Viruses, Viral Replication, and Mutations: Key Concepts for Biology

What is the Latin word for poison?

Virus

What are viruses classified as in terms of living status?

Acellular, nonliving infectious agents

What two components make up a virus?

Nucleic acid and protein coat

What is a virion?

A complete virus particle

What is the size range of viruses?

~10-400 nm in diameter

What is the difference between viruses and cellular organisms?

Viruses have a simple organization and cannot reproduce outside living cells, while cellular organisms have complex organization and can reproduce independently.

What is a capsid?

The protein coat of a virus that protects its genome and aids in transfer between host cells.

What are the three types of capsid structures?

Helical, icosahedral, and complex

What is the function of viral envelopes?

They surround some viruses, composed of host-derived lipids/carbohydrates and virus-specific proteins.

What are peplomers?

Attachment spikes on the viral envelope.

What are the two main types of viral genomes?

DNA and RNA

What is the typical structure of most DNA viruses?

Double-stranded DNA (dsDNA)

What are the stages of viral replication?

1. Adsorption, 2. Entry, 3. Synthesis, 4. Assembly, 5. Release

What happens during the adsorption stage of viral replication?

The virus interacts with the host membrane via viral surface proteins and/or enzymes.

What are the two mechanisms of entry for enveloped viruses?

Fusion of envelope with host membrane and endocytosis.

What occurs during the synthesis stage of viral replication?

Early genes take over the host, leading to the synthesis of viral DNA/RNA.

How do naked viruses typically release from the host cell?

By lysis of the host cell.

What is the process of viral assembly for naked viruses?

Empty procapsids are formed, and nucleic acid is inserted.

What is the role of late genes in viral replication?

They encode capsid proteins necessary for assembly.

What is a unique feature of enveloped viruses during release?

The formation of the envelope occurs concurrently with the release of the virus.

What is the significance of tropism in viral infections?

It refers to the variation in receptor distribution that affects which cells a virus can infect.

What is the role of viral enzymes in some viruses?

They assist in processes like viral release and nucleic acid replication.

What is the typical genome structure of most RNA viruses?

Single-stranded RNA (ssRNA)

What is the difference between + strand and - strand RNA viruses?

+ strand RNA viruses have genomic RNA that serves as mRNA, while - strand RNA viruses have genomic RNA complementary to mRNA.

What are enveloped viruses?

Viruses that acquire their envelope from the host's plasma membrane.

What are the two main types of phage life cycles?

Lytic and lysogenic.

What is the difference between virulent and temperate phages?

Virulent phages, like T4, cause lytic infections, while temperate phages, like lambda, can integrate into the host genome.

What is neoplasia?

Abnormal new cell growth or reproduction, often associated with tumors.

What is carcinogenesis?

A complex, multistep process of cancer development, often involving oncogenes.

Name a virus implicated in Burkitt's lymphoma.

Epstein-Barr Virus (EBV).

What type of cancer is associated with hepatitis B?

Hepatocellular carcinoma.

What is the role of oncogenes in cancer?

Oncogenes are cancer-causing genes that regulate cell growth and differentiation.

What is the CRISPR/Cas system?

A bacterial immune system that provides defense against phages by storing viral DNA sequences.

What happens during the adaptation stage of the CRISPR/Cas system?

A DNA sequence from a survived viral infection is added to the CRISPR region.

What is the interference stage in the CRISPR/Cas system?

The stage where the cell transcribes stored viral DNA into crRNA to target and destroy the virus.

What is a plaque assay?

A method to measure viral concentration by counting the number of plaques formed on host cells.

What does ID50 represent?

The infectious dose required to infect 50% of host cells.

What are viroids?

Infectious agents composed only of circular ssRNA that cause diseases in plants.

What are prions?

Infectious proteinaceous agents that cause neurodegenerative diseases.

What is the normal form of prion protein called?

PrPC.

What is the altered form of prion protein that causes disease?

PrPSC.

What diseases are associated with prions?

Scrapie, bovine spongiform encephalopathy, and Creutzfeldt-Jakob disease.

What is the significance of Koch's postulates in viral research?

They are used to establish a causal relationship between a virus and a disease, though often only correlative evidence is available.

What is the role of restriction endonucleases in bacterial defense?

They modify bacterial DNA to cleave unmodified viral DNA.

How does genetic resistance help bacteria survive viral infections?

Random mutations may lead to the expression of altered receptor proteins, making it harder for viruses to infect.

What is a mutation?

A stable, heritable change in nucleotide sequence that may or may not affect phenotype.

What are the two main types of mutations?

Spontaneous and induced mutations.

What causes spontaneous mutations?

Errors in DNA replication, natural DNA damage, or transposon insertion.

What are tautomeric shifts?

Alterations in hydrogen bonding of nucleotides that can lead to replication errors.

What is a frameshift mutation?

A mutation caused by the deletion or addition of base pairs that alters the reading frame.

What are induced mutations?

Mutations caused by chemical or physical agents that damage or alter DNA chemistry.

Give an example of a base analog that can cause induced mutations.

5-bromouracil, which is a thymine analog.

What are alkylating agents?

Chemical agents that can modify DNA and cause mutations, such as methyl nitrosoguanidine.

What is a silent mutation?

A mutation that does not change the amino acid sequence of a protein.

What is a missense mutation?

A mutation that results in a change in one amino acid in a protein.

What is a nonsense mutation?

A mutation that creates a premature stop codon, leading to early termination of protein synthesis.

What are morphological mutations?

Mutations that affect the colonial or cellular morphology of an organism.

What are conditional mutations?

Mutations that are expressed only under certain conditions, such as elevated temperature.

What is an auxotroph?

A mutant that cannot synthesize a required product for growth due to a mutation in a biosynthetic pathway.

What is a prototroph?

A strain that can grow in minimal media without supplements.

What are regulatory mutations?

Mutations that change regulatory sequences and alter control of gene expression.

What is horizontal gene transfer?

The transfer of DNA from a donor organism to a recipient, which can create genetic variability.

What is homologous recombination?

A type of recombination that involves the rearrangement of DNA molecules with similar sequences.

What are insertion sequences?

The simplest type of transposable elements that carry only the genes required for transposition.

What are composite transposons?

Transposable elements that carry additional genes, such as those for antibiotic resistance.

What is the 'cut-and-paste' method of transposition?

A method where transposase cuts the transposable element and inserts it into a new target site.

What is the replicative method of transposition?

A method where a copy of the transposable element is inserted into a new target site while the original remains.

What is recombination in genetics?

Rearranging or combining of one or more nucleic acid molecules to produce a new nucleotide sequence.

What is site-specific recombination?

Insertion of primarily nonhomologous DNA into a chromosome, requiring only a short region of homology, often occurring during viral genome integration.

What are transposons?

Segments of DNA that move within the genome, also known as 'jumping genes'.

What are the effects of transposition on genes?

Transposition can cause mutations in coding regions, arrest translation or transcription, activate genes, generate new plasmids, and transfer resistance among plasmids or chromosomes.

What are plasmids?

Small, circular double-stranded DNA molecules that are replicons and can exist independently or integrated into the host genome.

What are fertility (F) factors?

Conjugative plasmids that play a major role in bacterial conjugation, such as the F factor of E. coli.

What are resistance (R) factors?

Plasmids that carry antibiotic resistance genes, which can destroy or modify antibiotics.

What are col plasmids?

Plasmids that encode colicin, a type of bacteriocin that destroys closely-related bacteria.

What are virulence plasmids?

Plasmids that carry genes conferring resistance to host defense mechanisms or encode toxins.

What is bacterial conjugation?

The transfer of DNA between bacteria through direct cell-to-cell contact.

What was the significance of Bernard Davis' U-tube experiment?

It demonstrated that contact between bacterial cells is required for conjugation, as no prototrophs were obtained when a filter prevented contact.

What is transformation in bacteria?

The uptake of DNA from the environment and its incorporation into a heritable form.

What is a competent cell?

A bacterial cell that is capable of taking up DNA from its environment.

What is natural transformation?

Transformation that occurs naturally in certain genera of bacteria, such as Streptococcus and Bacillus.

What is artificial transformation?

Laboratory techniques used to introduce DNA into bacterial cells that are not naturally competent.

What is transduction?

The transfer of bacterial genes by bacteriophages.

What are virulent bacteriophages?

Bacteriophages that reproduce using a lytic life cycle.

What are temperate bacteriophages?

Bacteriophages that reproduce using a lysogenic life cycle.

What is generalized transduction?

A process where any part of the bacterial genome can be transferred during the lytic cycle.

What is specialized transduction?

A process where only specific portions of the bacterial genome are transferred, occurring when a prophage is incorrectly excised.