Biology 100/101
Lecture 13
Genes, Traits, and Proteins
(Print Version)

Announcements

Objectives

Web Resources

Review

DNA
Chromosomes
Genes

Traits

Cystic Fibrosis

Protein Structure

Sickle Cell

Lecture Syllabus

IB 100/101 Home Page

Text Readings in Lewis et al.

Chapter 13, Gene Function
Review Chapters 11 & 12

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 text chapter you want and use the links to the e-learning modules or other available materials. There is also a collection of study materials called the "Essential Study Partner" that you may find useful.

Web Crossing

You may also ask questions and see answers to your classmates' questions in Web Crossing in the "Talk to Sarah and Ed" discussion.

Objectives:

The content of this lecture will help you complete these assignments:

Take-Home Assignment #4 - Meiosis and Genetics due At Lecture Monday October 15.

Take-Home Assignment #5 - Human Genetics due At Lecture Monday October 22.

Second Web Crossing Assignment, Due by 8:00 AM, Monday October 29.

Take-Home Assignment #6 - Gene Expression and Mutation due At Lecture Monday November 5.

After studying this material you should be able to:

1. Draw a diagram, create a concept map, or write a paragraph that explains the relationships among these terms:

DNA	nucleotide bases	homologous chromosomes
genes	gene loci	alleles
gene expression	proteins	traits
sister chromatids

2. Use your chromosome models from discussion or lab to illustrate the location of a gene for the production of a particular protein. Illustrate the location of the gene on homologous chromosomes, as well as on sister chromatids.

3. Explain in general terms how the structure of the DNA molecule is related to the production of a specific protein.

4. Describe the connections among:

   • variations in the structure of the DNA molecule of a gene for a particular trait;

   • the existence of different alleles for a gene;

   • different proteins produced by different alleles for the same gene; and

   • different expressions of the trait.

5. Explain in general terms how the order and kinds of amino acids that make up a protein determine its final conformation and, ultimately, its function.

Web Resources:

• Glossary of Genetic Terms, from Lecture 11: Heredity and Meiosis

• Genes and Disease (Selected genes and their functions and locations on the chromosomes) from the National Center for Biotechnology Information.

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

• PREVIEW: Protein Synthesis for learning the details of protein synthesis (from Access Excellence). Print this out for next lecture.

REVIEW (DNA, Chromosomes, Genes)

DNA

What is DNA, Why do we need it, and Where does it come from?

• Each DNA Nucleotide includes: (Lewis text, pg. 233, fig. 13.8)

• One Nitrogenous Base (A, C, G, or T)

• One Sugar (Deoxyribose)

• One Phosphate group

• Nucleotide & Complementary Base Pairing - A-T & C-G (Lewis et al., Page 233, Fig. 13.7)

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What are Chromosomes?

• Chromosomes consist of a very tightly wound molecule of DNA plus associated proteins (See Lewis et al., Page 235, Fig. 13.11)

• Human Chromosomes. Electron micrograph of human chromosome. (See Lewis et al., Page 208, Fig. 12.1)

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What are Genes?

• What are Genes? from Access Excellence Resource Center. "Working Subunits of DNA." A sequence of DNA specifying the sequence of amino acids of a particular protein involved in the expression of a trait.

• Different forms of the same gene are called alleles. Alleles are formed by mutations of pre-existing alleles. Different alleles produce variations in inherited characterisitics (traits).

• Homologous Chromosomes, (See Lewis et al., Page 186, Fig. 11.14). Remember, you get one chromosome of each homologous pair from each parent (by way of their gametes). Homologous chromosomes have the same sequence of gene locations that control the same characteristics (traits). A gene locus (plural, loci) is the specific location of a gene on a particular chromosome. You have two copies of every gene, but the two members of any gene pair do not necessarily have identical DNA sequences. If you carry two different DNA sequences at a particular site on a chromosome (alleles), you are said to be heterozygous at that site. If you carry two identical alleles of a gene, you are homozygous.

• Chromosomes 7. Zoom in and note cystic fibrosis (CFTR) locus listed on the right hand side about 1/5 the way up from the bottom of the illustration of Chromosome 7.

The Relationship Between Genes, Proteins, and Traits

• A gene codes for a particular protein that is involved in the expression of a trait.

• Characteristics determined by single genes are called Mendelian traits.

• Unusual Mendelian Traits, Table 11.2, Lewis et al., Page 190

• Some Mendelian Disorders in Humans, Table 10.4, Lewis et al. (Fifth edition), Page 186. Over 5,000 human disorders are caused by mutations in single genes, such as sickle cell anemia and cystic fibrosis.

• Genes and Disease (Selected genes and their functions and locations on the chromosomes) from the National Center for Biotechnology Information.

• Gene Expression via Protein Synthesis, from Access Excellence. For a cell to make protein, DNA is used as a template to manufacture messenger RNA (transcription). mRNA moves to the ribosomes in the cytoplasm where it directs the assembly of amino acids that fold into completed proteins (translation).

• How are genes linked to disease? Genetic diseases are the result of alterations in the normal sequence of nucleotides in a gene which results in an altered protein that has an altered function. Some protein changes are insignificant; others are disabling. Also, see How does a faulty gene trigger disease?, from Access Excellence.

Cystic Fibrosis (An example of gene expression gone wrong)

• Cystic Fibrosis from NCBI. CF is the most common fatal disease in the US today. It causes the body to produce a thick, sticky mucus that clogs the lungs, impairs breathing, and leads to infections. The pancreas also becomes clogged, stopping digestive enzymes from reaching the intestines where they are required to digest food. The pancreas form cysts and become fibrous.

  See also:
  CFTR: The Gene Associated with Cystic Fibrosis.
  CF Phenotype, from The Centers for Disease Control.

• Cystic Fibrosis testing goes mainstream from USA Today

• CF is the most common inherited disease among Caucasians in US.

• 1 in 29 Caucasians (10 million) carries a defective allele for the CF gene.

• 30,000 children and young adults have CF.

• Cystic Fibrosis, like sickle cell disease, is an autosomal recessive trait (See figure 10.08 in Lewis et al., page 183 . See also Cystic Fibrosis, from Access Excellence, explaining the hereditary nature of the disease.

• CF is caused by defective gene CFTR (Cystic Fibrosis Transmembrane Regulator Protein) on Chromosome 7. The normal gene produces an active transport protein that functions to pump salt (sodium and chloride) ions across membranes of epithelial cells that line the airways of the lungs and ducts of other organs. Mutations in the gene result in an alteration of the protein so that epithelial cells are defective in transporting these ions out of cells.

• Because less salt is secreted from the cells lining these airways and ducts, there is less water "drawn out" of the cells. This causes the mucous that normally line these passageways to be unusually thick and sticky. The thick mucous clogs the passageways and harbors the growth of bacteria and fungi that cause further problems.

• The role of the CTFR gene from the UK Cystic Fibrosis Gene Therapy Consortium. An excellent resource explaining how the chloride channel (CFTR protein) works.

• CFTR genomic DNA sequence. Click here to see the DNA sequence of the CFTR gene. Click on the numbers along the line representing the gene to see the DNA sequence of different sections of the gene (its huge!).

• Gene Mutations. There are over 1000 different mutated forms (alleles) of the CF gene. The severity of the disease is related to the particular mutation(s) that have been inherited.

• Cystic Fibrosis transmembrane regulator protein

• Different mutations in the same gene can produce a wide range of effects, from severe symptoms to no symptoms, from Access Excellence.

• Summary Table of CFTR Mutations (Click on "CFMDB Statistics")

• Detailed data base of CFTR Mutations (Click on "Search Database" and then select a purple "exon" region on the gene diagram to see detailed info for mutations in each region.)

• Summary: DNA to RNA to Protein to Trait. An excellent summary of the expression of the CFTR gene from Dr. Robert Huskey from the University of Virginia (Ret.).

Protein Structure

As a protein (polypeptide) is synthesized in a cell, it folds into a three-dimensional structure (conformation). The order and kinds of amino acids that compose a protein (polypeptide) determine its conformation. The final shape of a protein arises from its interactions with other proteins and other molecules, and determines its function. Errors in protein structure can cause diseases, such as sickle cell anemia or cystic fibrosis.

The structure of a protein may be described at four levels. See Fig. 2.20, in Lewis et al., page 34. Also, see Primary, Secondary, Tertiary, and Quaternary Structures of Protein Molecules from accessexcellence.org

• Primary Structure

• The sequence of amino acids in a polypeptide chain from accessexcellence.org.

• Secondary Structure

• Hydrogen bonds between parts of the peptide backbone create the secondary structure. The polypeptide may be folded into several distinctive shapes, such as coils, sheets, loops, or combinations of these shapes.

• Alpha helices and pleated sheets from Web Chemistry

• Tertiary Structure

  • Interactions among side chains (R groups) occur, folding the polypeptide into three dimensions and giving it a unique shape.

  • Insulin- 3D image of the insulin protein. from Endocrine System Hypertext - Colorado Sate University.

  • Molecule picture and movie gallery from the Tan Lab, at Penn State University

  • Cytochrome b one of the electron transport chain proteins in the mitochondria

  • RAS protein a protein involved in the control of cell division - mutant forms associated with cancer.

  • DNA Polymerase- 3D structure of the enzyme responsible for DNA replication.

  • WD40 propeller domain of G protein beta subunit - G proteins help transmit hormone signals within cells.

• Quaternary Structure

• The joining of different polypeptide units to form a larger, functional protein. The blood protein hemoglobin is composed of four polypeptide chains, encoded by two sets of genes.

• Hemoglobin from The Worlds of David Darling Hemoglobin is made up of two alpha globin chains and two beta globin chains plus 4 heme groups that carry oxygen. In this illustration each of the 4 globin molecules is a different color. The 4 heme groups are blue in this illustration.

Sickle Cell Disease and natural Selection

This is an example of adaptation. Unique genetic information that determines the amino acid sequence in hemoglobin was acquired in regions where malaria was prevalent. Resistance to malaria resulted and survival improved. The consequence of this improvement is the possibility of Sickle Cell disease.

• HBB (hemoglobin B): The Gene Associated with Sickle Cell Anemia

• Malaria and the Red Cell: Natural Selection

• World Malaria Report 2005