MMG 301 mcat questions

Frameshift mutations can be very severe. What is one reason why they are often so serious?

When a frameshift mutation occurs, it causes changes in many bases downstream and can affect many of the amino acids in the protein.

A farmer finds that his soybean plants do not look healthy. They appear stunted and the leaves are a yellowish color, indicating possible lack of nitrogen. To have a more successful crop next year, he should consider__________.

inoculating his fields with the appropriate cross-inoculation group of rhizobia

Microbial mats differ from biofilms in that they __________.

are currently found only in extreme habitats

All of the following are true of biofilms EXCEPT that __________. biofilms are composed of only one species at a time biofilms protect organisms from antibiotics biofilm formation and dispersal are regulated processes biofilms form on virtually all submerged surfaces in nature

biofilms are composed of only one species at a time

According to the RNA world hypothesis, which of the following was the correct sequence of developments?

biological building blocks (e.g., amino acids, sugars, and nucleosides), then RNA (including catalytic and self-replicating RNA), then protein synthesis, then DNA, then lipid bilayers surrounding early cellular life

Compared with pure cultures grown in the lab, microbes in nature usually experience a wider range of environmental conditions, more variation in conditions over time, and more contact with other organisms. Therefore, the same organism in nature will __________.

typically grow slower than in pure culture

A soil clump has an oxic (oxygen containing) zone containing aerobic and facultatively aerobic organotrophs, and an anoxic zone containing fermentative bacteria, sulfate reducers, and denitrifyers. This soil clump has at least __________ different habitats, __________ different communities and __________ different guilds.

2,2,5

Why are antibiotics often ineffective in treating food poisoning (food intoxication)?

Antibiotics target bacteria; they do not damage toxins.

The genetic code has many important characteristics. For example, a specific codon always means the same thing in a particular species. Codons mean the same thing in most species (even though there are some exceptions). In some cases, a particular amino acid can be specified by more than one codon (the genetic code is degenerate). Which of the following answers describes an example of the degenerate nature of the code? AUU, AUC, and AUA all code for Ile AUU codes for Ile in a wide variety of species The sequence "AUGCCGAUU" is read as three codons, AUG, then CCG, then AUU. There are no pauses or commas in the code.

AUU, AUC, and AUA all code for Ile

All of the following are Gram-positive genera typically found on the skin EXCEPT __________. Staphylococcus Corynebacterium Bacteroides Propionibacterium

Bacteroides

Which of the following explains why treatment of symptomatic tetanus requires an antitoxin and an antibiotic?

Because C. tetani bacteria excrete tetanus toxin, it is important to neutralize the toxin while also killing the bacteria that are producing more.

Whether a molecule is oxidized or reduced in a redox reaction depends on its reduction potential relative to the available electron donors and acceptors present that the organism can utilize. Given the following reduction potentials for various redox half reactions, in a lithotroph capable of utilizing ammonia as an energy source, which substances would be potential terminal electron acceptors for respiration? NO2 -/NH3 +0.34 V NO3 -/NO2 - +0.43 V O2/H2O +0.82 V

Both O2 and NO3 - are possible electron acceptors

Decomposition of organic carbon ultimately results in the formation of __________.

CO2 in aerobic environments and CO2 plus CH4 in anoxic environments

The resistance of bacterial endospores to heat, harsh chemicals, and radiation has several implications, including all EXCEPT which of the following?

Endospores will not survive passage through the stomach.

Clostridium tetani is an obligate anaerobe that can cause tetanus. When it enters the human body, it can produce tetanus toxin. Considering that C. tetani is an obligate anaerobe, which of the following explains how it can survive and cause disease in the human body?

Especially in deep wounds, C. tetani can sometimes survive in areas with damaged tissue that have become anoxic because of poor-to-no blood flow

What is the difference between an F+ and an Hfr bacterium?

F+ bacteria have a nonintegrated F plasmid, while Hfr bacteria have an F plasmid that is integrated into their main chromosome.

A microbiologist wants to study the virus particles from a urine sample, but not any bacteria that might be present. How can the bacteria be eliminated without harming the viruses?

Filter the sample with a 0.2 ïm pore filter.

Antibiotic resistance is a major concern as microbes can rapidly develop resistance when antibiotics are not used appropriately. Which of the following examples best describes how this occurs?

In any population of microbes, some individuals may have resistance genes. When exposed to an antibiotic, there is selection for the microbes that have these genes.

Horizontal gene transfer refers to the transfer of genes from one organism to another, as occurs during conjugation between bacteria. How does this differ from vertical gene transfer?

In horizontal gene transfer, genes are transferred from one mature adult organism to another. In vertical gene transfer, genes are transferred from adults to offspring.

Eosin-methylene blue agar inhibits the growth of gram-positive organisms while allowing gram-negative organisms to grow. Colonies of lactose fermenters turn a blackish color while nonfermenters are colorless. How would you classify EMB? Is EMB a differential medium or a selective medium? Think about the meaning of the terms differential and selective to choose your answer.

It is a differential medium and a selective medium.

The Ames test is commonly used to test whether a particular chemical is mutagenic. When you conduct an Ames test, you need two groups of plates. One group of plates contains bacteria that are exposed to the chemical of interest, while the other plates contain bacteria that are not exposed to the chemical. Why is the latter group needed if you are just interested in the rate of mutation caused by the chemical?

It is important to compare the rate of mutations with the chemical to the normal background mutation rate. Mutations occur spontaneously even without the presence of a mutagen.

In the lac operon, which of the following conditions would allow the structural genes to be transcribed?

Lactose is present and glucose is absent.

Water supplies are treated with chlorine to kill pathogens. Chlorine reacts well with many other chemicals and bacterial cells because it is a strong oxidant. However, Legionella pneumophila can sometimes evade killing by residual chlorine. How does it do this?

Legionella tends to form biofilms and infect other microbial cells as intracellular pathogens.

Meningococcal meningitis is definitively diagnosed from cultures isolated from nasopharyngeal swabs, blood, or cerebrospinal on Thayer-Martin medium, a selective medium for the growth Neisseria. However, preliminary diagnosis is often based on clinical symptoms, and treatment with antibiotics is started before culture tests confirm infection with N. meningitidis. Why?

Life-threatening symptoms can develop very rapidly.

What is one piece of evidence for the endosymbiotic hypothesis?

Mitochondria have 70S ribosomes.

Which of the following is NOT evidence that mitochondria originated as independent prokaryotes, as stated by the endosymbiont hypothesis?

Mitochondria have a membrane that includes peptidoglycan.

In the first reported epidemiological study in 1854, John Snow attempted to discover the source of a London cholera epidemic by going house-to-house and recording deaths. When he mapped the results, he was able to identify the Broad Street water pump as the likely source of contaminated water. The data collected in this study was__________.

Mortality

A farmer wants to stock small fish in a pond on his property, but the water looks a bit murky to him. He asks a microbiologist friend to analyze the pond water to see if fish could survive there. The microbiologist finds that the water has a very high BOD. Should she tell the farmer to stock the pond with fish?

No; the pond is likely to be anoxic.

One way to test if someone has immunity to a particular pathogen is to measure the antibody titer. What does it mean if someone has a positive antibody titer?

Previous exposure to the pathogen (or through a vaccination) has caused B cells to produce memory B cells. When re-exposed to the pathogen, they rapidly produce antibodies against the antigen (resulting in a positive antibody titer).

Which of the following best explains the endosymbiont hypothesis?

Prokaryotes capable of cellular respiration and prokaryotes capable of photosynthesis took up residence in larger prokaryotes, forming obligate mutualisms. The prokaryotes capable of cellular respiration evolved into mitochondria and the prokaryotes capable of photosynthesis evolved into chloroplasts.

Some organisms are capable of using aerobic respiration or anaerobic respiration but use aerobic respiration preferentially. Why is aerobic respiration favored?

Respiration with oxygen as a terminal electron acceptor generates more energy than respiration with other terminal electron acceptors.

A small farm pond containing many species of microorganisms (bacteria, cyanobacteria, algae, and protozoa) was perturbed when runoff from a manure pile entered the pond. The added nutrients soon turned the water green due to a bloom of cyanobacteria. How did this affect the microbial community in the pond?

Species richness decreased and species abundance increased.

If an organism used glycolysis (Embden-Meyerhof-Parnas pathway) to break down glucose and produce ATP but was unable to subsequently use fermentation or an electron transport chain (respiration), what problem would develop?

The available NAD+ would be converted to NADH and glycolysis would eventually stop due to the lack of NAD+.

Researchers discover a new species of bacterium that has an unusual metabolism. However, it has biochemical and morphological similarities to other species. What is the most comprehensive and effective approach to determine how to classify these bacteria?

The bacteria should be classified by using genomic analyses to construct phylogenies.

Two-component regulatory systems rely on a balance of phosphorylation and dephosphorylation of sensor kinases and response regulators. If the response regulator became permanently phosphorylated due to lack of phosphatase activity, which of the following would NOT happen?

The cell would become more sensitive to the environmental stimulus.

Which of the following would result in a frameshift mutation? The deletion of three nucleotides in a codon The deletion of two nucleotides in a codon The deletion of one nucleotide from one codon and two nucleotides from the adjacent codon The addition of three nucleotides between two existing codon.

The deletion of two nucleotides in a codon

What would be the most likely effect of a mutation in the operator of a lac operon?

The genes would be constitutively expressed.

If a bacterial culture contains 1 cell at time zero, 4 cells after 1 hour, and 16 cells after 2 hours, then all EXCEPT which of the following are true?

The growth rate is increasing with each generation.

Plaque assays are often used to estimate the number of virions in a sample of a particular volume (the titer). The count is given as plaque-forming units. Which of the following is NOT generally a concern that must be considered in evaluating the results of plaque assays?

The largest problem is that single viruses may create multiple plaques, resulting in overestimates of the number of viruses present.

A nurse takes a urine sample from a patient suspected of having contracted a urinary tract infection. The nurse uses careful aseptic technique in collecting the sample. Which is NOT a reason for using aseptic technique in this situation?

The nurse wants to get as many organisms as possible to grow in the culture medium.

A single base substitution happens to cause a nonsense mutation early in the gene for a protein. What will be the result?

The protein will be truncated so much that it is unlikely to function normally.

Which of the following describes an example of antigenic shift?

The surface antigens of a virus become drastically changed as a result of the combining of genetic material from different viruses within one organism.

When a child begins to get its first teeth, what happens to the microbiota in the oral cavity?

The teeth are rapidly colonized by anaerobes, in particular Streptococcus, that are specifically adapted to growth in biofilms on the surfaces of the teeth.

Considering that they require an oxygen-free environment, how do obligate anaerobes survive in the human body?

They are able to survive in places where aerobic organisms quickly use the available oxygen. They can also survive in areas with impaired blood flow (reducing oxygen availability).

In a culture of bacteria, there are some individuals that are unable to synthesize histidine. What is the best and most likely description of how these individuals differ from the other bacteria in the culture?

They differ in their genotype and in their phenotype.

Wild rodents are the major reservoir of the plague organism, Yersinia pestis, but pandemic plagues were historically associated with crowded, unsanitary urban areas. Why is this the case?

Yersinia pestis can be transmitted by fleas from wild rodents to urban rats, which quickly die of the disease. Humans are accidental hosts due to fleas seeking out blood meals after most rats have succumbed to the disease.

Staining increases the visible contrast of cells compared with the background. Because the Gram stain results in some types of bacteria staining purple and other types appearing pink, this is called __________ stain.

a differential

One way that regulation is often studied is by examining the effects of mutations. For example, mutations within the parts of the lac operon have been well studied. Which of these mutants would be considered a constitutive mutant?

a mutation that disables the repressor

Some viruses have plus sense RNA genomes. Which of the following could describe one of those viruses?

a virus that contains RNA with the same nucleotide sequence as the functional mRNA that its host cell will translate to produce viral products

The main functions of the bacterial cell wall include all of the following EXCEPT __________.

actively transporting solutes against the concentration gradient

While most of the oil spilled into the Gulf of Mexico from the Deepwater Horizon drilling rig in 2010 has disappeared, some of the oil spilled from the Exxon Valdez oil tanker into Prince William Sound, Alaska, in 1989 still remains in the coastal sand and sediments. What possible differences in these two spills could account for the different rates of petroleum degradation?

ambient temperatures and the types of hydrocarbons present

Phylogenetic trees for bacteria are constructed by which of the following?

analyzing molecular similarities and then using computer algorithms or optimality criteria to construct phylogenetic trees showing hypothesized evolutionary relationships

Symbionts can be acquired by an individual host organism horizontally (from the environment) or vertically (from a parent). In humans, there is evidence that infants are largely colonized by their parents' microbes, and family members living in the same household have microbiomes that are more similar than those of individuals living nearby. However, no two humans have identical microbiota, and certain factors, such as diet and antibiotics, can alter the microbiome. This indicates that humans may be colonized by __________.

both vertical and horizontal transmission

The enzyme lysozyme kills bacterial cells by cleaving the β-1,4-glycosidic bonds in the peptidoglycan. This leads to which of the following?

breaches of the cell wall and cell lysis due to osmotic swelling

The step in Koch's postulates that most critically enabled him to determine that a particular microbe was the cause, and not an effect, of a particular disease was __________.

cells from a pure culture of the suspected pathogen must cause the disease in a healthy susceptible animal

In 2011, the CDC reported a 28-state outbreak of Listeria monocytogenes that killed 33 people in the United States. The victims were found to have eaten portions of whole cantaloupe melons originating from a single farm in Colorado. The FDA traced the source of bacterial contamination to a piece of used equipment that had been recently purchased to wash the melons, nearby puddles of water, and a truck that hauled spoiled melons to a field to be fed to cattle. This would be an example of __________.

common-source transmission

The strategy for bioremediation of large sites contaminated by inorganic pollutants like toxic metals and radionuclides is usually to __________.

contain the pollutants by converting them into a less mobile form

By isolating total community RNA, using reverse transcriptase to make cDNA copies of it, and then sequencing the cDNA, ecologists can __________.

determine the community genome expression at the moment of sampling

The emergent H5N1 strain of avian influenza can occasionally be transmitted from birds to humans with a resulting 60% mortality rate (compared with a 2.5% mortality rate for the 1918 pandemic influenza). In 2012, after a single dead chicken in a wholesale market in Hong Kong tested positive for H5N1, all 17,000 chickens in the market and surrounding area were culled. This was an attempt to__________.

eliminate a reservoir.

Phylogenetic analysis of microbial communities in nature using various PCR techniques has revealed that only a minority of phylotypes have been cultured from the environment and the most common phylotypes have not been grown in in the laboratory. This is due in part to __________.

enrichment bias

Trace elements are found in bacterial cells in very small amounts because they __________.

function only in a limited set of enzymes and cofactors

Which of the following would NOT be required to grow an autotroph? water trace elements potassium phosphate glucose

glucose

For many years the CDC focused its seasonal influenza vaccination efforts on those groups in the population who suffered the highest influenza mortality rates, including the elderly aged 65 years and older. However, starting in 2008 the CDC shifted their focus to school-aged children and began recommending the vaccine for everyone aged at least 6 months. Research had shown no evidence for any protective effect of the vaccine in the elderly. By changing the recommendations for who should be vaccinated, the CDC planned to better protect the elderly by means of__________.

herd immunity.

Given that the cytoplasmic membrane has a fluid dynamic nature, with phospholipids and proteins able to move about within the bilayer structure, what force or structure keeps the membrane from falling apart?

hydrophilic/hydrophobic forces

The phylogenetic diversity analysis of complex microbial communities often targets small subunit (SSU) ribosomal RNA genes. This is because rRNA is found in all organisms and __________.

is highly conserved over evolutionary time

In a batch culture, bacterial cultures typically exhibit four different phases of growth. In which phase are the cells rapidly synthesizing proteins, but cell numbers are not changing?

lag phase

Given the extremely low concentrations of nutrients in the open ocean, most marine Bacteria typically need all of the following adaptations EXCEPT __________. many periplasmic binding proteins large cell size proteorhodopsins high surface area-to-volume ratios

large cell size

Which of the following presents processed antigens to T cells? immunoglobins major histocompatibility complex proteins bacterial cells transplanted tissues

major histocompatibility complex proteins

Although the existence of microorganisms was surmised long before, their discovery depended upon a technological development (the microscope) in order for scientists to

make direct observations of microbes

If a researcher wanted to compare the enzymatic capacity to degrade compounds in a water column at various depths under a specific set of conditions, which would be the most useful approach? genomics metaproteomics metagenomics metabolomics

metaproteomics

The evolution of plants that grow on dry land is thought to have depended in part on their development of symbiotic associations with which group of microorganisms?

mycorrhizae

Both ammonium (NH4+) and nitrate (NO3-) are assimilated by primary producers, but ammonium is the preferred form of nitrogen for fertilizers used in agriculture because __________.

nitrate leaches out of soils easily due to its negative charge

Fermentation occurs when there is no usable external electron acceptor (like O2) available for respiration. Fermentation products are made following glycolysis as a result of reactions that __________.

oxidize NADH so that NAD+ can be reused again in glycolysis

Genes that retain their function yet change over evolutionary time as organisms diverge are called orthologs. Organisms with identical or very similar orthologous genes belong to the same __________.

phylotype

A student has a pure culture of bacteria growing in a flask and wants to know how many living cells are in the culture at a given time. Which method should she employ to get an estimate?

plate counts

Which of the following is NOT included in the genome?

proteins

As a microbiologist, you have been asked to advise a town council on the possible ways to remove PCB contaminants from the local groundwater. Which microbial process is most likely to have bioremediation potential in this case?

reductive dechlorination

Metagenomics involves the analysis of a microbial community by __________.

sampling and sequencing all of the genes in an environment

About half of the clinical cases of severe sore throat are due to Streptococcus pyogenes, and most of the rest are due to viral infections. Accurate and rapid diagnosis of a severe sore throat is important because untreated group A streptococcal infections can lead to __________.

scarlet fever, rheumatic fever, acute glomerulonephritis, and streptococcal toxic shock syndrome

Enrichment cultures are often effective for isolating bacteria from complex communities in natural samples because they __________.

select both for and against certain bacteria

The cytoplasmic membrane is termed "semi-permeable" because some substances, like water and alcohols, can pass freely through while others, like sugars, amino acids, and ions, cannot. What molecular characteristics largely determine whether or not a substance can pass through the membrane?

size and hydrophobicity

Electron carriers used in electron transport chains are always found in membranes. Which one of the following statements is NOT a reason why electron transport chains are found in membranes? so that the electron carriers can be oriented within the membrane such that protons are passed from one side of the membrane to the other So that electron-only carriers can be arranged to alternate with electron-plus-proton carriers in the chain. so that they can transport NADH out of the cell to the periplasm so that they can efficiently pass electrons in sequence from the carriers with the more negative reduction potentials to those with the more positive reduction potentials

so that they can transport NADH out of the cell to the periplasm

Industrial production of nitrogenous fertilizers from N2 now equals or exceeds the amount of nitrogen fixation carried out by microbes in the biosphere. The resulting increase in primary production is an example of the fact that __________.

the C and N cycles are closely coupled

Gene duplication is thought to have had a significant influence on the evolution of microbes because __________.

the duplicated gene can be mutated, possibly leading to a useful new gene function or product, while the original copy can still perform its original (and possibly essential) genetic function

The reduction potential (E0′) of a substance reflects its tendency to donate or accept electrons. The larger the difference (ΔE0′) between the reduction potentials of the electron donor and the electron acceptor, __________.

the greater the change in free energy (ΔG0′), and the greater the energy released

What was the LUCA?

the last organism prior to the divergence of bacteria and archaea

Which of the following is an example of humoral immunity? dendritic cells presenting antigens to leukocytes. the stimulation of fever by a pyrogen the production of antibodies by T cells the production of antibodies by B cells

the production of antibodies by B cells

In a bacterial cell undergoing binary fission and balanced growth, __________.

the proportion of all cell constituents will remain the same over time

Electron microscopy can produce images with much higher magnification and resolution than light microscopy due to

the shorter wavelength of an electron.

Transport proteins (transporters) require energy expenditure for each molecule of substrate transported. The reason for this energy requirement is __________.

the solute must be transported against a concentration gradient

Bacterial fermenters themselves are a significant source of nutrition for ruminants, but not for hindgut fermenters, because __________.

they pass through an acidic chamber and are digested

A patient is brought to the hospital with severe gastrointestinal distress, including cramps, dehydration and diarrhea. Which of the following symptoms would indicate that the pathogen is Vibrio cholerae?

voluminous watery diarrhea

Rickettsia are obligate intracellular parasites that are transmitted by arthropods. In which of the following places would you most likely find the parasites living in the host organism during the course of infection?

within macrophages

Immunoassays are techniques that use immunology to determine the presence of antigens, antibodies, or both. In one type of enzyme-linked immunoassay test, antibodies are attached to a matrix (such as the bottom of a microtiter plate). Next, the sample to be tested (such as patient serum) is added. An antibody-enzyme complex is then added. Finally, the enzyme substrate is added. The enzyme must catalyze a reaction that is visible (such as a color change), meaning that it is possible to see if the antibodies were present by seeing if there is a color change. The development of the colored product is proportional to the concentration of antibody. What would this sort of test be useful for?

It would be useful for detecting a virus in a patient's blood, as the antibody on the matrix would bind to the virus. The second antibody (attached to the enzyme) is able to bind because it is specific for the antigen.

Which of the following is true about viral infection? Viruses can infect any cell in a particular species; it does not matter which tissue they infect as long as the species (or group of similar species) is correct. Viruses can infect any cells within a large group, but they are not more specific than that. For example, there are plant viruses that can affect many types of plants, bacteriophages that affect many types of bacteria, and animal viruses that affect a range of viruses. Viruses have what is needed to infect a host cell; they do not need anything specific from the host cell in order to cause infection and therefore can infect a wide range of cells. Viruses are very specific in which cells they infect. For a virus to be taken up by a cell, it must find a cell with appropriate receptors on the surface; it cannot be taken up by cells without the appropriate receptors.

Viruses are very specific in which cells they infect. For a virus to be taken up by a cell, it must find a cell with appropriate receptors on the surface; it cannot be taken up by cells without the appropriate receptors.

During the early 20th century, pandemics typically took months to years to span the globe, while the 2009 H1N1 swine flu spread globally within weeks and had affected most countries within 6 months. This difference in the rate of spread is mainly due to__________.

the increased volume and speed of global transportation.