Problem 1
Babel fish. Why is protein synthesis also called translation?
Problem 2
Correct phrasing. What is meant by the phrase reading frame?
Problem 3
Match \(e m .\) Match each term on the right with the terms in parts \(a, b,\) and c. (a) Initiation (b) Elongation (c) Termination 1\. GTP 2\. AUG 3\. fMet 4\. RRF 5\. IF2 6\. Shine-Dalgarno 7\. EF-Tu 8\. Peptidyl transferase 9\. UGA 10\. Transformylase
Problem 4
Wasted effort? Transfer RNA molecules are quite large, given that the anticodon consists of only three nucleotides. What is the purpose of the rest of the tRNA molecule?
Problem 5
Light and heavy ribosomes. Density-gradient centrifugation is a technique that allows the separation of biological molecules and molecular complexes by differences in density. Ribosomes were isolated from bacteria grown in a "heavy" medium ('' C and ' \(^{15}\) N) and from bacteria grown in a "light" medium ( \(^{12} \mathrm{C}\) and \(^{14} \mathrm{N}\) ). These \(70 \mathrm{S}\) ribosomes were added to an in vitro system undergoing protein synthesis. An aliquot removed several hours later was analyzed by density-gradient centrifugation. How many types of 70S ribosomes differing in density would you expect to see in the density gradient?
Problem 6
The price of protein synthesis. What is the smallest number of molecules of ATP and GTP consumed in the synthesis of a 200 -residue protein, starting from amino acids? Assume that the hydrolysis of \(\mathrm{PP}_{1}\) is equivalent to the hydrolysis of ATP for this calculation.
Problem 7
Viral mutation. An mRNA transcript of a T7 phage gene contains the base sequence 1 5'-AACUGCACGAGGUAACACAAGAUGGCU-3' Predict the effect of a mutation that changes the G identified by the arrow to A.
Problem 8
Enhancing fidelity. Compare the accuracy of (a) DNA replication, (b) RNA synthesis, and (c) protein synthesis. What mechanisms are used to ensure the fidelity of each of these processes.
Problem 9
You have to know where to look. Bacterial messenger RNAs usually contain many AUG codons. How does the ribosome identify the AUG specifying initiation?
Problem 10
Triggered GTP hydrolysis. Ribosomes markedly accelerate the hydrolysis of GTP bound to the complex of EF-Tu and aminoacyl-tRNA. What is the biological significance of this enhancement of GTPase activity by ribosomes?
