Viruses Overview and Classification

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Questions and Answers

Which statement about viruses is false?

Viruses are classified as prokaryotes (correct)

Viruses must invade a living host cell to reproduce

Viruses have genes

Viruses are generally smaller and less complex than bacteria

What structures are found in all viruses?

Nucleic acid genome (correct)

Protein capsid (correct)

Lipid envelope

Peptidoglycan cell wall

What term best describes the capsid of Norovirus?

Complex

Icosahedral (correct)

Helical

Filamentous

What must be synthesized when a naked DNA virus infects a host cell?

DNA, RNA, and proteins Signup and view all the answers

Which process allows Norovirus to enter gastrointestinal epithelial cells?

Endocytosis Signup and view all the answers

Which viral enzyme makes a DNA copy of the viral RNA genome during HIV infection?

Reverse transcriptase Signup and view all the answers

During which step of the HIV infectious cycle is inhibited by protease inhibitors?

Assembly and maturation Signup and view all the answers

Which classification describes the structure of a virus with a phospholipid bilayer and viral spike proteins?

Envelope Signup and view all the answers

What is the primary target of the fusion inhibitor enfuviritide?

HIV gp41 Signup and view all the answers

Which mechanism of anti-microbial resistance does not involve a change in the targeted enzyme?

Efflux pumps Signup and view all the answers

What characterizes a propagated epidemic?

A sharp rise to a peak followed by a decline Signup and view all the answers

What is the role of clavulanate in antibiotic treatment?

A beta-lactamase inhibitor Signup and view all the answers

Endotoxins primarily produce which type of effects?

Systematic effects at an unsafe level Signup and view all the answers

Which of the following is considered a disease reservoir?

A water source contaminated with pathogens Signup and view all the answers

Which of the following toxins is associated with food poisoning through fluid secretion?

Enterotoxins Signup and view all the answers

What is the primary role of protease inhibitors in HIV treatment?

To inhibit virus assembly and maturation Signup and view all the answers

What is the purpose of nucleic acid synthesis in a viral lifecycle?

To make copies of viral genome Signup and view all the answers

In which type of virus is fusion primarily used for entry into the host cell?

Enveloped viruses Signup and view all the answers

What happens during the process of latency in a viral infection?

The virus remains dormant Signup and view all the answers

What is the main effect of sterilization in microbiology?

It kills all forms of viable microbes Signup and view all the answers

Which method is commonly used for disinfection of surfaces?

Spraying bleach Signup and view all the answers

Which biological process is targeted by azithromycin?

Protein synthesis Signup and view all the answers

What is the significance of peptidoglycan synthesis as a target for antibiotics?

It maintains cell wall structure Signup and view all the answers

What distinguishes bactericidal agents from bacteriostatic agents?

Bactericidal agents kill bacteria, while bacteriostatic agents inhibit growth. Signup and view all the answers

What does the term 'prions' refer to?

Infectious protein particles Signup and view all the answers

Which method is used to ensure the destruction of endospores in a laboratory setting?

Tyndallization Signup and view all the answers

How does rifampin affect bacterial cells?

Interferes with RNA synthesis Signup and view all the answers

Which antibiotic class inhibits mycolic acid synthesis in bacteria?

Isoniazid Signup and view all the answers

What is the proper order of resistance for the following microorganisms?

Prions, endospores, protozoan cysts, fungal spores, enveloped viruses Signup and view all the answers

What defines a 'magic bullet' in the context of antimicrobial agents?

A chemical that selectively kills pathogens without harming the host Signup and view all the answers

Study Notes

Viruses

Viruses are obligate intracellular parasites, meaning they require a living host cell to reproduce.
Viruses are generally smaller and less complex than bacteria.
Viruses are not classified as prokaryotes.
Viruses contain genes, which are made of either DNA or RNA.
Viruses have a protein capsid that encloses the genetic material.
Some viruses have a lipid envelope surrounding the capsid.
Norovirus is a naked RNA virus with an icosahedral capsid.
Norovirus enters gastrointestinal epithelial cells through endocytosis.
Viruses are classified based on their genome (DNA or RNA), capsid shape (helical or polyhedral), and envelope (naked or enveloped).
Bacteriophages are viruses that infect bacteria.
Viruses can cause cytopathic effects beyond cell death.
Some viruses can enter a latent state, where they hide within host cells and become reactivated later.
The five steps of the viral infection cycle include: adsorption, entry & uncoating, synthesis, assembly, and release.
The specific host cell that a virus can infect is determined by its tropism.
Enveloped viruses can enter host cells through fusion.
Naked viruses can enter host cells through endocytosis.
Nucleic acid synthesis refers to the process of making copies of the viral genome.
Protein synthesis involves making viral enzymes, viral capsomers, and viral envelope spikes.
RNA viruses require viral enzymes for synthesis.
RNA retroviruses use an enzyme called reverse transcriptase to make a DNA copy of their RNA genome.
Latency refers to the dormant period of a viral infection.
Integration occurs when viruses incorporate their genome into the host cell's chromosome.
Budding is the process by which enveloped viruses are released from the host cell.
Lysis is the death of a host cell, often caused by the release of viral progeny.
Prions are infectious protein particles.

Microbial Control

Microbes are ordered from most resistant to least resistant:
- Prions
- Endospores
- Protozoan cysts
- Fungal spores
- Enveloped viruses
The five levels of decontamination are:
- Sterilization
- Disinfection
- Antisepsis
- Sanitation
- Degermation
Sterilization destroys all viable microbes, including endospores and viruses, from inanimate objects.
Disinfection destroys or removes vegetative pathogens but not endospores from inanimate objects.
Antisepsis destroys or inhibits vegetative pathogens but not endospores from living tissues.
Sanitation reduces the number of microorganisms on inanimate objects to acceptable levels.
Degermation reduces the number of microorganisms on living tissues.
Moist heat is used to denature or coagulate microbial proteins.
Dry heat dehydrates cells, denatures proteins, and oxidizes biological molecules.
Endospore-forming bacteria are difficult to kill due to their spore coat and metabolic inactivity.
Thermoduric microbes are resistant to heat killing.
Boiling water is a moist heat method that does not kill endospores.
Steam under pressure (autoclaving) sterilizes inanimate objects and destroys endospores.
Tyndallization involves intermittent exposure to steam for 30-60 minutes over three days, allowing endospores to germinate and be killed by the next cycle.
Pasteurization is a disinfection method that heats beverages to 71.6 °C for 15 seconds.
Cold temperatures reduce metabolic activity and inhibit microbial growth.
Lyophilization is a process of freeze drying.
Hypertonic environments inhibit microbial growth by increasing osmotic pressure.
Non-ionizing radiation (UV rays) can damage microbial DNA but do not kill bacterial endospores.
Filtration physically removes microbes and endospores from fluids.

Antimicrobial Drugs

The "magic bullet" refers to a chemical that could kill a pathogen without harming the host:
- Selective toxicity for the pathogen
- Non-toxic to the host
- Easily delivered
- Stable and retained
- No resistance
Paul Ehrlich created Salvarsan for the treatment of syphilis.
Alexander Fleming discovered penicillin.
Howard Flory and Ernest Chain developed penicillin based on Fleming's discovery.
Bactericidal drugs kill bacteria, while bacteriostatic drugs inhibit bacterial growth.
Broad-spectrum antibiotics can cause superinfections.
Bacterial targets for antibiotics include:
- Protein synthesis (ribosomes)
- Folic acid synthesis
- DNA/RNA synthesis
- Cell wall synthesis
Peptidoglycan, a major component of bacterial cell walls, is an important antibiotic target.
Glucosyltransferase builds glycan chains (NAG-NAM) in peptidoglycan, and transpeptidase forms peptide cross-links.
Penicillin inhibits transpeptidase, preventing the formation of peptide cross-links and weakening the peptidoglycan wall.
The target of penicillin is penicillin-binding protein (PBP).
Beta-lactam antibiotics, such as penicillin and amoxicillin, inhibit transpeptidase.
Ciprofloxacin targets DNA gyrase, interfering with DNA synthesis and causing cell death.
Rifampin targets RNA polymerase, interfering with RNA synthesis and causing cell death.
Protein synthesis inhibitors include:
- Azithromycin (binds to 50S ribosomes)
- Neomycin (binds to 30S ribosomes)
- Doxycycline (binds to 30S ribosomes)
Folic acid synthesis inhibitors prevent the metabolism of DNA, RNA, and amino acids by inhibiting key enzymes in the pathway.
- Sulfamethoxazole interferes with the conversion of PABA to DHPA.
- Trimethoprim interferes with the conversion of DHFA to THFA.
Isoniazid interferes with mycolic acid synthesis.
Azoles are commonly used antifungal agents.
Antiviral agents are typically virus-specific.
Fusion inhibitors, such as enfuviritide, target HIV gp41 and prevent viral entry.
Reverse transcriptase inhibitors, such as azidothymidine, target HIV reverse transcriptase and inhibit viral genome replication.
Protease inhibitors, such as saquinavir, target HIV protease and inhibit viral assembly and maturation.
Anti-microbial resistance mechanisms include:
- Efflux pumps
- Inactivating enzymes
- Alternative enzymes
- Mutations
Clavulanate is a beta-lactamase inhibitor that prevents the breakdown of penicillin.
Methicillin is not inactivated by beta-lactamase.
Vancomycin is a last-resort treatment for MRSA.
Noncompliance with antibiotic treatment is a major factor contributing to antibiotic resistance.
Combination therapies can suppress antibiotic resistance.
Point-source epidemics involve a large number of cases followed by a decline.
Common-source epidemics show a more typical epidemic curve with a plateau.
Propagated epidemics show a gradual increase in cases.
Endemic diseases have a steady state of cases.
Sporadic diseases occur intermittently.
Epidemics are outbreaks of disease.
Pandemics are global outbreaks.
Incidence refers to new cases in a specific timeframe.
Prevalence refers to the total number of existing cases.
John Snow discovered the connection between contaminated water and the cholera outbreak.
Robin Warren and Barry Marshall discovered H. pylori as the etiologic agent of gastric ulcers.
Robert Koch developed the postulates for identifying the etiologic agent of a disease.
Nosocomial infections are those acquired in healthcare settings.
Biological vectors are blood-feeding living animals that transmit pathogens.
Zoonotic infections are those that are transmitted from animals to humans.
A disease reservoir is where a pathogen survives and multiplies, providing a source for transmission to hosts.
Placental transmission occurs during pregnancy.
Perinatal transmission occurs during birth.
An access portal of exit allows transmission of a pathogen from one host to another.
Endotoxins produce systematic effects, which can cause severe side effects.
Enterotoxins cause fluid secretion, peristalsis, and gastrointestinal distress.
Neurotoxins cause paralysis and weaken the host.
Cytotoxins cause cell lysis and tissue damage.
Exotoxins are proteins excreted by some bacteria that are toxic in small doses and target specific cell types.
Exoenzymes damage host tissues and promote invasion.
Mucinase digests mucus.
Hyaluronidase breaks down hyaluronic acid.
Collagenase digests collagen.
For a pathogen to cause disease, it must be able to:
- Access a portal of entry
- Colonize the host
- Survive host defenses
- Cause damage
- Exit the host

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Description

This quiz covers the fundamental characteristics of viruses, their classification, and their life cycle. Learn about the differences between viruses and bacteria, how they reproduce within host cells, and the structural features that define different types of viruses. Test your knowledge on key concepts such as genomes, capsid shapes, and viral infections.