Microbiology and Virology: Virus Structure, Lifecycle, and Genetic Elements

Capsomere

the viral protein subunit, capsid is made of these

Capsid

protein structure to house the genome

Nucleocapsid

single molecule of nucleic acid surround by a capsid, come in several shapes such as helical, complex, and icosohedral

Virion

virus outside of the host cell

Bacteriophage

virus that infects bacteria

Enveloped Virus

virus that has an outer lipoprotein or lipopolysaccharide coat that was acquired by budding through a cell membrane

Lysozyme

enzyme inside virion, makes holes in cell wall to allow nucleic acid entry, lyses bacterial cell to release new virions

Neuraminidases

destroy glycoproteins and glycolipids to allow liberation of viruses from the host cell

RNA Replicase

RNA-dependent RNA polymerases

Reverse Transcriptase

RNA-dependent DNA polymerase

Pinocytosis

active "cell drinking", non-enveloped viruses

Fusion

enveloped viruses, viral envelope fuses with plasma membrane

Latent Period

part of infection to assembly of virion

Virulent Bacteriophages

cause acute infections, only do lytic cycle, host cell supports multiplication and virion assembly

Temperate Bacteriophages

causes chronic infections, does both lytic and lysogenic cycles, host cell genetically altered during lysogeny to include viral genome

Eclipse Phase

genome replicated and virion proteins translated

Maturation

packaging of nucleic acids in capsids

Latent Period

eclipse phase + maturation phase

Release

cell lysis, budding, or excretion

Integration

the process of viral DNA being put into host DNA

Quiescence and cI

lambda repressors, keeps viral genome inside bacterial genome

cII and cIII

help cI

Cro

allows viral DNA to be expressed outside of genome

Lysogeny Cycle

a method of viral reproduction where the virus integrates its genetic material into the host cell's genome, remaining dormant as a prophage without immediately killing the host

Lytic Cycle

a rapid, 5-6 step viral reproduction process where a bacteriophage infects a host bacterium, replicates, and kills the host, releasing 100-300 new viruses

Antigenic Shift

an abrupt, major change in a virus's surface antigens, usually influenza, caused by the reassortment of genetic material when two different strains infect the same cell

Antigenic Drift

the gradual, continuous accumulation of small genetic mutations in influenza viruses (specifically HA and NA surface proteins) that alter their structure over time

Topoisomerase

insert and remove supercoils in DNA

DNA Gyrase

type of topoisomerase, introduces supercoils into DNA via double-strand breaks

Chromosome

main genetic element in prokaryotes, typically circular, "house-keeping" genes

Plasmids

usually circular, beneficial genes

Transposable Elements

small segments of DNA can move from one site to another on same or different DNA molecule

Replicon

portion of genome that contains the origin of replication (oriC)

Origin-Binding Protein

binds origin of replication to open double helix

Helicase Loader

loads helicase at origin

Helicase

unwinds double helix at replication fork

Primase

primes new strands of DNA

DNA Polymerase III

main polymerizing enzyme

Tau Protein

helds together the two core enzymes for the leading and lagging strands

DNA Polymerase

excises RNA primer and fills in gaps

DNA Ligase

seals nicks in DNA

Replisome

large replication complex of multiple proteins

Primosome

helicase and primase subcomplex within replisome

DNA Proofreading

DNA polymerase I and III can move backwards to replace previous bases, proofreads as it lays down bases

DNA-Dependent RNA Polymerase

only RNA-polymerizing enzymes in prokaryotes, requires sigma factor to transcrie selectively

Strong Promoters

promoters conforming most closely to consensus sequences more effective in binding RNA polymerase

Type I Secretion Systems

proteins moved outside the cell in 1 step

Type II Secretion System

uses Sec or Tat to move folded protein past inner membrane, then out the cell

Type V Secretion System

uses Sec or Tat to move unfolded protein past inner membrane, then folded protein out of cell

Type III Secretion System

moves protein straight into another cell in 1 step

Type IV Secretion System

moves viral DNA straight into host cell in 1 step

Type VI Secretion System

uses a sheath that can retract and contract to send protein straight into another cell

Mutations

heritable and lead to change in genome

Horizontal Gene Transfer

large change in genome

Selective Media

choosing population based on if they grow on plate or not

Differential Media

shows growth that has different characteristics that are visible

Selectable Mutations

have a known benefit (antibiotic resistance)

Nonselectable Mutations

no advantage even though they may lead to a phenotypic change

Auxotrophs

cannot grow without a certain nutrient that is required for their survival

Spontaneous Mutations

random change in the DNA due to errors in replication that occur without known cause

Induced Mutations

those made environmentally and deliberately, radiation or chemicals that chemically modify DNA

Point Mutations

mutations that change only one base pair, can lead to single amino acid change in a protein, an incomplete protein, or no change at all

Silent Mutations

does not affect phenotype at all, normally 3rd base pair

Missense Mutation

changes one nucleotide, changing the amino acid that is coded for, has potential to alter protein function

Nonsense Mutation

coding codon changes to a stop codon, ending translation early

Frameshift Mutations

shifts the readng frame, resulting in a completely different protein that will be nonfunctional

Mutagens

chemical, physical, or biological agents that increase mutation rates

Nucleotide Base Analogs

resemble nucleotidea but have faulty base-pairing, causing extra mutations, and structural issues

Alkylating Agents

introduce mutations in coding and noncoding DNA, allows for wrong base-pair substitutions

Intercalating Agents

insert between two DNA base pairs, push them apart, causing sungle base insertions and deletions

Nonionizing Radiation

UV radiation, causes pyrimidine dimers, causes DNA polymerase to misread it

Ionizing Radiation

X-rays, causes double-stranded and single-stranded breaks in the backbone of DNA

Ionizing Radiation

X-rays, causes double-stranded and single-stranded breaks in the backbone of DNA

SOS Repair System

a DNA repair system activated by DNA damage

LexA

represses the SOS system, represses error-prone DNA polymerase IV, error-free DNA repair, and error-prone DNA repair, and Lex A

RecA

activated by DNA damage to inactivate LexA