Exam 14: The Mechanism of Translation

Transfer RNAs are thought to improve the fidelity of mRNA translation by

Aminoacyl-tRNA synthetases are enzymes that

The stop codon is recognized by

Does a special tRNA bind to the stop codon in the mRNA during termination?

Which step of translation requires mRNA decoding by a protein?

Explain (or draw a clearly labeled diagram) the sequence of events that occurs during translation in eukaryotic cells as a protein elongates by one amino acid. At each step, specify what is happening in the ribosome's A site, P site, and E site. Indicate at what points GTP hydrolysis is required.

Describe a toeprint assay involving mammalian ribosomal subunits and a mRNA in a cell-free extract that contains all the factors necessary for translation. (a) What results would you expect to see with 40S ribosomal subunits alone? (b) With 60S subunits alone? (c) With both subunits and all amino acids except serine, which is required in the 15^th position of the polypeptide?

Ribosomes carry out the process of protein synthesis in the ____________ after assembly in The _____________ within a special compartment called the ______________.

GTP hydrolysis is required for

The E. coli trigger factor has been described as hunching over the exit of the ribosome tunnel "like a crouching dragon." What is it doing?

Which component is not directly involved in the process known as translation?

Draw a diagram to summarize the process of translation initiation in eukaryotes. Indicate at what points ATP or GTP hydrolysis are required.

Diagram the pathway for assembly in the nucleolus, maturation, and nuclear export of ribosomal subunits in yeast.

Hydrolysis of ATP indirectly fuels protein synthesis by

Which component of mammalian ribosomes accounts for 60% of the mass?

Describe an in vitro assay to demonstrate that aminoacylation of tRNA_CUA with pyrrolysine requires a novel archael aminoacyl synthetase, PylS.

A skeptic thinks that only proteins can be enzymes. Provide X-ray crystallographic and biochemical evidence in support of the view that the ribosome is a ribozyme.

When the translation initiation factor eIF2 is phosphorylated in response to a sudden temperature increase or viral infection, translation can be greatly inhibited. In this case, phosphorylated eIF2 is under _______________ control, and the phosphorylation of eIF2 leads to global (general or widespread) _____________ control.

Below is a simplified diagram of several components of the translation machinery. The ribosome is moving from left to right in this figure. The arrow points to the:

In response to unfavorable conditions such as hypoxia or osmotic shock, translation can be globally repressed by