MCAT Biology : Prokaryotic Genetics

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

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Example Question #31 : Microbiology

Which of the following is false regarding plasmids?

Possible Answers:

Plasmids may provide antibiotic resistance

A plasmid is a single-stranded DNA molecule found outside the nucleoid

Plasmids can contain genes that code for the sex pilus

A plasmid is a circular DNA molecule

Correct answer:

A plasmid is a single-stranded DNA molecule found outside the nucleoid

Explanation:

Plasmids are circular, double-stranded DNA molecules found outside the nucleoid (extrachomosomal DNA). They can serve a variety of functions and code for traits that may vary within a single species, since different individuals may carry different plasmids.

Most notable are the plasmids related to antibiotic resistance and plasmids required for formation of the sex pilus in conjugation. Recall that antibiotic resistance is the ability of a bacterial cell to survive in the presence of antibiotics. This ability is facilitated by antibiotic resistant proteins that are coded by certain genes found on the plasmid of a bacterial cell.

Example Question #32 : Microbiology

Viruses can infect host cells by incorporating themselves into the host cell’s genome. Based on this information, what will you most likely find in a virus?

Possible Answers:

Episomes because they can integrate with chromosomes

Plasmids because they contain genes for antibiotic resistance

Plasmids because they can integrate with chromosomes

Episomes because they contain genes for antibiotic resistance

Correct answer:

Episomes because they can integrate with chromosomes

Explanation:

The question states that a virus infects a host cell by integrating with the host cell’s genome; therefore, the virus integrates with the chromosomes inside the nucleus of the host cell. Recall that both plasmids and episomes are extrachromosomal DNA molecules (DNA molecules found outside the chromosomes), however, only episomes can integrate with the chromosomes inside the nucleus of a host cell. This means that a virus will only be able to infect host cells if it contains an episome. Plasmids are only found in bacteria and cannot integrate with chromosomal DNA.

Example Question #33 : Microbiology

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

Possible Answers:

Glycerol

Pentose sugar

Phosphate group

Adenine

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 #34 : Microbiology

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

Conduction

Conjugation

Transduction

Transformation

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:

Inability to create proton gradients

Presence of a cell wall

Post-transcriptional modification of mRNA

Lack of a cytoplast

mRNA translation simultaneous to transcription

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:

Conjugation

Transformation

Genetic translation

Genetic anticipation

Transduction

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 #33 : 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:

Genetic translation

Transformation

Conjugation

Transduction

Genetic anticipation

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.

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