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

Announcements

Objectives

Web Resources

DNA

Chromosomes

Genes

Traits

Cystic Fibrosis

Protein Folding

Lecture Syllabus

IB 100 Home Page

Text Readings in Lewis et al.	Testing Your Knowledge	Thinking Scientifically
Chapter 13, Gene Function Review Chaps. 11 & 12	Pages 264-5, Questions 1-6, 8 & 9	Page 266, Question 2

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.

The "Mastering Concepts" boxes are valuable summaries of the main ideas in these sections of the text.

Objectives:

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

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.
• The Biology Project - Cell Biology from the University of Arizona. The Biology Project is an interactive online resource for learning biology, developed at The University of Arizona.
• Cystic Fibrosis Web Links from the University of Virginia
• Database of articles on Cystic Fibrosis from Online Mendelian Inheritance in Man.
• PREVIEW: Protein Synthesis for learning the details of protein synthesis (from Access Excellence). Print this out for next lecture.

DNA

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

• Each DNA Nucleotide includes:
• 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 227, Fig. 12.7)

What are Chromosomes?

• Chromosomes consist of a very tightly wound molecule of DNA plus associated proteins (See Lewis et al., Page 231, Fig. 12.11
• Human Chromosomes. Electron micrograph of enlarged human chromosome, where even strands of DNA can be seen!

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, Figure 10.04, in Life et al. Remember, you get one of each pair of numbered chromosomes 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 5-8. Note CFTR locus on 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 10.3, Lewis et al., Page 184
• Some Mendelian Disorders in Humans, Table 10.4, Lewis et al., Page 186. Over 5,000 human disorders are caused by mutations in single genes, such as sickle cell anemia and cystic fibrosis.
• 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

• 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 become clogged, stopping digestive enzymes from reaching the intestines where they are required to digest food. The pancreas form cysts and become fibrous. See also CF Phenotype, from the University of Virginia, for further characterization of the disease.

• Cystis 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.

• Figure 10.08 in Lewis et al., page 183 Cystic Fibrosis, like sickle cell disease, is an autosomal recessive trait. See 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 chloride and sodium ions across membranes of epithelial cells that line the lungs and other organs. Mutations in the gene result in an alteration of the protein so that epithelial cells are defective in transporting these ions.
• Information on the role of the CTFR gene from the UK Medical Research Council. An excellent resource showing how the chloride channel (CFTR protein) works.
• CFTR genomic DNA sequence. Click here to see the DNA sequence of the entire CFTR gene.
• 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.
• Different mutations in the same gene can produce a wide range of effects, from severe symptoms to no symptoms, from Access Excellence.
• Cystic Fibrosis (CFTR) Gene Sequence showing locations of mutations. (For summary of mutations, put mouse over shaded region.)
• Table of CFTR Mutations
• Summary: DNA to RNA to Protein to Trait. An excellent summarization.

Protein Folding

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