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CHAPTER 12:
DNA and RNA
Review of Reader’s Guide
Technique
Griffith
Avery
Hershey/Chase
Chargaff
Franklin
Watson/Crick
Findings
Place the correct technique and
finding with the scientist in your chart.
Techniques
Findings
X-Ray diffraction
X shaped, twisted coil, 2 strands,
bases in middle
Bacteriophage – phosphorus-32
(DNA) and sulfur-35 (protein)
Phosphorus was left behind, DNA
was the part that carried on the
disease
Extract to rule out proteins, lipids,
carbohydrates and RNA
Determined the factor was DNA
Noticed a % of G&C and A&T were
the same in different organisms
A=T
Mice/pneumonia. Heat killed
deadly+ harmless = death
Transformation of a FACTOR (now
known as DNA)
Modeled DNA + X Ray evidence
DNA is a double helix
G=C
Technique
Griffith
Avery
Hershey/Chase
Chargaff
Franklin
Watson/Crick
Mice/pneumonia. Heat
killed deadly+ harmless
= death
Extract to rule out
proteins, lipids,
carbohydrates and RNA
Bacteriophage –
phosphorus-32 (DNA)
and sulfur-35 (protein)
Noticed a % of G&C and
A&T were the same in
different organisms
X-Ray diffraction
Modeled DNA + X Ray
evidence
Findings
Transformation of a
FACTOR (now known as
DNA)
Determined the factor
was DNA
Phosphorus was left
behind, DNA was the part
that carried on the disease
A=T
G=C
X shaped, twisted coil, 2
strands, bases in middle
DNA is a double helix
Figure 12–2 Griffith’s
Experiment
Section 12-1
Heat-killed,
disease-causing
bacteria (smooth
colonies)
Disease-causing
bacteria (smooth
colonies)
Harmless bacteria Heat-killed, disease(rough colonies) causing bacteria
(smooth colonies)
Dies of pneumonia
Lives
Lives
Control
(no growth)
Harmless bacteria
(rough colonies)
Dies of pneumonia
Live, disease-causing
bacteria (smooth colonies)
Rough and smooth Bacteria
Figure 12–2 Griffith’s
Experiment
Section 12-1
Heat-killed,
disease-causing
bacteria (smooth
colonies)
Disease-causing
bacteria (smooth
colonies)
Harmless bacteria Heat-killed, disease(rough colonies) causing bacteria
(smooth colonies)
Dies of pneumonia
Lives
Lives
Control
(no growth)
Harmless bacteria
(rough colonies)
Dies of pneumonia
Live, disease-causing
bacteria (smooth colonies)
Transforming factor altered the Rough (harmless) Bacteria
into Smooth (harmful) Bacteria
Avery, MacLeod and others
• Did the same experiment as Griffith except
with isolated:
– Carbohydrates, Lipids, Proteins and DNA
• Only DNA was necessary for the
transformation to occur; therefore it is the
transforming factor.
Hershey Chase Experiment
Figure 12–4 Hershey-Chase
Experiment
Section 12-1
Bacteriophage with
phosphorus-32 in
DNA
Phage infects
bacterium
Radioactivity inside
bacterium
Bacteriophage with
sulfur-35 in protein
coat
Phage infects
bacterium
No radioactivity inside
bacterium
Figure 12–4 Hershey-Chase
Experiment
Section 12-1
Bacteriophage with
phosphorus-32 in
DNA
Phage infects
bacterium
Radioactivity inside
bacterium
Bacteriophage with
sulfur-35 in protein
coat
Phage infects
bacterium
No radioactivity inside
bacterium
Figure 12–4 Hershey-Chase
Experiment
Section 12-1
Bacteriophage with
phosphorus-32 in
DNA
Phage infects
bacterium
Radioactivity inside
bacterium
Bacteriophage with
sulfur-35 in protein
coat
Phage infects
bacterium
No radioactivity inside
bacterium
Validated that DNA is the agent of genes
Percentage of Bases in Four
Organisms
Section 12-1
Source of DNA
A
T
G
C
Streptococcus
29.8
31.6
20.5
18.0
Yeast
31.3
32.9
18.7
17.1
Herring
27.8
27.5
22.2
22.6
Human
30.9
29.4
19.9
19.8
• X-Ray Diffraction
– Rosalind Franklin and
Maurice Wilkins
• Watson and Crick
Final DNA model
Technique
Griffith
Avery
Hershey/Chase
Chargaff
Franklin
Watson/Crick
Mice/pneumonia. Heat
killed deadly+ harmless
= death
Extract to rule out
proteins, lipids,
carbohydrates and DNA
Bacteriophage –
phosphorus-32 (DNA)
and sulfur-35 (protein)
Noticed a % of G&C and
A&T were the same in
different organisms
X-Ray diffraction
Modeled DNA + X Ray
evidence
Findings
Transformation of a
FACTOR (now known as
DNA)
Determined the factor
was DNA
Phosphorus was left
behind, DNA was the part
that carried on the disease
A=T
G=C
X shaped, twisted coil, 2
strands, bases in middle
DNA is a double helix
12-2: Chromosomes and DNA Replication
CHROMOSMOES
• Prokaryotes (Bacteria)
–
–
–
–
–
No nucleus
Circular DNA = chromosome
1.6mm long packaged into a
prokaryote not visible to the
naked eye (10µm).
Has approximately 5 million
base pairs
Must package/fold up inside
the cell to fit into a space
1/1000 its size.
• Eukaryotes
– DNA is contained in the nucleus.
– Every cell in an organism has
identical DNA organized into
linear chromosomes.
– Different organisms have
different numbers of
chromosomes
– Humans 46, Drosophila 8,
Sequoia Tree 22
• On chromosome 1 of human DNA
there are 249 million base pairs
coding for approximately 4000
genes.
• An average eukaryotic cell (100µm)
has over 6 billion base pairs and
measures over 1 meter but only 2.2
nm wide
• How do these organisms pack so much
DNA in such a tiny space?
• Chromosome Structure
– Chromatin

•
•
•
Double helix + Histones -> Nucleosomes
Nucleosomes wind into coils
DNA is in this state in normal cell activity
Not visible
– Visible Chromosome
 Coils wind into supercoils
• only during cell division is the chromosome wound so tightly
• ~ 700 nm wide
Chromosome
Nucleosome
DNA
double
Coils
Supercoils
Histones
helix
THE REPLICATION OF DNA
• Remember DNA:
– holds the genetic code in the sequence of
nucleotides (monomer)
– is double stranded
– consists of two antiparallel strands of sugarphosphate groups (covalent bonds).
– Pairs of nitrogenous bases link the two strands
together with hydrogen bonds
– forming a double helix.
– the N-base pairing is complementary
Let us review the structure of DNA . . .
The Structure of DNA
= Phosphate
= Deoxyribose
(5-c sugar)
= N-base
(A-T)
(G-C)
Hydrogen bonds
Q: Why does DNA need to replicate?
A: When a cell divides to form new cells, the
DNA must replicate to ensure the new
cells have an identical copy.
G1
M-phase
s
G2
The steps of DNA Replication (DNA Synthesis) are
made possible by enzymes:
STEP 1: Helicase - separates or “unzip” the
two strands of the double helix
– Replication fork forms
STEP 2: DNA Polymerase -inserts the appropriate
bases, new hydrogen bonds form
• Each strand of the double helix of DNA serves as a template
or pattern for the new strand
STEP 3: DNA Polymerase - covalently bond the
sugar to the phosphate backbone of the new
strand
STEP 4: DNA Polymerase - proofreads the bases
to make sure they were paired correctly
The Replication of DNA
Try your own:
AATTTCGATGGC
T TAAAG C TAC C G
(Strand 1)
(Strand 2)
DNA Replication
New strand
Original
strand
DNA
polymerase
Growth
DNA
polymerase
Growth
Replication
fork
Replication
fork
New strand
Original
strand
Nitrogenous
bases
The Replication of DNA
Unzip
Base Pairing
http://www.abbysenior.com/biology/dna_protein_synthesis.htm
2 New Strands
12-3 RNA AND PROTEIN SYNTHESIS
• DNA holds the genetic code to make proteins
• Proteins are made outside the nucleus on ribosomes
• DNA cannot leave the nucleus
Q: How does DNA get the code outside the nucleus?
A: RNA (ribonucleic acid) acts as a messenger between
DNA and the ribosome and carries out the process by
which proteins are made from amino acids.
DNA 
RNA
transcription
 PROTEIN
translation
OVERVIEW
THE STRUCTURE OF RNA
• RNA is similar to DNA with a few differences:
DNA
Strand
Double Stranded
Sugar
Bases
Deoxyribose
A-T G-C
RNA
Single Stranded
(can form double strand if it
folds back on itself)
Ribose
A-U
G-C
• 3 types of RNA:
– mRNA (messenger RNA): goes
in the nucleus and copies the
code off of DNA and brings it to
the ribosome
– tRNA (transfer RNA): it carries
amino acids to the ribosomes
– rRNA (ribosomal RNA): along
with proteins, rRNA makes the
subunits of the ribosomes
Different Forms of RNA
50S
30S
mRNA and DNA interaction
Adenine (DNA and RNA)
Cystosine (DNA and RNA)
Guanine(DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)
RNA
polymerase
DNA
RNA
TRANSCRIPTION: RNA SYNTHESIS
•Transcription= the process by which a molecule of DNA is
copied into a complementary strand of RNA
Transcription: RNA Synthesis
• Steps of Transcription:
Step #1: RNA polymerase (enzyme) attaches to
a sequence of DNA known as the “start” site and
separates the two strands
Step #2: RNA nucleotides base pair with
complementary DNA nucleotides
DNA
A
T
C
G
mRNA
U
A
G
C
Now try your own:
DNA= T T T A G A G A C C G T A T C
mRNA= A A A U C U C U G G C A U A G
**Remember, RNA does not have Thymine!
Step #3: RNA polymerase terminates
transcriptions when it reaches the “stop”
site on the DNA
Step #4: The final RNA strand leaves the
nucleus through pores in the nuclear
membrane
TRANSLATION: PROTEIN SYNTHESIS
• proteins are responsible for:
– controlling biochemical pathways (enzymes)
– synthesis of lipids, carbohydrates, and
nucleotides
– cell structure and cell movement
• DNA and RNA control the process of
making proteins
• DNA
RNA
Protein
Transcription
Translation
(Protein
Synthesis)
Review:
1. Proteins are polymers
• Proteins are made of
monomers known as
amino acids
3. There are 20 different
kinds of amino acids
(p303)
4. Amino acids form peptide
bonds
5. A string of amino acids is
known as a polypeptide
THE NATURE OF THE
GENETIC CODE
• DNA contains a code to make
proteins
• The code is copied onto
mRNA in transcription
• Every 3 nitrogenous bases on
the mRNA makes up a codon
• Each codon specifies a
particular amino acid that is to
be placed in the polypeptide
chain (p303)
– An amino acid can have more
than one codon
– Ex: Glycine= GGG & GGA &
GGU & GGC
The Genetic Code (p. 303)
The Nature of the Genetic Code
Example:
DNA: T A C C A G C T C A C T
mRNA: A U G G U C G A G U G A
Valine
Glutamic
“Stop”
Amino Acid: Methionine
Acid
“Start” Codon
Codon
TRANSLATION
• Translation= The
decoding of a
messenger RNA
message into a
polypeptide (protein)
• The nucleic acid
language is translated
into protein language
Translation
KEY PLAYERS (draw)
Ribosomal RNA
ANTICODON
Steps of Translation:
(See Translation Handout)
Step #1: After leaving the
nucleus, mRNA binds to the
ribosomes on which rRNA is
found
Step #2: In the cytoplasm,
tRNA picks up amino acids
and carries them to the
mRNA
Step #3: First the anticodon on
tRNA attaches to the
corresponding initiator (start)
codon in mRNA
If the mRNA is AUG what will
the anticodon be?
Step #4: tRNA continues to match their anticodon with
corresponding mRNA codons
Step #5: As each anticodon and codon bind together, a
peptide bond forms between the two amino acids
Step #6: Finally, when the ribosome reaches the stop
codon on mRNA, the new polypeptide is released
Translation
Translation part 2
http://library.thinkquest.org/C0123260/basic%20knowledge/images/basic%20knowledge/RNA/translation%20steps.jpg
12-4 MUTATIONS
• Mutations in genes = the ultimate source of genetic
variation
– Can change one nucleotide, one gene or an entire
chromosome
• Gene Mutations
– May be one nucleotide or several nucleotides
– Point Mutations
• Occur on one or a few nucleotides
• Results in the change of one amino acid
• EX. Substitution
– Frameshift Mutations
• Groups of codons have been shifted altering many amino acids
• EX. Insertion or Deletion
TYPE
DEFINITION
Substitution One base is replaced
by another base
Deletion
Nucleotide is removed
Insertion Nucleotide is added
EXAMPLE
AGTGGATC
AGTGGGTC
AGTGGATC
AGTGATC
AGGTGGATC
AGGTGGATTC
Gene Mutations:
Substitution, Insertion, and Deletion
Substitution
Go to
Section:
Insertion
Deletion
Chromosomal Mutations:
Involve the movement of large sections of
chromosome
Deletion
Duplication
Inversion
Translocation