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Chapter 12: DNA & RNA
What do you already know about
DNA?
12.1 Contributors to the Genetic Code
1. Griffith and Transformation
–
–
Worked with bacteria causing pneumonia
Two Strains
1. S – strain (smooth) – DEADLY
2. R – strain (rough) - HARMLESS
12.1. Contributors to the Genetic Code
1.
Griffith Experiment
1. The Experiment
• Mouse + R = Life
• Mouse + S = Death
• Mouse + heat-killed S =
Life
• Mouse + heat-killed S and
R = Death
Transformation: changing one strain of bacteria into another
using genes. Pointed to some type of “transforming” factor.
12.1. Contributors to the Genetic Code
1.
Griffith
• Conclusion: “something” transformed the living R-strain
(harmless) into the S-strain (deadly) = Transformation
2.
Oswald Avery – repeated Griffith’s work
• Destroyed all the organic compounds in heat killed
bacteria except DNA: Result = transformation occurred.
• Destroyed all the organic compounds and DNA: Result =
transformation did not occur.
• Conclusion: DNA was the transforming factor that
caused the change in the R-strain
12.1 Contributors to the Genetic Code
3. Alfred Hershey & Martha Chase
•
•
Question: Are genes made of DNA or Proteins
What they know: viruses use other organisms to
reproduce
Phage attaches
to bacterial cell.
Phage injects DNA.
Phage DNA directs host
cell to make more phage
DNA and protein parts.
New phages assemble.
Cell lyses and releases
new phages.
12.1. Contributors to the Genetic Code
3. Alfred Hershey and Martha Chase
•
Experiment
•
•
They tagged the virus DNA with blue radioactive
phosphorous
They tagged the protein coat with radioactive
sulfur
Conclusion: Virus only injects DNA
(DNA is the genetic material)
Bacteriophage Images
HIV Images – NPR Story Toddler
12.1 Three important functions of DNA
1. Store genetic information – stores genes
2. Copy information – copy genes prior to cell
division
3. Transmit the information – pass genetic
information along to next generation
12.2 Structure of DNA
•
•
•
DNA = Deoxyribonucleic Acid
A nucleotide is composed of:
1. Sugar (deoxyribose)
2. Phosphate group
3. Nitrogenous Base
A nucleotide is the monomer of a DNA strand (polynucleotide):
Sugar-phosphate backbone
Phosphate group
A
C
Nitrogenous base
A
Sugar
DNA nucleotide
C
Nitrogenous base
(A, G, C, or T)
Phosphate
group
O
H3C
O
T
T
O P
O
CH2
O–
G
C
HC
O
C
N
N
C
H
O
Thymine (T)
O
C H
G
H
C
HC
CH
H
Sugar
(deoxyribose)
T
T
DNA nucleotide
DNA polynucleotide
12.2 Structure of DNA
Nitrogenous Bases
1. Purines – Adenine & Guanine (two rings in
structure)
2. Pyrimidines – Cytosine & Thymine (one ring)
H
O
H3C
H
C
C
C
H
H
N
C
H
N
C
N
C
C
C
N
O
H
N
H
H
Thymine (T)
Cytosine (C)
Pyrimidines – one ring structure
H
N
H
O
N
H
O
C
C
N
C
C
N
H
C
N
N
H
H
C
N
C
C
N
C
C
N
H
Adenine (A)
H
Guanine (G)
Purines – two ring structure
N
H
H
12.2 Structure of DNA
DNA is a double-stranded helix
James Watson and Francis Crick
• Worked out the three-dimensional structure of
DNA, based on work (photos taken using x-ray
crystallography) by Rosalind Franklin
12.2 Structure of DNA
The structure of DNA
• Consists of two polynucleotide strands wrapped
around each other in a double helix (twisted ladder)
Twist
12.2 Structure of DNA
Hydrogen bonds (weak) between bases
• Hold the strands together
Each base pairs with a complementary partner
• A with T, and G with C
G
C
T
A
A
Base
pair
T
C
G
C
C
G
A
T
O
OH
P
–O
O
O
H2C
O
O
P
–O
O
H2C
–O
T
OH
A
T
O
A
O
P
O
H2C
O
–O
A
T
A
O
P
O
H2C
O
CH2
O O–
P
O
O
O
CH2
O O–
O P
O
O
CH2
O
O–
P
O
O
O
CH2
O
O–
P
HO O
G
C
O
A
O
C
G
O
G
T
Hydrogen bond
A
T
T
OH
G
A
Ribbon model
C
T
Partial chemical structure
Computer model
12-3 DNA Replication
When does DNA replicate?
– DNA must copy before cell division (mitosis)
How does it replicate?
1. DNA is separated by helicase (enzyme)
2. Nucleotides are added according to base pairing
rules, using DNA polymerase (enzyme).
A
T
A
T
A
T
A
T
A
T
C
G
C
G
C
G
C
G
C
G
G
C
G
C
G
C
G
C
A
T
A
T
A
T
A
T
T
A
T
A
T
A
T
A
Parental molecule
of DNA
C
A
Both parental strands serve
as templates
Two identical daughter
molecules of DNA
12-3 DNA Replication
DNA replication is semi-conservative
1. The parent strand gives rise to two daughter strands.
2. Each daughter strand is composed of one half the
parent (old strand) and one half new.
Parental strand
Origin of replication
Daughter strand
Bubble
Two daughter DNA molecules
12.3 DNA Replication
DNA replication is a complex process:
• The helical DNA molecule must untwist
• Each strand of the double helix is oriented in the
opposite direction (antiparallel)
5 end
3 end
• DNA has three prime (3’) and
five prime (5’) ends. Numbers
P 5
HO
4
2
refer to the position of the carbon 3 A
3
T 1
1
4
2
atoms on ribose sugar.
5
P
P
G C
C
A T
G
C
G
C
A T
T
T A
A T
T
A
A
C
G
C
C G
G
A
G TA
C
G
A
G
P
P
G
T
C
T
C
P
G
C G
C G
C
C
A
T
G
T
A
A
T
P
T
T
A A
T
OH
3 end
A
P
5 end
12.3 DNA Replication
Using the enzyme DNA polymerase
• The cell synthesizes one daughter strand as a
continuous piece (leading strand)
The other strand is synthesized as a series of short pieces
(lagging strand). Short pieces are called Okazaki
fragments
• Okazaki fragments
are then connected
by the enzyme DNA
ligase
DNA polymerase
molecule
5
3
Parental DNA
3
5
Daughter strand
synthesized
continuously
3
5
DNA Replication Video
5
3
DNA ligase
Overall direction of replication
Daughter
strand
synthesized
in pieces
DNA polymerase needs to build in a 5’ to 3’ direction
DNA polymerase
molecule
3
5
Daughter strand
synthesized
continuously
Parental DNA
5
3
3
Daughter
strand
synthesized
in pieces
5
Okazaki fragments
3
5
5
3
DNA ligase
3
5
Overall direction of replication
Chapter 13: Protein Synthesis
Chapter 13 Protein Synthesis - Overview
– The DNA of the gene is transcribed into RNA
• Which is translated into protein
• The flow of genetic information from DNA to RNA to
Protein is called the CENTRAL DOGMA
DNA
Transcription
RNA
Translation
Protein
Chapter 13 Protein Synthesis (Overview)
Central Dogma - FLOW IS FROM
DNA TO RNA TO PROTEIN
Chapter 13 Protein Synthesis (Overview)
FLOW IS FROM DNA TO RNA TO PROTEIN
• Genes on DNA are expressed through proteins, which provide
the molecular basis for inherited traits
• A particular gene, is a linear sequence of many nucleotides
– Specifies a polypeptide (long protein made of amino acids)
Chapter 13 Protein Synthesis (Overview)
Genes - discrete units of hereditary
information comprised of a nucleotide
sequence found in a DNA molecule.
13-1 Messenger (mRNA)
1. Monomer: nucleotide
2. Parts of a mRNA Nucleotide
•
•
•
Ribose Sugar
Phosphate
Nitrogenous Base
3. Three main differences between mRNA and
DNA
•
•
•
Ribose instead of deoxyribose
mRNA is generally single stranded
mRNA has uracil in place of thymine (U instead of T)
13.1 RNA
4. Three Types of RNA
•
•
•
Messenger RNA (mRNA)
– carries copies of genes
(DNA) to the rest of the
cell.
Ribosomal RNA (rRNA) –
make up the ribosomes.
Transfer RNA (tRNA) –
transfers the amino acids to
the ribosomes as specified
by the mRNA
13.1 TRANSCRIPTION:
The process of making
mRNA from DNA
DNA
– Why do you need this
process?
• Location of DNA?
Nucleus
• Location of Ribosome?
Cytoplasm
Strand to be transcribed
T
A
C
T
T
C
A
A
A
A
T
C
A
T
G
A
A
G
T
T
T
T
A
G
U
A
G
Transcription
A
U
G
A
A
G
U
U
U
RNA
– mRNA takes code from
DNA in the nucleus to
Polypeptide
the cytoplasm
Start
condon
Stop
condon
Translation
Met
Lys
Phe
13.1 Transcription produces genetic messages
in the form of mRNA
– A close-up view of transcription
RNA nucleotides
RNA
polymerase
T C C A
A U
A
T
T
A
C C A
T A G G T
Direction of
transcription
Newly made RNA
Template
Strand of DNA
13.1 In the nucleus, the DNA helix unzips
• And RNA nucleotides line up along one strand of the
DNA, following the base pairing rules
– As the single-stranded messenger RNA (mRNA)
peels away from the gene
• The DNA strands rejoin
RNA nucleotides
RNA
polymerase
T C C A A T
A U C C A
T A G G T T A
Direction of
transcription
Newly made RNA
Template
Strand of DNA
RNA polymerase
DNA of gene
– Transcription of a gene
Promoter
DNA
• Initiation
• Elongation
• Termination
Terminator
DNA
1 Initiation
Area shown
In Figure 10.9A
2 Elongation
3 Termination
Completed RNA
Growing
RNA
RNA
polymerase
Exon Intron
13.1 Eukaryotic mRNA is
processed before leaving the
nucleus
– Noncoding segments called
introns are spliced out leaving
only the coding exons
Exon
Intron
Exon
DNA
Cap
RNA
transcript
with cap
and tail
Transcription
Addition of cap and tail
Introns removed
Tail
Exons spliced together
mRNA
Coding sequence
• A 5’ cap and a poly A tail are
added to the ends of mRNA
• Cap and tail protect mRNA
Nucleus
Cytoplasm
5’
3’
T
C
C
A
A
U
C
C
A
T
A
G
G
T
Direction of
transcription
A
T
T
A
13.2 Translation
tRNA
molecules
Growing
polypeptide (protein)
Large
subunit
mRNA
Small
subunit
13-2 Protein Synthesis - Translation
• Translation is defined as going from mRNA
to protein
– tRNA which have amino acids attached are
going to the ribosome.
• What are amino acids? monomers of proteins
• Does the order of amino acids matter? Yes, they
must be in order for the protein to fold correctly.
– How does the correct tRNA (with amino acid
attached) bind to the mRNA? The tRNA
contains an anticodon which matches up with
the mRNA sequence (codon).
Transfer RNA (tRNA) molecules serve as
interpreters during translation
– Translation
• Takes place in the cytoplasm
– A ribosome attaches to the mRNA and translates its message into
a specific polypeptide aided by transfer RNAs (tRNAs)
• tRNAs can be represented in several ways
Amino acid
attachment site
Amino acid attachment site
Hydrogen bond
RNA polynucleotide chain
Anticodon
Anticodon
13.2 Translation
– Each tRNA molecule
• Is a folded molecule bearing a base triplet called
an anticodon on one end
– A specific amino acid
• Is attached to the other end
Amino acid
attachment site
Anticodon
13.2 Translation
Ribosomes build polypeptides (proteins)
– A ribosome consists of two subunits
• Each made up of proteins and a kind of RNA
called ribosomal RNA
• Translation at Ribosome
tRNA
molecules
Growing
polypeptide
Large
subunit
mRNA
Small
subunit
13.2 Translation
– The subunits of a ribosome
• Hold the tRNA and mRNA close together during
translation
tRNA-binding sites
Large
subunit
Next amino acid
to be added to
polypeptide
Growing
polypeptide
tRNA
mRNAbinding site
Small
subunit
mRNA
Codons
– An initiation codon marks the start of an
mRNA message
– mRNA, a specific tRNA, and the ribosome
subunits assemble during initiation
Met
Met
Large
ribosomal
subunit
Initiator tRNA
P site
U
A C
A U G
U
A C
A U G
Start
codon
1
mRNA
A site
Small ribosomal
subunit
2
Elongation adds amino acids to the polypeptide
chain until a stop codon terminates translation
– Once initiation is complete amino acids are added
one by one to the first amino acid
– The mRNA moves a codon at a time
• A tRNA with a complementary anticodon pairs with
each codon, adding its amino acid to the peptide chain
– Each addition of an amino acid
• Occurs in a three-step elongation process
Amino
acid
Polypeptide
P site
A site
Anticodon
mRNA
Codons
1 Codon recognition
mRNA
movement
Stop
codon
2 Peptide bond
formation
New
Peptide
bond
Figure 10.14
3 Translocation
Figure out the exact sequence of amino acids needed
1. Take the DNA and transcribe it into mRNA
Example:
mRNA:
TAC ATA CTA GCG ACT
AUG UAUGAU CGC UGA
2. Take the mRNA sequence and decode it using
the codon chart.
AUG = MET
UAU = TYR
GAU = ASP
CGC = ARG
Animation
13.3 Mutations
• Mutations – heritable changes in genetic information (changes to the
DNA sequence)
• Two types - gene and chromosomal mutations
• Mutations can be caused by chemical or physical agents (mutagens)
– Chemical – pesticides, tobacco smoke, environmental pollutants
– Physical – X-rays and ultraviolet light
13.3 Mutations
• Gene mutations
– Point Mutation: mutations that affect a single nucleotide
– Frameshift mutation: shift the reading frame of the genetic
message.
• Can change the entire protein so it doesn’t work
• Gene Mutations Explained
13.3 Mutations
13.3 Chromosomal Mutations
• Chromosomal mutation: mutation
that changes the number or structure
of chromosomes.
13.3 Chromosomal Mutations
• Types of chromosomal mutations:
– Deletion: The loss of all or part of
a chromosome
– Duplication: A segment is
repeated
– Inversion: part of the
chromosome is reverse from its
usual direction.
– Translocation: one chromosome
breaks off an attaches to another
chromosome.
DNA Modeling
1. Each person, Construct the DNA Strand Below
2. Then, construct the complimentary strand to make a complete DNA molecule
3. Ignore the color scheme below. Use:
Cytosine = Blue
Deoxyribose Sugar = Black Pentagon
Thymine = Green
Phosphate = White Tubes
Adenine = Orange
Ribose Sugar = Purple Pentagon
Guanine = Yellow
tRNA = Purple Plastic
Uracil = Purple
Amino Acid = Black Plastic
4. When you have constructed the complementary strand join the two strands together
with Hydrogen bonds
Transcription and Translation Modeling
1.
2.
3.
4.
Each group will construct an mRNA strand from the DNA strand below
Then, take your mRNA strand outside the nucleus to the ribosome
Use the codons of mRNA and anticodons of tRNA to manufacture proteins
Use the following model pieces:
Cytosine = Blue
Deoxyribose Sugar = Black Pentagon
Thymine = Green
Phosphate = White Tubes
Adenine = Orange
Ribose Sugar = Purple Pentagon
Guanine = Yellow
tRNA = Purple Plastic
Uracil = Purple
Amino Acid = Black Plastic
Peptide Bonds (between AAs) – Grey Tubes
5. When you have constructed the complementary strand join the two strands together
with Hydrogen bonds
Making a DNA Molecule
• Must Contain
– Deoxyribose Sugar – Pentagon shape
Backbone
– Phosphate Group – Circle
– At least 6 base pairs (complimentary base pair
must be interlocking)
– Label all parts of the DNA
– Question: How could the structure of a DNA
molecule allow it to carry information and
replicate (make copies of itself).
Phage attaches
to bacterial cell.
Phage injects DNA.
Phage DNA directs host
cell to make more phage
DNA and protein parts.
New phages assemble.
Cell lyses and releases
new phages.
DNA – Structure Questions
1.What pair of scientists are largely credited for
discovering the shape of the DNA molecule?
2.Name the scientist whose photographs helped
solve the mystery of DNA’s structure
3.DNA is in the shape of a _______ _______.
4.What are the sides of the DNA molecule made
of? (2 things)
5.What are the rungs of the ladder made of?
6.What is the monomer of DNA?
7.What holds nitrogenous bases together?
DNA – early scientists
• Scientist/Experiments
– What did Griffith call the phenomenon he
observed in the mouse experiment?
– What did Hershey and Chase mark the
bacteriophage with? What parts were marked?
– How did marking the bacteriophage assist in
determining DNA was the transforming factor?
Bryson Reading – Discovery of DNA
Section 1.
a. Why is it surprising that the scientists working
in England even discovered the structure of
DNA?
b. When did Watson start college and when did he
get his Ph.D.?
Section 2.
a. Why was understanding the shape of DNA so
important?
b. What did Watson remark about that is surprising
in his autobiography?
Bryson Reading – Discovery of DNA
Section 3.
a. How did Watson depict Rosie Franklin in his book
The Double Helix?
b. What did Rosie Franklin have that at the time was
the best in the field?
c. What method was Franklin using to capture DNA
Section 4.
a. How were women treated at Kings College?
b. What did Franklin do to throw her colleagues off
the trail?
c. How did Watson and Crick eventually see
Franklin’s photos?
Central Dogma Questions
1.The flow of genetic information is from
______ to ______ to ______.
2.Why does DNA send a “messenger” out into
the cytoplasm?
3.The manufacture of mRNA from DNA is
called _____________.
4.What cellular organelle uses the DNA codes
to manufacture proteins?
5.How is DNA ultimately associated with our
phenotype or outward appearance?
Homework Chapter 13 Sections 13.3 and 13.4
Section 13.3 Mutations 372-376
a. Explain the difference between the three types of “point”
mutations?
a.
How do point mutations differ from chromosomal
mutations?
a.
Explain how mutations could be harmful or beneficial
Section 13.4 Gene Regulation and Expression 377-383
a. Describe how prokaryotes turn lac genes on and off
(mention: promoters, operators, lactose, repressor, and
RNA polymersase)?
a.
How do eukaryotes regulate genes during transcription?
a.
What do homeotic genes like homeobox and hox genes
have to do with development? What is the difference
between homeobox and hox genes?
Twist
Drawing a DNA Molecule
• Must Contain
– Deoxyribose Sugar – Pentagon shape
Backbone
– Phosphate Group – Circle
– At least 6 base pairs (complimentary base pair
must be interlocking)
– Label all parts of the DNA
– Question: How does the structure of a DNA
molecule allow it to carry information and
replicate.
– Worth 20 Points
Please complete the following:
– The complementary DNA strand for:
• GACTGAGGA
– The mRNA strand for:
• GACTGAGGA
– Translate the mRNA sequence to amino acids:
• CCAUUUACG
– Translate the mRNA codons to tRNA anticodons:
• CCAUUUACG
Mutations
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