micro - acellular agents

What is the process of lytic bacteriophage replication?

The bacteriophage attaches to the bacterium, injects its DNA, takes over the host to produce viral parts, assembles new virions, and causes the host to burst (lysis) releasing new phages.

What is the process of lysogenic bacteriophage replication?

The viral DNA integrates into the host bacterium’s chromosome as a prophage, replicates with the host cell, and can later be induced to enter the lytic cycle.

What is the process of generic animal virus replication?

Animal virus replication includes adsorption, penetration (fusion or endocytosis), uncoating, synthesis of viral components, assembly, and release (budding for enveloped viruses or lysis for naked viruses).

What are ligands and receptors?

Ligands are viral proteins that bind specifically to receptors, which are proteins or molecules on the surface of host cells, allowing viral attachment.

What are the ligand and receptor for the influenza virus?

The influenza virus uses hemagglutinin (HA) as its ligand to bind sialic acid receptors on host cells.

What are the functions of hemagglutinin and neuraminidase in influenza virus replication?

Hemagglutinin allows viral entry by binding to host cells; neuraminidase facilitates release of new virions by cleaving sialic acid residues.

What are the key mechanisms by which influenza viruses mutate?

Influenza mutates by antigenic drift (small point mutations over time) and antigenic shift (major genetic reassortment leading to new virus strains).

How is the influenza vaccine produced and why might it not protect against future infections?

The flu vaccine is made based on predictions of circulating strains. Antigenic drift and shift can cause the virus to change, making the vaccine less effective.

What are the ligands and receptors for SARS-CoV-2?

SARS-CoV-2 uses the spike protein (S-protein) as a ligand to bind to the ACE2 receptor on human cells.

What are the key mechanisms by which SARS-CoV-2 mutates?

SARS-CoV-2 mutates through errors during RNA replication by RNA-dependent RNA polymerase, leading to new variants.

What are prions, how are they transmitted, and how do they replicate?

Prions are misfolded proteins that cause normal proteins to misfold. They are transmitted by ingestion, surgical instruments, or organ transplants. They replicate by inducing misfolding of normal cellular proteins.

What types of diseases are caused by prions?

Prions cause TSEs: Creutzfeldt-Jakob disease (CJD), kuru, scrapie, BSE (mad cow), and chronic wasting disease.

What is the mechanism of prion-caused disease?

Prions convert normal α-helix proteins into β-sheet forms, forming aggregates (fibrils) that damage brain tissue and cause neurodegeneration.

Who discovered that the agent of Tobacco Mosaic Disease could pass through a filter that trapped bacteria?

Dmitri Iwanowski.

Who first called these infectious agents "viruses"?

Martinus Beijerinck.

What important tool allowed scientists to first visualize viruses?

The electron microscope.

What are viruses classified as in terms of living organisms?

Obligate intracellular parasites.

What is a viral envelope made of?

A lipid bilayer stolen from the host cell membrane during budding.

What is the function of the viral capsid?

To protect the viral nucleic acid.

What types of nucleic acids can viruses have?

DNA or RNA (never both), which can be single- or double-stranded, circular, linear, or segmented.

Why are viruses metabolically inactive?

They cannot generate their own energy (ATP).

What determines a virus's host range?

The specific interaction between viral ligands and host cell receptors.

What is a bacteriophage?

A virus that infects bacteria.

What are the steps of lytic bacteriophage replication?

Attachment, entry, synthesis, assembly, release (lysis).

What is a temperate phage?

A bacteriophage whose DNA integrates into the host genome as a prophage.

What triggers a prophage to enter the lytic cycle?

DNA damage that destroys the repressor protein.

How do naked animal viruses typically enter host cells?

By direct penetration or endocytosis.

How do enveloped viruses typically enter host cells?

By fusion of the viral envelope with the host plasma membrane.

What is the role of reverse transcriptase in retroviruses?

It makes a complementary DNA (cDNA) copy from viral RNA.

Why do retroviruses have high mutation rates?

Because reverse transcriptase lacks proofreading ability.

How are enveloped animal viruses released from the host cell?

By budding from the host plasma membrane.

What does "cytopathic effect" mean in virus-infected cells?

Changes in cell morphology or behavior, like detachment, fusion (syncytia), or death.

What are two examples of anti-HIV drugs?

AZT (a reverse transcriptase inhibitor) and Indinavir (a protease inhibitor).

What does Tamiflu (oseltamivir) inhibit?

Neuraminidase, which helps release new influenza viruses.

What are latent infections?

Viral infections that remain dormant within a host and can reactivate later.

What is a provirus?

Viral DNA that is permanently integrated into a host cell's genome.

What is teratogenesis?

Birth defects caused by viral destruction of embryonic cells.

Name a virus known to cause cancer.

Human Papillomavirus (HPV).

What are the influenza virus surface proteins and their functions?

Hemagglutinin (HA) for binding and Neuraminidase (NA) for viral release.

What is antigenic drift?

Small, gradual mutations in viral genes that alter surface proteins.

What is antigenic shift?

Major genetic reassortment creating a new virus subtype.

How are viruses cultured?

In living hosts, embryonated eggs, or tissue cultures.

What are prions?

Infectious, misfolded proteins that induce other proteins to misfold.

What diseases are caused by prions?

CJD, kuru, scrapie, BSE, and chronic wasting disease.

How are prions sterilized in medical settings?

By incineration or autoclaving in NaOH.

What happens in prion diseases at the cellular level?

Misfolded proteins form fibrils that kill neurons and create brain lesions.

What is the difference between PrPc and PrPsc?

PrPc is normal cellular prion protein; PrPsc is the infectious, misfolded form.

What are the five basic steps of lytic phage replication?

Attachment, penetration, biosynthesis, maturation, release.

What is a prophage?

A phage genome that has been integrated into the bacterial host chromosome.

What triggers a prophage to enter the lytic cycle?

Stress like UV light or chemicals that damage bacterial DNA.

What is the difference between lytic and lysogenic replication?

Lytic replication immediately destroys the host, while lysogenic replication integrates the phage DNA into the host genome.

What is viral uncoating?

The process where the viral capsid is removed after entry into the host cell.

How do naked viruses typically enter a host cell?

By direct penetration or endocytosis.

How do enveloped viruses typically enter a host cell?

By fusion of the viral envelope with the host cell membrane.

What viral enzyme do retroviruses use to replicate their genome?

Reverse transcriptase.

What does viral budding refer to?

Enveloped viruses exiting the host cell by pinching off part of the host membrane.

What is the basic structure of influenza virus?

Segmented RNA genome with an envelope, hemagglutinin (HA) and neuraminidase (NA) proteins.

What is antigenic drift?

Small gradual mutations in viral genes leading to changes in HA and NA proteins.

What is antigenic shift?

Major genetic reassortment between different influenza strains, producing new viral subtypes.

Why is antigenic shift more dangerous than antigenic drift?

It can create completely new influenza strains that the population has little to no immunity against.

What is the role of hemagglutinin (HA) in influenza infection?

Allows the virus to bind to host cell receptors and enter cells.

What is the role of neuraminidase (NA) in influenza infection?

Helps newly formed viruses exit the infected host cell.

How does Tamiflu (oseltamivir) work against influenza?

It inhibits neuraminidase, blocking viral release from infected cells.

What is the genome type of SARS-CoV-2?

Single-stranded positive-sense RNA.

What host receptor does SARS-CoV-2 bind to?

ACE2 receptor on human cells.

What viral protein allows SARS-CoV-2 to bind to host cells?

Spike (S) protein.

What is unique about SARS-CoV-2 replication?

It uses an RNA-dependent RNA polymerase with a proofreading function.

What kinds of mutations are common in SARS-CoV-2?

Point mutations and deletions in the spike protein that can affect infectivity and immune evasion.

What is a prion?

A misfolded protein that can induce other normal proteins to misfold, causing disease.

What is the normal form of prion protein called?

PrPc (cellular prion protein).

What is the disease-causing form of prion protein called?

PrPsc (scrapie prion protein).

How do prions propagate?

By inducing the misfolding of normal PrPc into PrPsc.

What happens to brain tissue in prion diseases?

Formation of sponge-like holes (spongiform encephalopathy).

Name two human prion diseases.

Creutzfeldt-Jakob disease (CJD) and kuru.

Name two animal prion diseases.

Scrapie (sheep) and bovine spongiform encephalopathy (BSE or mad cow disease).

How are prions resistant to normal sterilization?

They are extremely resistant to heat, radiation, and chemicals that usually destroy pathogens.

What methods are used to destroy prions?

Incineration or autoclaving in strong sodium hydroxide (NaOH).

Why are prion diseases so difficult to control?

Because prions lack nucleic acids and cannot be easily detected or inactivated by standard dis