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Chapter 8
From DNA to Proteins
DNA rap
Look at the image of the mice below. Notice
anything that seems odd?
These mice have had a jellyfish gene (Green
Fluorescent protein) inserted into their DNA by way of
a virus. The virus inserted the GFP gene into the DNA
of the mice.
What is DNA?
In your own words, write down what DNA is
What is DNA?
How does it transmit genetic information?
What is the structure of DNA?
These were all questions
scientists raced to figure
out from 1923 – the 1960’s.
It was The Race for the
Double Helix
There were a number of scientist who
worked on trying to figure out what was
the genetic material in a cell.
Was it the proteins or the nucleic acids?
They worked with bacteria and viruses as
models and figured out that it was the
nucleic acids that were responsible for
passing on traits.
Therefore, the DNA is the
heredity material
Conclusion:
Nonpathogenic mice were transformed
by nucleic acid
Used S35
Used P32
Found that the
S35 stayed
outside the
cell &
P32 ended up
in the bacteria
and then in
new viruses
*
Conclusion:
DNA is the genetic material which is transmitted from one
generation to the next
Erwin Chargaff – 1950
Noticed a pattern in the
amounts of the four bases:
Adenine, Guanine, Cytosine,
and Thymine
• Found the # of
Guanine = # of
Cytosine nitrogen
bases in DNA
• The # of Thymine = #
of Adenine
• Didn’t know why though!
What else did they know?
Knew that:
• DNA was a polymer made up of repeating
units (monomers) called nucleotides
• Nucleotides are made up of:
– a 5 carbon sugar (called Deoxyribose)
– a phosphate group
– 4 different nitrogen bases P
S
4 Nitrogen Bases
•
•
•
•
Thymine (T)
Adenine (A)
Cytosine (C)
Guanine (G)
Remember that the amount
of Guanine = Cytosine
and the amount of
Thymine = Adenine
Label the diagram of the nucleotide below
Phosphate group
Nitrogen base
Deoxyribose sugar
Identify the 4 nitrogen
bases in DNA
Guanine
1. _________________
Cytosine
2. _________________
Adenine
3. _________________
Thymine
4. _________________
The Main Characters in Cracking the
Genetic Code
Maurice Wilkins
Watson & Crick
Rosalind Franklin
Putting all the evidence together
1. Rosalind Franklin worked in Maurice Wilkins’ lab.
– Purified, then crystallized DNA and then shot
X-Rays through the crystal.
– Took Photo 51 (100 hr exposure!!)
– Showed that DNA was a double helix with the
bases in a regular pattern inside the 2 twisting
strands.
2. James Watson and Francis Crick
– Model builders trying to figure
out the structure of DNA.
– Somehow, they saw
Franklin’s Photo 51
– Immediately figured out the
same thing that Franklin did
but published faster than she
did.
– DNA was a double helix
• Two twisting strands of
alternating sugars and
phosphates with the
nitrogen bases inside
– Win Nobel Prize along with
Wilkins. (Franklin dies prior to
the award).
Structure of DNA
Deoxyribonucleic acid
It is a polymer of Nucleotides (monomer)
5 carbon sugar –
deoxyribose
P
A phosphate group
S
N-base
Nucleotide
Single nucleotide
A nitrogen base
DNA is a double helix
with the sugars and
phosphate groups
alternating along the
sides rungs
The nitrogen bases are
paired together
(following the base
pairing rules)
Guanine – Cytosine
Adenine - Thymine
What holds DNA together?
• The alternating Sugars
and Phosphate groups
are held together by
covalent bonds
• The nitrogen bases are
attached to the sugar
molecules by covalent
bonds
• The bond between the
two nitrogen bases is a
weak hydrogen bond.
Covalent
bonds
S
S
S
S
S
S
S
S
Label the DNA strand
shown to your right.
1. Put a P on each of
the Phosphate groups
2. Put an S on each of
the Sugars
3. Using the base
pairing rules, fill in the
base pairs
4. Label the bond
indicated by the arrow
DNA Model Lab
You will need to cut
out and label:
24 Phosphates - P
24 Deoxyribose – S
6 Adenine – A
6 Thymine – T
6 Cytosine – C
6 Guanine - G
Need for more DNA
We have over 100 billion cells. Each cell has
exactly the same DNA in its nucleus except for
the gametes (sex cells)
DNA needs to be replicated EXACTLY each time a
new cell is produced during Interphase of
Mitosis
Watson and Crick looked at the structure of DNA
and figured out how it could make a copy of
itself
“It has not escaped our notice that the specific
pairing we have postulated immediately
suggests a possible copying mechanism for
the genetic material”.
Why would a zipper be a good analogy to
DNA?
1. DNA and a zipper
have two strands
2. The teeth of the
zipper are like the
nitrogen bases of
DNA
3. The teeth are held
together by a bond
like the Hydrogen
bonds holding the
bases together
If you wanted to make an exact copy of DNA,
how would you do it precisely and quickly?
The process of making an exact copy of DNA is
called DNA Replication
As a result of Replication, there will be two identical
strands of DNA
The two strands of DNA act as templates for the new
strands.
DNA Replication
Original DNA
strand
Hydrogen bonds
are broken
between the
bases exposing
the base
New DNA
nucleotides bind
with the exposed
bases, following
the base pairing
rules
Two identical
strands of DNA
are produced
with the old
strand on the
outside of each
new strand
How does DNA Replication occur?
1. The DNA helix needs to flatten out
– No one likes a twisted zipper
2. In order to expose the nitrogen bases, the helix
needs to be unzipped by Helicase. The hydrogen
bonds are broken, exposing the bases.
– Just like the slide on a zipper exposes the
teeth
3. An enzyme called DNA polymerase “re-zips” the
two strands by allowing free DNA nucleotides in
the nucleus to bond to the exposed bases on
both sides of the helix
The helix
is being
flattened
The hydrogen
bonds are being
broken by
Helicase
In the space below, write out the
3 steps in DNA Replication
1.
2.
3.
Animation
Glenn
Here is a song
Maybe you will like this one better
It’s your turn to Replicate DNA
Original DNA strand
C–G
A–T
T–A
G–C
C–G
C–G
T–A
T–A
A–T
G–C
DNA being replicated
C–G
A–T
T–A
G–C
C–G
C G
T-__ __-A
T-__
__-A
A-__
__-T
G-__
__-C
New DNA strands
following replication
C – __
A – __
T – __
G – __
C – __
C – __
T – __
T – __
A – __
G – __
__ – G
__ – T
__ – A
__ – C
__ – G
__ – G
__ – A
__ – A
__ – T
__ – C
Listen to the song and then explain what DNA’s real job is?
Central Dogma Song
What is DNA’s job?
Francis Crick figured out that the role of
DNA in the production of proteins.
He called this the Central Dogma.
DNA to RNA, RNA to
Proteins
The Production of Proteins is
called Protein Synthesis
Remembering back to the cell, where in a cell
does Protein Synthesis take place?
Occurs in the Ribosomes of all cells, both
prokaryotic (bacterial) and eukaryotic
Protein
Amino acid
Ribosome
mRNA
Ribosome
tRNA
Big problem with DNA and Protein Synthesis
We have always referred to DNA as the Boss
The DNA (Boss) stays in its office – the nucleus.
Only problem is that the DNA is too large to get
out of the nucleus.
DNA has the message (gene) to produce a
particular protein. Since it can’t deliver the
message itself, it needs a messenger to deliver
the message to the ribosomes.
It also can’t make the protein itself from available
amino acids in the cytoplasm so it needs some
molecule to transfer the amino acids to the
ribosomes to make the protein.
RNA
Ribonucleic acid
The other Nucleic Acid
Acts as a messenger between DNA and the
ribosomes and carries out protein synthesis by
delivering the amino acids to the ribosome
How DNA & RNA
Differ
1. RNA is single
stranded. DNA is
double stranded
2. Has Ribose sugar
instead of
Deoxyribose
3. Can be found in the
nucleus, cytoplasm or
at the ribosomes
DNA is only in the
nucleus
1. Contains Uracil in
place of Thymine so
Adenine bonds with
Uracil
Three different kinds of RNA
• Messenger RNA (mRNA)
Is produced in the nucleus
of eukaryotes and gets
DNA’s message. Then goes
to the ribosomes
• Transfer RNA (tRNA)
Found in the cytoplasm &
transfers amino acids to
the mRNA in the
ribosomes
• Ribosomal RNA (rRNA)
Makes up the ribosomes
Label the three types of RNA and tell
what each of them does
mRNA
tRNA
rRNA
Steps in Protein Synthesis
1. Transcription
DNA’s message on the gene gets “read” (in
reverse) by messenger RNA (mRNA).
– RNA polymerase enzyme will allow free RNA
nucleotides to temporarily bind to DNA
– This message on mRNA will go to the
ribosomes.
2. Translation
mRNA will attach into the ribosomes and amino
acids will be transferred in the proper order
according to the gene by transfer RNA (tRNA)
– The amino acids will string together to form a
protein (polypeptide)
Transcription
Occurs in the nucleus:
•If DNA is: ATG CCG TTA GAC CGT TGA
TAC GGC AAT CTG GCA ACT
mRNA is: AUG CCG UUA GAC CGU UGA
(Remember, U substitutes for T in RNA)
•This is called Transcription. Animation Another one
mRNA
What happens in transcription?
Translation
Process that converts an mRNA message
into a polypeptide
mRNA will now go to the ribosomes
mRNA has the reverse code for DNA’s gene.
Remember that DNA’s genes code for
proteins and proteins are made up of amino
acids
Now we must consult the Genetic Code
decoding wheel
Going off of the mRNA’s codons, we use
this to figure out which amino acid is
needed (according to DNA’s message)
Stop Codons
Try:
GGG: ____________
CAU: ____________
AUG: ____________
UUU: ____________
GAC: ____________
Start codon
UAG:____________
mRNA is:
AUG CCG UUA GAC CGU UGA
tRNA will bind with specific amino acids and
transfer them to the codon (3 bases in a
row on mRNA)
mRNA is:
AUG CCG UUA GAC CGU UGA
Amino acid: Methionine (start codon)
Proline
Leucine
Aspartic Acid
Arginine
Stop codon means to stop translation
Every 3 consecutive bases on mRNA is a codon.
CUA AAU GAU
•
tRNA with the anticodon (complimentary to
mRNA) links to mRNA. It carries a specific Amino
Acid (specified by mRNA).
If DNA reads:T A C G T C G A T T G G CAA…
mRNA:
A U G C A G C U A A CC GUU…
tRNA:
U A C G U C G A U U GG CAA…
Translation:
Amino Acids: Methionine - Glutamine – Leucine -Threonine – Valine
Please note that DNA’s code and tRNA match!!
Translation!!!!!
•
When adjacent Amino Acids link
together, they link together with a
peptide bond and form a Polypeptide
(protein).
Peptide
bonds
Growing Polypeptide
Animation
Amino
acid
Protein Synthesis
DNA
mRNA
Transcription
Translation
Protein
Protein Synthesis
• Animation Protein Synthesis - Learning
• You tube animation – really good!
• McGraw animation
• http://www.youtube.com/watch?v=41_Ne5
mS2ls – HHMI one
• Replication & Protein synthesis – song
with only typed words but good
• Does this process ever make a mistake?
• Have you ever had to copy a large amount
of information?
• What is the likelihood of you making a
mistake or more?
Changes in genetic material
Gene Mutations:
Change in the nucleotide sequence
which alters one or more genes
Chromosomal Mutations:
Change in the chromosome
structure which could alter the entire
chromosome or a portion of it.
Gene Mutations
Point Mutations – usually affect only
one amino acid
Frameshift mutations – May affect an
entire amino acid sequence.
Point mutation
• Involves a change in one or a few
nucleotides.
• Influences a single amino acid in the
polypeptide chain.
• Caused by a substitution of a Nitrogen
base.
•
•
•
•
THE FAT CAT ATE THE RAT
Take out “C” in Cat & substitute a “B”
THE FAT BAT ATE THE RAT
Does not really change the meaning to
the sentence or the protein formed
except for the bat but the rat is still gone!
• If DNA reads: A T G G T C G A T T G G CAA
• mRNA:
U A C C A G C U A AC C GUU
• Amino Acid:
Tyrosine - Glutamine – Leucine -Threonine – Valine
• But if mRNA: U A C C A G C A A AC C GUU
• The AA:
Tyrosine – Glutamine – Glutamine – Threonine – Valine
Only 1 Amino acid in the sequence was altered.
Frameshift mutation
• Involves a change in the entire protein
formed or a large portion of it.
• Caused by insertions (additions) or
deletions of Nitrogen bases.
• THE FAT CAT ATE THE RAT
• Take out “E” in THE & group into
3’s
• THF ATC ATA TET HER AT_
This makes no sense at all!!
• If DNA reads: A T G G T C G A T T G G CAA
• mRNA:
U A C C A G C U A AC C GUU
• AA:
Tyrosine - Glutamine – Leucine -Threonine –
Valine
• BUT if mRNA: U A C C A G U A A C C G U U _
• THEN Amino Acid: Tyrosine - Glutamine – STOP!!!!
• The entire sentence makes no sense. The protein formed
would be totally different
So which form of a mutation
would be more severe?
• Frameshift mutation …
since an entirely new protein would
be formed
Blame it on the DNA
CHROMOSOMAL MUTATIONS
• involve changes in number and
structure of the chromosomes.
• Could change location of genes on the
chromosomes or the number of copies
of some of the genes.
• Deletions – part of a chromosome is missing
• Duplications – Extra copies of genes are
inserted
• Inversions – Reverse direction of parts of the
chromosome
Translocations
Parts of one non-homologous chromosome
breaks off and attached onto another nonhomologous chromosome
5. tRNA carries
___________________ to the
mRNA in the
______________________
6. tRNA complementing mRNA at
the ribosome occurs during
(transcription/translation).
7. The codon is made up of 3
nitrogenous bases on _______
while the anticodon is on the
______
8. The bond that connects the
amino acids together to form the
polypeptide is a ___________
bond.