Biology 100
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 Home Page

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 Beth, Carrie, and Ed" discussion.

Objectives:

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:

• 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"

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 Lewis chapter 40, Human Reproduction and Development

• 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 137-8
• 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:
• The first Human Cloned Embryo from Scientific American
• Theraputic cloning methods from Scientific American
• Tissue Engineering.net
• 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 Lewis, pg 246, fig. 13.5)
• Transcription factors - Proteins that bind to specific base sequences on the Promoter Region of a gene.
• Transcription Factors and the Initiation of Transcription by RNA Polymerase
• TATA Binding Protein
• *Transcription Factor that binds to DNA.
• *"Zipper" protein transcription factor|
• Human Transcription Factors in 3-D
• 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.
• *RNA Polymerase - the enzyme that constructs the RNA from the base sequence in the protein encoding region of the Gene.
• 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.
• 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.

*from the Biomolecules Galery

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.
• 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)
• Steroid Receptor Molecules are proteins that bind to the promotor regions of genes.

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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.
• an artist's rendition of a receptor protein binding with an extra cellular molecule and initiating a response in the cell From Hybrid Medical Annimation
• Water soluble hormone (like CCK) 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 loose the ability to bind to the DNA of the promoter region(s) of one or several genes.
• Pancreas cells and insulin hormone production and reaction to CCK hormone
• 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.

  • 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
  • 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.
  • 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.
  • Gene Doping from Scientific American
    How genes are designed to increase athletes' abilites and how genes are delivered to appropriate body parts is discussed in this article.

  • Light as an Environmental Signal

  • The Scientific Basis For Autumn

  • Environmental Estrogens (EEs)

    • Endocrine disruptors from the whyfiles.org.

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  Other "Levels" of Control of Gene Expression