MCAT Biology : Biology

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #31 : 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:

Transformation

Reproduction

Transduction

Conjugation

Conduction

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 #32 : Microbiology

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

Possible Answers:

Presence of a cell wall

mRNA translation simultaneous to transcription

Lack of a cytoplast

Post-transcriptional modification of mRNA

Inability to create proton gradients

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 #973 : Biology

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:

Transduction

Conjugation

Genetic translation

Transformation

Genetic anticipation

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 #974 : Biology

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 anticipation

Conjugation

Transformation

Transduction

Genetic translation

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 #33 : Microbiology

A researcher isolates a strain of bacteria. When he adds an antibiotic, he notices that the bacterial cell division stops and the sample of bacteria dies out over time. What can the researcher conclude about the antibiotic and its effects on mitosis?

Possible Answers:

Mitosis is irrelevant to this question because bacterial cells do not undergo mitosis

It stops mitosis, but the researcher needs more information to determine the prevention mechanism

It stops mitosis by improperly aligning DNA at the metaphase plate

It stops mitosis by preventing the formation of the mitotic spindle apparatus

Correct answer:

Mitosis is irrelevant to this question because bacterial cells do not undergo mitosis

Explanation:

The question states that the antibiotic halts the bacterial cell division. Recall that mitosis is a form of asexual reproduction that produces two diploid daughter cells with identical DNA. Mitosis, however, is only found in eukaryotic cells. The analogous asexual reproduction in prokaryotic cells is called binary fission. In binary fission, bacterial cells replicate their circular DNA in such a way that the end products are two double-stranded, circular DNA molecules. Each DNA molecule migrates to opposite ends of the cell and the cell splits into two new daughter cells with identical DNA. The question asks about the effect of the antibiotic on mitosis; since the process doesn’t occur in prokaryotic cells, mitosis is irrelevant to this question.

Example Question #34 : Microbiology

Which of the following is a form of asexual reproduction in prokaryotic cells?

Possible Answers:

Binary fission and meiosis

Binary fission

Binary fission and mitosis

Binary fission and transformation

Correct answer:

Binary fission

Explanation:

Prokaryotic cells can reproduce either sexually and asexually. In a bacterial cell, sexual reproduction occurs via three different methods: conjugation, transformation, and transduction. Conjugation involves the exchange of genetic material (plasmids) between bacterial cells through a bridge called the sex pilus. Transformation involves the incorporation of extracellular DNA from the environment. Transduction involves the transmission of genetic material from one bacterial cell to another by a viral vector. These three processes are considered forms of sexual reproduction because all of them involve genetic recombination.

Prokaryotic cells can reproduce asexually only through binary fission. Binary fission is the process by which a bacterial cell splits into two identical daughter cells. This is a very fast process and contributes to the rapid growth and replication of bacteria.

Mitosis and meiosis are only found in eukaryotic cells. Mitosis is a form of asexual reproduction and meiosis is a form of sexual reproduction, since it involves genetically unique daughter cells. Binary fission is the prokaryotic analog of mitosis, but is a distinctly different process.

Example Question #1 : Prokaryotic Reproduction And Physiology

What is the significance of endospores?

Possible Answers:

They allow fungi to store nutrients that can survive extreme conditions

They allow fungi to survive in extreme climates

They allow gram-negative bacteria to reproduce

They are produced by gram-positive bacteria which can survive extreme conditions

Correct answer:

They are produced by gram-positive bacteria which can survive extreme conditions

Explanation:

Endospores are produced by gram-positive bacteria and can lie dormant for years. Endospores are crucial to growth of gram-positive bacteria because they resist harsh conditions such as extreme temperatures, ultraviolet radiation, and many chemicals. Endospores are not used by fungi by any means. They are also uninvolved in the reproductive processes of bacteria. 

Example Question #41 : Microbiology

Which of the following types of bacterial reproduction is most similar to mitosis?

Possible Answers:

Transformation

Conjugation

Binary fission

Transduction

Correct answer:

Binary fission

Explanation:

Mitosis is a form of asexual reproduction in which genetic recombination does not take place; the daughter cells are identical to the parent cell. Prokaryotes are able to divide asexually using binary fission, producing two exact copies of the parent cell. The mechanisms governing binary fission are quite different from those governing mitosis, but the end result is the same.

The other three options are examples in which prokaryotic genetic recombination takes place. Conjugation involves the transfer of genetic material between two bacteria via a sex pilus. Transduction is the transfer of genetic material to a bacterium via a vector, such as a bacteriophage. Transformation occurs when the bacterium uptakes exogenous DNA from the environment.

Example Question #2 : Prokaryotic Reproduction And Physiology

A microbiologist sees that a certain strain of E. coli grew in population size from 20,000 cells to 160,000 cells in two hours. How long would it take this strain to undergo 15 doubling cycles?

Possible Answers:

600hr

10hr

30h

20hr

5h

Correct answer:

10hr

Explanation:

We must first find out how long a doubling cycle is for this strain.  We can determine the following relationships from the information in the question.

So, in two hours, the bacteria has undergone three doubling cycles from 20000 to 160000. That means the doubling time is one-third of two hours, or one-third of 120 minutes.

 

The doubling time is 40 minutes.

The bacteria will undergo 15 doubling cycles in 600 minutes, or ten hours.

Example Question #1 : Bacteria And Types Of Prokaryotes

All of the following are characteristics of prokaryotic cells except for __________.

Possible Answers:

unicellularity

lack of membrane-bound organelles

they are usually found in protists and fungi

lack of a nucleus

a cell wall

Correct answer:

they are usually found in protists and fungi

Explanation:

Protists, fungi, plants, and animals are eukaryotic, while bacteria are prokaryotic. The rest of the answer choices are characteristic of prokaryotic cells.

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