Transcript DNA to Protein

Molecular Basis of
Genetics and
Biotechnology
The central dogma of molecular biology describes the flow of genetic
information from DNARNAprotein. This flow happens through
precise mechanisms, although mistake can happen during the process.
Many technologies take advantage of the properties of DNA to generate
novel products and tools.
Each group will be given a different
experiment or insight that led to the structure
and function of DNA.
 Griffith experiment (2 groups) (190-191)
 Avery experiment (191, additional handout)
 Hershey-Chase experiment (2 groups) (192-193)
 Chargaff ’s observation, structure of the 4 bases
(195, 196)
 Wilkins and Franklin’s X-ray diffraction (196)
 Watson and Crick’s DNA model and pairing
between bases (196-197)
Griffith experiment
Avery experiment
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Repeated Griffith experiment to see which
molecule actually transformed into the harmless
strain
Treated extract of heat killed smooth colonies
with enzymes that broke down everything
except for DNA. What happened?
Did same with enzyme that broke down DNA.
What happened?
Hershey-Chase experiment
Watson and Crick Model
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What did they know: DNA was a molecule involved in genetic
information
What did they not know: The structure of the molecule
What evidence did they use?
 X-Ray diffraction: Scattered pattern of DNA X-rays on film
produced by Rosalind Franklin (showed coiled strand and
angle of stands) DNA
A
T
G
C
source
 Chargaff ’s rule
Streptoc
occus
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
Reading quiz – Read through WB 34. I will stamp
SG 1 for full credit today only. I will also stamp SG
3 on Thursday for full credit (if not done)
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What is the basic unit (monomer) of a nucleic
acid?
What are the 3 subunits of a nucleotide. Draw
them.
Which of these subunits are the same in all
nucleic acids?
What are the 4 bases of DNA?
What is the function of DNA, can it leave the
nucleus?
Analysis question 2
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Draw a labeled diagram of your DNA molecule.
Keep the illustration in a straight “ladder” form
as seen in figure 5. Do not attempt to draw the
helical shape. Identify each nitrogen base.
Do this on the back of WB 34
Structure of DNA
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Double stranded helix
Deoxyribose sugar
Phosphate group
4 nitrogen bases
Guanine : Cytosine
 Adenine : Thymine
 Hydrogen bonds connect bases
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DNA replication
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Each strand is complementary
Replication steps
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DNA Helicase (enzyme) “unzips”
the DNA strand, breaking the
hydrogen bonds
DNA polymerase adds
complementary bases to each strand
(5’ to 3’)
Sugar phosphate links extend the
chain and DNA polymerase “proof
reads” new strand
DNA ligase seals fragements
together
Reading quiz
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Person closest to the
molecular modeling kit
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Read through WB 35
Rebuild your double helix
exactly as it was on
Monday/Tuesday. (You
can use your instructions).
Make sure you have the
correct base sequence and
base pairing. THIS IS
YOUR READING
QUIZ!
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Everyone else at the
table
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Read through WB 35 and
define the following
terms.
1. Anticodon
2. Codon
3. Nucleotide
4. Ribosome
5. Transcription
Reading quiz answers
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DNA model
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Check with model up front
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1. Anticodon: 3 nucleotides on a
tRNA complementary to the codon
2. Codon: 3 nucleotides of an
mRNA that codes for an amino acid
3. Nucleotide: Monomer of a
nucleic acid consisting of a sugar,
base, and phosphate
4. Ribosome: Organelle which is the
site of protein synthesis
5. Transcription: Process of
producing an mRNA molecule from
a DNA strand
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Complete letters C-F using the DNA molecule
just made
Answer these questions on the back of WB 35
(yep, we’re conserving paper)
3. A partial DNA stand has the following sequence:
CACTTGCAC. What would be the complementary
mRNA sequence
 4. How can protein be synthesized in the cytoplasm
of a cell when DNA is contained in the nucleus?
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Structure of RNA
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Can leave the nucleus
Single stranded
Ribose sugar
Phosphate group
4 nitrogen bases
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Guanine : Cytosine
Adenine : Uracil
Transcription
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The process of copying
part of a DNA strand
into a complementary
RNA strand, so the
information can be taken
outside of the nucleus
without affecting the
DNA molecule
Reading quiz. Use study guide and WB 34-35.
Staple exam to back of test corrections and turn in.
 Complete the following chart
Nucleic
Acid
DNA
mRNA
tRNA
Actual Shape Location Function during
Name
in the cell protein synthesis
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Complete letter G
Answer the following questions on the back of WB 36
5. You have the following mRNA sequence
GUGAACGUG. What would be the anticodon
base sequence on the corresponding tRNAs? Circle
each codon and anticodon.
6. Using a venn diagram, compare and contrast codons
to anticodons (structure? Function? Location?)
Genetic code
Genetic code
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Has a four letter alphabet
There are 20 different amino
acids (protein building blocks)
How many letters codes for
each amino acid?
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Codon: 3 letter combination of
mRNA strand
English code
tRNA
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Anticodon (complementary to mRNA)
Attached amino acid
Codon:
AAA, then
anticodon
is ____
Reading quiz
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Left table of your group.
Put together the mRNA
molecule produced in
letter F (hint, look at the
diagram on WB 40 and
think about which sugar
to use)
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Right table of your
group. Put together the
tRNA molecules
produced in letter G.
Add appropriate amino
acid (black) to each
tRNA
Translation
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Goal of genetic code is to produce a protein.
How does this happen?
1) Transcription produces mRNA strand
2) mRNA binds with ribosome
3) tRNA anticodon binds with mRNA
4) Amino acids attached to tRNA bond together
Hookin’ up amino acids
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mRNA and first tRNA bind to ribosome (but
not each other yet). This is always the anti
codon UAC (amino acid – methionine)
Ribosome scans mRNA and keeps first codon
sequence (AUG) at the P site. Anticodon
hydrogen bonds with 1st codon
Anticodon complementary to the 2nd codon
hydrogen bonds to it at the A site.
Amino acid of 1st tRNA detaches and forms
peptide bonds with amino acid of 2nd tRNA
mRNA and 2nd tRNA move to the left as the
1st tRNA leaves ribosome
When a “stop codon” is reached polypeptide
chain leaves, other parts dissemble
Polypeptide may be modified (where?) before
it is a functional protein
Write response in notebook
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Use the genetic code (on your desk) to find the
amino acid sequence coded by the mRNA
sequence AUGAAGUUU
Use the genetic code (on your desk) to find the
amino acid sequence coded by the DNA
sequence TATCATGCC
Mutations
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Point
Frameshift
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THE CAT ATE THE RAT
THC ATA TET HER AT
Mutations constantly happen
(about 1 in every 1000 bases) and
are important for variation Severity
depends on location and number
of mutations
Chromosomal mutations
Gene regulation
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All cells in an organism have the same genes
Do all cells look the same and do the same job?
Why?
How is this possible?