Download Chapter 12: DNA & RNA

Chapter 12: DNA & RNA
What do you already know about
DNA?
DNA Clearly Stated
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
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 chain 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 an 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 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
• Shadow Labs Transcription/Translation
RNA nucleotides
RNA
polymerase
T C C A A
T
A U C C A
T A G G T T
Direction of
transcription
Newly made RNA
A
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
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 (shown below)
Amino acid
attachment site
Amino acid attachment site
Hydrogen bond
RNA polynucleotide chain
Anticodon
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
• A tRNA with a complementary anticodon pairs with each
codon, adding its amino acid to the peptide chain
tRNA-binding sites
Large
subunit
Next amino acid
to be added to
polypeptide
Growing
polypeptide
tRNA
mRNAbinding site
Small
subunit
mRNA
Codons
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