Region in Gene Expression (see Hoefnagels, pg 246, fig. 12.11)

• Transcription factors - Proteins that bind to specific base sequences on the Promoter Region of a gene.

• Transcription Factors from the Transcription animation from DNA Interactive.

• Transcription DNA --> RNA

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"

• Transcription Factors and the Initiation of Transcription by RNA Polymerase from Access Excellence

• TATA Binding Protein from Biology at Occidental College

• Transcription Factor that binds to DNA. from The Protein NMR Structure Gallery at Rutgers University.

• Human Transcription Factors in 3-D from the Berkley Lab, www.lbl.gov/.

• Scientists snap first 3-D pictures of the "heart" of the transcription machine from U C Berkely.

• Each gene locus has its own specific set of transcription factor proteins.

• One gene may be expressed differently in different tissues.

• 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.

• 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 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.

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Fat-Soluble Hormones

Easily pass through the phospho-lipid bilayer of the cell membrane of all cells.

• 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.

• Fat soluble hormone, like estrogen interacting with a hormone receptor protein. (Hoefnagels text, pg 619, fig 30.4b)

• The Hormone-Receptor Protein Complex in some way interacts with Transcription Factors.

• 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

• Examples of gene control by Steroid Hormones - Sex Hormones in Women and Men

• The general mode of action of steroid hormones (glucocorticoid hormone) from Access Excellence.

• Steroid Receptor Molecules are proteins that bind to the promotor regions of genes. from Kimball's Biology Pages.

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Water-Soluble Hormones

Can't pass through the cell membrane.

• Hormone Molecules interact with specific Receptor Proteins embedded in the surface of the cell membrane of only certain types of cells.

• Water soluble hormone interacting with a hormone receptor protein (Hoefnagels, et. al. text, pg 619, fig 30.4a)

• 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 loose the ability to bind to the DNA of the promoter region(s) of one or several genes.

• EPO Receptor - JAK - STAT5 pathway

• Animation of a complex series of steps that illustrate the reaction of liver cells to the extracellular hormone, epinephrine from sumanasinc.com.
  Select "Extracellular Signaling".
  Just watch the animation to get the "gist" of how a water soluble hormone interacts with a cell surface receptor protein to turn on genes in the nucleus.

• Nerve Growth Factor and its TRKA Receptor pathway from biocarta.com

• Pancreas cells and insulin hormone production. (Hoefnagels text, pg. 626, fig. 30.9 and pg. 627, fig 30.10)

• Insulin Signaling Pathway From the The CANCER GENOME ANATOMY PROJECT

Environmental Signals

May be chemical substances or in some cases energy in the form of light.

• 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.

• Environmental interactions with cells. (Hoefnagels text, pg 56, fig 3.8)

• 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 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

• The Science of Color in Autumn Leaves from the U S National Arboretum

Environmental Estrogens (EEs)

• Endocrine disruptors from the whyfiles.org.

• Environmental Estrogens from from e.hormone at Tulane University.

Other "Levels" of Control of Gene Expression