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Chapter 12:
Molecular Genetics
• DNA structure
• Replication
• Protein synthesis
DNA: The Genetic Material
Section 1 – p. 329
The “OLD” people of DNA
1.Fredrick Griffith
2.Oswald Avery
3.Hershey and
Chase
4.Erwin Chargaff
5.Watson and
Crick
Fredrick Griffith-1928
 In 1928, British scientist Fredrick Griffith was
trying to learn how certain types of bacteria caused
pneumonia.
 He isolated two different strains of pneumonia
bacteria from mice and grew them in his lab.
 Performed the first major experiment that led
to the discovery of DNA as the genetic
material
So Griffith, Avery, Hershey and Chase
all helped discover DNA and the
importance that it plays in transferring
Genes.
But what is DNA???
what is it made of???
what does it look like??????
What is DNA?
1. A genetic code
2. A molecule made of
subunits called
nucleotides
3. A complex molecule
that is arranged as a
double helix.
NUCLEOTIDES
are repeating subunits
(monomers) that include:
Phosphate group
5-Carbon sugar
Nitrogen base
NUCLEOTIDES
the smallest subunit of DNA
Two Kinds of bases in DNA
 Pyrimidines are single ring bases.
Thymine & Cytosine
Memory trick “Y” are you single?
 Purines are double ring bases.
Adenine & Guanine
A
G
C
T
Erwin Chargraff Analyzed the amounts of A, C, T, and G in
DNA; Discovered A=T & C=G
The Shape of DNA
 DNA often is compared
to a twisted ladder.
 Rails of the ladder are
represented by the
alternating deoxyribose
and phosphate.
 The pairs of bases
(cytosine–guanine or
thymine–adenine) form
the steps.
Watson and Crick
 Built a model of the double helix that
conformed to the others’ research
 1. two outside strands consist of
alternating deoxyribose and phosphate
 2. cytosine and guanine bases pair to each
other by three hydrogen bonds
 3. thymine and adenine bases pair to each
other by two hydrogen bonds
Watson and Crick
 suggested the structure for DNA and
Hypothesized a method of replication
Refer to the DNA handout
1. Locate the Phosphate groups
(small circles). Label each one with
“P”
2. Color all phosphate groups orange
3. Locate the deoxyribose sugar
molecules (large pentagon shapes
attached to the P’s). Label them by
name.
4. Color all sugars blue
Refer to the DNA handout
1.Locate the nitrogen bases.
Label the first base by name
and the others “NB”.
2.What do you notice about
these molecules?
4 Nitrogen Bases
Purines are
Pyrimidines are
larger bases
smaller bases
Adenine
Thymine
Guanine
Cytosine
Refer to the DNA handout
1. Locate the nitrogen bases – 2 large, 2
small
2. Label one of the large bases Adenine
3. Label the other large base Guanine
4. Label one of the smaller bases Thymine
5. Label the other small base Cytosine
6. Color each base a different color.
CHARGAFF’S BASE
PAIRING RULES
A binds with T
G binds with C
Hydrogen
Bonds
Fig. 4. Adenine-Thymine
base pair with two
hydrogen bounds.
C = Carbon = gray
Fig. 5. Guanine-Cytosine
base pair with three
hydrogen bounds
N = Nitrogen = blue
O = Oxygen = red
3-D Animation
of DNA
http://www.umass.edu/molvis/tutorials/dna/dnapairs.htm
Stop & Review
1. What is the smallest subunit of DNA?
2. List 3 parts to #1?
3. What are the side chains of DNA made
of?
4. What are the “steps” of DNA made of?
5. What are the base pairing rules of
DNA?
6. Describe the structure of DNA in 2
words.
ANSWERS
1.Nucleotide
2.Sugar, phosphate and a
nitrogen base
3.Sugar and phosphate
4.Nitrogen base
5.A=T, C=G
6.Double Helix
How are genes, chromosomes
and DNA related?
Genes are
portions of
DNA that are
tightly packed
into
chromosomes
and code for
the
manufacture of
proteins.
How are genes, chromosomes
and DNA related?
Think of
chromosomes
as socks and
genes as stripes
on the socks.
Place in order from smallest to
largest.
Gene
DNA
Chromosomes
Have Your DNA & eat it too!
1.Collect materials
2.Follow instructions
*A (pink) pairs with
T (green)
*C (orange) pairs with
G (yellow)
Semi-conservative
replication
Part 2
Essential Questions
What is replication and how is
it done?
What’s the role of the enzymes
helicase and DNA polymerase?
Replication
A complete copy of the
DNA is made
The DNA code is in the middle of the helix, so how does it get copied if it’s
obscured by the side chains and twist of the helix shape?
Replication
DNA replication is an important part
of the cell division process.
Before a cell divides, it first
duplicates its DNA so that the new
cell will have the same genetic
information.
The specific base pair matching
during replication ensures that exact
DNA copies are made.
The DNA code is in the middle of the helix, so
how does it get copied if it’s obscured by the
side chains and twist of the helix shape?
Replication
1. Enzymes (helicase) will “unzip” or
unwind the double helix by
weakening H-bonds creating a
replication fork where the two chains
separate
2. DNA polymerase
assembles new
DNA using each original strand as a
template
3. The replicated DNA is proofread and
mistakes are edited
Replication fork
Boring person explaining 
Replication is discontinuous
 Short fragments of DNA called
Okazaki fragments are added
near the replication fork
 Then gaps are filled in by DNA
polymerase
 Bases are added following the
base pairing rules (A-T, C-G)
* The lengths of Okazaki fragments are between 1,000 to
2,000 nucleotides long in bacteria and are generally
between 100 to 200 nucleotides long in eukaryotes.
Copy the following sequence to your
foldable.
T-- --A
A-- --T
C-- --G
A-- --T
A-- --T
A-- --T
C-- --G
T-- --A
T-- --A
A-- --T
C-- --G
T-- --A
Remember that
H-bonds hold
complementary
bases together
Unzip sequence to your foldable.
T
A
A
T
C
G
A
T
A
T
A
T
C
G
T
A
T
A
A
T
C
G
T
A
Step 1:
Helicase
enzyme
“unzips”
double helix
by weakening
H-bonds
Using the original DNA sequence on the
foldable make a copy.
T
A
C
A
A
A
C
T
T
A
C
T
A
T
G
T
T
T
G
A
A
T
G
A
Step 2: DNA
polymerase
enzyme
adds DNA
bases to the
exposed
nucleotides
on the
leading
strand
A
T
G
T
T
T
G
A
A
T
G
A
Using the original DNA sequence on the
foldable make a copy.
T
A
C
A
A
A
C
T
T
A
C
T
A
T
G
T
T
T
G
A
A
T
G
A
While Okazaki
fragments are
added on the
lagging strand
A
A
C
A
T
G
T
T
A
C
T
G
A
A
C
T
A
T
G
A
Using the original DNA sequence on the
foldable make a copy.
T
A
C
A
A
A
C
T
T
A
C
T
A
T
G
T
T
T
G
A
A
T
G
A
Step 3:
Polymerase
also
proofreads
and edits any
gaps
T
A
C
A
A
A
C
T
T
A
C
T
A
T
G
T
T
T
G
A
A
T
G
A
RESULTS
TWO strands of identical DNA
DNA replication is known as
semiconservative meaning each
DNA molecule contained one original
strand an one new strand.
Have Your DNA & eat it too!
1.Now replicate the
DNA, using 2 more
pieces of licorice
but use black sticks
3-2-1
3
steps cells undergo in replication
2
1
words meaning the structure of DNA
word for duplicating cell DNA
Protein synthesis
Part 3
Warm-Up Quiz:
DNA 101
1.
DNA is a double stranded sequence of ___________ (smallest
unit of DNA).
2.
DNA is a code of instructions for building ___________
(molecule).
3.
DNA is stored in the _________ (control center of the cell).
4.
The DNA code must be transmitted to the ___________ where
proteins are built. Today we’ll see how this happens.
Essential Questions
7. What is the primary function of
DNA?
8. How do RNA and DNA compare?
9. What are the three main types of
RNA? What are their roles?
10. How do the base-pairing rules for
RNA compare to the rules for DNA?
11. Describe the roles of DNA and RNA
in the overall process of protein
synthesis.
The role of DNA is to
store and transmit
genetic information
How do DNA & RNA compare?
DNA
 Deoxyribose sugar &
phosphate “backbone”
 N-bases: A, C, G, T
 Double helix
RNA
 Ribose sugar & phosphate
“backbone”
 URACIL replaces thymine
 Single-stranded, globular,
hairpin (huh? Hairpin???)
Check your
understanding…
Decide with your partner whether the
following describes DNA or RNA:
1. Master Plan
2. Blueprint copy
6. Involves Uracil
3. Stays in nucleus
7. Single-stranded
4. Goes to ribosome
8. Double-stranded
5. Involves Thymine
9. Involves codons
10.Polymerase
Types of RNA
Messenger
RNA
(mRNA)
The original DNA
code is
transcribed then
carried from the
nucleus to the
ribosome.
mRNA is written
in the form of
codons.
Types of RNA
Transfer
RNA (tRNA)
The anticodon that
matches the codon
found on mRNA.
It transfers an
amino acid in order
to assemble a
protein chain.
Types of RNA
Ribosomal
RNA
(rRNA)
RNA &
proteins that
make up
ribosomes
where
proteins are
made.
Base Pairing in DNA vs. RNA
DNA
A-T
C-G
RNA
A - Uracil
C-G
PROTEIN
SYNTHESIS
Step 1 Transcription
Step 2 Translation
Step 1:
TRANSCRIPTION
 DNA is changed into a different form
of nucleic acid called RNA
(ribonucleic acid)
 The new code is “read” 3 nucleotides
at a time called a codon
 Occurs in the nucleus
Why? Because mRNA can leave the nucleus
whereas DNA cannot.
TRANSCRIPTIO
N
1. Enzymes unzip helix
2. RNA polymerase assembles
mRNA nucleotides but base
pairing rules changes slightly
a.
Thymine in DNA pairs with Adenine
b.
Adenine in DNA pairs with
c.
Cytosine still pairs with Guanine
Uracil
Copy the following DNA sequence.
C--G
A--T
A--T
A--T
C--G
T--A
T--A
T--A
G--C
A--T
DNA
U --A
A --T
C --G
A --T
A --T
A --T
Slide 
C --G
Step 2: RNA
U --A
polymerase
enzyme forms
U --A
complementary
U --A
mRNA strand
G --C
A --T
mRNA
Write the complementary codon sequence.
A--T
Write the complementary nucleotide sequence.
T--A
Step 1:
Helicase
enzyme
“unzips”
double helix
by weakening
H-bonds
Step 2:
TRANSLATION
 The language of DNA is
translated into the language
of amino acids
 Occurs in the cytoplasm on
a ribosome
TRANSLATION
1.
The mRNA travels to the ribosome where each codon is read
2.
The codon of mRNA matches an anticodon on tRNA
3.
When the codon and anticodon match the amino acid being
carried by the tRNA is transferred to a growing protein chain.
Let’s use your foldable from before.
A
T
G
T
T
T
G
A
A
A
C
T
DNA
U
A
C
A
A
A
C
U
U
U
G
A
mRNA
 Open the foldable
and translate the
mRNA code into the
correct amino acid
sequence.
The translation…
A
T
G
T
T
T
G
A
A
A
C
T
DNA
U
A
C
A
A
A
C
U
U
U
G
A
mRNA
Tyrosine
Lysine
Leucine
STOP
Central Dogma of Biology
DNA codes for RNA, which
guides the synthesis of
proteins.
DNA  RNA  Protein
1.DNA is unzipped
2.RNA polymerase uses DNA as a template for making mRNA
(Uracil is incorporated instead of thymine)
3.mRNA moves out of nucleus to ribosome
4.tRNA carries amino acids to ribosome where they are
assembled into a peptide chain
5.Upon reading a STOP codon, the complete protein chain is
released
Now consider
this…
1. On a sheet of paper, write the word
CATS.
2. Try rearranging the letters to form as
many 3-letter words as you can.
3. Write each word on your paper, and
then add a definition for each word.
4. Did any of the codes you formed have
the same meaning?
The DNA Alphabet
• Like CATS, there are only 4
nitrogen bases in the DNA
alphabet.
• Like the CATS activity, DNA
“words” are only 3-letters. These
triplet base sequences are called
codons.
BRAIN TEASER
How many codons can be made using
the four letters of the four different
bases?
Hint:
 A codon is made up of 3 nucleotides.
 So there are 3 spots and a possibility of 4
bases in each.
4 bases x 4 bases x 4 bases
= 64 possible codon combinations.
Since the nitrogen base is the only unit to
change, the sequence of bases makes up the
code.
How is DNA
like Morse
code?
How is DNA
like Morse
code?
It is a series of single repeating units (sounds or symbols) that make
up a message. The repeating units are the nucleotides of the DNA
molecule. The message is the final protein that is produced. Proteins
can be structural, enzymatic, hormones, etc.