MCAT Biology Review

Chapter 1: The Cell

Practice Questions

1. Hyperbaric oxygen may be used as a treatment for certain types of bacterial infections. In this therapy, the patient is placed in a chamber in which the partial pressure of oxygen is significantly increased, increasing the partial pressure of oxygen in the patient’s tissues. This treatment is most likely used for infections with:

1. obligate aerobic bacteria.

2. facultative anaerobic bacteria.

3. aerotolerant anaerobic bacteria.

4. obligate anaerobic bacteria.

2. Which of the following does NOT describe connective tissue cells?

1. They account for most cells in muscles, bones, and tendons.

2. They secrete substances to form the extracellular matrix.

3. In organs, they tend to form the stroma.

4. In organs, they provide support for epithelial cells.

3. Which of the following types of nucleic acid could form the genome of a virus?

1. Single-stranded RNA

2. Double-stranded DNA

3. Single-stranded DNA

1. I only

2. II only

3. I and II only

4. I, II, and III

4. Which of the following activities occurs in the Golgi apparatus?

1. Synthesis of proteins

2. Modification and distribution of proteins

3. Breakdown of lipids and carbohydrates

4. Production of ATP

5. Mitochondrial DNA is:

1. circular.

2. self-replicating.

3. single-stranded.

1. I only

2. II only

3. I and II only

4. I, II, and III

6. Which of the following is NOT a function of the smooth endoplasmic reticulum?

1. Lipid synthesis

2. Poison detoxification

3. Protein synthesis

4. Transport of proteins

7. What is the main function of the nucleolus?

1. Ribosomal RNA synthesis

2. DNA replication

3. Cell division

4. Chromosome assembly

8. Which of the following organelles is surrounded by a single membrane?

1. Lysosomes

2. Mitochondria

3. Nuclei

4. Ribosomes

9. Which of the following is NOT a difference that would allow one to distinguish a prokaryotic and a eukaryotic cell?

1. Ribosomal subunit weight

2. Presence of a nucleus

3. Presence of a membrane on the outside surface of the cell

4. Presence of membrane-bound organelles

10.Which of the following does NOT contain tubulin?

1. Cilia

2. Flagella

3. Microfilaments

4. Centrioles

11.Herpes simplex virus (HSV) enters the human body and remains dormant in the nervous system until it produces an outbreak after exposure to heat, radiation, or other stimuli. Which of the following statements correctly describes HSV?

1. While it remains dormant in the nervous system, the virus is in its lytic cycle.

2. During an outbreak, the virus is in the lysogenic cycle.

3. Herpes simplex virus integrates itself into the DNA of the cell.

4. The herpes simplex virus contains a tail sheath and tail fibers.

12.Resistance to antibiotics is a well-recognized medical problem. Which mechanism(s) can account for a bacterium’s ability to increase its genetic variability and thus adapt itself to different antibiotics?

1. Binary fission

2. Conjugation

3. Transduction

1. I and II only

2. I and III only

3. II and III only

4. I, II, and III

13.A bacterial cell is noted to be resistant to penicillin. The bacterium is transferred to a colony that lacks the fertility factor, and the rest of the colony does not become resistant to penicillin. However, the penicillin-resistant cell has also started to exhibit other phenotypic characteristics, including secretion of a novel protein. Which of the following methods of bacterial recombination is NOT likely to account for this change?

1. Conjugation

2. Transformation

3. Transduction

4. Infection with a bacteriophage

14.In Alzheimer’s disease, a protein called the amyloid precursor protein (APP) is cleaved to form a protein called β-amyloid. This protein has a β-pleated sheet structure and precipitates to form plaques in the brain. This mechanism of disease is most similar to which of the following pathogens?

1. Bacteria

2. Viruses

3. Prions

4. Viroids

15.After infection of a cell, a viral particle must transport itself to the nucleus in order to produce viral proteins. What is the likely genomic content of the virus?

1. Double-stranded DNA

2. Double-stranded RNA

3. Positive-sense RNA

4. Negative-sense RNA

PRACTICE QUESTIONS

Answers and Explanations

1. D

Obligate anaerobes cannot survive in the presence of oxygen and would likely be killed by such a therapy, treating the infection. The other types of bacteria listed can all survive in the presence of oxygen and would likely not be treated using this therapy.

2. A

While bones and tendons are composed predominantly of connective tissue cells, muscle tissue is considered a different tissue type. Other examples of connective tissue include cartilage, ligaments, adipose tissue, and blood. Connective tissue often secretes substances to form the extracellular matrix, such as collagen and elastin, eliminating choice (B). Choices (C) and (D) are essentially identical and can both be eliminated: in organs, connective tissue often forms the support structure for epithelial cells, called the stroma.

3. D

In a virus, the nucleic acid can be either DNA or RNA and—in both cases—can be either single- or double-stranded. Therefore, all of the types of nucleic acids listed here could be used for a viral genome, making choice (D) the correct answer.

4. B

The Golgi apparatus consists of a stack of membrane-enclosed sacs. It receives vesicles and their contents from the endoplasmic reticulum, modifies them (through glycosylation, phosphorylation, and other mechanisms), repackages them into vesicles, and distributes them to appropriate locations in the cell. Protein synthesis occurs in ribosomes and rough endoplasmic reticulum, eliminating choice (A). Lipid and carbohydrate breakdown takes place in the peroxisomes and cytoplasm, eliminating choice (C). ATP production occurs in the mitochondria, eliminating choice (D).

5. C

Mitochondria are thought to have evolved from an anaerobic prokaryote engulfing an aerobic prokaryote and establishing a symbiotic relationship; therefore, mitochondrial DNA, or mDNA, is likely to be similar to bacterial DNA. Both mDNA and bacterial DNA are organized into a single circular chromosome of double-stranded DNA that can replicate during binary fission. Therefore, Statements I and II are correct, while Statement III is incorrect.

6. C

The smooth endoplasmic reticulum is involved in the transport of materials throughout the cell, in lipid synthesis, and in the detoxification of drugs and poisons. Proteins from the rough ER can cross into the smooth ER, where they are secreted into cytoplasmic vesicles and transported to the Golgi apparatus. Thus, from the given choices, protein synthesis is not a function of the smooth ER, but rather of the free ribosomes or the ribosomes associated with the rough ER. Choice (C) is therefore the correct answer.

7. A

The nucleolus (not to be confused with the nucleus in general) is a dense structure within the nucleus where ribosomal RNA (rRNA) is synthesized. Choice (A) is therefore the correct answer.

8. A

Lysosomes are vesicular organelles that digest material using hydrolytic enzymes. They are surrounded by a single membrane. Both mitochondria and nuclei are surrounded by double membranes, eliminating choices (B) and (C). Ribosomes must not be surrounded by membranes because they are found not only in eukaryotes, but also in prokaryotes, which lack any membrane-bound organelles, eliminating choice (D).

9. C

The main differences between prokaryotes and eukaryotes include: prokaryotes do not have a nucleus, while eukaryotes do, eliminating choice (B); prokaryotes have ribosomal subunits of 30S and 50S, while eukaryotes have ribosomal subunits of 40S and 60S, eliminating choice (A); and prokaryotes do not have membrane-bound organelles, whereas eukaryotes do, eliminating choice (D). The presence of a membrane on the outer surface of the cell could not distinguish a prokaryotic cell from a eukaryotic one because both gram-negative bacteria and animal cells share this feature. Thus, choice (C) is the correct answer.

10.C

Tubulin is the primary protein in microtubules, which are responsible for the structure and movement of cilia and flagella, eliminating choices (A) and (B). Centrioles organize microtubules in the mitotic spindle, eliminating choice (D). Microfilaments are not composed of tubulin, but rather actin, making choice (C) the correct answer.

11.C

Viruses can exist in either the lytic or lysogenic cycle; they may even switch between them throughout their lifetime. During the lytic cycle, the virus’s DNA takes control of the host cell’s genetic machinery, manufacturing numerous progeny. In the end, the host cell bursts (lyses) and releases new virions, each capable of infecting other cells. In the lysogenic cycle, viral DNA is integrated into the host cell’s genome, where it can remain dormant for days or years. Either spontaneously or as a result of environmental circumstances, the provirus can reemerge and enter a lytic cycle. Thus, choices (A) and (B) are incorrect because they reverse which part of the cycle the virus is in. Choice (D) describes features of bacteriophages, which are viruses that infect bacteria—not the human nervous system. Choice (C) accurately describes how HSV operates during the lysogenic cycle, making it the correct answer.

12.C

Bacterial cells reproduce by binary fission, an asexual process in which the progeny is identical to the parent. Therefore, Statement I does not increase genetic variability. Conjugation can be described as a sexual mating in bacteria; it is the transfer of genetic material between two bacteria that are temporarily joined. Transduction occurs when fragments of the bacterial chromosome accidentally become packaged into viral progeny produced during a viral infection and can subsequently be introduced into another bacterium by the viral vector. Therefore, both Statements II and III increase bacterial genetic variability.

13.A

A bacterial cell that does not rapidly cause a phenotypic change in the rest of the colony is likely not F⁺, meaning that this cell is not able to form a sex pilus for conjugation. The expression of new phenotypic characteristics indicate that this bacterium may have acquired some quantity of genetic information, which can be acquired by either transformation, choice (B), or transduction (which occurs via bacteriophage infection), choices (C) and (D).

14.C

Prions are infectious proteins that cause misfolding of other proteins. Primarily, prions cause a shift toward β-pleated sheet confirmations, which leads to decreased solubility and degradability of proteins, ultimately leading to disease. This mechanism is very similar to the one described here for Alzheimer’s disease, making choice (C) the correct answer.

15.A

A virus that requires transport to the nucleus in order to produce viral proteins likely requires use of nuclear RNA polymerase in order to create mRNA that can be translated to protein. Only DNA viruses require this transport before any protein can be synthesized.