Micro Test 4: Viruses

Viruses

Genetic elements requiring host for replication.

Virions

Extracellular virus form with nucleic acid and protein.

Capsid

Protein coat surrounding viral nucleic acid.

Nucleocapsid

Combination of capsid and viral nucleic acid.

Baltimore Classification

Virus classification based on genome type.

Animal Viruses

Viruses that infect animal hosts.

Plant Viruses

Viruses that infect plant hosts.

Bacteriophage

Viruses that infect bacterial cells.

ssDNA

Single-stranded DNA virus type.

dsDNA

Double-stranded DNA virus type.

ssRNA

Single-stranded RNA virus type.

• Strand RNA

RNA strand identical to mRNA.

• Strand RNA

RNA strand complementary to mRNA.

dsRNA

Double-stranded RNA virus containing both strands.

Retrovirus

RNA virus replicating via DNA intermediate.

Smallest Virus Size

Approximately 3500 bases in length.

Largest Virus Size

Up to 500,000 base pairs in length.

Helical Symmetry

Capsomers form filamentous structures.

Icosahedral Symmetry

20-sided shape formed by capsomers.

Naked Virus

Virus with only capsid and nucleic acid.

Enveloped Virus

Virus with capsid and phospholipid bilayer.

Complex Viruses

Viruses with additional structural elements.

Complexity

Larger genomes encode additional proteins in viruses.

Tail Proteins

Interact with host receptor proteins for attachment.

Enzymes in Virions

Required for viral functions during infection.

Lysozymes

Break peptidoglycan to allow viral genome entry.

Polymerases

Enzymes required for viral genome replication.

Host-lytic Enzymes

Lyse host cells to release new virions.

Viral Growth

Requires host cells for replication and growth.

Contact Inhibition

Cells grow until they cover the entire culture plate.

PFU

Plaque forming unit, indicates infectious virus particles.

Plaque Assay

Measures virus infectivity through clear zones.

Bacterial Virus Replication

Process includes attachment, penetration, synthesis, assembly, release.

Eclipse Phase

Initial viral particles destroyed; no detectable virus.

Latent Period

Follows eclipse, early enzymes and nucleic acids replicate.

Maturation Phase

Formation of capsids and assembly of virions.

Attachment Specificity

Viruses bind specific host receptors for infection.

Uncoating

Removal of capsid inside the host cell.

Endocytosis

Method for viral entry into host cells.

Restriction Enzymes

Modify host DNA to inhibit foreign DNA use.

Modification Systems

Methylation prevents endonucleases from cleaving DNA.

7 Classes of Viruses

Categorized by genome type and replication method.

Class 1 Viruses

Double stranded DNA, classical semiconservative replication.

Class 6 Viruses

Single stranded RNA with reverse transcription to DNA.

Lambda Phage

Incorporates into host genome, can enter lytic cycle.

Lytic Phage

Replicates within host, kills host upon release.

Rolling Circle Replication

DNA synthesis occurs from a circular template.

Prophage

Viral DNA integrated into host DNA during lysogeny.

Animal Viruses

Can be enveloped, with diverse genome types.

Transformation

Virus-induced genetic changes can lead to tumors.

Latent Infection

Virus remains dormant, can reactivate later.

Antigenic Shift

Genome rearrangement produces new virus strains.

Antigenic Drift

Minor mutations cause small changes in virus.

Retrovirus Structure

Contains two RNA genomes and reverse transcriptase.

Gag Protein

Encodes structural proteins of the retrovirus.

Pol Protein

Encodes reverse transcriptase for RNA to DNA conversion.

Env Protein

Encodes envelope protein that targets host membranes.

Reverse Transcription

Process converting viral RNA into DNA.

Viroids

Small circular ssRNA particles infecting plants.

Naked Nucleic Acid

Viroids lack protein-coding regions.

Regulatory RNA

Viroids disrupt normal protein expression.

Secondary Structure

Viroids form self-binding complementary regions.

Prions

Infectious agents composed solely of protein.

Neurological Diseases

Prions cause diseases in animal hosts.

Host Genetic Information

Prions rely on host's genetic material.

Refolding Mechanism

Prions induce misfolding of normal proteins.

Accumulation Damage

Prions damage host as they accumulate.

Creutzfeldt-Jakob Disease

A fatal prion disease in humans.

Kuru

Prion disease spread via cannibalism.

Transmissible Spongiform Encephalopathies

Group of prion diseases, includes mad cow disease.

Scrapie

Prion disease affecting sheep and goats.

Mutation

Heritable changes in genetic information.

Point Mutation

Change in a single base pair.

Missense Mutation

Codon change leads to different amino acid.

Nonsense Mutation

Codon change creates a premature stop codon.

Silent Mutation

Codon remains unchanged despite mutation.

Insertions and Deletions

Alter DNA reading frame, affecting gene function.

Mutation Rates

Frequency of mutations during DNA replication.

Mutagens

Agents that increase mutation rates.

DNA Repair

Processes to fix DNA damage.

Transformation

Uptake of naked DNA from environment.

Transduction

Virus-mediated DNA transfer between bacteria.

Conjugation

Direct DNA transfer via bacterial cell contact.

Competent Cells

Cells capable of taking up DNA.

Stable Transformation

Successful DNA incorporation into host genome.

Unsuccessful Transformation

DNA uptake without incorporation into host.

Temperate Virus Life Cycle

Virus can replicate or integrate into host.

Hfr Strain

High-frequency recombination strain transferring DNA rapidly.

IS3

Repeated DNA fragment aiding homologous pairing.

RecA Protein

Facilitates homologous recombination in DNA.

Transcription

Process of synthesizing RNA from DNA template.

RNA Polymerase

Enzyme that synthesizes RNA during transcription.

Promoter

DNA sequence where RNA polymerase binds to initiate transcription.

Terminator

Sequence that signals RNA polymerase to stop transcription.

Coding Strand

DNA strand identical to RNA, runs 5' to 3'.

Template Strand

DNA strand complementary to RNA, runs 3' to 5'.

TATAAT Box

Common promoter sequence, also known as Pribnow box.

Intrinsic Termination

Transcription termination without additional factors.

Rho Protein

Binds RNA to terminate transcription at specific sites.

Cytoplasmic Transcription

Transcription occurs in the cytoplasm of prokaryotes.