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Announcements
Objectives
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DNA
Chromosomes
Genes
Traits
Cystic Fibrosis
Protein Folding
Lecture
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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 Jim 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:
- 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 |
|
|
- 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.
- Explain in general terms how the structure of the DNA molecule is related to
the production of a specific protein.
- 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.
- 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:
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, 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.
- Karyotypes
and Spreads of human chromosomes.
- 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.
- 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.
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.
-
- 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.
- 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
Primary Structure
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.
Tertiary Structure
- Interactions among side chains (R groups) occur, folding the polypeptide into
three dimensions and giving it a unique shape.
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.
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