BCH5413 Exam 3 UPDATED Exam
Questions and CORRECT Answers
What are the subunits of 70s and 80s ribosomes and their main functions? - CORRECT
ANSWER - 70S has two subunits : 30S is the small submit that decodes mRNA and 50S is
the subunit links amino acids together through peptide bonds
80S has two subunits: 40S and 50S:
40S small subunit, analogous to the 30S subunit in the prokaryotic ribosome
60S large subunit, analogous to the 50S subunit in the prokaryotic ribosome
The ribosome consists of both ribosomal RNA and ribosomal proteins.
Which part primarily determines the shape of the ribosome - CORRECT ANSWER - The
structure of the ribosome is dependent on the ribosomal RNA and how they might base pair with
each other at different segments.
The ribosome consists of both ribosomal RNA and ribosomal proteins.
Which part contains the peptidyl transferase activity? - CORRECT ANSWER - The 50S
subunit (large subunit) contains the peptidyl transferase activity.
The ribosome consists of both ribosomal RNA and ribosomal proteins.
Which part contains the GTP hydrolysis activity? - CORRECT ANSWER - The 50S
subunit (large subunit) contains GTPase activity.
During protein synthesis, what kind of bond joins the amino acids? Which parts (functional
groups) of the amino acids are bonded together? - CORRECT ANSWER - The 50S
subunit links amino acids together through peptide bonds. Amino acids connect to form a peptide
bond through a reaction between the amino group and carboxyl group. A peptide bond is formed
through a dehydration reaction. This involves the removal of two hydrogens and an oxygen.
,tRNA Charging: How does the aminoacyl-tRNA synthetases recognize which tRNA gets its
amino acid? - CORRECT ANSWER - Recognition will depend on nucleotides within the
tRNA and binding sites within the protein.
tRNA Charging: Describe the 2-step process for charging the tRNA. - CORRECT
ANSWER - The first step is the activation of the amino acid with the help of ATP to form
aminoacyl-AMP. The second step will use the energy from the aminoacyl-AMP bond to transfer
the amino acid onto the acceptor stem of the tRNA.
tRNA charging: Where does the amino acid get added to the tRNA? Be specific about the end of
the RNA and the position of binding on the RNA. - CORRECT ANSWER - The high-
energy bond between the aminoacyl and AMP will be used to transfer the amino acid to the 3'
end of the tRNA; specifically, the amino acid will form an ester bond between the 3'carbon
hydroxyl group on the adenosine of the tRNA and the carboxyl group of the amino acid.
What is the wobble hypothesis? What is its significance? - CORRECT ANSWER - The
wobble hypothesis is: The 3rd position base on a codon which is allowed to be different to
accommodate different tRNA, this exception allows it to form a non Watson-Crick base pair with
the anticodon.
This is significant because the wobble allows some aminoacyl-tRNAs to pair with more than one
codon
True/False: Protein synthesis requires GTP. - CORRECT ANSWER - TRUE, When
binding an aminoacyl-tRNA to the A site
True/False: Wobble allows the different aminoacyl-tRNA to pair with same codon. - CORRECT
ANSWER - TRUE, 3rd base of a codon is allowed to move slightly from it snormal
position, allowing same aminoacryl-tRNAs to pair with more than one codon
True/False: Ligase enzyme joins the amino acids to the respective tRNAs - CORRECT
ANSWER - FALSE, AA attached by ester bond between 2'-OH of terminal adenosine of
tRNA
, True/False: Aminoacylation of tRNAs requires GTP - CORRECT ANSWER - FALSE, 2
step process reuire AMP from ATP to activate AA, then,AMP is used to transfer the AA to tRNA
True/False: Fmet-tRNA is the initiator tRNA in Eukaryotes - CORRECT ANSWER -
FALSE, N-Formylmethionine=Fmet-tRNA is the initiator of Prokaryotes
What differences are there between the ribosome binding in prokaryotes vs. eukaryotes? -
CORRECT ANSWER - During translation in prokaryotes, the ribosome binds an operon at
a ribosome binding site that precedes an open reading frame. Once the ribosome binds, there are
various soluble factors that ensure the ribosome reads the correct code to make the correct
protein.During translation in eukaryotes, the ribosome binds the 5' cap, then scans the mRNA for
the AUG start site. The ribosome also requires soluble factors to initiate translation.
What is the function of IF1? - CORRECT ANSWER - binds to the A site and keeps the
fmet-tRNA from binding there
What is the function of IF2? - CORRECT ANSWER - binds to the fmet-tRNA and GTP
and brings the complex to the P site
What is the function of IF3? - CORRECT ANSWER - binds to 30S subunit to keep it
separate from the large subunit
What is the function of hydrolysis of GTP after 70s initiation complex is formed? - CORRECT
ANSWER - releases IF2 and GDP from the complex so polypeptide chain elongation can
begin
Explain the three steps in formation of 70s complex. - CORRECT ANSWER - The
ribosome first dissociates. The 30S initiation complex is the first to form. IF3 binds to the 30s
ribosome to prevent reassociation of the 2 ribosomal subunits. With the assistance of IF1 and
IF2, IF3 binds to the Shine-Delgarno sequence (RBS) on the 5' end mRNA. This sequence is also
recognized by a complementary sequence in the 16S rRNA.. IF2 will bind to the fmet-tRNA and
to GTP and bring them to the P-site. No GTP hydrolysis occurs at this point. IF3 will leave the
30S initiation complex, allowing the 50S subunit to join the complex. At this point, GTP is
hydrolyzed by the GTPase of the 50S subunit. This hydrolysis allows the release of IF2 (and
Questions and CORRECT Answers
What are the subunits of 70s and 80s ribosomes and their main functions? - CORRECT
ANSWER - 70S has two subunits : 30S is the small submit that decodes mRNA and 50S is
the subunit links amino acids together through peptide bonds
80S has two subunits: 40S and 50S:
40S small subunit, analogous to the 30S subunit in the prokaryotic ribosome
60S large subunit, analogous to the 50S subunit in the prokaryotic ribosome
The ribosome consists of both ribosomal RNA and ribosomal proteins.
Which part primarily determines the shape of the ribosome - CORRECT ANSWER - The
structure of the ribosome is dependent on the ribosomal RNA and how they might base pair with
each other at different segments.
The ribosome consists of both ribosomal RNA and ribosomal proteins.
Which part contains the peptidyl transferase activity? - CORRECT ANSWER - The 50S
subunit (large subunit) contains the peptidyl transferase activity.
The ribosome consists of both ribosomal RNA and ribosomal proteins.
Which part contains the GTP hydrolysis activity? - CORRECT ANSWER - The 50S
subunit (large subunit) contains GTPase activity.
During protein synthesis, what kind of bond joins the amino acids? Which parts (functional
groups) of the amino acids are bonded together? - CORRECT ANSWER - The 50S
subunit links amino acids together through peptide bonds. Amino acids connect to form a peptide
bond through a reaction between the amino group and carboxyl group. A peptide bond is formed
through a dehydration reaction. This involves the removal of two hydrogens and an oxygen.
,tRNA Charging: How does the aminoacyl-tRNA synthetases recognize which tRNA gets its
amino acid? - CORRECT ANSWER - Recognition will depend on nucleotides within the
tRNA and binding sites within the protein.
tRNA Charging: Describe the 2-step process for charging the tRNA. - CORRECT
ANSWER - The first step is the activation of the amino acid with the help of ATP to form
aminoacyl-AMP. The second step will use the energy from the aminoacyl-AMP bond to transfer
the amino acid onto the acceptor stem of the tRNA.
tRNA charging: Where does the amino acid get added to the tRNA? Be specific about the end of
the RNA and the position of binding on the RNA. - CORRECT ANSWER - The high-
energy bond between the aminoacyl and AMP will be used to transfer the amino acid to the 3'
end of the tRNA; specifically, the amino acid will form an ester bond between the 3'carbon
hydroxyl group on the adenosine of the tRNA and the carboxyl group of the amino acid.
What is the wobble hypothesis? What is its significance? - CORRECT ANSWER - The
wobble hypothesis is: The 3rd position base on a codon which is allowed to be different to
accommodate different tRNA, this exception allows it to form a non Watson-Crick base pair with
the anticodon.
This is significant because the wobble allows some aminoacyl-tRNAs to pair with more than one
codon
True/False: Protein synthesis requires GTP. - CORRECT ANSWER - TRUE, When
binding an aminoacyl-tRNA to the A site
True/False: Wobble allows the different aminoacyl-tRNA to pair with same codon. - CORRECT
ANSWER - TRUE, 3rd base of a codon is allowed to move slightly from it snormal
position, allowing same aminoacryl-tRNAs to pair with more than one codon
True/False: Ligase enzyme joins the amino acids to the respective tRNAs - CORRECT
ANSWER - FALSE, AA attached by ester bond between 2'-OH of terminal adenosine of
tRNA
, True/False: Aminoacylation of tRNAs requires GTP - CORRECT ANSWER - FALSE, 2
step process reuire AMP from ATP to activate AA, then,AMP is used to transfer the AA to tRNA
True/False: Fmet-tRNA is the initiator tRNA in Eukaryotes - CORRECT ANSWER -
FALSE, N-Formylmethionine=Fmet-tRNA is the initiator of Prokaryotes
What differences are there between the ribosome binding in prokaryotes vs. eukaryotes? -
CORRECT ANSWER - During translation in prokaryotes, the ribosome binds an operon at
a ribosome binding site that precedes an open reading frame. Once the ribosome binds, there are
various soluble factors that ensure the ribosome reads the correct code to make the correct
protein.During translation in eukaryotes, the ribosome binds the 5' cap, then scans the mRNA for
the AUG start site. The ribosome also requires soluble factors to initiate translation.
What is the function of IF1? - CORRECT ANSWER - binds to the A site and keeps the
fmet-tRNA from binding there
What is the function of IF2? - CORRECT ANSWER - binds to the fmet-tRNA and GTP
and brings the complex to the P site
What is the function of IF3? - CORRECT ANSWER - binds to 30S subunit to keep it
separate from the large subunit
What is the function of hydrolysis of GTP after 70s initiation complex is formed? - CORRECT
ANSWER - releases IF2 and GDP from the complex so polypeptide chain elongation can
begin
Explain the three steps in formation of 70s complex. - CORRECT ANSWER - The
ribosome first dissociates. The 30S initiation complex is the first to form. IF3 binds to the 30s
ribosome to prevent reassociation of the 2 ribosomal subunits. With the assistance of IF1 and
IF2, IF3 binds to the Shine-Delgarno sequence (RBS) on the 5' end mRNA. This sequence is also
recognized by a complementary sequence in the 16S rRNA.. IF2 will bind to the fmet-tRNA and
to GTP and bring them to the P-site. No GTP hydrolysis occurs at this point. IF3 will leave the
30S initiation complex, allowing the 50S subunit to join the complex. At this point, GTP is
hydrolyzed by the GTPase of the 50S subunit. This hydrolysis allows the release of IF2 (and
