MCAT Biology : Prokaryotic Genetics

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

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Example Question #1 : Prokaryotic Genetics

Which answer choice correctly pairs the mode of bacterial genetic transfer with its definition?

Possible Answers:

Transformation—a bacteriophage picks up genetic material from one bacterium and then infects another, transferring the material to the second cell

Conjugation—a bacterium picks up a piece of genetic material from its external environment

Transduction—a bacterium picks up a piece of genetic material from its external environment

 Transduction—a bacteriophage picks up genetic material from one bacterium and then infects another, transferring the material to the second cell

Transformation—a bacterial cell directly transmits part of its F plasmid to another bacterium via a bridgelike structure called a pilus

Correct answer:

 Transduction—a bacteriophage picks up genetic material from one bacterium and then infects another, transferring the material to the second cell

Explanation:

The three main modes of genetic transfer for prokaryotes are transformation, transduction, and conjugation. Transformation occurs when a bacterium picks up a piece of genetic material from its external environment and incorporates it into its own genome. Transduction is genetic transfer using a bacteriophage as a vector. Conjugation is direct gene transfer via sex pili.

Example Question #2 : Prokaryotic Genetics

Frederick Griffith's experiments showed that formerly harmless IIR bacteria had become deadly in mice. This change took place when the harmless IIR bacteria were exposed to the remains of heat killed IIIS bacteria. Based on this experiment, what was the process that converted the harmless bacteria to a deadly strain?

Possible Answers:

Transformation

Transduction

Mutation

Binary fission

Conjugation

Correct answer:

Transformation

Explanation:

The IIR bacteria became deadly when exposed to the remains of the IIIS bacteria. This means that the IIR bacteria managed to receive genetic material from the environment and incorporate it into their genome. This is an example of transformation, a process that results in genetic recombination. In this case, the recombination made the formerly harmless bacteria deadly in mice.

Transduction is the process by which new genetic information is introduced to a bacterium via a vector, such as a bacteriophage. Conjugation is the transfer of genetic material between bacteria via a sex pilus. Binary fission is not a means of recombination; rather, the parent cell divides to produce two identical copies of itself.

Example Question #2 : Understanding Prokaryotic Inheritance

Which recombinant process depends on a F factor plasmid?

Possible Answers:

Conjugation

Translocation

Transformation

Transduction

Correct answer:

Conjugation

Explanation:

Beginning the process of conjugation requires the trait encoded by the F (fertility) plasmid. Transformation is the uptake of naked DNA, transduction is the transfer of genetic material via a virus, and translocation is the movement of a ribosome during protein translation.

Example Question #3 : Understanding Prokaryotic Inheritance

What type of prokaryotic genetic recombination requires the presence of plasmids?

Possible Answers:

Transduction

Binary fission

Conjugation

Transformation

Correct answer:

Conjugation

Explanation:

Conjugation is a type of genetic recombination that requires one bacterium to have the F-plasmid in order to create a sex pilus. This sex pilus will connect with another bacterium and allow DNA to pass between the bacteria.

Transduction is the transfer of genetic information to a bacterium via a vector, such as a bacteriophage. Transformation occurs when a bacterial cell receives genetic material from its surrounding environment. Binary fission does not involve recombination, and is the term for bacterial cell division that results in two identical offspring from a single parental cell.

Example Question #3 : Prokaryotic Genetics

Which of the following is false about conjugation?

I. It is a form of sexual reproduction

II. It forms a bridge between two bacterial cells; the bridge is called a plasmid

III. It involves transport of genetic material via vectors

Possible Answers:

I only

I and II

II and III

II only

Correct answer:

II and III

Explanation:

Bacterial cells are capable of conjugation, a form of sexual reproduction. The process involves the formation of a bridge between bacterial cells that facilitates the movement of genetic material from one cell to the other. This bridge is called a sex pilus. A plasmid is a circular extrachromosomal DNA fragment. To initiate conjugation, a bacterium must possess a plasmid that enables formation of the sex pilus.

Bacterial cells can also exchange genetic material indirectly via viral vectors (certain bacteriophages) that carry bacterial genetic information from one cell to another; however, this does not occur in conjugation. It occurs in another form of sexual reproduction called transduction.

Example Question #4 : Prokaryotic Genetics

A bacterial cell must possess a __________ gene on the __________ in order to initiate conjugation.

Possible Answers:

sex pilus . . . plasmid

sex pilus . . . nucleoid

plasmid . . . nucleoid

plasmid . . . sex pilus

Correct answer:

sex pilus . . . plasmid

Explanation:

Conjugation is a form of sexual reproduction in bacterial cells. It involves formation of a bridge, called the sex pilus, between two bacterial cells. After sex pilus formation, the donor cell will pass genetic information to the recipient cell via the sex pilus. In order to initiate conjugation, a bacterial cell must contain the genes that code for the sex pilus, which are usually found on a specific plasmid. Recall that a plasmid contains the extrachromosomal DNA (found outside the bacterial cells’ chromosomes), whereas the nucleoid contains the chromosomal DNA. Sex pilus genes are always found on the plasmid, and can be passed from one cell to another during conjugation. This exchange increases the number of cells capable of forming the sex pilus, increasing the ability for bacterial cells to perform sexual reproduction and increase genetic variation.

Example Question #5 : Prokaryotic Genetics

Which of the following is true of both bacterial conjugation and meiosis?

Possible Answers:

Both processes involve genetic recombination

Both processes produce four haploid cells

Bacterial conjugation is a form of sexual reproduction, whereas meiosis is a form of asexual reproduction

Both processes are a form of asexual reproduction

Correct answer:

Both processes involve genetic recombination

Explanation:

The only similarity between conjugation and meiosis is that both processes are types of sexual reproduction. Remember that sexual reproduction is characterized by the presence of genetic recombination (the ability to exchange genetic material between two DNA molecules). The result of both processes are daughter cells that are genetically unique from the parent cells.

In meiosis, genetic recombination occurs during crossing over in prophase I. In conjugation, genetic recombination occurs when the DNA from the donor bacterial cell is incorporated into the recipient bacterial cell. Only meiosis produces four daughter cells; conjugation produces only two.

Example Question #3 : Prokaryotic Genetics

What is the structure in prokaryotic cells that often holds antibiotic resistance genes?

Possible Answers:

Prophage

Nucleus

Nuclear area

Nucleoid

Plasmid

Correct answer:

Plasmid

Explanation:

Antibiotic resistance genes are often found on plasmids, which are small DNA molecules which are easily transfered to other prokaryotic cells.

Example Question #6 : Prokaryotic Genetics

In a small village, a doctor over-prescribed Ciprofloxin (an antiobiotic) to his patients. The result was that the majority of his patients had developed a new strain of bacteria that had become resistant to Ciprofloxin. 

What is a possible route that may have caused these bacteria to become antibiotic resistant?

Possible Answers:

The bacteria developed a way to prevent the antibiotic from entering into their cells

The antibiotic resistant bacteria had the ability to degrade the antibiotic in their lysosomes

The antibiotic lost its potency

An antibiotic resistant gene was passed on through the plasmids in a group of antibiotic resistant bacteria

The bacteria learned to metabolize the antibiotic

Correct answer:

An antibiotic resistant gene was passed on through the plasmids in a group of antibiotic resistant bacteria

Explanation:

Antibiotic resistant genes are commonly transferred through plasmids. Plasmids are small, circular, extra-chromosomal pieces of DNA that contain supplemental genes, which can be passed from bacteria to bacteria.

Example Question #4 : Prokaryotic Genetics

Which of the following characteristics make plasmid DNA useful for researchers?

Possible Answers:

All of the answers

Capable of being isolated from genomic DNA 

Readily incorporate cloned DNA

Capable of autonomous replication

Correct answer:

All of the answers

Explanation:

Plasmids are phenomenally useful for a number of reasons. They are capable of autonomous replication inside a suitable host (such as simple prokaryotes). Because they are non-genomic DNA (not located in the nucleus), plasmids are easily isolated and separated from the host's DNA. It is also relatively easy to insert cloned DNA into plasmid vectors. This allows for expression of recombinant proteins in prokaryotic cells.

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