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DNA Basics
The Structure of DNA
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A VERY long polymer of repeating units
called nucleotides
Double-stranded helix
Sugar-phosphate backbone
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sugar is Deoxyribose
Four bases hang off the backbone
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Adenine, Thymine, Guanine, Cytosine
Order of the bases is key to genetic function
The DNA Double Helix
Terminology
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Chromosomes contain genes which are
made up of DNA and protein
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Humans have 46 chromosomes (23 pairs)
23 from mother, 23 from father
DNA = long string of A,T,G,C’s
Gene = short section of DNA
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contains recipe for one protein
less than 10% of DNA is genes, 90% “junk”
approx 25,000 genes in humans
Base Pairing
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Everything about the function of DNA is
due to base pairing
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Nitrogen bases from one strand of DNA form
weak hydrogen bonds with complementary
bases of other strand
A always bonds to T, G always bonds to C
A to T Base Pairing
C to G Base Pairing
DNA Replication
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DNA is double-stranded
Strands are connected by the bases
A on one strand double hydrogen bonds to T on
the other strand
 C on one strand triple hydrogen bonds to G on the
other strand
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Strands are coiled in a double helix
Strands are unzipped by enzyme helicase
New bases hydrogen bond to exposed
bases on parent strands, creating 2 new
double helixes
DNA Replication
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Before a cell divides:
The Central Dogma of Biology
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DNA makes RNA makes Protein
Proteins make you what you are
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eye color, diabetic, etc…
DNA is sacred, can’t leave nucleus (too
big)
Cell makes messenger RNA copy of DNA’s
instructions that can leave the nucleus
Copying mRNA from DNA is called
Transcription
The Central Dogma
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DNA  RNA 
Protein
Transcription Animations
“DNA makes RNA”
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Animation
Differences between DNA and
RNA
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DNA is double stranded; RNA is single
stranded – relevance?
DNA has deoxyribose; RNA has ribose
sugar
DNA has bases adenine, thymine,
guanine, and cytosine; RNA has bases
adenine, URACIL, guanine, and cytosine
Many types of RNA – main ones are:
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rRNA, tRNA, and mRNA
RNA makes Protein
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mRNA codes for protein in a process
called Translation
Occurs at the cell’s ribosomes
Proteins are long strings of amino acids
tRNA molecules bring amino acids to the
mRNA molecule and link up by base
pairing
Translation
Practice
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Use the table of
Codon Triplets to
translate this bit of
mRNA
Translation Practice
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mRNA codons (a codon is a set of three
mRNA bases
GCU ACG GAG CUU CGG AGC UAG
Order of amino acids according to
sequence above
_____ ____________________________
When The Process Goes Wrong
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Genetic disease – Sickle Cell Anemia
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A single base is wrong in the DNA
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There is an A where a T belongs
This causes a single amino acid to be wrong in the
hemoglobin protein (452 amino acids big)
Valine goes where glutamate belongs
Hemoglobin is slightly mis-shapen as a result
Applications of DNA Technology
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Recombinant DNA - inserting genes into
DNA strands
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Transgenics – a genetically altered organism
(bacteria producing human insulin)
Gene therapy
DNA fingerprinting
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Complete the following w/s
Quick review
DNA basics
DNA technology
Practice transcription and translation