Mobile Genetic Elements: Viruses and Plasmids

Viruses

Obligate intracellular parasites requiring host for replication.

Bacteriophage

Viruses specifically infecting bacteria.

Capsid

Protein coat surrounding viral nucleic acid.

Envelope

Membrane acquired from host during viral release.

Viral Genome Size

Ranges from 1,700 bases to over 2 million bp.

Nucleic Acid Types

Can be DNA or RNA, single or double-stranded.

Viral Shapes

Viruses exist in various basic structural forms.

Viral Replicative Cycle

Consists of attachment, entry, gene expression, replication.

Attachment

Specific binding to host cell surface receptors.

Entry

Transfer of viral nucleic acid into host cell.

Early Gene Expression

Production of enzymes for viral nucleic acid replication.

Replication of Viral Nucleic Acid

New virions package original nucleic acid type.

Late Gene Expression

Production of capsid proteins for viral assembly.

Assembly

Formation of new virus particles from nucleic acid.

Release

New virus particles exit host cell via budding or lysis.

Endocytosis

Viral entry method involving host cell membrane engulfment.

Fusion

Process where enveloped viruses merge with host membrane.

Viral Enzymes

Proteins required for replication and release of viruses.

Lysis

Bursting of host cell to release non-enveloped viruses.

Segmented Genome

Viral genome divided into multiple segments.

Non-segmented Genome

Viral genome consisting of a single piece.

Glycoproteins

Proteins on viral surface aiding in host recognition.

Viral Particle

Complete virus structure ready for infection.

Viral Infection

Process by which viruses invade host cells.

ds-DNA viruses

Most common type of DNA viruses.

Phage T4

A well-studied virulent bacteriophage.

Bacteriophage λ

Example of a temperate bacteriophage.

Lytic pathway

Viral replication leading to host cell lysis.

Lysogenic pathway

Viral DNA integrates into host genome.

Prophage

Phage in a lysogenic state within host.

Viral replicase

Enzyme synthesizing RNA from RNA template.

Reverse transcriptase

Enzyme converting RNA to DNA in retroviruses.

(+) sense RNA

RNA that can be directly translated.

(-) sense RNA

RNA complementary to mRNA, not directly translatable.

Retroviruses

RNA viruses that reverse transcribe to DNA.

RNA-dependent RNA polymerase

Enzyme synthesizing RNA from RNA template.

Viral assembly

Process of forming new viral particles.

Integrase

Enzyme integrating viral DNA into host DNA.

Protease

Enzyme cleaving viral polyproteins into functional proteins.

Mobile genetic elements

Includes viruses and plasmids that transfer genes.

Plasmids

Circular, extrachromosomal DNA molecules in cells.

Origin of replication

Site where DNA replication begins in plasmids.

Copy number

Number of plasmid copies in a cell.

Conjugation

Process of plasmid transfer between bacteria.

Bacteriocins

Substances produced by bacteria to inhibit others.

Toxic metal resistance

Ability of bacteria to survive in contaminated soils.

Antibiotic resistance factors

Genes that modify or destroy antibiotics.

Viral genome

Genetic material of a virus, either DNA or RNA.

Viral proteins

Proteins synthesized from viral mRNA.

Host RNA polymerase

Host enzyme modified for viral transcription.

Viral tail proteins

Proteins involved in attaching and injecting viral DNA.

Viral capsid

Protein shell enclosing viral genetic material.