Chapter 12 Notes
A. First Discoveries
1. Griffith- experiment showed that live uncoated
bacteria acquired the ability to make coats
from dead coated bacteria. He called the
process transformation.
Figure 12–2 Griffith’s Experiment
Section 12-1
Heat-killed, diseasecausing bacteria
(smooth colonies)
Disease-causing
bacteria (smooth
colonies)
Dies of pneumonia
Go to
Section:
Harmless bacteria Heat-killed, disease(rough colonies) causing bacteria
(smooth colonies)
Lives
Lives
Control
(no growth)
Live, disease-causing
bacteria (smooth colonies)
Harmless bacteria
(rough colonies)
Dies of pneumonia
2. Avery- discovered that DNA is the nucleic
acid that stores and transmits the genetic
information from one generation to the next.
3. Hershey & Chase- used radioactive labeling to
identify DNA. They showed that DNA, not
protein, is the genetic material of a
bacteriophage (virus).
Figure 12–4 Hershey-Chase
Experiment
Section 12-1
Go to
Section:
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
DNA Structure
1. DNA is composed of subunits called nucleotides.
2. Nucleotides have three parts: a) sugar
b) phosphate group
c) base
a. The sugar is a 5 carbon sugar called deoxyribose.
b. There are four kinds of nitrogenous bases- these
form the “rungs” of the ladder
1. Adenine
2. Guanine
3. Cytosine
4. Thymine
Figure 12–5 DNA Nucleotides
Section 12-1
Purines
Adenine
Guanine
Phosphate
group
Go to
Section:
Pyrimidines
Cytosine
Thymine
Deoxyribose
DNA Structure
c. The two larger bases- adenine and guanine are
called purines.
d. The two smaller bases- cytosine and thymine are called
pyrimidines.
e. The backbone of the DNA chain is formed by all
sugar and phosphates, the bases hook onto the
sugar part of the chain
3. Chargaff’s Rule
a. A (adenine) always equals (joins) to T (thymine)
b. G (guanine) always equals (joins) to C (cytosine)
Figure 12–7 Structure of DNA
Section 12-1
Nucleotide
Hydrogen
bonds
Sugar-phosphate
backbone
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
Go to
Section:
DNA RNA
4. Rosalind Franklin
Used a technique called X-ray diffraction to
determine DNA was helical.
5. Watson and Crick
Built a 3 dimensional model of a DNA molecule
which was called a double helix
6. DNA is tightly coiled around a protein called
histones. The coil then forms your Chromatin.
Coiled chromatin forms your chromosomes.
Figure 12-10 Chromosome
Structure of Eukaryotes
Section 12-2
Chromosome
Nucleosome
DNA
double
helix
Coils
Supercoils
Histones
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Section:
C. DNA Replication
1. Before a cell divides DNA is copied (replicated)
2. During DNA replication, the DNA molecule
separates into 2 strands. Each new strand will hook
up with it’s complementary base partner, making 2
new complementary strands. The strands follow
Chargaff’s rule on base pairing.
3. The sites where separation and replication occur are
called replication forks.
4. The replication is carried out by enzymes that
“unzip” the DNA called DNA polymerase.
Figure 12–11 DNA Replication
Section 12-2
New strand
Original
strand
DNA
polymerase
Growth
DNA
polymerase
Growth
Replication
fork
Replication
fork
New strand
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Section:
Original
strand
Nitrogenous
bases
DNA
DNA Replication
• Complementary base pairs form new strands.
DNA
Concept Map
Section 12-3
RNA
can be
Messenger RNA
also called
which functions to
mRNA
Go to
Section:
Ribosomal RNA
Carry instructions
also called
which functions to
rRNA
Combine
with proteins
from
to
to make up
DNA
Ribosome
Ribosomes
Transfer RNA
also called
which functions to
tRNA
Bring
amino acids to
ribosome
III. RNA Structure
A. RNA Structure
1. Nucleic Acid made of single chains of
nucleotides
2. The sugar is called Ribose
3. Base pairs are cytosine & guanine,
adenine & Uracil.
4. Uracil replaces the Thymine
B. Types of RNA
1. Messenger RNA (mRNA)- carries the
instructions to make a particular protein
from DNA
2. Ribosomal RNA (rRNA)- makes up the
major part of ribososmes
3. Transfer RNA (tRNA)- transfers the amino
acids to ribosomes during protein synthesis
III. Transcription
A. The process of producing mRNA from DNA.
1. RNA polymerase binds to the DNA and
separates the strands.
2. RNA polymerase uses one strand of DNA as
a template to form a strand of mRNA.
3. RNA polymerase enzymes will only bind to
regions of DNA called promoters (it has a
specific base sequence).
Figure 12–14 Transcription
Section 12-3
Adenine (DNA and RNA)
Cystosine (DNA and RNA)
Guanine(DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)
RNA
polymerase
DNA
RNA
Go to
Section:
B. RNA Editing
1. Intron- intervening sequences that are
removed from the mRNA molecules before
they become functional.
2. Exons- the remaining portions that are
spliced back together to form the final
mRNA.
IV. Genetic Code
A. Three bases long, called codons (Ex. GCA)
B. Proteins are made of long chains called
polypeptides
C. Codons specify a single amino acid that is to
be added to the polypeptide
D. D. Polypeptides are made by joining the
amino acids.
Figure 12–17 The Genetic Code
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Section:
V. Translation (Protein synthesis)
A. The decoding of an mRNA message into a protein
B. Takes place in the ribosomes
C. Steps involved:
1. mRNA is transcribed from DNA and released in
the cytoplasm
2. Translation begins when mRNA attaches to a
ribosome in the cytoplasm at the start
codon
(AUG)
3. Each transfer RNA as an anticodon whose bases
are complementary to a codon on the mRNA. This
has an amino acid attached to one end.
4. The ribosome positions the start codon to attract its
anticodon, which is part of tRNA and binds them
together.
5. Once the first and second codon and anticodon are
bound, the ribosome joins the two amino acids and
the tRNA breaks away.
6. Chains of amino acids continue to grow until the
ribosome reaches a stop codon on the mRNA
strand. Then it replaces the chain.
Figure 12–18 Translation
Section 12-3
Nucleus
Messenger RNA
Messenger RNA is transcribed in the nucleus.
Phenylalanine
tRNA
The mRNA then enters the cytoplasm and
attaches to a ribosome. Translation begins at
AUG, the start codon. Each transfer RNA has
an anticodon whose bases are complementary
to a codon on the mRNA strand. The ribosome
positions the start codon to attract its
anticodon, which is part of the tRNA that binds
methionine. The ribosome also binds the next
codon and its anticodon.
Ribosome
Go to
Section:
mRNA
Transfer RNA
Methionine
mRNA
Lysine
Start codon
Figure 12–18 Translation
(continued)
Section 12-3
The Polypeptide “Assembly Line”
The ribosome joins the two amino acids—
methionine and phenylalanine—and breaks
the bond between methionine and its tRNA.
The tRNA floats away, allowing the ribosome
to bind to another tRNA. The ribosome moves
along the mRNA, binding new tRNA molecules
and amino acids.
Lysine
Growing polypeptide chain
Ribosome
tRNA
tRNA
mRNA
Completing the Polypeptide
mRNA
Ribosome
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Section:
Translation direction
The process continues until the ribosome reaches
one of the three stop codons. The result is a
growing polypeptide chain.
http://www.pbs.org/wgbh/aso/tryit/dna/#
Section 12-4
Gene Mutations:
Substitution, Insertion, and Deletion
Deletion
Substitution
Go to
Section:
Insertion
Section 12-4
Figure 12–20 Chromosomal Mutations
Deletion
Duplication
Inversion
Translocation
Go to
Section: