Download DNA Synthesis aka DNA Replication

DNA
Structure &
Function
Watson, Crick, and Franklin’s
crystallography image
Some important vocabulary
1.
2.
3.
4.
5.
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10.
11.
12.
DNA
Gene
Chromatin
Chromatid
Chromosome
Protein
Replication
Transcription
Translation
Dogma
Phosphodiester-bond
Hydrogen bonds
DNA
•Deoxyribonucleic acid
What is DNA?
• DNA is the code for
making of proteins used
for structure and
function (enzymes).
The Central Dogma
“the fully accepted thoughts or
ideas”
DNA
Transcription
→
mRNA
Translation
→
Protein
→
Trait
What is the “central dogma?”
• Dogmatic ideas are those that govern
irrefutably. (No one argues with it)
• In biology, the central dogma is that DNA
carries the code necessary to build life and
the components needed for life
How did scientists know that DNA
carries the information for life?
• Many thought that proteins instead of DNA
were inherited from parent to offspring.
• Scientists (Griffith, Hershey and Chase,
Chargaff, etc) showed that DNA actually
carries the blueprint.
Hershey and Chase’s experiment
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
Griffith’s experiment
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)
Griffith’s Experiment
S strain – deadly
R strain – harmless
S strain (heated) – harmless
S strain (heated) + R strain – deadly
Transformation – when one bacteria
takes up genetic information of
another bacteria, changing it’s
phenotype
Deoxyribonucleic Acid
• Nucleotides
– Building block of DNA
After determining the connection between
DNA and genetics, figuring out the structure
of DNA became important.
Purines
Adenine
Guanine
Phosphate
group
Pyrimidines
Cytosine
Thymine
Deoxyribose
• Each strand
of DNA is
made of
repeating
nucleotide
units.
• A nucleotide
is either a
purine or a
pyrimidine.
Phosphate
Phosphate
C
G
Deoxyribose
Deoxyribose
Guanine Nucleotide
Cytosine Nucleotide
The 4 DNA Nucleotides
Phosphate
Phosphate
T
A
Deoxyribose
Deoxyribose
Adenine Nucleotide
Thymine Nucleotide
Nitrogenous Bases
• Purines:
– Adenine
– Guanine
• Pyrimidines:
– Thymine
– Cytosine
• Antiparallel
structure:
• 5’(phosphate) to
3’(sugar)
DNA: the genetic basis of life
• Do you notice any commonalities in the
percentages of adenine, thymine, guanine,
and cytosine? Between species?
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
Base Pairing
• Chargoff’s
Base-pairing
rule:
– Adenine
always bonds
with Thymine
– Guanine
always bonds
with Cytosine
Hydrogen Bonds
• Three between G & C
• Two between A & T
Nitrogen(ous) bases pair up
1. Adenine pairs with Thymine
A
T
2. Guanine pairs with Cytosine
G
C
Rosalind Elsie Franklin
(25 July 1920 – 16 April 1958)
Rosalind Elsie Franklin
(25 July 1920 – 16 April 1958)
Franklin is best known for her work on the X-ray
diffraction images of DNA which led to discovery
of DNA double helix.
Her data, according to Francis Crick, was "the
data we actually used to formulate Crick and
Watson's 1953 hypothesis regarding the
structure of DNA.
Rosalind Elsie Franklin
(25 July 1920 – 16 April 1958)
Franklin's X-ray image, confirming the helical structure of
DNA, was shown to Watson without her approval or
knowledge.
Though this image and her accurate interpretation of the
data provided valuable insight into the DNA structure,
Franklin's scientific contributions to the discovery of the
double helix are often overlooked.
Watson and Crick won the Nobel Prize in
1962 for figuring out the DNA is actually 2
strands twisted together,
called a double helix.
Nucleotide
Hydrogen
bonds
Sugar-phosphate
backbone
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
Phosphodiester bonds
create the backbone (side rails)
of DNA
Phosphodiester bond
• Phosphodiester bonds make up the
sugar/phosphate backbone of the strands
of DNA.
• (Pre AP) In DNA and RNA, the
phosphodiester bond is the linkage
between the 3' carbon atom and the 5'
carbon of the sugar ribose
Double helix structure
DNA Structure
• Remember: Nucleic acid is the polymer
that is made up of monomers called
NUCLEOTIDES
Bacterial DNA
• Prokaryotic DNA is a single loop of
genetic material.
Chromosome
E. coli bacterium
Bases on the chromosome
Eukaryotic DNA
• Eukaryotic DNA is in the form of linear
chromosomes.
Chromosome
Nucleosome
DNA
double
helix
Coils
Supercoils
Histones
Why do cells divide/replicate?
• Cells replicate for
– Growth
– Replacement
– Repair
–GRR!!!!!
Before DNA replication
begins…
• Chromosomes must be “unwound” back to
chromatin through the removing of
histone proteins.
What is Replication
• DNA replication is the process of creating
new IDENTICAL strands of DNA.
• Replication happens before a cell begins
cell division.
Replication
When does DNA replication
take place?
• Replication happens in the S stage of
interphase in the cell cycle
• “S” stands for synthesis (to make) of DNA
• During the S stage, DNA is not only copied
it is also repaired if the cell finds
something wrong
What does replication do?
• DNA replication creates identical copies of DNA by
using one strand as a template.
• The original strand is used as a template along with
“Chargoff’s rules” to base pair up the
complementary strand
Replication Example
• Original DNA: T A C G C C A T T A G C
• Using Chargoff’s rules A pairs with T AND
G pairs with C, so…
•
Original DNA: T A C G C C A T T A G C
• Complementary DNA: A T G C G G T A A T C G
Semiconservative
• Because each new strand of DNA has ½
of the original DNA, its called
SEMICONSERVATIVE
DNA synthesis overview
A
B
C
D
Enzymes for DNA replication
•
•
•
•
•
Helicase
Single stranded binding protein
Topoisomerase
DNA polymerase
Ligase
DNA Replication
1. Replication fork made when Helicase separates parent strands
Helicase “unzips” the two sides
2. DNA polymerase links new nucleotides to the growing strand (only
on the 3’ end)
3. Leading strand made as single polymer
4. Lagging strand is produced in a series of short fragments (Okazaki
fragments)
5. Ligase joins Okazaki fragments
Helicase
• Breaks hydrogen bonds between
nitrogen bases of nucleotides
• Opens double helix starting at origin of
replication
Helicase
Topoisomerase & SSBP
• SSBP (single stranded binding proteins):
stabilize open helix because DNA is stable
when double-stranded
• Topoisomerase: helps to relieve the
tension created when helicase creates
“replication bubble”
Topoisomerase and SSBP
Topoisomerase
SSBP
Topoisomerase
SSBP
DNA polymerase
• Builds DNA polymer according to
Chargaff’s base pairing rules
• A–T
• C–G
• DNA polymerase also “edits” to check for
mistakes in the DNA.
DNA polymerase
• Polymerase can ONLY add onto the 3’
end with they –OH group.
• DNA can not be created by adding to the
5’ end that has the –(phosphate group)
DNA polymerase
Leading strand
C
G A T T A C A - 3’
T
T A A T G T - 5’
T
Lagging strand
A
5’ – A A A T T C G T
3’ – T T T A A G C A A
T
A C G
G
C T A A T G T - 5’
DNA replication in 5’ to 3’ direction
New strand
Original
strand
DNA
polymerase
Growth
DNA
polymerase
Growth
Replication
fork
Replication
fork
New strand
Original
strand
Leading vs. Lagging strands
• Leading strand: made continuously
• Lagging strand: made in fragments (called
Okazaki fragments)
Ligase
• Connects the pieces of Okazaki fragments
together
Why do we need DNA?
• DNA is the code for the
making of proteins used for
structure &
function(enzymes).
What is a Gene
• A gene is a sequence of nitrogenous
bases (segment of DNA) that code for a
trait.
• The gene is
stored in the
sequence of
bases
GENE