Exam 14: From Dna to Protein: Gene Expression

A researcher is interested in determining the kinetics of synthesis and secretion of a protein that is known to be produced by kidney cells.The researcher modifies the gene by inserting a sequence encoding a region of a protein that can be visualized in the electron microscope.The marker is inserted just after the codon for the initiating methionine, within a region of hydrophobic amino acid residues.To determine the kinetics, the researcher will track the green-labeled proteins as they are synthesized in the RER, pass through the Golgi apparatus, and arrive at the cell surface in secretory vesicles.To the researcher's surprise, the green-labeled protein accumulates in the cytoplasm of the kidney cells and none appears in the RER, Golgi apparatus, or secretory vesicles.When the researcher repeats the experiment, but with the genetic marker inserted at the 3′ end of the gene just before the stop codon, the experiment proceeds as expected.These results indicate that, unintentionally, the researcher has confirmed that

Imagine that a novel life-form is found deep within Earth's crust.Although its DNA is composed of the same four nucleotides as other life-forms, its codons are four bases in length.This organism could therefore be composed of _______ different amino acids.

Wild-type Neurospora was treated with X rays to induce heritable mutations.Treated Neurospora cultures were grown on minimal medium ("no addition" in the table) and minimal medium supplemented with the indicated compounds.Growth is indicated as dry weight of fungal material after 5 days.The table shows the results of three mutated strains that were linked to the metabolic pathway that generates arginine. Without arginine production, Neurospora cannot grow.Considering the biochemical pathway of arginine production and experimental outcomes shown, which two strains are represented by the double mutant? Explain the evidence for your answer and why the other combinations cannot be correct.

Which statement about pre-mRNA splicing is false?

The enzyme that charges the tRNA molecules with appropriate amino acids is

What would happen if the tRNA synthetase for tryptophan added a phenylalanine instead of tryptophan to the tryptophan tRNAs?

Suppose the DNA of a gene contains five regions-A, B, C, D, and E, in that order.Regions A, B, and D are located in introns, while regions C and E are located in exons.What is the order of the regions in the mature mRNA transcribed from that sequence?

There are _______ different codons in the genetic code, and each codon is _______ nucleotides long.

Gene X encodes an enzyme subunit.A researcher is studying an allele of gene X that does not produce a protein product.Experiments show that the pre-mRNA transcript undergoes RNA processing and is successfully transported out of the nucleus.However, in the cytoplasm, the mRNAs accumulate without binding to ribosomes.These results suggest a problem with the addition of the _______ to the pre-mRNA.

A researcher has created a gene construct that is expressed in a cell line.The researcher has evidence that the gene is being fully translated but is quickly degraded, resulting in low production of the gene's protein product.Evaluating the gene construct, the researcher realizes that the poor mRNA stability is probably due to the absence of a _______ sequence at the gene's 3′ end.

Where would you most likely find partially translated polypeptides that are undergoing processing?

In the experiments by Benzer and colleagues, the cysteine in a cys-tRNA molecule was converted into alanine.Suppose, instead, that the cysteine had appeared in the synthesized protein where it normally does.The most likely conclusion would have been that the protein synthesis system

Benzer and his group modified the amino acid part of a charged tRNA molecule.This experiment demonstrated

Suppose that two different mutant strains of a bacterium are unable to grow on a minimal medium without the addition of the amino acid lysine.Explain how this phenotype might be caused by different mutations in each strain, perhaps in the same gene and perhaps in two different genes.

Normally, Neurospora can synthesize all 20 amino acids specified by the genetic code.A certain strain of this mold cannot grow in minimal nutritional medium but grows only when the amino acid leucine is added to the medium.This strain

Humans share the same genetic code with

Refer to the figure. In the figure, ________ represents a protein whose tertiary conformation has been altered by the activity of one or more protein kinases.

After nucleic acid hybridization with the DNA from a eukaryotic gene as the target and mRNA as the probe, you observe a 1:1 complementarity between the RNA and the DNA.From this result, you can infer that

How have retroviruses caused us to reevaluate the "central dogma"

The stop codons code for