GRE Subject Test: Biology : Genetics, DNA, and Molecular Biology

Study concepts, example questions & explanations for GRE Subject Test: Biology

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Example Questions

Example Question #961 : Biology

Which of the following molecules will you least likely find in a plasmid structure?

Possible Answers:

Glycerol

Adenine

Phosphate group

Pentose sugar

Correct answer:

Glycerol

Explanation:

A plasmid is a circular DNA molecule that is found outside the bacterial nucleoid (chromosomal DNA). DNA, or deoxyribonucleic acid, is a type of nucleic acid; therefore, a plasmid must contain substances that make up a nucleic acid. Recall that nucleic acids are made up of three main molecules per monomer: a pentose sugar, a phosphate group, and a nitrogenous base (adenine, thymine, uracil, guanine, or cytosine). Like the nucleoid DNA, plasmid DNA will be made of nucleotide monomers that contain a deoxyribose sugar, a phosphate, and a nitrogenous base.

Glycerol is the three carbon backbone for phospholipid and triglyceride structures. In triglycerides, a fatty acid chain is bound to each of the three glycerol carbons, whereas in phospholipids, two carbons are bound to fatty acids and the third is bound to a phosphate group. Glycerol is a chief structural component of lipid molecules, but will not be found in a nucleic acid plasmid.

Example Question #11 : Prokaryotic Genetics

Which of these processes is the means by which a bacterium can directly uptake and incorporate foreign DNA from the environment into its genome?

Possible Answers:

Reproduction

Transformation

Conduction

Transduction

Conjugation

Correct answer:

Transformation

Explanation:

Transformation is defined as the process by which bacteria can incorporate exogenous DNA from the environment into their genome via direct uptake. Transduction and conjugation are also processes by which exogenous DNA is incorporated, but involve other methods.

Example Question #31 : Microbiology

Which of the following is a unique characteristic of prokaryotic cells?

Possible Answers:

Presence of a cell wall

Post-transcriptional modification of mRNA

Inability to create proton gradients

mRNA translation simultaneous to transcription

Lack of a cytoplast

Correct answer:

mRNA translation simultaneous to transcription

Explanation:

Prokaryotes lack a nuclear membrane, which allows translation to occur at the same time as transcription.

In eukaryotic cells the mRNA has to be exported to the cytoplasm before it can be translated. This transport requires post-transcriptional modification to protect the mRNA from degradation as it leaves the nucleus, a process unnecessary to prokaryotic cells. Both prokaryotes and eukaryotes can have cell walls and cytoplasts (cytoplasm). Prokaryotes do, in fact, generate proton gradients in order to complete cellular respiration. These gradients are created across the prokaryotic cell membrane, rather than across the mitochondrial membrane.

Example Question #31 : Microbiology

Sexually transmitted diseases are a common problem among young people in the United States. One of the more common diseases is caused by the bacterium Neisseria gonorrhoeae, which leads to inflammation and purulent discharge in the male and female reproductive tracts.

The bacterium has a number of systems to evade host defenses. Upon infection, it uses pili to adhere to host epithelium. The bacterium also uses an enzyme, gonococcal sialyltransferase, to transfer a sialyic acid residue to a gonococcal surface lipooligosaccharide (LOS). A depiction of this can be seen in Figure 1. The sialyic acid residue mimics the protective capsule found on other bacterial species.

Once infection is established, Neisseria preferentially infects columnar epithelial cells in the female reproductive tract, and leads to a loss of cilia on these cells. Damage to the reproductive tract can result in pelvic inflammatory disease, which can complicate pregnancies later in the life of the woman.

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A doctor uses a new antibiotic to fight off Neisseria infection. Shortly thereafter, resistance develops and the doctor finds that inoculating wild type bacteria with the pure DNA of resistant Neisseria organisms produces resistant colonies. Which of the following is the method of modification that the doctor is using?

Possible Answers:

Genetic anticipation

Transduction

Conjugation

Transformation

Genetic translation

Correct answer:

Transformation

Explanation:

Transformation is the uptake of nucleic acid by competent cells, as was described in this question. Conjugation invovles cell-to-cell DNA transfer and transduction involves the use of a viral vector.

Example Question #32 : Microbiology

Sexually transmitted diseases are a common problem among young people in the United States. One of the more common diseases is caused by the bacterium Neisseria gonorrhoeae, which leads to inflammation and purulent discharge in the male and female reproductive tracts.

The bacterium has a number of systems to evade host defenses. Upon infection, it uses pili to adhere to host epithelium. The bacterium also uses an enzyme, gonococcal sialyltransferase, to transfer a sialyic acid residue to a gonococcal surface lipooligosaccharide (LOS). A depiction of this can be seen in Figure 1. The sialyic acid residue mimics the protective capsule found on other bacterial species.

Once infection is established, Neisseria preferentially infects columnar epithelial cells in the female reproductive tract, and leads to a loss of cilia on these cells. Damage to the reproductive tract can result in pelvic inflammatory disease, which can complicate pregnancies later in the life of the woman.

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The doctor wants to study the resistance further, so he creates a bacteriophage that transmits the plasmid to other bacterial cells to produce new resistant colonies. Which of the following is the method that the doctor is now using?

Possible Answers:

Conjugation

Genetic translation

Genetic anticipation

Transduction

Transformation

Correct answer:

Transduction

Explanation:

The use of bacteriophage viral vectors to transmit genetic information is transduction, an alternative form of genetic modification to transformation or conjugation. Transformation involves direct uptake of genetic material. Conjugation involves cell-to-cell transfer of DNA.

Example Question #11 : Mitosis And Meiosis

Which answer choice incorrectly matches the type of chromatin with the phase of mitosis?

Possible Answers:

Heterochromatin—prophase

Heterochromatin—metaphase

Euchromatin—interphase

Euchromatin—telophase

Heterochromatin—interphase

Correct answer:

Euchromatin—telophase

Explanation:

DNA is stored in loosely wound euchromatin before mitosis. During mitosis, the DNA condenses into chromosomes, which are made of heterochromatin. It becomes more dense during prophase, and stays that way until the end of mitosis. Euchromatin is more lightly packed than heterochromatin.

Mitosis follows the following sequence: prophase, metaphase, anaphase, telophase, cytokinesis. Interphase refers to the time period between mitotic divisions. During interphase, most DNA is euchromatin, but some regions remain as heterochromatin to prevent unwanted transcription; thus DNA exists as both types of chromatin during interphase, but only as heterochromatin during mitosis. Matching euchromatin to telophase is the answer, as this is a false statement.

Example Question #1 : Chromatin And Chromosomes

What is a nucleosome?

Possible Answers:

A membrane-bound organelle that contains epigenetic information

A complex of proteins that controls nuclear import 

Non-chromosomal DNA that is free floating in the cytosol

A repeating unit of chromatin

Correct answer:

A repeating unit of chromatin

Explanation:

Nucleosomes are the basic, repeating units of eukaryotic chromatin. They consist of chromosomal DNA wrapped around special DNA-binding proteins called histones. There are many examples of non-chromosomal DNA, such as plasmids, but they do not contain nucleosomes. Nuclear import is controlled by importin proteins.

Example Question #2 : Chromatin And Chromosomes

__________ are proteins used to package DNA. 

Possible Answers:

Nucleosomes

Chromatins

Telomerases

Histones

Correct answer:

Histones

Explanation:

Histones are proteins that bind and package DNA. The strand of DNA is wound around histone proteins, condensing it to fit in the nucleus and acting to moderate gene expression. Chromatin is the term given to the complex of DNA associated with histones. A nucleosome is the smallest repeating unit of chromatin, formed from eight histone proteins and two loops of coiled DNA. Telomerase is an enzyme responsible for maintaining the integrity of the telomeres.

Example Question #3 : Chromatin And Chromosomes

__________ is also known as "light" chromatin and represents DNA that can actively undergo __________.

Possible Answers:

Heterochromatin . . . translation

Euchromatin . . . translation

Heterochromatin . . . transcription

Euchromatin . . . transcription

Correct answer:

Euchromatin . . . transcription

Explanation:

Euchromatin is the name given to chromatin that appears lighter when viewed under a microscope. It is actually relatively decondensed chromatin that is available for active transcription. Because it is decondensed it is more accessible to RNA polymerase and, therefore, easier to transcribe. In contrast, heterochromatin is tightly wound, dense DNA that is inaccessible by RNA polymerase and is considered inactive.

Translation is the process of synthesizing proteins from mRNA transcripts and does not directly involve DNA or chromatin.

Example Question #4 : Chromatin And Chromosomes

Which of the following is true of chromatin?

Possible Answers:

Nucleosomes consist of DNA wrapped in proteins known as transcriptions factors

Chromatin is present in all eukaryotic and prokaryotic DNA

Chromatin never gets further compacted than the 10nm fiber

Patterns of methylation or acetylation of histones can regulate gene expression

Correct answer:

Patterns of methylation or acetylation of histones can regulate gene expression

Explanation:

Chromatin is not present in all eukaryotic and prokaryotic DNA; most prokaryotic DNA is circular and does not require the complex folding of eukaryotic chromatin. Chromatin exists in more compacted states than 10nm. In particular, the 30nm version is commonly recognized as heterochromatin (DNA that is not being actively transcribed). Packaging can also be more condensed during certain stages of mitosis. Nucleosomes are the smallest units of chromatin and are strands of DNA wrapped in proteins known as histones.

Patterns of methylation and acetylation of these histones have been shown to repress and activate gene expression, respectively, and are important factors in regulating gene expression and epigenetics.

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