Download Chapter 12: DNA & RNA

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
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
Chromosome structure
• Chromatin = DNA that is tightly
packed around proteins called
histones
- during cell division, chromatin form
Nucleosome
packed chromosomes
Chromosome
DNA
double
helix
Coils
Supercoils
Histones
12-3 DNA Replication
When does DNA replicate?
– DNA must copy before cell division (mitosis)
How does it replicate?
1. DNA is separated
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
P 5
4
3
2
T
T A
A T
T
A
C
G
C
C G
G
A
G TA
C
3
4
5
T 1
A
P
C
A T
G
C
G
C
A T
G
1 A
P
G C
A
HO
2
G
P
P
G
T
C
T
C
P
G
C G
C G
C
C
A
T
G
T
A
A
T
T
A A
T
P
T
OH
3 end
A
P
5 end
DNA Replication
Replication = process of copying DNA
- occurs during S phase of Interphase
- process:
1. DNA is separated into two strands
by an enzyme
2. Free nucleotides are added by DNA
polymerase according to base pairing rule
DNA Replication
New strand
Original
strand
DNA
polymerase
Growth
DNA
polymerase
Growth
Replication fork
Replication fork
New strand
Original
strand
Nitrogenous bases
Chapter 13: Protein Synthesis
Central Dogma of Cell Biology
• DNA codes for DNA = REPLICATION
• DNA codes for RNA = TRANSCRIPTION
• RNA codes for protein = TRANSLATION
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)
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)
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
RNA
can be
Messenger RNA
also called
Ribosomal
RNA
which functions to
mRNA
Transfer
RNA
also called
which functions to
rRNA
Combine
with
proteins
Carry
instructions
from
to
to make up
DNA
Ribosome
Ribosomes
also called
which functions to
tRNA
Bring
amino acids to
ribosome
13.1 TRANSCRIPTION:
The process of making
mRNA from DNA
DNA
– Why do you need this
process?
• Location of DNA?
Nucleus
• Location of Ribosome?
RNA
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
– mRNA takes code from
DNA in the nucleus to
Polypeptide
the cytoplasm
U
G
A
A
G
U
U
U
Start
condon
Stop
condon
Translation
Met
Lys
Phe
13.1 Transcription produces genetic
messages in the form of mRNA
– During transcription, segments of DNA
serve as templates to produce
complementary RNA molecules.
Adenine (DNA and RNA)
Cytosine (DNA and RNA)
Guanine(DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)
RNA
polymerase
DNA
RNA
Transcription
– Transcription requires an enzyme, known as
RNA polymerase, that is similar to DNA
polymerase.
– RNA polymerase binds to DNA during transcription
and separates the DNA strands.
Adenine (DNA and RNA)
Cytosine (DNA and RNA)
Guanine(DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)
RNA
polymerase
DNA
RNA
Promoters
– RNA polymerase binds only to promoters,
regions of DNA that have specific base
sequences.
– Promoters are signals in the DNA molecule
that show RNA polymerase exactly where to
begin making RNA.
– Similar signals in DNA cause transcription to
stop when a new RNA molecule is completed.
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)
is released 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
Exon Intron
13.1 Eukaryotic
mRNA is processed
before leaving the
nucleus
– Noncoding
segments called
introns are spliced
out leaving only the
coding exons
• A 5’ cap and a
poly A tail are
added to the ends
of mRNA
• Cap and tail
protect mRNA
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
Nucleus
Cytoplasm
The Genetic Code
– Proteins are made by joining amino acids together
into long chains, called polypeptides.
– As many as 20 different amino acids are commonly
found in polypeptides.
The Genetic Code
– The specific amino acids in a polypeptide,
and the order in which they are joined,
determine the properties of different
proteins.
– The sequence of amino acids influences
the shape of the protein, which in turn
determines its function.
The Genetic Code
– RNA contains four different bases: adenine,
cytosine, guanine, and uracil.
– These bases form a “language,” or genetic code,
Each three-letter “word” in mRNA is known as a
codon.
– A codon consists of three consecutive bases that
specify a single amino acid to be added to the
polypeptide chain.
How to Read Codons
– Because there
are four different
bases in RNA,
there are 64
possible threebase codons (4 ×
4 × 4 = 64) in the
genetic code.
How to Read Codons
– Most amino acids can
be specified by more
than one codon.
– For example, six different
codons—UUA, UUG, CUU,
CUC, CUA, and CUG—
specify leucine. But only
one codon—UGG—
specifies the amino acid
tryptophan.
Start and Stop Codons
– The methionine codon
AUG serves as the
initiation, or “start,” codon
for protein synthesis.
– Following the start
codon, mRNA is read,
three bases at a time, until
it reaches one of three
different “stop” codons,
which end translation.
DNA:CCGTCATGTTCGCGCTACAAA
TGAAATGAGGCAGTACAAGCGCGA
TGTACTTTACT
mRNA:
Polypeptide:
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
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
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.