Question 1

Which of the following statements about spontaneous mutation is True?

Accepted Answer

The probability of a cell being resistant to both antibiotics is the product of the individual mutation rates: 10⁻⁹ * 10⁻⁶ = 10⁻¹⁵.

Question 2

A patient comes to see you complaining of a spider bite. He shows you a sore on his wrist—the area around it is red and swollen, and the lesion is leaking pus. The patient tells you he found a spider in his car, which is why he thinks this is a bite. He also tells you that he has been taking penicillin tablets that his wife had left over after being prescribed the drug a few months previously for pneumonia. Even though he has taken the tablets for four days, the lesion is not healing and that he is really feeling terrible, with pain, fever, and chills. You suspect that your patient has a wound infection, so you sample the pus and send it to the lab for analysis.
-Your patient asks whether there is any way for him to get rid of this infection. You tell him that he will be given a different antibiotic such as doxycycline. This antibiotic works by binding to a cell structure called the 30S ribosomal subunit, which stops the bacterial cells from growing by

Accepted Answer

Doxycycline works by inhibiting protein synthesis, which stops bacterial cells from growing. It does this by binding to the 30S ribosomal subunit and preventing the tRNA molecule from bringing amino acids to the ribosome, which is necessary for building proteins. This ultimately leads to bacterial cell death.

Question 3

A patient comes to see you complaining of a spider bite. He shows you a sore on his wrist—the area around it is red and swollen, and the lesion is leaking pus. The patient tells you he found a spider in his car, which is why he thinks this is a bite. He also tells you that he has been taking penicillin tablets that his wife had left over after being prescribed the drug a few months previously for pneumonia. Even though he has taken the tablets for four days, the lesion is not healing and that he is really feeling terrible, with pain, fever, and chills. You suspect that your patient has a wound infection, so you sample the pus and send it to the lab for analysis.
-You explain to your patient that there has been an increase in the number of strains of S. aureus that are now resistant to methicillin. The gene conferring resistance has moved from one strain to another via mobile gene elements, an example of which is a(n) ________.

Accepted Answer

The mobile gene elements that transfer antibiotic resistance genes from one bacterial strain to another are called transposons. Bacteriophages (not bacterioviruses) can also transfer genes between bacteria, but they are not usually associated with antibiotic resistance. Insertional dividers and histones are not relevant to this situation. While antibiotic resistance genes can be found on the bacterial chromosome, the context in which they are typically transferred involves mobile genetic elements like transposons.

Question 4

A mutation in E. coli results in the loss of both restriction endonucleases and modification enzymes. Would you expect any difference in the frequency of gene transfer via transduction FROM Salmonella INTO this E. coli strain?

Accepted Answer

The loss of both restriction endonucleases and modification enzymes would make the recipient E. coli unable to break down invading viral DNA from the transducing phage and unable to tag its own DNA as "self," leaving the viral DNA untagged and recognizable as "foreign," and targeted for destruction. Together, these would lead to higher rates of successful transduction.

Question 5

In order for insertional inactivation to occur, the transposon must be placed

Accepted Answer

Insertional inactivation occurs when a transposon inserts itself within a gene, disrupting its normal function.

Question 6

A patient comes to see you complaining of a spider bite. He shows you a sore on his wrist—the area around it is red and swollen, and the lesion is leaking pus. The patient tells you he found a spider in his car, which is why he thinks this is a bite. He also tells you that he has been taking penicillin tablets that his wife had left over after being prescribed the drug a few months previously for pneumonia. Even though he has taken the tablets for four days, the lesion is not healing and that he is really feeling terrible, with pain, fever, and chills. You suspect that your patient has a wound infection, so you sample the pus and send it to the lab for analysis.
-Further tests indicate that your patient has a methicillin-resistant Staphylococcus aureus (MRSA) infection. You explain to the patient that these bacteria are not impacted by penicillin or the related drug methicillin. This resistance is thought to have arisen originally by a random change in the cell's chromosome through a process called

Accepted Answer

Methicillin-resistant Staphylococcus aureus (MRSA) infections are caused by strains of bacteria that have developed resistance to methicillin and other beta-lactam antibiotics such as penicillin. This resistance is primarily due to the acquisition of the mecA gene, which encodes for a modified penicillin-binding protein that is not affected by these antibiotics. The mecA gene is believed to have originated in a different species of bacteria and was transferred to S. aureus through horizontal gene transfer. While vertical gene transfer (inheritance from parent to offspring) can also contribute to the spread of antibiotic resistance, in the case of MRSA, it is primarily due to spontaneous mutation and horizontal gene transfer.

Question 7

You are a volunteer for Nurses Without Borders and are being sent on a humanitarian mission. You are somewhat concerned because you have learned from the CDC website that antibiotic-resistant Haemophilus influenzae is common in the country to which you are being sent. This encapsulated, Gram-negative bacterium can cause a variety of illnesses, including community-acquired pneumonia. You do some research on the genetics of this pathogen. 
-What concerns you most about the strain of H. influenzae that you may be exposed to while you are away is antibiotic resistance. The genes for resistance can be acquired by this organism as naked DNA from the environment, an example of

Accepted Answer

Naked DNA uptake by bacterial cells is known as transformation. H. influenzae can acquire the genes for antibiotic resistance through this process. Conjugation involves the transfer of DNA through cell-to-cell contact, transduction involves bacteria-specific viruses transferring DNA, and induced mutation and vertical gene transfer are not relevant processes for this scenario.

Question 8

Cells that are His⁻, Strᴿ could be isolated from a mixed sample by using a medium containing

Accepted Answer

The cells that are His⁻, Strᴿ are sensitive to histidine and resistant to streptomycin. Therefore, a medium containing histidine and streptomycin would allow for the growth of only the His⁻, Strᴿ cells. Choice A and D include only streptomycin, which would not select for the His⁻ cells. Choice B includes both histidine and glucose, but glucose is not necessary for selecting the His⁻, Strᴿ cells. Choice C includes penicillin, which is not relevant to the selection of these specific cells.

Question 9

You are a volunteer for Nurses Without Borders and are being sent on a humanitarian mission. You are somewhat concerned because you have learned from the CDC website that antibiotic-resistant Haemophilus influenzae is common in the country to which you are being sent. This encapsulated, Gram-negative bacterium can cause a variety of illnesses, including community-acquired pneumonia. You do some research on the genetics of this pathogen. 
-Which of the following statements is CORRECT regarding transformation?

Accepted Answer

Transformation is a process in which bacteria take up DNA from the environment, often from dead or lysed bacteria. This DNA can then potentially be incorporated into their own genome. The other options given (A, C, D, E) describe other processes of genetic exchange in bacteria, but not transformation.

Question 10

Colonies of the bacterium Serratia marcescens are red when incubated at 22°C but white when incubated at 37°C. This is an example of

Accepted Answer

The change in color of Serratia marcescens colonies is a phenotypic change, meaning the expression of a certain gene or genes is influenced by environmental factors like temperature. This does not necessarily imply a change in the genetic sequence or genotype of the bacteria.

Question 11

You are a volunteer for Nurses Without Borders and are being sent on a humanitarian mission. You are somewhat concerned because you have learned from the CDC website that antibiotic-resistant Haemophilus influenzae is common in the country to which you are being sent. This encapsulated, Gram-negative bacterium can cause a variety of illnesses, including community-acquired pneumonia. You do some research on the genetics of this pathogen. 
-H. influenzae has genes that it needs to make pili for attachment to host cells. These pili genes are not always expressed; sometimes the bacterium turns them off and does not produce pili. This is an example of

Accepted Answer

The turning on and off of the pili genes is an example of phase variation, which is a mechanism used by bacteria to switch between different phenotypic variations in response to changing environmental conditions.

Question 12

A patient comes to see you complaining of a spider bite. He shows you a sore on his wrist—the area around it is red and swollen, and the lesion is leaking pus. The patient tells you he found a spider in his car, which is why he thinks this is a bite. He also tells you that he has been taking penicillin tablets that his wife had left over after being prescribed the drug a few months previously for pneumonia. Even though he has taken the tablets for four days, the lesion is not healing and that he is really feeling terrible, with pain, fever, and chills. You suspect that your patient has a wound infection, so you sample the pus and send it to the lab for analysis.
-The lab results indicate that the pus from your patient's "bite" contains clusters of spherical cells that stained purple in the Gram stain. You tell your patient that his wound contains bacteria from the genus ______ and is classified as a ________ organism.

Accepted Answer

The presence of clusters of spherical cells that stained purple in the Gram stain indicates that the organism is Staphylococcus, which is a Gram-positive bacterium commonly associated with skin and wound infections. The fact that the patient has been taking penicillin tablets for several days without any improvement suggests that the Staphylococcus bacteria may be resistant to the antibiotic.

Question 13

You make two agar plates: one is a nutrient agar plate (plate A) that contains histidine and penicillin. The other is a glucose salts agar (plate B) that also contains penicillin. You inoculate a sample onto both plates using replica plating technique, incubate the plates, and compare the growth after 48 hours. There are 12 colonies on the nutrient agar plate and 11 colonies on the glucose salts medium. Which of the following statements is INCORRECT?

Accepted Answer

The answer of You make two agar plates: one is...

Question 14

A patient comes to see you complaining of a spider bite. He shows you a sore on his wrist—the area around it is red and swollen, and the lesion is leaking pus. The patient tells you he found a spider in his car, which is why he thinks this is a bite. He also tells you that he has been taking penicillin tablets that his wife had left over after being prescribed the drug a few months previously for pneumonia. Even though he has taken the tablets for four days, the lesion is not healing and that he is really feeling terrible, with pain, fever, and chills. You suspect that your patient has a wound infection, so you sample the pus and send it to the lab for analysis.
-Your patient asks why the penicillin he has been taking hasn't helped his infection. Which of the following is a possible explanation for your patient?

Accepted Answer

The bacteria causing the infection are most likely resistant to penicillin, which is why the medication has not been effective in treating the wound infection. It is important to perform a culture and sensitivity test to determine the appropriate antibiotic(s) to use for effective treatment.

Question 15

The restriction-modification system always has two genes involved, the cutting enzyme and the methylating enzyme.

Accepted Answer

The restriction-modification system always involves two genes, one encoding the cutting enzyme (restriction endonuclease) and the other encoding the methylating enzyme (DNA methyltransferase).

Question 16

Please select the INCORRECT statement regarding mutation.

Accepted Answer

A missense mutation is not synonymous, as it leads to a change in the amino acid encoded.

Question 17

You mix two bacterial stains in a tube of glucose-salts agar. One strain is His−, Val−, while the other strain is Trp−, Leu−. You previously showed that neither strain grows on glucose-salts agar. After incubating the tube, you plate a sample onto a new glucose-salts agar plate. Several colonies grow. What do you know is True about these colonies?

Accepted Answer

The bacteria in the colonies must be His⁺, Val⁺, Trp⁺, Leu⁺ because the original strains could not grow on glucose-salts agar due to their auxotrophic mutations. The growth of colonies indicates that the bacteria have complemented each other's nutritional deficiencies, suggesting that they have acquired the necessary genes to synthesize all four compounds: histidine (His), valine (Val), tryptophan (Trp), and leucine (Leu).

Question 18

The clustered, regularly interspaced short palindromic repeats (CRISPR) system in bacterial cells has been called the "immune" system of bacteria. CRISPR protect bacteria from a repeat infection from the same phage because bacterial cells

Accepted Answer

The CRISPR system works by incorporating short fragments from the phage DNA into the bacterial chromosome. These fragments act as a memory of the previous infection, and if the bacteria are exposed to the same virus in the future, they use these fragments to guide a protein called Cas9 to cleave and destroy the viral DNA. This ensures that the bacteria are protected from future infections by the same phage.

Question 19

A bacterial strain is resistant to infection by a bacteriophage. Which statement is False?

Accepted Answer

The bacterial host DNA is protected from restriction enzyme degradation by methylation, not phosphorylation. Methylation adds methyl groups to the DNA, distinguishing host DNA from foreign DNA, which the restriction enzymes then target for degradation.

Question 20

If you were carrying out a penicillin enrichment culture and you forgot to add penicillinase before plating the sample onto nutrient agar, what would happen?

Accepted Answer

Penicillin inhibits the growth of bacteria by interfering with the synthesis of the cell wall. Without penicillinase to neutralize the penicillin, both prototrophs and auxotrophs would be inhibited or killed by the penicillin present. Only penicillin-resistant (Penᴿ) mutants would be able to grow, thus failing to enrich for auxotrophs as intended.

Quiz 8: Bacterial Genetics