Chapter 12: Gene Function, Gene Regulation, and Biotechnology
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The content of this lecture will help you complete these
After studying this material you should be able to:
Draw a diagram, create a concept map, or write a paragraph
explains the relationships among these terms:
|| gene loci
Use your chromosome models from discussion or lab to
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
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;
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
make up a protein determine its final conformation and, ultimately, its
REVIEW (DNA, Chromosomes, Genes)
What is DNA, Why do we need it, and Where does it come from?
What are Chromosomes?
What are Genes?
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.
are formed by mutations of pre-existing alleles. Different alleles
produce variations in inherited characterisitics (traits).
Homologous Chromosomes Hoefnagels, pg. 182, fig.
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
bottom of the illustration of Chromosome 7.
The Relationship Between Genes, Proteins, and Traits
A gene codes for a particular protein that is involved
expression of a trait.
Characteristics determined by single genes are called
Expression via Protein Synthesis, from Access Excellence. For a
cell to make protein, DNA is used as a template to manufacture
RNA (transcription). mRNA moves to the ribosomes in the cytoplasm where
it directs the assembly of amino acids that fold into completed
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
Cystic Fibrosis (An example of gene expression gone wrong)
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.
CFTR: The Gene Associated with Cystic Fibrosis.
Cystic Fibrosis testing goes mainstream from USA Today
CF is the most common inherited disease among
1 in 29 Caucasians (10 million) carries a defective
allele for the
30,000 children and young adults have CF.
Cystic fibrosis like sickle cell disease, is an
recessive trait (See figure 10.7 in Hoefnagels, page 201) . See
Fibrosis, from Access Excellence, explaining the hereditary nature
of the disease.
CF is caused by defective gene CFTR (Cystic
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
Because less salt is secreted from the cells lining
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.
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
(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.).
As a protein (polypeptide) is synthesized in a cell, it
three-dimensional structure (conformation). The order and kinds of
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
The structure of a protein may be described at four
See Fig. 2.21, in Hoefnagels, page 39. Also, see Primary, Secondary, Tertiary, and Quaternary
of Protein Molecules from accessexcellence.org
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
Interactions among side chains (R groups) occur,
polypeptide into three dimensions and giving it a unique shape.
Stereo pictures of a protein molecule from the Kuriyan Lab, UC Berkeley.
If you de-focus your eyes, such that your brain
melds the two stereo images into a third image between the two on the
screen, you can create a 3 dimensional image of the protein molecule in
Sickle Cell Disease and natural Selection