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Problem 1
Some proteins are composed of two or more polypeptides. Suppose the DNA template strand sequence 3′-TACGTAGGCTAACGGAGTAAGCTAACT-5′ produces a polypeptide that joins in pairs to form a functional protein.
What term is used to identify a functional protein like this one formed when two identical polypeptides join together?Problem 1
Some proteins are composed of two or more polypeptides. Suppose the DNA template strand sequence 3′-TACGTAGGCTAACGGAGTAAGCTAACT-5′ produces a polypeptide that joins in pairs to form a functional protein. What is the amino acid sequence of the polypeptide produced from this sequence?Problem 2
In the experiments that deciphered the genetic code, many different synthetic mRNA sequences were tested.
Describe how the codon for phenylalanine was identified.Problem 2
In the experiments that deciphered the genetic code, many different synthetic mRNA sequences were tested.
What was the result of studies of synthetic mRNAs composed exclusively of cytosine?Problem 2
In the experiments that deciphered the genetic code, many different synthetic mRNA sequences were tested.
What result was obtained for synthetic mRNAs containing AG repeats, that is, AGAGAGAG...?Problem 2
In the experiments that deciphered the genetic code, many different synthetic mRNA sequences were tested.
Predict the results of experiments examining GCUA repeats.Problem 2
You conduct a study in which the transcriptional fusion of regulatory sequences of a particular gene with a reporter gene results in relatively uniform expression of the reporter gene in all cells of an organism. A translational fusion with the same gene shows reporter gene expression only in the nucleus of a specific cell type. Discuss some biological causes for the difference in expression patterns of the two transgenes.
Problem 3
Several lines of experimental evidence pointed to a triplet genetic code. Identify three pieces of information that supported the triplet hypothesis of genetic code structure.
Problem 3
The human mitochondrial genome encodes only 22 tRNAs, but at least 32 tRNAs are needed for cytoplasmic translation. How are all codons in mitochondrial transcripts accommodated by only 22 tRNAs? The Plasmodium mitochondrial genome does not encode any tRNAs; how are genes of the Plasmodium mitochondrial genome translated?
Problem 4
Outline the events that occur during initiation of translation in E. coli.
Problem 5
Describe the gene and protein defects in phenylketonuria (PKU). How are these defects connected to disease symptoms?
Problem 5
A portion of a DNA template strand has the base sequence 5′-...ACGCGATGCGTGATGTATAGAGCT...-3′
Identify the sequence and polarity of the mRNA transcribed from this fragmentary template-strand sequence.Problem 5
A portion of a DNA template strand has the base sequence 5′-...ACGCGATGCGTGATGTATAGAGCT...-3′
Which is the third amino acid added to the polypeptide chain?Problem 5
A portion of a DNA template strand has the base sequence 5′-...ACGCGATGCGTGATGTATAGAGCT...-3′
Assume the mRNA is written in the correct reading frame. Determine the amino acid sequence encoded by this fragment. Identify the N- and C-terminal directions of the polypeptide.Problem 6
What are the differences between the universal code and that found in the mitochondria of some species? Given that some changes (UGA =stop→Trp) have occurred multiple independent times in evolution, can you think of any selective advantage to the mitochondrial code?
Problem 6
Describe three features of tRNA molecules that lead to their correct charging by tRNA synthetase enzymes.
Problem 7
Identify the amino acid carried by tRNAs with the following anticodon sequences.
5′-UAG-3′Problem 7
Identify the amino acid carried by tRNAs with the following anticodon sequences.
5′-AAA-3′Problem 7
Identify the amino acid carried by tRNAs with the following anticodon sequences.
5′-CUC-3′Problem 7
Identify the amino acid carried by tRNAs with the following anticodon sequences.
5′-AUG-3′Problem 7
Identify the amino acid carried by tRNAs with the following anticodon sequences.
5′-GAU-3′Problem 8
For each of the anticodon sequences given in the previous problem, identify the other codon sequence to which it could potentially pair using third base wobble.
Problem 9
What is the role of codons UAA, UGA, and UAG in translation? What events occur when one of these codons appears at the A site of the ribosome?
Problem 10
Compare and contrast the composition and structure of bacterial and eukaryotic ribosomes, identifying at least three features that are the same and three features that are unique to each type of ribosome.
Problem 11
Consider translation of the following mRNA sequence:
5′-...AUGCAGAUCCAUGCCUAUUGA...-3′
Diagram translation at the moment the fourth amino acid is added to the polypeptide chain. Show the ribosome; label its A, P, and E sites; show its direction of movement; and indicate the position and anticodon triplet sequence of tRNAs that are currently interacting with mRNA codons.Problem 11
Consider translation of the following mRNA sequence: 5′-...AUGCAGAUCCAUGCCUAUUGA...-3′ What is the anticodon triplet sequence of the next tRNA to interact with mRNA?
Problem 11
Consider translation of the following mRNA sequence: 5′-...AUGCAGAUCCAUGCCUAUUGA...-3′ What events occur to permit the next tRNA to interact with mRNA?
Problem 12
The diagram of a eukaryotic ribosome shown below contains several errors.
Examine the diagram carefully, and identify each error. <>Problem 12
The diagram of a eukaryotic ribosome shown below contains several errors.
Redraw the diagram, and correct each error using the mRNA sequence shown. <>Problem 13
Third-base wobble allows some tRNAs to recognize more than one mRNA codon. Based on this chapter's discussion of wobble, what is the minimal number of tRNA molecules necessary to recognize the following amino acids?
leucine
