Chapter 8 Protein Synthesis • MHR 271
SECTION REVIEW
- Explain how the wobble feature of the genetic
code helps a cell conserve energy. What other
advantage(s) does this feature give the cell?
- List the components of the protein synthesis
equipment that a cell uses during translation. Identify
whether each component is a polypeptide, a nucleic
acid, or a combination of the two.
- Explain how a “stop” codon triggers the
termination of the translation cycle.
- Arrange the following events into the order in
which they occur during the elongation cycle of
translation. Start from the binding of an aa-tRNA
complex at the A site of the ribosome assembly:
translocation
transfer of the polypeptide chain from the tRNA in
the P site to the tRNA in the A site
departure of tRNA from the E site
formation of a peptide bond
binding of tRNA to an amino acid to create an
aa-tRNA complex
- You are working at a research facility that prides
itself on developing creative ways to explain science
to children. Your latest assignment is to develop a
short story about protein synthesis using a dinosaur
character called Toby the tRNA tyrannosaurus. Write
a short chapter that follows Toby’s path through the
elongation cycle of translation.
6. A student researcher has developed a new form
of activating enzyme. This enzyme works much faster
than the activating enzyme normally found in
mammalian cells because its amino acid binding site
can recognize and bind any free amino acid found in
the cell cytoplasm. “This enzyme will speed up the
rate of protein synthesis and could have important
medical benefits,” claims the researcher. Is the
researcher right? Explain your reasoning.
7. Draw a polyribosome complex that identifies
the following structures or features: 5 ′end of the
mRNA molecule; large and small ribosome sub-units;
polypeptide chains; direction of translation.
8. Some antibiotics work by paralyzing bacterial
ribosomes. With a partner or as part of a small
group, identify other substances, such as
medications or environmental toxins, that can alter
the activity of eukaryotic ribosomes. Write a brief
summary of your findings, including a description of
the effects these substances can have on people.
9. Discuss the implications of this statement: “The
process of translation is very similar in prokaryotic
and eukaryotic cells.”
- Among the three types of RNA molecules
involved in translation, which is/are responsible for
determining the polypeptide sequence of a particular
protein? How would you demonstrate this in an
experiment?
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Figure 8.23In this bacterial cell, mRNA is being transcribed
from a DNA template (the pale linear strand). You can see
the ribosomes (in red) already attached to the elongating
mRNA molecules.
A prokaryotic cell typically has a very short life
span. Consequently, it must be able to synthesize
proteins very quickly in response to its rapidly
changing needs. By way of contrast, a eukaryotic
cell tends to live longer and have more complex
metabolic requirements. By separating the
processes of transcription and translation, the
eukaryotic cell sacrifices some of the protein
synthesis speed of a prokaryotic cell. As a result,
however, it gains an additional opportunity to
regulate the rate of its protein synthesis. In the next
section, you will examine some of the mechanisms
that regulate gene expression in both eukaryotic
and prokaryotic cells.
