Micro Lab Exam 1 Questions

Which of the following toxin properties belong to exotoxins? [make sure that you can identify the properties of endotoxins also] 1. made of protein 2. made exclusively by gram-negative bacteria 3. cannot be neutralized in patients 4. typically produce fevers 5. released exclusively from actively growing bacteria

1, 5

The ID50 for inhalational anthrax is 11,000 endospores. Based upon this information, choose the true statement.

11,000 endospores must be inhaled to establish an infection in 50 percent of susceptible hosts

How many codons code for the amino acid histidine?

2

Put the following steps of protein synthesis in the order that they occur in a eukaryotic cell: 1) Translation ends at a stop codon 2) RNA polymerase transcribes mRNA from DNA 3) Protein sequence is elongated 4) Translation initiates 5) mRNA is processed and travels to a ribosome

2, 5, 4, 3, 1

Put the following steps of protein synthesis in the order that they occur in a eukaryotic cell: 1) Translation ends at a stop codon 2) RNA polymerase transcribes mRNA from DNA 3) Protein sequence is elongated 4) Translation initiates 5) mRNA is processed and travels to a ribosome

2, 5, 4, 3, 1

Place the following events in the correct order as they occur in the lytic cycle: 1) Assembly 2) Penetration 3) Release 4) Replication 5) Attachment

5, 2, 4, 1, 3

What is the anticodon sequence of a tRNA molecule for the mRNA codon UCA?

AGU

Why is ATP required for glycolysis?

ATP makes it easier to break apart glucose into two three-carbon molecules

Cystic fibrosis is a disease caused by a DNA mutation in the cystic fibrosis transmembrane regulator (CFTR) gene. What is the most likely effect of a mutation in an intron of the CFTR gene?

An intron mutation would most likely result in the production of an abnormal amount of CFTR protein.

Why is a specimen smaller than 200 nm not visible with a light microscope?

Anything smaller than 200 nm cannot interact with visible light.

At what site on a bacterial chromosome does DNA replication begin?

At the origin of replication

What does the "A" in S.M.A.R.T. stand for?

Avoid distractors.

Bacillus anthracis, like other Bacillus species, are Gram-positive bacteria that produce endospores. Samples were taken from infected patients and stained as indicated. Which of the following show a sample that contain endospores?

B

Identify the icosahedral capsid.

B

Legionella is a Gram-negative, pleomorphic bacterium that is an obligate aerobe. After sampling various water sources, the following results were obtained. Based on the data below, which water source(s) is (are) contaminated with this microorganism?

B

Which energy-rich molecule directly powers cell work?

B (ATP)

What is the function of single-strand binding proteins?

Bind to the DNA strands near the replication fork to keep them separated

Why are diabetics at risk for wound infections by anaerobic bacteria like Clostridium perfringens?

C. perfringens colonizes unhealthy tissues that do not receive enough oxygen, and diabetics have difficulty transporting oxygen to body tissues, especially in the extremities.

Candida albicans can thrive in the absence of oxygen, so how can it also grow in the human mouth?

Candida is a facultative anaerobe.

What step of binary fission is occurring in step 1?

DNA replication

Which step in carbohydrate metabolism yields the most ATP?

ETS

David had a painful lesion on his hand and went to his college's Student Health Services to have it assessed. After the initial test results were negative for the presence of bacteria, he was referred to an infectious disease specialist to determine the cause of his lesion. The doctor wanted to test David's lesion for Bacillus anthracis. If this organism is grown in stressful conditions, what differential stain would most add to the presumptive diagnosis of cutaneous anthrax?

Endospore stain

Explain why low blood pH, like that seen in ketoacidosis, is potentially deadly.

Enzymes that are necessary for cells and tissue to function depend on an optimal body pH.

Even though the CFTR gene is in every cell of the body, only certain cells contribute to the CF phenotype due to CFTR mutations. Discuss a possible explanation for this.

Epigenetic modifications (such as DNA methylation) may silence production of the CFTR gene in certain cell types

Using your knowledge of organism's gram staining properties, which of the following organisms would grow on EMB?

Escherichia coli

Which of the following events might trigger induction of a temperate bacteriophage?

Exposure to UV light

You inoculate a semisolid thioglycolate medium with a pure culture of Staphylococcus aureus. You incubate the sample under optimal growth conditions (37°C). Following incubation, you observe heavy growth at the top of the tube and moderate growth near the middle and bottom portions of the tube. Based on this observation, Staphylococcus aureus would be best classified as a(n)?

Facultative anaerobe

What does the term facultative anaerobe mean?

Facultative anaerobes can grow with or without oxygen. More growth is evident when oxygen is present.

How does the azole drug fluconazole damage yeast? Why does this drug not target human cells?

Fluconazole targets ergosterol within the fungal cell membrane, but does not target human cells because human cells do not have ergosterol.

The _______ resembles a series of flat sacs called cisternae. This organelle modifies, builds, sorts, and distributes products to the cell membrane to be secreted.

Golgi apparatus

Identify the organelle that contains hydrolytic enzymes?

H

Julia has contracted Clostridium botulinum from a contaminated food source. What is the main reason that antibiotics should not be used to treat Julia?

It could have increased toxin release from the bacteria.

Which of the following statements about fermentation is true?

It is an alternative way to return electron carriers to their oxidized state.

How would the results be different if this organism was Salmonella?

It would produce hydrogen sulfide.

Which enzyme is responsible for breaking down a host bacterium's cell wall so that the virus can leave the cell?

Lysozyme

This image shows the results of three different bacterial species streaked onto MSA and allowed to grow overnight at 37ºC. What do the observed results of Micrococcus luteus indicate?

M. luteus is not a halophile or facultative halophile

Urinary tract infections are commonly caused by Staphylococcus saprophyticus and Escherichia coli, less commonly caused by Proteus mirabilis. You have a mixed culture of these pathogens, which you inoculate onto both MacConkey agar and nutrient agar, and then you incubate the plates at optimal growth conditions. On the MacConkey agar, E. coli appears pink, P. mirabilis appears colorless, and S. saprophyticus does not grow. All three microorganisms appear cream on the nutrient agar plate. What is the best explanation for this data?

MacConkey is both a differential and a selective medium.

How do electrons get from glycolysis, the intermediate step, and the Krebs cycle to the electron transport chain?

NADH and FADH2 transport electrons to the electron transport chain.

A rapid Strep test is often used in the clinic to determine whether a patient is infected with Streptococcus. After swabbing the patient's throat, the sample is mixed with specified reagents and then applied to a diagnostic strip. As the sample moves up the strip, various lines will appear or not appear, depending on the reaction. The "C" line is the positive control-it should always appear. The "T" line is the test-it should only appear if the result is positive. Two samples come into the clinic lab, and the following results are obtained. How would you interpret these results?

Patient 1 is positive for Strep throat; Patient 2's results are inconclusive and must be redone.

How does the number of infectious prions increase?

Prions transform normal proteins into the misfolded beta-pleated sheet configuration; therefore, prions multiply by conversion.

What enzyme is necessary for transcription?

RNA polymerase

Select the best explanation for why Steptococcus pyogenes is classified in the domain Bacteria as opposed to the domain Archaea?

S. pyogenes has a peptidoglycan enriched cell wall

Which disease did Stanley Prusiner first identify as being caused by prions?

Scrapie

Information located in the exercise, "Think Clinically: Be S.M.A.R.T. About Cases- Cholera", stated that before it was determined that Vibrio cholerae was the causative agent of cholera, it was theorized that the stench of bilge (sewage) water caused the disease to spread. We now know the miasma "harmful air" theory is wrong, but discovered that proper sewage management reduces the incidence of disease. How did proper sewage management help reduce cholera cases, if not by reducing the stench?

Sewage management led to decreased incidence of human feces in drinking water.

How does the ribosome know if the entering charged tRNA is correct?

The anticodon on the tRNA base pairs to the codon on the mRNA.

How does a capsule help certain bacteria evade detection by the immune system?

The capsule is composed of polysaccharides that are similar to those found in the host; thus, the immune system does not recognize it as foreign.

What enables the copied chromosomes to separate during binary fission?

The chromosomes are attached to different parts of cell membrane, which elongates and thus separates the chromosomes.

What test result indicates that the unknown can utilize citrate as its sole carbon source?

The medium turns blue.

In a typical brightfield microscope, at which point does magnification begin?

The objective lens

An individual with type I diabetes hasn't been able to afford insulin since he lost his job over a week ago. He goes to the clinic complaining of nausea and breathing difficulty. Blood work revealed that the patient was in a state of ketoacidosis and had high blood glucose levels. However, ketoacidosis results when the body is "starving" for glucose. Why can these two conditions simultaneously exist in a diabetic patient?

The patient was not taking insulin, which means that the glucose in the bloodstream couldn't get into the patient's cells to be catabolized.

What is sporulation?

The process by which a bacterium forms an endospore

During transcription, what is the initial target of RNA polymerase?

The promoter

The mutations described in "The Case of the Spreading Superbug" affected Klebsiella's response to antibiotics. If a new mutation instead changed a stop codon into one that coded for the amino acid leucine, what effect would be had on the protein?

The protein would be longer and may not function correctly.

Which statement about simple staining FALSE?

The simple staining method uses a single acidic dye that stains the slide background.

Researchers discover that six people who had transfusions around the same time were exposed to a new virus. The doctors monitored all of the patients over a period of years. They found that viral titers in these patients could shift from being undetectable to being very high in cycles that occurred as frequently as every six months. What does this suggest about the virus?

The virus causes a latent, persistent infection.

What would be the fate of a lytic bacteriophage if the host cell died prior to the assembly stage?

The virus would not be able to infect new hosts.

Which of the following is NOT a way that researchers could isolate and grow a particular virus from a patient's blood?

The viruses can be plated on nutrient agar for overnight incubation.

How does the yeast form of a fungus differ from the hyphal form?

The yeast form is unicellular

What happens to the light rays when they hit the specimen?

They are reflected, refracted, or absorbed by the specimen.

How do fibrinolysins enhance a pathogen's virulence?

They break down fibrin proteins that are involved in clot formation, allowing the cells to penetrate deep into damaged skin.

David had a lesion on his hand that was assessed by a nurse at his college's Student Health Services. The lack of bacterial growth on a nutrient agar plate indicated that the lesion was not caused by a bacterial infection. He was referred to an infectious disease specialist who ordered gram and acid-fast stains, and bacterial culturing on a blood agar plate of the lesion sample. The absence of bacteria observed by gram staining, and lack of bacterial growth the agar plate initially implied that bacteria were not present, but the detection of acid-fast organisms confirmed that the lesion was indeed cause by a bacterial infection. Why did the cultures at Student Health and at the Hospital not grow originally?

This organism is suited for growth at lower temperatures.

David had a lesion on his hand, so he went to his college's Student Health Services to have it assessed. After the nurse asked him background questions, she decided to swab the wound. Why did the healthcare provider swab the wound?

To get samples of any pathogens in the wound.

AB toxins belong to which family of exotoxins?

Type III

Which of the following is NOT a stop codon?

UGG

The first human virus was discovered in 1901. What scientist discovered the first human virus?

Walter Reed

How is translation terminated?

When a protein called a release factor enters and binds to the A site

When would endotoxins be released from a bacterial cell?

When the cell dies

What observations could you make in the case of a positive catalase test?

You may see bubbles develop upon adding hydrogen peroxide to the sample.

The red arrows are pointing to _________________.

a single bacterial colony

Which of the following is NOT a way that pathogens cause host immunosuppression?

activation of memory cells

By which of the following mechanisms could the antibiotic resistance from a bacterium conceivably be transmitted to other bacteria?

all of the mechanisms could cause the transmission of antibiotic resistance

A variety of bacteria normally inhabits the vagina. How could a practitioner differentiate between these normally present bacteria and Candida albicans just by looking at a wet mount sample under the microscope without differential staining procedures?

all of the statements are correct

Clostridium difficile causes severe diarrhea. Many times proliferation of this microbe in the gut is associated with the overuse of _____________.

antibiotics

The image shows the results of a type of structural staining method called a negative stain that uses the dye, crystal violet. What are the purple colored structures depicted by the arrows?

bacterial cells

Streptococcus pyogenes, the etiological agent of strep throat, scarlet fever and rheumatic fever, exhibits complete clearing of RBCs when grown on sheep's blood agar. What type of hemolytic pattern does this indicate?

beta

The biochemical test shown in the image is used to detect the presence or absence of a certain enzyme that differentiates staphylococci (positive) from streptococci (negative). Using your knowledge of the test and the results observed in this image, name the enzyme.

catalase

In order to kill the fungus in a patient's body without causing unnecessary damage to his cells, a drug must be used that targets a structure common to fungi but not found in human cells. Which of the following would make an ideal drug target in this case?

cell wall

A certain species of bacteria grows the best on 25% glucose, 5% NaCl, and 0.2% magnesium sulfate agar plates. From this description, identify this general type of growth media.

chemically defined

Which of the following is not involved in nutrient acquisition by an invading pathogen?

coagulases

Mad cow disease is transmitted to humans by _______________________.

consuming contaminated beef

The biochemical test shown in the image is used to identify bacteria that produce a certain enzyme of the bacterial electron transport chain that is present in aerobic bacteria. Name the enzyme and state which of the results observed in the image is a positive result.

cytochrome C oxidase/A

Where does glycolysis occur in prokaryotes and eukaryotes?

cytoplasm

The structural framework in a cell is the

cytoskeleton

An exotoxin that has the ability to kill or damage host cells is referred to as a(n)

cytotoxin.

What is the arrangement of the circled bacterial cells.

diplococci

Which of the following properties of RNA is false?

double-stranded

NADH and FADH2 play an important role in energy production by donating electrons for redox reactions that occur in the ___________.

electron transport chain

The image shows the results of a structural staining method that uses malachite green as the primary stain and safranin as the counterstain. What is the name of the staining method?

endospore stain

The image shows the results of a structural staining method that uses malachite green as the primary stain and safranin as the counterstain. What are the green colored structures depicted by the arrows?

endospores

What occurs when a high-energy bond in ATP is broken resulting in ADP?

energy is released that will drive chemical reactions

"Naked" viruses lack what structural component?

envelopes

Identify the prokaryotic cell structure labeled "D"

fimbriae

Identify the compound microscope part labeled "C"

fine adjustment knob

If a nucleotide is inserted or deleted from the DNA sequence, the resulting mutation is known as a _________________ mutation.

frameshift

Escherichia coli yields whitish colonies when grown on sheep's blood agar. What type of hemolytic pattern does this indicate?

gamma

Standard precautions are used by healthcare providers when working with patients to protect themselves, and minimize the spread of infection. Which of the following precautionary measures is used as a contact precaution? [make sure that you can recognize airborne and droplet precautions]

gloves

Pyruvic acid is utilized during various fermentation processes. What process produces pyruvic acid that fuels fermentation?

glycolysis

What category of bacteria is resistant to physical disruption and drying, but are highly susceptible to penicillin and anionic detergents?

gram-positive bacteria

Sheep's blood agar differentiates between bacteria that produce a toxin called __________, which is indicated by the partial or complete destruction of red blood cells contained in the media.

hemolysin

The immediate result of electron movement through the electron transport chain is the pumping of protons across the bacterial cell membrane, creating a _____ outside the cell than inside the cell.

higher concentration of protons

Most polyhedral viruses have 20 triangular-shaped sides and are called ____________.

icosahedral

The selective & differential media called MAC contains a chemical called neutral red that will detect a change in pH if the sugar in the media is metabolized by the growing organism. What is the general term for the chemical added to media that detect changes in pH?

indicator

Which process of glucose catabolism doesn't generate ATP?

intermediate step

Eukaryotic mRNA have non-coding sequences called _______ that are spliced out before the RNA leaves the nucleus.

introns

A health department technician takes a sample of water from a hot tub back to the lab to identify the microbe(s) present. If the technician runs biochemical tests, then they must use bacteria in their healthiest state. Which growth stage is usually ideal for this purpose?

log phase (exponential growth)

Mismatch-repair enzymes cannot repair a DNA mutation once it becomes ______________.

methylated

The image shows the result of a certain differential staining method that detects the presence of mycolic acid in a bacterial cell wall. What is the name of the counterstain used in this method?

methylene blue

Studies have demonstrated that people living in areas where helminth infections are common have less allergies and autoimmune disorders in comparison with people living is areas where these infections are rare. Research has indicated that helminth infections may moderate the activities of certain immune cells. This observation has led to clinical trials where helminths were introduced into patients, to ascertain if certain autoimmune disease symptoms were relieved. What two autoimmune diseases discussed in the article "A Possible Link between Lost Normal Microbiota and Immune System Disorders" are showing promising results using helminth therapy?

multiple sclerosis and Crohn's disease

Copepods are small crustaceans found worldwide in estuaries, rivers, and ponds; they naturally harbor Vibrio cholerae in their gut and as biofilms on their surface. It has been determined that copepods and V. cholera have a symbiotic relationship. The bacteria secrete a substance that helps the copepod egg sac rupture to release the eggs that are ready to be fertilized. The bacteria benefit by having an environment rich in food and are also safe from protozoans that normally graze on marine bacteria. How would you define this symbiotic relationship between copepods and V. cholerae?

mutualism

Identify the prokaryotic cell structure labeled "G"

nucleoid region

Prokaryotic DNA is found in the __________ region and eukaryotic DNA is located in the ___________.

nucleoid, nucleus

Some scientists theorize that an ancient virus infected a bacterium helping it produce the first cell ___________.

nucleus

Which type of phosphorylation mechanism is used to generate ATP in the ETS?

oxidative phosphorylation

Which route of entry occurs when microbes enter the body through bites, cuts, injections, or surgical incision?

parental route

Prokaryotic and eukaryotic extrachromosomal DNA is called ______ DNA.

plasmid

The ability of certain bacterial cells to take on different cell shapes is known as

pleomorphism

Antigenic drift occurs in microbes mainly due to _________ mutations that result in antigenic differences. These differences require the host immune system to generate a new immune response to the microbe.

point

An inactive bacteriophage is a/an_____________ that can remain in the host chromosome and render the bacterium resistant to additional infection by other similar viruses.

prophage

Prions are misfolded ___________.

proteins

Organisms in the domain archaea have cell walls that possess _______________.

pseudopeptidoglycan

Many food spoilage bacteria are characterized by temperature as ___________.

psychrotrophs

The presence of specific ___________ on viruses determine whether it can infect a particular cell or not.

receptors

The image shows the results of a staining method that differentiates between bacteria that have thick or thin layers of peptidoglycan in their cell walls. Name the counterstain used in this method.

safranin

Antigenic _________ occurs when there is a reassortment of genetic material from coinfecting viruses that produce a new viral strain.

shift

Two carbons in the form of acetyl-CoA enter the Krebs cycle by joining with oxaloacetic acid, a 4-carbon molecule. During which step does carbon leave the Krebs cycle in the form of CO2?

step 3 and step 4

What are the nutrient requirements for an organism classified as a photoautotroph?

sun and CO2

A person who attended a picnic early in the day develops a very high fever and is unresponsive by the evening. This person most likely has been exposed to a(n)

superantigen

________________ cause(s) a massive immune response that can destroy immune cells by overstimulation.

superantigens

Measles viruses are capable of inactivating host defenses by

suppressing the immune system.

This image shows the results of different bacteria inoculated onto an EMB plate. What does the metallic green-colored growth indicate?

the bacteria are gram-negative lactose fermentors

An organism is inoculated on an MSA plate. After incubating the plate to allow for bacterial growth, no growth is observed. Why didn't the bacteria grow on MSA?

the bacteria couldn't grow in the presence of high salt concentrations

Why are RNA viruses that use RNA-dependent RNA polymerase for transcription more likely to have genome mutations?

the enzyme doesn't have proofreading capabilities

Describe the function of the indicator, neutral red, when the bacteria growing on MacConkey media ferment lactose.

the indicator will change from colorless to pinkish

An organism is streaked onto MSA and allowed to grow overnight at 37º C. The plate has bacterial growth, but the media remained a pinkish color. What do the results indicate about the organism?

the organism can grow in high salt conditions, but cannot ferment mannitol

Evidence in support of the endosymbiotic theory includes

the presence of 70S ribosomes in mitochondria and chloroplasts

The bacteria shown in the image were stained using a differential staining method that uses crystal violet as the primary stain and safranin as the counterstain. What statement about the circled bacteria is TRUE?

their cell wall contains a thin layer of peptidoglycan

When toxins enter the host's bloodstream, the resulting condition is called ____________.

toxemia

What is the portal of entry of the pathogen that causes gonorrhea?

urogenital

There are a variety of ways that microbes evade host immune defense mechanisms. Antigenic ___________ occurs when the pathogen changes surface antigens to remain undetected by the host immune system.

variation

Which of the following cell shapes look like a comma?

vibrio