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DNA
The Code of Life
Medical Detectives
© 2013 Project Lead The Way, Inc.
DO NOW
Tuesday September 13th
1. What is the name of gene responsible for
HD?
2. What is the mutation in this gene?
3. What kind of molecule do genes code
for?
4. How does this mutation result in damage
to brain cells?
PLAN
• Analyze how changes in the huntingtin gene affect
the resulting protein and nerve cell function.
• Use appropriate laboratory methods to isolate DNA
from cheek cells.
DO
• Check Thursday’s classwork in journals.
• Discuss DNA structure and answer questions in your
biomedical science journal to prepare for tomorrow’s
DNA Isolation Lab.
What is DNA?
• DNA (deoxyribonucleic acid) is the genetic
material in all known living organisms and
some viruses
• It can be passed from one generation to
another
The “Code of Life”
• Information in DNA
determines an organism’s
characteristics
• DNA contains 4 nitrogen
bases:
Adenine (A), Thymine (T),
Guanine (G), and Cytosine
(C)
– A pairs with T in DNA
– G pairs with C in DNA
The “Code of Life”
• DNA can be compared to a cookbook
with instructions about how to create and
maintain a specific living thing.
• Genes can be compared to the individual
recipes in the cookbook. They encode the
information to make proteins and
determine how many of those proteins to
make.
Packaging DNA
• The basic structure of DNA
is that of a twisted ladder
called a double helix.
• To fit into the nucleus, the
double helix wraps around
proteins called histones.
Packaging DNA
• The DNA then
condenses into
chromosomes.
• Human beings
have 46
chromosomes in
the nucleus of
almost every cell.
Chromosomes of a human male
DNA Structure
DO NOW Tuesday September 20th
Consider the pedigree above. Explain why
Jack’s daughter has a 50% chance of
having the gene for Huntington’s disease.
PLAN
• Use appropriate laboratory methods to isolate DNA
from cheek cells.
DO
•
•
•
•
•
Genetics/HD Quiz
Finish questions over DNA Isolation Lab
Discuss Lab
Conduct Lab
Discuss Inherited diseases while waiting for DNA to
precipitate
DNA Extraction
Step 1: Collect cheek cells
• Sports drink is used as a mouthwash
collection medium.
• Sports drinks contain salt in a
concentration similar to the cheek cells;
this prevents the cells from breaking open
and releasing their DNA before they are
collected.
DNA Extraction
Step 2: Cell lysis
• The membranes that surround and
protect the cell and nucleus must be
broken to release the DNA in a process
called cell lysis.
• A detergent-based cell lysis solution will
be used to degrade the membranes.
• The remaining solution is known as cell
lysate.
DNA Extraction
Step 3: DNA precipitation
• The DNA in the cell lysate is in
solution and is not visible (like sugar
in water).
• DNA is insoluble (wont dissolve) in
ethanol (like sand in water).
• So we add the ethanol to cause the
DNA to precipitate (come out of
solution) so we can see it.
Importance of DNA Extraction
• DNA extraction is the first step in many
in-depth experiments including:
– The study of heredity
– Potential treatments of diseases
• Extracted DNA can be used to create
DNA fingerprints to help:
– Diagnose genetic diseases
– Solve criminal cases
Image Resources
By KES47 (File:Chromosome zh.svg) [CC-BY-3.0
(http://creativecommons.org/licenses/by/3.0)], via Wikimedia
Commons
Free images courtesy of Wikimedia Commons
http://commons.wikimedia.org/wiki/Main_Page