Microbiology

Question 0

To determine whether a pathogen is bacterial or viral, what microscopy methods can be used?

Answer 0

Because viruses are significantly smaller than bacteria, they require electron microscopy. Therefore, is a pathogen is observed using light microscopy, it can be concluded that, between a bacteria or virus, it must be a bacteria.

Question 1

What are the two enzymes produced by bacteriophage viruses during the lytic cycle and what are their functions?

Answer 1

There are two enzymes produced by bacteriophages during the lytic cycle, one in early phase and the other in the late phase. HYDROLASE is synthesized during the early phase to degrade the host genome, supplying dNTPs to the virus. LYSOZYME is synthesized during the late phase to lyse the cell allowing the virus particles to escape.

Question 2

What is the main difference between enveloped and nonenveloped viruses in regards to their effect on the host cell?

Answer 2

Enveloped viruses bud off the host cell’s membrane, leaving the cell in tact. In contrast, unenveloped viruses cause the host cell to burst as it leaves.

Application: It can be determined experimentally whether a virus has an envelope or not. If the cells are infected, and none of the cells rupture over time, it can be concluded that the viruses are transmitting between cells via envelope.

Question 4

What are the 5 phases of bacteriophage infection?

Answer 4

1. Landing: phage TAIL recognizes specific bacterial receptors
2. Pinning: TAIL bend, BASE PLATE with its PINs come into contact with the cell surface and bind.
3. Lysozyme
4. Penetration of hollow tube located in tail sheath
5. Injection of genetic material

Question 5

If clathrin-coated receptor mediated endocytosis is blocked, which types or viruses are prevented from infection a host animal cell?

Answer 5

Clathrin-coated receptor mediated endocytosis allows for the entry of naked (unenveloped) and enveloped viruses. Enveloped viruses differ from naked viruses in that they can infect cells via a clathrin-independent method (fusion with the plasma membrane).

Question 6

If a host cells ribosomes or ATP production is blocked, can a virus use that cell to propagate itself?

Answer 6

No. Viruses are known as obligate intracellular parasites. They rely on host cell machinery to self replicate since they are not able to do this outside of the cell.

An example of this concept would be the application of cyanide to a cell which inhibits the electron transport chain. Since no ATP would be synthesized any longer, the host cell machinery would stall, preventing virus replication and transcription and translation.

Question 7

How can a single and double stranded viruses be differentiated? How can an RNA and DNA virus be differentiated?

Answer 7

Analyzing the base pair ratio and content is a method to differentiated between single and double stranded and RNA/DNA viruses. If the base pair ratio is NOT 1:1, as in the case of double stranded nucleic acids, it can be said that this virus is single stranded. If uracil is present in, the virus must be an RNA virus.

Question 8

How is the virus able to contain such a short genome but encode multiple proteins required for its replication and propagation?

Answer 8

Multiple reading frames

Question 9

Can a phage or plant virus be enveloped?

Answer 9

No. Bacteria have peptidoglycan cell walls and plants have cellulose cell walls both of which prevent budding. Therefore, all bacterial and plant viruses are naked viruses.

Question 10

If a phage viral capsid is radio-labeled as in the second step in the Hershey Chase experiments, will the capsid be found inside the bacterial cell?

Answer 10

No, the capsid becomes ECLIPSED to the cell while the genetic material penetrates the membrane. However, if phage genetic material is radiolabeled as in the first step of the Hershey Chase experiments, the bacteria will express radio labeled material.

Question 11

Where are RNA and DNA containing viral genomes located in the host cell?

Answer 11

Only DNA viruses can enter the nucleus of the host cell. The only RNA virus that can enter the nucleus are retroviruses. DNA viruses also have the option to remain within the cytoplasm, but if so, they must carry their own DNA polymerases. RNA viruses are localized to the cytoplasm.

Question 12

What are the two key enzymes that retroviruses must posses in order to propagate?

Answer 12

Retroviruses (mRNA+) must 1) encode for RNA-dependent DNA polymerases (reverse transcriptase) and 2) integrase to randomly add the viral DNA in the host’s genome

Question 13

If a certain virus is packaged without an RNA-dependent RNA polymerase, which RNA virus is it, mRNA+ or mRNA-?

Answer 13

RNA viruses must either a) carry their own RNA-dependent RNA polymerases or b) encode RNA-dependent RNA polymerases for replication of their own genomes since no cell contains polymerases that synthesizes RNA FROM RNA. mRNA+ needs to CODE for RNA-dependent RNA polymerases while mRNA- viruses must CODE AND CARRY RNA-dependent polymerases

Question 14

How do bacteria differentiate between their own genome and viral genomes?

Answer 14

Methylation of bacterial genome.

Question 15

What are the steps of viral-directed transduction of genetic material?

Answer 15

1. Infection and host cell DNA degradation
2. Accidental packaging of host cell fragmented DNA with viral progeny
3. Infection to another cell
4. Incorporation of fragmented DNA into new host cell genome via homologous recombination

Question 16

What are the major and minor names of bacteria that differ based on shape?

Answer 16

Major: Cocci (round), bacillus (rod), Spirillus (spiral)

Minor: eubacteria and archea (extremophiles)

Question 17

What are the three ways in which gram positive and gram negative bacteria differ?

Answer 17

1. Gram - positive: stains purple
   Gram - negative: stains pink
2. Gram-positive: thick peptidoglycan layer
   Gram-negative: thin peptidoglycan layer
3. Gram-positive: no outer membrane
   Gram-negative: outer membrane (prevents crystal violet from penetrating peptidoglycan layer)

Question 18

What is the name of bacterial cell division?How does it differ from eukaryotic cell division?

Answer 18

Bacterial cell division is called binary fission. It differs from eukaryotic cell division (mitosis) in their method of separating replicated DNA. Binary fission utilizes the cell membrane to which the replicated DNA attaches to separate the DNA. In eukaryotes, the mitotic spindle and aster formation is utilized to separate replicated DNA during anaphase. Therefore, if a substance was added to a bacterial culture that disrupted spindle formation, this would have NO effect on bacterial replication.

Question 19

What is the composition of the cell walls in bacteria, plants, and fungi?

Answer 19

Bacteria - peptidoglycan
plants - cellulose
fungi - chitin

Question 20

What are three ways in which flagella differ between bacteria and eukaryotes?

Answer 20

1. Composition: bacterial flagella are made of protein flagellin; eukaryotes are made of microtubules (alpha and beta tubulin) in the 9+2 fashion (axoneme/dynein interaction)
2. Movement: bacterial flagella move in a corkscrew motion; eukaryotic flagella move in a planar fashion
3. Power: bacteria utilize mainly a proton gradient set up by the electron transport chain in the inner membrane - if the electron transport chain is disrupted, the bacteria can no longer move; eukaryotes use ATP

Question 21

Name an describe three ways bacteria maintain genetic diversity and adaptability without sexual reproduction? Which method may confer antibiotic resistance?

Answer 21

1. Transduction: bacteriophage undergoing lysogenic cycle introduces new DNA into the bacterial genome that may possess material from other strains that it previously inhabited
2. Transformation: bacteria takes in plasmids and DNA fragments (from other lysed bacterial cells) from environment and integrates them into its genome. The newly integrated DNA may confer antibiotic resistance.
3. Conjugation: transfer of DNA between bacteria via sex pillus. Male contains F+ plasmid that allows for growth of sex pillus. F+ plasmid may integrate into chromosome allowing the transfer of genetic material from one bacteria to another

Question 22

What is the shape of bacterial growth curve? What are the names of the 3 main phases of bacterial growth? What is the rate of growth for each phase?

Answer 22

Sigmoidal curve

lag phase: bacteria are adjusting to environmental conditions such as temperature, salinity, pH, etc. - no growth

log phase: exponential growth

stationary phase: rate of growth = rate of death; reached “carrying capacity”

Question 23

What are the names of the four different bacteria that react differently to the presence of oxygen? How do they act differently?

Answer 23

1. Obligate aerobe: requires O2 to live/grow, dies without
2. Obligate Anaerobe: Dies is presence of oxygen
3. Facultative Anaerobe: does not require O2 but can utilize it to produce ATP/growth
4. Tolerant Anaerobe: does not require O2 to produce ATP/grow but does not die in its presence

Question 24

Describe the three different prokaryotic symbiotic relationships

Answer 24

1. Parasitic: bacteria benefits at expense of host
2. Mutualistic: both bacteria and host benefits (gut flora, bacteria on your skin)
3. Commensalistic: one benefits while the other has no effect

Question 25

What are four general characteristics of bacterial plasmid DNA? Is it single or double stranded? What is the nature of its replication? What is their pattern of inheritance? Are plasmids required for bacterial growth and reproduction?

Answer 25

1. Plasmids are double stranded 2. Replicate independently of genomic DNA/may be integrated within genomic DNA 3. Inheritance: as plasmids undergo binary fission, the plasmids are replicated and the daughter cells each inherit a copy of the plasmid DNA 4. Plasmids are not essential for growth or reproduction of bacteria in the wild

Question 26

What is the difference between endotoxins and exotoxins? Where are they derived? Do both gram-positive and gram-negative possess endotoxins and/or exotoxins? What human conditions are associated with both?

Answer 26

Endotoxins are components of the outer membrane such as lipopolysaccharide found in gram-negative bacteria ONLY. When bacteria die and lyse, they are released into circulation. This causes sepsis. Exotoxins are secreted by BOTH gram-negative and gram-positive bacteria and function as bacterial "guns" to ward off other bacteria. Conditions associated with exotoxins are botulism, diptheria, tetanus, and toxic shock syndrome.

Question 27

What are the names of the three different temperature-sensitive bacteria? What is their associated optimal temperature?

Answer 27

Thermophiles - love heat Mesophiles - tolerate moderate heat Psychrophiles - hate heat/love cold

Question 28

What are the two different nutritional sources that differentiate bacteria? What are the names of the bacteria for each source? What are examples of each?

Answer 28

Energy source 1. sun - phototroph 2. reduced molecules - chemotrophs Carbon source 1. CO2 - autotrophs 2. Organic molecules - heterotrophs chemoautotrophs - utilize CO2 to make their own organic molecules but use reduced molecules such as hydrogen sulfide for energy

Question 29

How is population size calculated during the log phase of bacterial growth?

Answer 29

1. What is the doubling time? 2. What is the final time? 3. Final time/doubling time = # division cycles 4. 2^# division cycles 5. (Initial # bacteria)(Number calculated in #4)

Question 30

What is fermentation and how does it differ from respiration? What is respiration? What is the function of an external electron acceptor during respiration? What are three different external electron acceptors utilized by prokaryotes in anaerobic respiration?

Answer 30

Glucose catabolism mandates an end electron accepter in order for it to continue. If an external electron acceptor is not present such as O2, pyruvate, the glycolytic end-product, is reduced (accepts the electrons) to form either ethanol (prokaryotes) or lactic acid (eukaryotes). If O2 is present, it functions as the external electron accepter for respiration for eukaryotes. Certain prokaryotes can utilize other external electron acceptors: 1. Sulfate (SO42-) to Hydrogen Sulfide (H2S) 2. Carbon Dioxide to Methane 3. Nitrate (NO3-)

Question 31

What is an endospore and what is its function? Do both gram-negative and gram-positive have the ability to form endospores? What is the term for the bacterium's reactivation?

Answer 31

An endospore is the bacterium under hibernation during unfavorable conditions. Only gram-positive bacteria can form endospores. Bacteria will reactive its machinery when conditions are better known as germination. Application: If both gram-negative and gram-positive bacteria are placed under unfavorable conditions, what can be expected of the staining? Because only gram-positive bacteria can form endospores, purple staining should be expected.

Question 32

What is the name of a cell that allows the integration of extrachromosomal elements (F-plasmid) into its genome? What is the technical consequence of this occurrence?

Answer 32

High frequency of recombination cell (Hfr) conjugation mapping - more info needed

Question 33

Prokaryotic Gene Regulation: What is the order of the four genetic elements of an operon?What are the two ways that prokaryotes regulate gene expression? What are their mechanisms? What are common examples of each?

Answer 33

Regulator (repressor protein) - Promoter - Operator - Structural gene 1. Inducible System: Operon is constitutively repressed by the repressor binding to the operator until conditions require the synthesis of the structural gene. Because operator is in front of promoter, even if RNA Pol binds, it gets blocked by repressor. An example of this is lac operon. When glucose is low and lactose is high, lactose acts as inducer, binding to repressor, preventing its binding to operator, allowing RNA Pol to transcribe structural gene. 2. Repressor System: Operon is constitutively expressed even though repressor is still synthesized. Repressor cannot bind to operator in this system without co-repressor. The metabolic product due to the structural proteins presence can act as a co-repressor as shown in Trp operon. Once Trp level is high, it binds to repressor, allowing it to bind to operator, preventing RNA Pol from synthesized more structural product that produces Trp.

Question 34

What is an auxotroph? What are the two macromolecules that define the nature of an auxotroph?

Answer 34

An auxotroph is a bacteria that does not have the machinery to either 1)break down a sugar or b) synthesize and amino acid

Question 35

Translation regulation b/w prokaryotes and eukaryotes: How does the prokaryote regulate translation? What are three ways in which eukaryotes regulate translation?

Answer 35

Prokaryotes regulate translation by the nature of the Shine-Dalgarno sequence located on the mRNA. Eukaryotes 1. Extend poly-A tail (longer mRNA life time) 2. Regulate translation machinery via phosphorylation of initiation factors 3. mRNA storage

Question 36

What is the complexity order of Fungi?

Answer 36

Cell-->hyphae-->mycelium-->thallus

Question 37

What is the carbon source of fungi? What is the mechanism by which they obtain their carbon source?

Answer 37

Fungi are heterotrophs, they are either parasitic of saprobes (feed off dead organic matter). They receive their carbon source via absorption by releasing digestive enzymes that degrade organic matter.

Question 38

Name and describe the three modes of asexual reproduction of fungi? How does it separate its replicated DNA? Are the daughter cells genetically distinct or the same?

Answer 38

1. Budding: fungal cell grows out of an existing cell. The daughter cell is smaller than the parent cell (different from prokaryotic binary fission). It separates its DNA via mitosis (mitotic spindle formation/anaphase/chromatid separation) 2. Mycelial fragmentation: mycelium breaks down to allow formation of new mycelium 3. Asexual spore formation: produced by mitosis, germinate under favorable conditions * Daughter cells are genetically the same.

Question 39

Describe sexual reproduction of fungi. Is the adult phase of the fungal life cycle diploid or haploid? How is the last step of the sexual reproduction cycle different from human?

Answer 39

1. Fusion of haploid gametes 2. Fusion produces dikaryon - posses two nuclei 3. Fusion of nuclei to form diploid zygote 4. Meiosis to produce adult haploid progeny. This is different from human because the diploid zygote then undergoes MITOSIS 5. Haploid cells then undergo mitosis/asexual reproduction to grow

Question 40

What are the implications of fungi being eukaryotic and bacteria being prokaryotic?

Answer 40

Fungi possess a nuclear envelope and membrane organelles while bacteria do not.