microbiology final exam

Peptidoglycan is composed of?

NAG/NAM disaccharide with a peptide cross linker

What is an enzyme that obligate aerobes would have, but obligate anaerobes lack?

Catalase

What are electron acceptors during anaerobic respiration?

• NO3-

• SO42-

• CO32-

What is a characteristic of fungi?

Chitin cell wall

What microorganism has 70S ribosomes?

Bacteria

What best defines an operon?

A group of genes controlled by a single promoter and transcribed together

An operon contains three structural genes involved in lactose metabolism? What is the primary advantage of organizing these genes in an operon?

The gene can be regulated and transcribed together

E. Coli is grown in a medium lacking tryptophan. What would most likely happen to the trp operon?

Transcription of the operon increases so enzymes can synthesize tryptophan

What best describes a plasmid?

A small, circular DNA molecule that can replicate independently of the chromosome

Which scenario best describes horizontal gene transfer?

A bacterium acquires an antibiotic resistance plasmid from a neighboring cell

Which mechanism involves the uptake of free DNA from the environment by a bacterial cell?

Transformation

Which mechanism of genetic recombination requires direct cell-to-cell contact between 2 bacterial cells?

Conjugation

In Griffith’s classic experiment, mice were injected with a mixture of heat-killed pathogenic capsulated (S) bacteria and living encapsulated (R) bacteria. The mice died, and living virulent (S) bacteria were recovered from the mice. What conclusion can be drawn from this result?

The living R bacteria acquired genetic material from the dead S bacteria and were transformed into virulent cells

A scientist wants to distinguish between conjugation, transformation, and transduction. Which feature is unique to transduction?

Transfer of DNA by a bacteriophage

A patient is diagnosed with an infection caused by an agent that contains DNA requires a host cell to reproduce and lacks ribosomes. Which statement best identifies the infectious agent?

It is a virus because it must use a host cell’s machinery to reproduce

Which structural feature is found in an enveloped virus, but not in a nonenveloped virus?

Lipid membrane surrounding the capsid

Which statement best defines a viral species?

A group of viruses sharing similar genetic characteristics and occupying a specific ecological niche

A microbiologist wants to determine the number of bacteriophages in a sample. Which method would most likely be used?

Mixing the phages with susceptible bacteria and observing plaque formation

A T4 bacteriophage successfully infect E. Coli, but cannot infect Staphylocpccus aureus. What is the most likely explanation?

S. Aureus lacks specific surface receptors recognized by the phage

Which event occurs after penetration during the lytic cycle of a T4 bacteriophage?

Synthesis of viral proteins

A virus infect only respiratory epithelial cells in humans, but not skin cells or other species. What does this observation best illustrate?

Host range

A lambda bacteriophage infects a bacterial cell and enters the lysogenic cycle. What happens to the viral DNA?

It integrates into the host chromosome as a prophage

What is the correct life cycle of lytic bacteriophage?

Attachment —> Penetration —> Biosynnthesis —> Maturation —> Release

Which statement best distinguishes the lysogenic cycle from the lytic cycle?

Viral DNA remains dormant in the host genome during the lysogenic cycle

Which statement correctly compares DNA and RNA animal viruses?

DNA viruses generally replicate on the nucleus, whereas most RNA viruses replicate in the cytoplasm

An RNA virus enters an animal cell carrying an RNA-dependent RNA polymerase within its virion. Why is this enzyme important?

Host cells do not normally produce enzymes that replicate RNA from an RNA template

Which step occurs in the multiplication cycles of both DNA and RNA animal viruses?

Attachment to host-cell receptors followed by entry into cell

Human immunodeficiency virus (HIV) is a retrovirus with an RNA genome. Which enzyme allows HIV to establish a DNA copy of its genome inside the host cell?

Reverse transcriptase

What type of RNA virus can directly use its genomic RNA as mRNA for translation?

+ sense RNA

Acyclovir is commonly used to treat infections caused by herpeviruses, which are DNA viruses. It works by interfering with viral DNA replication. Based on this mechanism, which class of antiviral drugs forms acyclovir belong to?

Nucleoside analogs

An infectious protein is called a ____.

Prion

A bacterium acquires a prophage through lysogeny. Which of the following is a possible consequence of carrying a prophage?

• immunity to reinfection by the same phage

• Acquisition of new traits through phage conversion

• Transfer of nearby bacterial genes during excision through specialized transduction

If you have a patient with HIV that is left untreated, which viral load line is most likely the outcome of this chronic infection?

• spike in the infection at first

• There’s a spike in the infection later on and then death

A strain of Corynebacterium diphtheriae becomes capable of producing diptheria toxin only after infection by a lysogenic phage. This is an example of?

Phage conversion

Which statement best describes how both DNA and RNA viruses can contribute to cancer development?

They can alter the expression of normal cell-growth genes, leading to uncontrolled cell division

A patient with influenza is prescribed an antiviral medication shortly after symptoms begin. Which statement best explains why antiviral drugs can be difficult to develop?

Viruses use many of the host cell’s metabolic processes, making it difficult to target the virus without harming the host

What is specialized transduction?

Where there are specific bacterial DNA that is picked up during transduction

What is generalized transduction?

Picks up random bacterial DNA during transduction

What are the things attached to the Lac operon?

• operator

• Promoter

• Regulator

When there is no glucose and no lactose present what happens in the Lac operon?

• CAP is active since there is no glucose

• Repressor is active since no lactose

• No expression

What happens when there is glucose present, but no lactose present?

• CAP inactive since glucose is present

• Repressor is active since there is no lactose

• No expression

What happens to the Lac operon when there is glucose and lactose present?

• CAP inactive since there is glucose present

• Repressor inactive since there is lactose present

• No expression

What happens to the Lac operon when there is no glucose present but there is lactose present?

• CAP active

• Repressor inactive

• Expression

What are the steps of retrovirus starting at attachment?

1. Attachment

2. Penetration/entry

3. Uncoating

4. Biosynthesis

   1. Reverse transcriptase

   2. Integrase

   3. Transcription

   4. Translation

5. maturation

6. Release

What are the key targets of HARRT therapy?

• entry of the virus

• Reverse transcriptase

• Integrating into the host machinery

• Releasing more infected virus genes

Why do you need to use HARRT therapy all at once for HIV?

HIV mates fast, but it cannot be resistant to all of these inhibitors at once

Microorganisms play an important role in each of the following processes except?

Production of medical products

What is a normal microbiota?

Microorganisms that permanently live on or in a host without causing disease under normal conditions

What are the six major groups of microorganisms that microbiologist’s typically study?

1. Bacteria

2. Archea

3. Fungi

4. Algae

5. Helmiths/parasits

What is something unique about bacteria?

They have a peptidoglycan cell wall

What is a distinct feature about archaea?

Lack peptidoglycan cell wall

What is something that is unique about fungi?

Chitin cell wall

What is something unique about Protozoa?

Lack a cell wall

What is something unique about algae?

They have cellulose

What is something unique about helmiths/parasites?

They have a complex life cycle

A researcher isolates a microorganism and observes that it contains ribosomes, a plasma membrane, and DNA, but no membrane-bound organelles. Based on these observations, the organisms is most likely?

A bacterium because prokaryotes lack membrane-bound organelles

What is true about endospores?

Endoscopes survive in hostile environments

What does an axial filament look like?

Spiral round like filament

Two strains of the same bacteria species are compared. Strain X readily forms biofilms on medical implants, whereas Strain Y rarely adheres to surfaces. Which bacterial structure is most likely responsible for this difference?

Glycocalyx

A bacterium isolated from a urinary tract infection is highly effective at attaching to epithelial cells lining the bladder. Which structure is most directly responsible?

Fimbriae

Fimbriae differs from pili in which way?

Pili are used for horizontal gene transfer of plasmids

A newly discovered bacterium has a thin peptidoglycan layer, an outer membrane, and stains pink during a Gram stain. Which conclusion is best supported?

The bacteria is gram-negative

Bacterial endospore germination occurs when _____.

Spores encounter favorable conditions and metabolism is able to restart

What bacterial cell type has LPS?

Gram negative

A researcher discovers a mutant bacterium with a damaged plasma membrane. Which cellular process would be most directly impaired?

ATP production through cellular respiration

A bacterial cell takes up oxygen from the environment without using membrane proteins or energy. This is an example of:

Simple diffusion

A physician prescribes an antibiotic that is effective against both Gram-positive and Gram-negative bacteria. This antibiotic would be classified as:

Broad-spectrum

Quinolones kill bacteria by:

Inhibiting nucleic acid synthesis

An antibiotic binds specifically to the 30S ribosomal subunit. Why is the drug more toxic to bacteria than to human cells?

Bacterial ribosomes differ structurally from human ribosomes

Which antibiotic prevents the attachment of tRNA molecules to the ribosome?

Tetracycline

Why are sulfonamides selectively toxic to bacteria?

Bacteria synthesize folic acid, whereas humans obtain it from their diet

A strain of Staphylococcus aureus becomes resistant to penicillin by producing an enzyme that destroys the drug before it reaches its target. Which resistance mechanism is being demonstrated?

Enzymatic inactivation of the drug

Explain why broad spectrum antibiotics cause an overgrowth of yeast in patients using them?

They target both gram positive and gram negative bacteria which kills the normal good bacteria in the microbiota of the body

Methicillin-resistant Staphylococcus aureus (MRSA) is resistant because it possesses an altered penicillin-binding protein that has low affinity for beta-lactam antibiotics. This is an example of:

Modification of the drug’s target

A food manufacturer stores packaged salad at 4 degrees Celsius. Which group of microbes is most likely to continue growing and potentially spoil the food?

Psychrophiles

If cells are grown in media containing amino acids labeled with radioactive nitrogen, most of the radioactivity will be found in the cells’ ___.

DNA and proteins

A bacterium grows optimally at pH 7. During incubation, the medium drops to pH 2.5. What is the most likely outcome?

Growth is inhibited because enzymes may become less functional

Jams and jellies often contain high concentrations of sugar. Their resistance to microbial spoilage is primarily due to:

High osmotic pressure that limits microbial growth

Most bacteria reproduce by ______.

Binary fission

The functions of the glycocalyx in bacteria include?

Binary fusion

______ occurs by transfer of a single-stranded plasmid between two bacteria of opposite mating type via sex pili or mating bridge.

Conjugation

Transduction requires a(n) _____ to move DNA from one bacterial cell to another.

Bacteriophage

What type of RNA virus can directly use its genomic RNA as mRNA for translation?

• sense RNA

Which conditions would result in the activation of the lac operon?

- glucose; + lactose

A student examines a fungal colony and observes long, branching filaments. What are these individual filaments called?

Hyphae

Which event distinguishes sexual reproduction in fungi from asexual reproduction?

Fusion of genetic material from compatible cells

A patient with a severely weakened immune system develops an infection caused by an obligate intracellular, spore-forming fungus. Which fungal group best fits this description?

Microsporida

Which characteristic would be most useful for distinguishing the major fungal phyla?

The structures and spores produced during reproduction

Unlike plants, algae generally:

Lack true roots, stems, and leaves

A marine microorganism has two flagella and is responsible for some harmful algal blooms. Which group best fits this description?

Dinoflagellates

After fertilizer runoff enters a lake, algae rapidly increase in number. Several days later, large numbers of algae die and bacterial decomposition increases. Why might fish subsequently die?

Decomposition consumes dissolved oxygen needed by the fish