Lesson 12-14 Microbio

Virus

Acellular infectious agent composed of nucleic acid (DNA or RNA) enclosed in a protein capsid that requires a host cell to replicate

Obligate intracellular parasite

An organism that can replicate only inside a living host cell

Capsid

Protein coat surrounding viral nucleic acid, made of capsomeres

Capsomeres

Protein subunits that make up the viral capsid

Nucleocapsid

Combination of viral nucleic acid and capsid

Enveloped virus

Virus surrounded by a lipid bilayer derived from the host cell membrane and containing glycoprotein spikes

Nonenveloped (naked) virus

Virus lacking a lipid envelope; consists only of nucleic acid and capsid

Viral spikes

Glycoproteins embedded in the envelope that mediate attachment to host cells

Sensitivity of enveloped viruses

Easily destroyed by heat, detergents, drying, and alcohol due to lipid envelope

Resistance of nonenveloped viruses

More resistant to disinfectants and environmental stress because they lack a lipid envelope

DNA virus replication

DNA viruses typically replicate their genome in the host cell nucleus using viral enzymes

RNA virus replication

RNA viruses replicate in the cytoplasm and must carry or encode RNA-dependent RNA polymerase

RNA-dependent RNA polymerase

Enzyme required by RNA viruses to replicate RNA from an RNA template

Animal virus multiplication cycle

Attachment, penetration, uncoating, biosynthesis, maturation, and release

Attachment (viral replication)

Viral binding to specific receptors on the host cell membrane

Penetration (viral replication)

Entry of viral nucleic acid into the host cell

Uncoating

Process by which viral capsid is removed to release nucleic acid

Biosynthesis

Host cell machinery is used to synthesize viral nucleic acid and proteins

Maturation

Assembly of new viral particles

Release

Exit of viruses from host cell by lysis or budding

Bacteriophage

Virus that infects bacteria

Lytic cycle

Phage replication cycle that results in host cell lysis and death

Lysogenic cycle

Phage replication cycle where viral DNA integrates into host chromosome as a prophage

Prophage

Viral DNA integrated into a bacterial chromosome during lysogeny

Virulent phage

Bacteriophage that only undergoes the lytic cycle

Temperate phage

Bacteriophage capable of both lytic and lysogenic cycles

Lysogenic conversion

Phenotypic change in a bacterium due to expression of prophage genes (e.g., toxin production)

Plaque

Clear zone on a bacterial lawn caused by lysis from bacteriophages

Cytopathic effects (CPE)

Visible structural changes in host cells caused by viral infection

Stages of viral disease

Incubation, prodromal, illness, decline, convalescence

Incubation period

Time between infection and appearance of symptoms

Prodromal period

Early symptoms such as fatigue and fever before full illness

Innate immunity

Nonspecific defense mechanisms present at birth that provide immediate protection

Adaptive immunity

Specific immune response involving lymphocytes and memory

Physical barriers of innate immunity

Skin and mucous membranes that prevent pathogen entry

Chemical barriers of innate immunity

Lysozyme, acidic pH, antimicrobial peptides, and sebum

Normal microbiota

Beneficial microbes that prevent pathogen colonization through competition

Phagocyte

Cell that engulfs and digests patho