Prokaryotic Genetics

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MCAT Biology › Prokaryotic Genetics

Questions 1 - 10
1

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

Plasmid

Nucleus

Prophage

Nucleoid

Nuclear area

Explanation

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

2

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?

Transformation

Conjugation

Transduction

Binary fission

Mutation

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.

3

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

sex pilus . . . plasmid

plasmid . . . sex pilus

plasmid . . . nucleoid

sex pilus . . . nucleoid

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.

4

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

Conjugation

Transformation

Transduction

Binary fission

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.

5

Which of the following is false regarding plasmids?

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

A plasmid is a circular DNA molecule

Plasmids can contain genes that code for the sex pilus

Plasmids may provide antibiotic resistance

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.

6

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

II and III

I only

II only

I and II

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.

7

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

Transformation

Transduction

Conjugation

Conduction

Reproduction

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.

8

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?

Episomes because they can integrate with chromosomes

Plasmids because they can integrate with chromosomes

Plasmids because they contain genes for antibiotic resistance

Episomes because they contain genes for antibiotic resistance

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.

9

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

Glycerol

Adenine

Phosphate group

Pentose sugar

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.

10

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

Both processes involve genetic recombination

Both processes produce four haploid cells

Both processes are a form of asexual reproduction

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

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.

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