Download DNA Notes

Students will explain classical
genetics at the molecular level
• Summarize the historical discovery of the
DNA molecular structure by Franklin,
Watson and Crick
• Describe how genetic information is
contained in the sequence of bases in DNA
• Describe DNA replication
Some History
• 1928
– Frederick Griffith (British)
– Studied Streptococcus Pneumoniae
• pneumonia bacteria
• two genetic strains
• Colonies appeared smooth (S type)
– Surrounded by a mucous coat or capsule
• Colonies that appeared rough (R type)
• In 1928, Frederick Griffith performed an
experiment using pneumonia bacteria and mice.
This was one of the first experiments that hinted
that DNA was the genetic code material.
• He used two strains of Streptococcus pneumoniae:
– a “smooth” strain which has a polysaccharide coating
around it that makes it look smooth when viewed with a
microscope,
– a “rough” strain which doesn’t have the coating, thus
looks rough under the microscope.
– When he injected live S strain into mice, the mice
contracted pneumonia and died.
– When he injected live R strain, a strain which typically
does not cause illness, into mice, as predicted they did
not get sick, but lived.
• Thinking that perhaps the polysaccharide coating
on the bacteria somehow caused the illness and
knowing that polysaccharides are not affected by
heat, Griffith then used heat to kill some of the S
strain bacteria and injected those dead bacteria
into mice.
– This failed to infect/kill the mice, indicating that the
polysaccharide coating was not what caused the
disease, but rather, something within the living cell.
– Since Griffith had used heat to kill the bacteria and heat
denatures protein, he next hypothesized that perhaps
some protein within the living cells, that was denatured
by the heat, caused the disease.
• He then injected another group of mice with
a mixture of heat-killed S and live R, and
the mice died!
– When he did a necropsy on the dead mice, he
isolated live S strain bacteria from the corpses.
• Griffith concluded that the live R strain
bacteria must have absorbed genetic
material from the dead S strain bacteria, and
since heat denatures protein, the protein in
the bacterial chromosomes was not the
genetic material.
• This evidence pointed to DNA as being the
genetic material.
Functions of DNA
• Controls cellular activities of
an organism by
1. Coding for structural proteins
2. Coding for enzymes
Nucleic Acids
• DNA
–
–
–
–
Deoxyribonucleic Acid
Genetic material
Can self-replicate
Made up of Nucleotides
• Shape = double helix
– A twisted rope ladder
– A full twist every 10 nucleotides
DNA Discovery
• Rosalind Franklin was using X-Ray
Diffraction to study DNA
• Her work allowed Watson and Crick to
come up with model of DNA
• Findings presented in 1953
• Visually confirmed in 1969
Nucleotides
•
Nucleotides are composed of
–
A sugar
•
•
–
A phosphate
•
–
five carbons
Deoxyribose
PO4-
One of 4 nitrogen bases
1.
2.
3.
4.
Adenine
Thymine
Cytosine
Guanine
[A]
[T]
[C]
[G]
The sugarphosphate
groups are the
side rails of
ladder and the
the nitrogen
bases are the
rungs
Nucleotides
•
The two strands of DNA are complimentary
because the nitrogen bases bond with each
other according to some rules.
1. Adenine will only bond with Thymine
2. Guanine will only bond with Cytosine
•
•
Nitrogen bases bond via hydrogen bonds.
These break over 70oC (denature)
DNA REPLICATION
• DNA must have the ability to
create an exact duplicate of itself
• The sequence in one strand
determines precisely what the
sequence of nucleotides in the
other strand will be. (A-T, G-C)
DNA REPLICATION
1. The hydrogen bonds holding the two
complimentary strands together break
2. DNA strands separate
3. Free floating complimentary nucleotides
match up with nucleotides on the parent
DNA strand.
–
Catalyzed by DNA polymerase
4. New, semi-conservative strands are
formed
DNA REPLICATION
• Semi-conservative
– The daughter strands are made up of one half
old strand on one half new strand
• The DNA unzips due to the hydrogen bonds
between the bases being broken (DNA
Helicase)
• These exposed bases attract free floating
bases, which are attached to the chain by
DNA polymerase.
Students will explain classical
genetics at the molecular level
• Describe RNA transcription
• Describe how genetic information is
translated into amino acid chains in proteins
• Explain how mutations result in
abnormalities or create genetic variability
• Explain how base sequences in nucleic
acids give evidence for evolution
DNA vs RNA
DNA
RNA
DNA vs RNA
DNA
• Double stranded
RNA
DNA vs RNA
DNA
• Double stranded
RNA
• Single stranded
DNA vs RNA
DNA
• Double stranded
• Deoxyribose sugar
RNA
• Single stranded
DNA vs RNA
DNA
• Double stranded
• Deoxyribose sugar
RNA
• Single stranded
• Ribose sugar
DNA vs RNA
DNA
• Double stranded
• Deoxyribose sugar
• Nitrogen bases
– Cytosine
RNA
• Single stranded
• Ribose sugar
DNA vs RNA
DNA
• Double stranded
• Deoxyribose sugar
• Nitrogen bases
– Cytosine
– Guanine
RNA
• Single stranded
• Ribose sugar
DNA vs RNA
DNA
• Double stranded
• Deoxyribose sugar
• Nitrogen bases
– Cytosine
– Guanine
– Adenine
RNA
• Single stranded
• Ribose sugar
DNA vs RNA
DNA
• Double stranded
• Deoxyribose sugar
• Nitrogen bases
–
–
–
–
Cytosine
Guanine
Adenine
Thymine
RNA
• Single stranded
• Ribose sugar
DNA vs RNA
DNA
• Double stranded
• Deoxyribose sugar
• Nitrogen bases
–
–
–
–
Cytosine
Guanine
Adenine
Thymine
RNA
• Single stranded
• Ribose sugar
• Nitrogen bases
– Cytosine
DNA vs RNA
DNA
• Double stranded
• Deoxyribose sugar
• Nitrogen bases
–
–
–
–
Cytosine
Guanine
Adenine
Thymine
RNA
• Single stranded
• Ribose sugar
• Nitrogen bases
– Cytosine
– Guanine
DNA vs RNA
DNA
• Double stranded
• Deoxyribose sugar
• Nitrogen bases
–
–
–
–
Cytosine
Guanine
Adenine
Thymine
RNA
• Single stranded
• Ribose sugar
• Nitrogen bases
– Cytosine
– Guanine
– Adenine
DNA vs RNA
DNA
• Double stranded
• Deoxyribose sugar
• Nitrogen bases
–
–
–
–
Cytosine
Guanine
Adenine
Thymine
RNA
• Single stranded
• Ribose sugar
• Nitrogen bases
–
–
–
–
Cytosine
Guanine
Adenine
Uracil [U]
DNA vs RNA
DNA
• One type of DNA
RNA
DNA vs RNA
DNA
• One type of DNA
RNA
• Many types of RNA
DNA vs RNA
DNA
• One type of DNA
RNA
• Many types of RNA
– Messenger RNA (mRNA)
DNA vs RNA
DNA
• One type of DNA
RNA
• Many types of RNA
– Messenger RNA (mRNA)
– Transfer RNA (tRNA)
DNA vs RNA
DNA
• One type of DNA
RNA
• Many types of RNA
– Messenger RNA (mRNA)
– Transfer RNA (tRNA)
– Ribosomal RNA (rRNA)
DNA vs RNA
DNA
• One type of DNA
RNA
• Many types of RNA
–
–
–
–
Messenger RNA (mRNA)
Transfer RNA (tRNA)
Ribosomal RNA (rRNA)
Small nuclear RNA (smRNA)
DNA vs RNA
DNA
• One type of DNA
• Mostly in nucleus
RNA
• Many types of RNA
–
–
–
–
Messenger RNA (mRNA)
Transfer RNA (tRNA)
Ribosomal RNA (rRNA)
Small nuclear RNA (smRNA)
DNA vs RNA
DNA
• One type of DNA
• Mostly in nucleus
RNA
• Many types of RNA
–
–
–
–
Messenger RNA (mRNA)
Transfer RNA (tRNA)
Ribosomal RNA (rRNA)
Small nuclear RNA (smRNA)
• Mostly found in cytoplasm
DNA vs RNA
DNA
• One type of DNA
RNA
• Many types of RNA
–
–
–
–
Messenger RNA (mRNA)
Transfer RNA (tRNA)
Ribosomal RNA (rRNA)
Small nuclear RNA (smRNA)
• Mostly in nucleus
• Mostly found in cytoplasm
• Can self-replicate under
the right conditions
DNA vs RNA
DNA
• One type of DNA
RNA
• Many types of RNA
–
–
–
–
Messenger RNA (mRNA)
Transfer RNA (tRNA)
Ribosomal RNA (rRNA)
Small nuclear RNA (smRNA)
• Mostly in nucleus
• Mostly found in cytoplasm
• Can self-replicate under
• Cannot self-replicate
the right conditions
Genes and Proteins
• A gene is a segment of DNA
–Carries the information of the
synthesis of a protein
• One gene codes for one
protein
Proteins in the Body
•
•
•
•
•
•
•
Enzymes
Hormones
Antibodies
Hemoglobin
Cell membranes
Receptor molecules
Carrier molecules
Composition of Proteins
• Made up of 20 different amino acids
• Sequence of a.a.’s identifies protein
• Sequence of bases in DNA determines Sequence of
a.a.’s
• One gene = one protein
• Protein Synthesis relies on 3 types of RNA
– rRNA
– mRNA
– tRNA
Types of RNA
• Ribosomal RNA (rRNA)
– Makes up the ribosomes
• Messenger RNA (mRNA)
tRNA & rRNA
- In cytoplasm only
mRNA
in cytoplasm & nucleus
– Involved in transcription (first stage of protein synthesis)
– Carries message from DNA in nucleus to ribosome in
cytoplasm
• Transfer RNA (tRNA)
– carries amino acids to mRNA
All RNA
produced in
nucleolus.
Protein Synthesis
• Occurs primarily in ribosomes
• Instructions for protein contained in DNA
• Message must get from nucleus to cytoplasm
(DNA to ribosome)
• Process occurs in 2 steps
– watch animations – click on the words below
1. Transcription
2. Translation
Protein Synthesis Summary
1.
2.
3.
4.
5.
6.
7.
8.
mRNA is made using DNA template
mRNA exits nucleus
Transcription
tRNA picks up aa’s
tRNA anticodon bonds to mRNA codon
Peptide bond forms between aa’s
Protein used by cell or packaged & exported
mRNA breaks into free nucleotides
tRNA’s free to pick up more aa’s
Translation
Transcription
• In nucleus
• mRNA made using DNA as a template
• If the DNA base sequence is
A A T T C C G G A (3 triplets)
• The mRNA molecule manufactured would be
U U A A G G C C U (3 triplets)
• Each triplet is a codon
Code must be transcribed then translated
Transcription
DNA used as template
to build mRNA
mRNA
built
using
DNA
as a
template
Codons
• Code for amino acids
• May code for start (initiator codon)
• May code for stop (terminator codon)
• AUG is an initiator codon but also codes for the
amino acid methioine
• If code AUG is in middle it must code for
methionine
Data table of mRNA codons
supplied in diploma!!
Can be used to work out
DNA, tRNA or
amino acid sequence
Translation
• mRNA arrives at ribosome
• tRNA molecules with a.a.’s are
attracted to this mRNA
– complimentary rule (A attracts U
etc….)
• 20 a.a.’s therefore
– 20 different tRNA’s
Translation
mRNA U U A
A G G
C C U
3 codons
Translation
mRNA U U A A G G C C U
tRNA A A U U C C G G A
3 anticodons
Transfer RNA
Translation Initiation
Identify codons and anticodons
Identify peptide bonds, ribosome & protein
Translation 1
Translation 2
Translation 3
Translation 4
Translation 5
Name the products!
Translation
Requires many Ribosomes
The golgi apparatus will package the protein to
be used for different functions throughout the
body.
Review Questions
•
•
•
•
•
•
•
•
mRNA codon for AAT DNA triplet =
DNA triplet for CCG mRNA codon =
tRNA anticodon for GCA DNA triplet =
mRNA codon for GAU tRNA =
tRNA anticodon for UUA mRNA codon =
DNA triplet for CUA anticodon =
codon for UAG anticodon =
anticodon for CTA DNA triplet =
Answers to Review Questions
•
•
•
•
•
•
•
•
mRNA codon for AAT DNA triplet = UUA
DNA triplet for CCG mRNA codon = GGC
tRNA anticodon for GCA DNA triplet = GCA
mRNA codon for GAU tRNA = CUA
tRNA anticodon for UUA mRNA codon = AAU
DNA triplet for CUA anticodon = CTA
codon for UAG anticodon = AUC
anticodon for CTA DNA triplet = CUA
Mutations
• Changes in the sequence of bases in DNA
• Caused by mutagenic substances like
–
–
–
–
X-rays
cosmic rays
UV light
Some chemicals
• Mutagens can affect a single point in the DNA or
it can affect large sections.
• Result = the proteins that the DNA codes for will
be altered.
Mutations
•
3 types of mutations.
1. INSERTION
– An extra nucleotide is inserted into the DNA
– Causes a frame shift
2. DELETION
–
–
A nucleotide is deleted from the DNA
Causes a frame shift
3. SUBSTITUTION
–
One nucleotide is substituted for another
Using DNA to explain Evolution
• Species that are closely related will share
very similar DNA sequences
• Scientists use mitochondrial DNA
(mtDNA) to study the relationship between
species
• Used to explain variety of ethnic groups
found throughout the world (all from
African descendents)
Using SINEs and LINEs
• SINEs and LINEs are repeated DNA
sequences that don’t code for anything, but
show an evolutionary relationship
• Finding a SINE or LINE in two species and
not in other species, signifies that the first
two species must be more closely related to
each other than to the other species
Students will explain classical
genetics at the molecular level
• Explain DNA transformation
– (recombinant DNA)
• Describe the role of restriction enzymes and
ligases in transformation
Genetic Engineering
• A desired gene can be isolated and millions
of copies made
• These copies can then be analyzed to
determine the gene’s nucleotide sequence
• This nucleotide sequence can be decoded to
find the sequence of amino acids in the
corresponding protein
Genetic Engineering
• Functioning genes can be transferred into cells
or bacteria, yeasts, plants, animals
– i.e. 1928 – Griffith
• DNA can be “made to order” using “gene
machines” that can be programmed to produce
short strands of DNA in any desired sequence
– Useful for studying DNA,
– protein synthesis experiments
• Change genetic code to eliminate particular amino acids
from a protein
• Find how the amino acid affects the protein’s function
Transformation
• Transformation is the process whereby
one strain of a bacterium absorbs genetic
material from another strain of bacteria and
“turns into” the type of bacterium whose
genetic material it absorbed. Because DNA
was so poorly understood, scientists
remained skeptical up through the 1940s.
Genetic Engineering
Recombinant DNA
• To recombine DNA
–A technique to determine gene
expression
–Gene segments from different
sources are recombined in vitro
and transferred into cells (usually
E. coli) to see what happens.
Genetic
Genetic Engineering
Engineering
Recombinant
Recombinant DNA
DNA
• First successful GE experiment with
human DNA took place in 1980
– Human gene which codes for the
protein interferon was successfully
introduced into a bacteria cell…
• The bacteria produced human protein.
– Interferon combats viral infections and
may help in fighting cancer
Genetic Engineering
Recombinant
Recombinant
DNA – How
DNAIt Works
1. The desired gene is isolated and cut out
of the DNA
• A “restriction enzyme” (restriction
endonuclease) does this
2. Isolated gene is inserted into a bacterial
plasmid using a ligase
• Ligase is an enzyme which normally
repairs breaks in the DNA backbone
• New DNA now called recombinant DNA
Genetic
GeneticEngineering
Engineering
Recombinant
RecombinantDNA
DNA
3. The plasmid is absorbed by a bacterium
• Reproduces asexually to produce many
clones containing the recombinant DNA
4. Bacterial cells produce the protein
coded by the foreign gene
• Desired protein can be isolated and
purified from the culture.
Genetic
GeneticEngineering
Engineering
Recombinant
RecombinantDNA
DNA
•
Examples of recombinant DNA
technology…
• Interferon
• Human growth hormone
• Human insulin
• Gene Therapy
• Agriculture…
Restriction
Enzymes cut
Ligase
acts as glue
rDNA
Recombinant DNA Technology
Restriction Enzyme
Sticky end
Gene insertion
Genetic
GeneticEngineering
Engineering
Recombinant
RecombinantDNA
DNA
•
Gene Therapy
–
Replacement of defective genes with normal
healthy genes
•
e.g. Cystic fibrosis, hemophilia, sickle-cell anemia,
immune-deficiencies
•
OBSTACLES today include …
– How to fit genes into the body cells
– How to control the introduced genes
Genetic Engineering
Recombinant DNA
• Agriculture
– Introduction of genes for resistance to
disease, drought, frost, increased
protein production, larger fruit…
Genetic Engineering
DNA Fingerprinting
•
Used in forensic studies…
•
Small quantities of blood, semen, or other tissue
can be tested for the DNA base sequence
•
The DNA nucleotide sequence is unique for every
individual (except identical twins)
•
A technology called RFLP auto-radiography is used
to display selected DNA fragments as bands
Genetic Engineering
DNA Fingerprinting
•
Radioactive probes mark the bands that
contain certain markers…
–
Only 5 or 10 regions of the entire genetic content
of the cell are tested
•
•
This was a defense argument used by the O.J.
Simpson lawyers
The probability of having matching DNA
fingerprints is about 1 in a million.