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


Announcements

Objectives

Web Resources

Review

Traits

Cystic Fibrosis

Protein Structure

Diseases and Evolution

Lecture Syllabus

IB 100/101 Home Page


Announcements


Text readings in Hoefnagels

Chapter 12: Gene Function, Gene Regulation, and Biotechnology

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Moodle

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Objectives:

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

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:

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

  3. 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.

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

  5. 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.

  6. 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:


REVIEW (DNA, Chromosomes, Genes)

    DNA

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


    What are Chromosomes?


    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 Hoefnagels, pg. 182, fig. 9.7. 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.

    • 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.

    DNA
    (Cystic Fibrosis
    Mutant Allele)
    --> Transcription
    (in nucleus)
    --> Abnormal
    mRNA
    --> Translation
    (in cytoplasm)
    --> Abnormal
    CF Protein
    (Chloride Ion
    Active Transport)
    • 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 10.7 in Hoefnagels, page 201) . 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.

    • 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. 2.21, in Hoefnagels, page 39. Also, see Primary, Secondary, Tertiary, and Quaternary Structures of Protein Molecules from accessexcellence.org


    Sickle Cell Disease and natural Selection