Download Is DNA the Genetic Material?

Is DNA the Genetic Material?
The T2
virus’s
protein coat staysviruses
on the outside
the host cell.
Using
bacteria-killing
as aofmodel
Virus protein coat
New virus
particles
Nucleic Acids are the Genetic Material.
Only T2 DNA, and not the proteins,
enters a cell and directs replication
Virus protein coat
Virus genes
Host cell
1. Start of infection.
2. Virus genes direct
3. End of infection.
Virus genes
enter
ONLY
VIRAL GENESthe
ENTER
A CELL THAT
IS BEINGNew
INFECTED.
production
of new
generation of
host cell. Protein
virus particles.
virus particles bursts
coat does not.
from host cell.
Thursday January 19st, 2017
Class 11 Learning Goals
Translation
•  After this class, you should be able to:
–  Label each molecule and strand (and give correct
polarity for each nucleic acid and amino acid polymer)
in a diagram of protein translation
–  Predict and give a rationale for the effect of a loss-offunction mutation in any component of the ribosome
–  Compare or contrast the three phases of translation
(initiation, elongation, termination) in terms of enzymes
and substrates
Peer Instruction
An ‘adapter molecule’ is needed to hold amino acids
and interact with mRNA codons.
Amino
acids
Adapter
molecules
mRNA
Codon
Codon
Codon
Codon
Why didn’t transcription require an adapter molecule?
How many total adapter molecules are needed?
Because NTPs and dNTPs can directly forms base-pairs
Peer Instruction
1) What are the important parts of a Transfer RNA (tRNA)?
Binding site for the amino acid
3ʹ
5ʹ
3ʹ
5ʹ
3ʹ
mRNA
5ʹ
5ʹ
mRNA
3ʹ
2) How is a tRNA “charged”?
The machine that does translation: The Ribosome
tRNA in A site
(red)
Ribbon model of ribosome during translation
tRNA in E site
(blue)
tRNA in P site
(green)
Large
subunit
Small
subunit
Ribosomes catalyze peptide bond formation
Today’s Translation Exercise
•  Work through the exercise together.
•  Be ready for clicker questions as we go.
Clicker Question #1
8b) Which is the best definition for the
anticodon?
1.  The three bases of the tRNA that bind to the
codon in the mRNA
2.  The three bases of mRNA that bind to the
codon in the tRNA
3.  Any three bases in the mRNA
4.  Any three bases in the tRNA
5.  None of these
Clicker Question #2
10) In which direction must the ribosome
translocate along the mRNA?
1.  5’ to 3’
2.  3’ to 5’
3.  Either direction,
depending on the
promoter on the RNA
Clicker Question #3
~11) What is the best characterization of the RBS?
1.  A strong binding site that helps to start translation
2.  A strong binding site that helps to end translation
3.  A weak binding site that helps to start translation
4.  A weak binding site that helps to end translation
Clicker Question #3
~11) In the schematic in Model 2, what is the
next codon that will be read by the ribosome?
1.  5’AUG3’
2.  5’AGC3’
3.  5’GAA3’
4.  5’CGU3’
Clicker Question #4
13C) What establishes the ‘frame’ of the triplet
codons for translation?
1. 
2. 
3. 
4. 
5. 
The primary sequence of the codons
The location of the start codon
The secondary sequence of the codons
The distance from the +1 site
The RBS
Clicker Question #8
21. In Model 4, a covalent bond is broken.!
What did that covalent bond hold together?
1. 
2. 
3. 
4. 
5. 
6. 
Two tRNAs
Two amino acids
An amino acid and a tRNA
DNA and RNA
Two parts of the ribosome
A ribosomal subunit and an amino acid
Clicker Question #9
Post-Model 4) Which of these is necessary for
all three phases of translation?
1.  f-Met tRNA
2.  mRNA
3.  ribosome
4.  release factor
5.  anticodon
Clicker Question #6
Hypothetically, which of the following molecules
could work as a replacement for tRNA?
1)  A protein that can bind to the major groove of DNA
and a specific amino acid.
2)  A carbohydrate that can recognize a short RNA
sequence and bind to a particular amino acid.
3)  A lipid that can basepair with RNA and will bind to
any amino acid.
4)  An ATP molecule can has been modified to bind
only Leucine and will bind to the ribosome
Clicker Question #7
What would happen if all the tRNAs in a cell
with anticodons for lysine carried glycine
amino acids instead of lysine amino acids?
Translation would:
1.  Still occur but the protein would contain glycines
instead of lysines
2.  Stop at the first lysine codon
3.  Still occur but there would be no lysines or glycines
in the protein
4.  Still occur but the protein would contain lysines
instead of glycines
Clicker Question #10
24) How does the structure of the release factor
impact its function?
1.  The release factor must be at least as big as the ribosome
2.  The structure must be made of animo acids to have a
tertiary structure
3.  The release factor structure must be made of the same
monomer components as the tRNA to fit into the ribosome
4.  The release factor structure must be similar to the size and
shape of a tRNA
Clicker Question #11
X3) Should there be tRNAs in the cell that can
base pair with a stop codon?
1) No, because they would not be able to enter the
ribosome
2) No, because then the peptide chain would keep
growing indefinitely
3) No, because the N-terminus of the growing
protein chain would not be able to extend out of the
ribosome
4) Yes (for any reason)
Peer Instruction
How does this enzyme create a charged tRNA?
ATP
1)
3)
4)
2)
Activated
enzyme
complex
What parts of the enzyme give it specificity?
Evaluate a molecular history:
Clicker Question 12
A nucleotide within a large mRNA polymer has:
1) Lost two phosphates,
2) Formed 2 or 3 hydrogen bonds,
3) Formed a phosphodiester bond, and then
4) Lost 2-3 hydrogen bonds
1.  This is the correct and complete process
2.  There is something missing in this process
3.  There is something extra in this process
Concept questions
•  To practice labeling of translation diagrams:
–  Build a sequence with 70+ bases of random RNA
–  Find a start codon and assess the location of ribosome binding
–  Indicate the codons and anticodons used, as well as the peptide
bonds created
–  Change the sequence of the RNA such that you program the
ribosome to create a 10-amino-acid polymer
•  What would happen to translation if:
–  The ribosome binding site were lost?
–  The start codon were mutated?
–  The stop codon was mutated
–  The shape of the release factor was altered
•  Write a complete reaction diagram for each of these:
–  Binding of the small ribosomal subunit to the RNA
–  Addition of the 5th amino acid
–  Termination of translation
–  Catalysis of charging a single tRNA
Lab Next Week
•  The Central Dogma Lab
–  A great place to practice what you know about
•  Trancription
•  Translation
•  Mutation
–  We’ll also talk about mutations and their
impact on human disease for the first time