Answers to many of these questions can be found on the "Answers to End-of-Chapter Questions" page at the text website.

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 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. Describe the role of oncogenes and tumor suppresser genes in cancer.

6. 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.

7. List some examples of responses to changes in the environmental that involve control of gene expression. (One of the qualities shared by all living organisms from Lecture #1.)

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

• The Central Dogma of Molecular Biology (see also Fig. 16.1, text)

• Protein Synthesis "Your Friend" (see also chapter 16, text)

• What are genes? from Access Excellence

• All of the living cells in our body have the same genetic information.

• 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.

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

  The Promise of Tissue Engineering, Scientific American, March, 1999

  Growing New Organs, Scientific American, March, 1999

A gene - a section of DNA controlling the production of a specific protein - consists of two parts:

• The Protein Encoding (structural) Region - This is the section of DNA that is transcribed to produce the mRNA "transcript" that is then processed and translated to produce a protein molecule.

• The Promoter Region - a section of DNA that acts as an on/off switch for the protein encoding region.

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

  • Structures of general transcription factor complexes (from the Richmond Lab)

  • Zipper Proteins (transcription factors) that bind to DNA.

• RNA Polymerase - the enzyme that produces the RNA transcript 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.

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

• Note that the transcription factors and the RNA polymerase are also proteins and thus, the products of the expression of other genes.

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

• Transcription factor proteins are affected directly or indirectly, through receptor proteins on the cell surface, by these signals.

  Signaling Pathways - (control of cell division), Scientific American, Sept. 1996

• The three dimensional shape of the transcription factor protein or its chemical properties are changed by the presence of the 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.

• Fat-Soluble Hormones (see text page 663-664, fig. 33.6)
  • Hormone molecules pass through the cell membrane.

  • Hormone molecules interact with receptor proteins

  • Hormone/ receptor protein somehow 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.

• Water-Soluble Hormones (see text page 662-663, fig. 33.5)
  • Hormone molecules can not pass through the cell membrane.

  • Hormone molecules interact with receptor proteins embedded in the surface of the cell membrane.

  • The receptor proteins are changed by the hormone and transmit a chemical signal inside the cell.

  • The chemical signal interacts through a series of intermediate chemical steps with transition 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.

Steps in Gene Expression

• Transcriptional control (discussed above) [DNA---->primary mRNA]

• Posttranscriptional control [primary mRNA---->mature mRNA]
  • mRNA molecules are processed before they leave the nucleus (that is, a leading and trailing sequence of DNA is added)

  • Transcription of DNA to mRNA and mRNA Processing (see also Fig. 16.10, text)

• Translational control [mRNA---->protein] at the ribosomes

• Posttranslational control - the proteins produced may require another chemical to be biologically active, or may be inactivated by some chemical signal.

• Scientific American Article "How Cancer Arises", September, 1996

• Signaling Pathways - (control of cell division)

• Tumor Development and Gene Control

• Some Genes Involved in Human Cancers

• turn genes on or off in the correct sequence during development
  • homeotic genes -- during development, genes need to be expressed in a particular sequence within particular groups of cells. One way to accomplish this is to have a "master gene" whose product "turns on" a sequence of coordinated events. See Lewis fig. 11.8.

  • changes induced by hormones during puberty

• control the types and quantities of proteins (gene products) produced
  some are needed in large quantities (ribosomal proteins)

  some are need in small quantities (many enzymes)

  muscle cells need lots of contractile proteins - brain cells don't

  intestinal cells produce lots of digestive proteins cells of the retina don't

  unregulated expression is energetically costly!

• respond to the environmental changes by turning on (or off) specific genes or groups of genes
  • Response to seasonal changes by using a pigment to measure day length.

  • Responding to the presence or absence of light

  • Responding to gravity

  • Changing rate of metabolism in response to temperature change

  • Timing Reproduction