Translation
Supplemental Instruction
Iowa State University
Leader:
Course:
Instructor:
Date:
Lilli Howard
BIOL/GEN 313
Dr. Rodermel/Dr. Tuggle
10/22/14
1. Elongation of translation has four requirements:
a. Ribosome: which has 3 important sites for tRNA binding
b. Elongation factors (EFs): EF-T, EF-Tu, EF-G
c. GTP (for energy)
d. Charged tRNAs
2. Describe the process of elongation in three steps.
1. Charged tRNA binds to A site
2. Peptide bond formation
3. Translocation: ribosome moves down the mRNA in a 5’ 3’ direction
3. Define ribozyme: an RNA molecule that can act as a biological catalyst
4. During elongation, how are the mRNA and tRNA held together?
-hydrogen bonds between codons and anticodons
5. Termination of translation has three requirements:
a. Termination codons on mRNA
b. GTP (hydrolysis causes conformational change)
c. Release factors – RF1, RF2, RF3
6. Describe the process of termination in three steps.
1. RRF1 binds to stop codon & growing polypeptide is released from tRNA in P site
2. RF3-GTP binding causes conformational change of ribosome that results in release of
RF1 (or RF2) the translocation of the last tRNA from P site to E site
3. GTP hydrolysis causes conformational change of ribosome that results in release of
everything from ribosome, and to dissociation of ribosome into its subunits
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7. What are 6 major differences between translation in eukaryotes and prokaryotes?
8. A polyribosome is an mRNA with many ribosomes attached.
9. Name and describe the three common post translational modifications.
a. Chemical modifications, such as methylation, acetylation, phosphorylation, or
attachment of carbohydrates, lipid molecules, ubiquitin
b. Amino acids are sometimes removed (e.g., targeting sequences to mitochondria
and chloroplasts)
c. Molecular chaperones: proteins that fold the nascent polypeptide into its correct
conformation for activity
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10. Why is translation a good target for antibiotics?
70S and 80S ribosomes have many differences; thus inhibition of translation on 70S
ribosomes will kill bacteria, but it will not affect translation on 80S ribosomes (in
eukaryotic cell cytoplasm)
11. During the initiation of translation, the small ribosome binds to which consensus
sequence in bacteria?
-Shine Dalgarno
12. In elongation, the creation of peptide bonds between amino acids is catalyzed by:
a.
b.
c.
d.
rRNA
protein in the small subunit
protein in the large subunit
tRNA
13. In a polyribosomes, the polypeptides associated with which ribosomes will be the
longest?
a. Those at the 5’ end of mRNA
b. Those at the 3’ end of mRNA
c. Those in the middle of mRNA
d. All polypeptides will be the same length
14. Arrange the following components of translation in the approximate order in which they
would appear or be used in protein synthesis: G, B, E, A, F, D, C
a. 70S initiation complex
b. 30S initiation complex
c. Release factor 1
d. Elongation factor G
e. Initiation factor 3
f. Elongation factor Tu
g. fMet-tRNAfMet
15. A system produces a peptide with the following amino acid sequence: Met-Pro-Ile-SerAla. What would be the effect on translation if the following components were omitted
from the system? What, if any, type of protein would be produced?
(a) Initiation factor 1
The lack of IF1 would decrease the amount of protein synthesized. IF1 promotes the
disassociation of the large and small ribosomal subunits. Translation initiation would
occur, but at a slower rate since more of the small ribosomal subunits would be bound
to the large ribosomal subunits.
(b) Initiation factor 2
No translation would occur. IF2 is necessary for translation initiation. The lack of IF2
would prevent fMet-tRNAfmet from being delivered to the small ribosomal subunit, thus
blocking translation.
(c) Elongation factor Tu
Although translation initiation or delivery of the Met to the ribosome-mRNA complex
would occur, no further amino acids would be delivered to the ribosome. EF-TU is
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necessary for elongation where it binds GTP and the charged tRNA. This three-part
complex enters the “A” site of the ribosome. If EF-TU is not present, then the charged
tRNA will not enter the “A” site, thus stopping translation.
(d) Elongation factor G
EF-G is necessary for the translocation of the ribosome along the mRNA in a 5' to 3'
direction. Once the formation of the peptide bond occurs between the Met and Pro, the
lack of EF-G would prevent the movement of the ribosome along the mRNA, so no new
codons would be read. However, the dipeptide Met-Pro would be formed since its
formation would not require EF-G.
(e) Release factors R1, R2, and R3
The release factors recognize the stop codons and promote cleavage of the peptide from
the tRNA at the “P” site. The absence of the release factors prevents termination of
translation at the stop codon, resulting in a larger peptide.
(f) ATP
ATP is required for the charging of the tRNAs with amino acids by the aminoacyl-tRNA
synthetases. Without ATP, the charging would not take place, and no amino acids will
be available for protein synthesis. So no protein synthesis will occur.
(g) GTP
GTP is required for initiation, elongation, and termination of translation. If GTP is
absent, no protein synthesis will occur.
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16. Consider the amino acids shown below. (A) Label the alpha carbon, the amino group, and
the carboxyl group. (B) In the tertiary structure of the protein, where would you expect to
see these amino acids? Why? (C) Link two amino acids together with a peptide bond and
indicate the polarity of the resulting di-peptide.
1060 Hixson-Lied Student Success Center  515-294-6624  sistaff@iastate.edu  http://www.si.iastate.edu
1060 Hixson-Lied Student Success Center  515-294-6624  sistaff@iastate.edu  http://www.si.iastate.edu