GRE Subject Test: Biochemistry, Cell, and Molecular Biology : DNA

Study concepts, example questions & explanations for GRE Subject Test: Biochemistry, Cell, and Molecular Biology

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Example Questions

Example Question #6 : Help With Epigenetics

Bees use enzymes called DNMT1 and DNMT3 (DNA methyltransferases) to create epigenetic changes that differentiate social castes at a common site pattern. What is this type of epigenetic change called?

Possible Answers:

ApT methylation

CpG methylation

Histone modification

Lysine acetylation

None of these are correct

Correct answer:

CpG methylation

Explanation:

CpG (cytosine-phosphate-guanine) methylation is a common type of epigenetic change caused by this set of enzymes. In this case, the bees use this to create difference castes of bees out of the same shared genome.

Example Question #1 : Help With Nucleoid Structure And Function

Which comparisons between eukaryotic and prokaryotic genomes are true?

Possible Answers:

Both genomes are replicated in the nucleus

Prokaryotic genomes frequently have many transposable elements

All of these

Both types of genomes have large spacer regions between genes

Eukaryotic genes are often single and not in operons like prokaryotic genes

Correct answer:

Eukaryotic genes are often single and not in operons like prokaryotic genes

Explanation:

The only true comparison of those listed is that eukaryotic genes are not often present in operons, like prokaryotes often have (think the frequently studied lac operon). Eukaryotes, not prokaryotes, have many transposable elements (a contributing factor to why our genomes are so large). Prokaryotes do not have large spacer regions between their genes, their genomes are often extremely compact. Prokaryotic cells lack nuclei, thus, DNA replication occurs in the cytosol.

Example Question #2 : Prokaryotic Genome

The Frederick Griffith experiment showed that previously safe pneumococcus can become lethal when it incorporates DNA from the surroundings into its genome.

What type of genetic transfer was displayed in the Frederick Griffiith experiment?

Possible Answers:

Transformation

Transduction

Conjugation

Binary fission

Correct answer:

Transformation

Explanation:

When a bacterium has incorporated DNA from the outside environment into its own genome, the process of transformation has occurred.

Example Question #2 : Help With Transduction, Conjugation, And Transformation

Which type of bacterial genetic recombination involves the use of a viral vector?

Possible Answers:

Conjugation

Transduction

Transformation

Assimilation

Correct answer:

Transduction

Explanation:

Sometimes a bacteriophage can encapsulate host bacterial DNA instead of viral DNA. When this virus infects another bacterium, it will inject the previous bacterium's DNA into the new bacterium. This process is referred to as transduction.

Example Question #3 : Prokaryotic Genome

What plasmid, usually in multiple copies in a prokaryote, is responsible for production of proteins to attack susceptible organisms?

Possible Answers:

Virulence plasmids

Col plasmids

Degradative plasmids

F plasmids

R plasmids

Correct answer:

Col plasmids

Explanation:

The correct answer is the Col plasmid, which produce attack proteins called colicins. These are generally small and in many copies in a prokaryote for efficiency. F plasmids are involved in conjugation, R plasmids in resistance, degradative plasmids in digestion of unusual substances, and virulence plasmids in the conversion of certain bacteria into pathogens.

Example Question #3 : Prokaryotic Genome

What type of phages facilitate specialized transduction?

Possible Answers:

Retroviruses

None of these

Animal viruses

Lytic phages

Lysogenic phages

Correct answer:

Lysogenic phages

Explanation:

Specialized transduction occurs when a prophages excises from the host bacterial genome incorrectly and brings some of the bacterial chromosome with it. This DNA then gets packaged into viral particles along with the viral genome and gets inserted into the next bacterium that virus infects. Since only lysogenic phage can become prophage, specialized transduction can only be mediated by lysogenic phage. Retroviruses are enveloped and thus infect animal cells, not bacterial cells. 

Example Question #1 : Help With Transduction, Conjugation, And Transformation

Bacteria are capable of "sharing" genetic material that can be advantageous in certain environments. This type of gene transmission is an example of which of the following?

Possible Answers:

Fission

Transformation

Transduction

Conjugation

Correct answer:

Conjugation

Explanation:

In this example, note that the new genes are being received from a donor bacterium. This is only seen in conjugation events.

Example Question #1 : Mutation And Variation

Which of the following is NOT a type of mutation that can occur in DNA?

Possible Answers:

Silent

Countersense

Missense

Nonsense

Correct answer:

Countersense

Explanation:

There are four principle types of mutation that can affect DNA. Most of these mutations result from point mutations affecting a single nucleotide residue, though nonsense mutations can be caused by insertions or deletions. Frame shift mutations are solely caused by insertions or deletions.

A silent mutation results from the degeneracy of the genetic code. In a silent mutation a single nucleotide is changed, but the overall translation product is unaffected. This can occur because multiple codons are capable of coding for the same amino acid.

A missense mutation results in the swapping of a single amino acid for another in the final translation product. If the amino acids are similar in character, missense mutations can still result in fully functional proteins. When the changed amino acid lacks characteristics of the original, it can result in protein misfolding and loss of function.

Nonsense mutations result in a premature stop codon, and early termination of the translation process. The final product is a shortened version of the protein, often lacking function.

Frame shift mutations cause a shift in the ribosomal reading frame. Every codon downstream of the mutation will be affected, and the protein will be completely altered. Frame shift mutations often result in premature stop codons.

Countersense is not a form of DNA mutation.

Example Question #2 : Mutation And Variation

Which of the following could cause a frameshift mutation?

Possible Answers:

Insertions or deletions

Deletions

Mismatches

Insertions

Correct answer:

Insertions or deletions

Explanation:

Both insertions and deletions are capable of creating frameshift mutations. A frameshift mutation results in a shift in the reading frame of the gene, significantly altering translation. The cause of such a mutation is the insertion or deletion of any sequence of nucleotides within the gene that is not a multiple of three. The following examples detail different types of frameshift mutations.

Normal gene: ATT-CGT-AGG-TAC

Frameshift deletion examples: ATC-GTA-GGT-AC or ATT-CTA-C

Frameshift insertion examples: ATT-TCG-TAG-GTA-C or ACC-CGA-TAG-GTA-C

Mismatches would not cause a shift in the reading frame, like insertions or deletions.

Example Question #1 : Help With Mutation Types

A researcher has finally managed to design a plasmid that will allow him to begin expressing an important recombinant protein. After analyzing the sequencing data of the plasmid, however, he discovers that a mutation has occurred in the coding region of his protein. If he still wishes to express the wild type protein, does he need to construct a new plasmid?

Possible Answers:

It depends; a frameshift mutation would not affect the structure of the protein

It depends; a silent mutation would not affect the structure of the protein

No; one mutation should not affect the overall protein's function

Yes; any mutation is undesirable and will affect the protein's function

Correct answer:

It depends; a silent mutation would not affect the structure of the protein

Explanation:

This question is somewhat vague because we are given no other information other than the fact that there is a "mutation". Mutations can take many different forms and, therefore, we would need to know more information about the specific type of mutation before we can say whether or not the plasmid still contains a functional gene for the wild type protein. In particular, a silent mutation would result in the insertion of the exact same amino acid despite having a different codon (this is due to the redundancy of the genetic code). If a silent mutation has altered the sequence of the plasmid, it will not alter the structure or function of the protein and the plasmid will still be effective.

A frameshift mutation, however, would have disastrous effects on the protein as the translational reading frame would be shifted and the protein would most likely be truncated and nonfunctional.

All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources

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