Microbiology Exam 4 Part 2

Viruses

Virus

Genetic elements that replicate independently of a cell's chromosome but require a living host in order to reproduce

Viruses are \___ parasites

Obligate intracellular

Viruses infect \___ cell types

All

Viruses are \___ infectious agents

Acellular

Viruses contain...

DNA or RNA

DNA or RNA segments in viruses

Circular, double or single stranded, linear, or segmented

Extracellular form of a virus

Virion

Virion

The complete virus particle

Virion composed of...

Nucleic acid surrounded by a protein coat and possibly external layers

Virion size range

10-2300 nm in diameter

Virion contains...

Nucleocapsid

Nucleocapsid

Nucleic acid (DNA or RNA) + protein coat (capsid) (some have additional components)

Types of virus symmetry

Complex, helical, and icosahedral

Purpose of nucleocapsid

Protect the nucleic acid

Capsomeres

Protein subunits that make up capsid

Helical symmetry

Virus RNA coiled and surrounded with capsomeres

Icosahedral symmetry

Geometric shape

Types of complex symmetry

Binal and vaccinia

Example of binal symmetry

T4 bacteriophage

Why is binal symmetry called binal symmetry?

Has both helical and icosahedral symmetry

Even though viruses are not living, they are still classified using...

Genus and species

Capsid \= \___ symmetry

Helical

Types of ssRNA viruses

Negative sense and positive sense

Positive sense viruses

Genome and mRNA are the same, plus strand, and positive

Negative sense viruses

Genome and mRNA are compliments, negative, and negative strand

Central dogma of biology

DNA \=\> mRNA \=\> protein

How to get negative sense virus

-RNA genome \=\> +mRNA \=\> protein

How to get positive sense virus

+RNA genome used as +mRNA or +RNA genome \=\> -DNA \=\> +mRNA \=\> protein (retro viruses)

Viral envelopes

Flexible, membranous, outer layer

Carbohydrates and lipids in viral envelopes are usually \___-derived

Host

May project from envelope surface

Envelope proteins

Types of envelope proteins

Peplomers and spikes

Envelope proteins are \___-encoded

Viral

Functions of envelope proteins (4)

Enzymatic activity, identification of virus, role in nucleic acid replication, and viral attachment to host cell

Most envelope viruses are \___ viruses

Animal (due to cell membrane and lack of cell wall)

Very few bacteriophages have...

Viral envelopes

Influenza

Negative sense RNA virus

Mechanism of viral replication used depends on...

Viral structure of genome

Steps of viral replication are...

Similar for all viruses

Steps of viral replication (in sequential order)

Attachment, entry, uncoating of genome, synthesis, assembly, and release

Immediately after infected with a virus

Latent period

Latent period

Eclipse and maturation

During latent period, it appears as if...

Nothing is happening

Eclipse

Early enzymes, nucleic acid, and protein coats

Maturation

Assembly and release before immune response occurs

Characteristics of bacteriophages

Structurally complex and very diverse

Most bacteriophages contain...

dsDNA genomes

Most bacteriophages are...

Naked

Infect with viruses

70% of marine prokaryotes

Chock full of bacteriophages

The ocean

Virulent/lytic bacteriophages begins multiplying...

Immediately after entering host

Lyse bacterial host cell for release (of virions)

Virulent/lytic bacteriophages

Lytic pathway only

Virulent/lytic bacteriophages

Temperate/lysogenic phages

Remain within host cell without destroying it or reproduce as virulent phages (lytic pathway)

Lysogeny

Temperate/lysogenic phages integrate genome into host genome

Can use either lytic pathway or lysogenic pathway

Temperate/lysogenic phages

Example of temperate/lysogenic phages

Lambda

Example of virulent/lytic bacteriophages

T4

Once viral DNA is integrated into host DNA, lysogenized cell is called...

Prophage

Lysogeny uses \____ relationship between a phage and its host

Nonlytic

Prophage

Integrated bacteriophage genome

Lysogeny uses \___ to integrate into host chromosome

Integrase enzyme

Temperate/lysogenic phages always integrate between...

Biotin and galactose operons (attachment site)

Lysogen

Infected bacterial host

Temperate/lysogenic phages replicate...

As host genome replicates

Lysogen appears...

Normal

Prophage may change...

The phenotype of its host

Lysogenic conversion

When a prophage changes the phenotype of its host

Upon induction, temperate/lysogenic phage may...

Switch from lysogenic to lytic cycle

Lambda is injected into the cell in \___ conformation

Linear

Lambda has \___ genome

double-stranded DNA

Induction of lytic cycle

Process by which temperate/lysogenic phage reproduction is initiated

Initiation of temperate/lysogenic phage reproduction results in...

Switch to lytic cycle

Results in switch of temperate/lysogenic phage switch to lytic cycle

Initiation of reproduction

Induction of lytic cycle triggered by...

Drop in levels of lambda repressor

Drop in levels of lambda repressor usually caused by...

Exposure to UV light or chemical mutagens that cause DNA damage

Excisionase

Binds to integrase enzyme and enables integrase to reverse integration process

Cuts chromosome out of host cell

Excisionase

Will animal viruses, \___ enters the animal cell

Entire virion

Most bacteriophages have \___ genome

Double-stranded DNA

Animal viruses have \___ genome

Double-stranded DNA or single-stranded RNA

Animal viruses may replicate in...

The nucleus of the animal cell

Many animal viruses are...

Enveloped

Effects of animal viruses

Cancer, latent, persistent, and virulent

Latent viral infection

Virus stops remaining stops reproducing and remains dormant for some time

During latency...

Antivirus-antibodies, symptoms, and viruses are not detectable

Examples of latent viral infection

Herpesvirus and varicella-zoster (i.e., chicken pox then shingles)

Virulent viral infection

Virus infects cells and causes lysis (lytic pathway)

Cancer viral infection

While unlikely, virus can repress tumor repressor genes so that tumors can grow

Persistent viral infection

Clinical symptoms absent or mild for long periods, and virus almost always detectable

Examples of persistent viral infection

Hepatitis B and HIV

Oncoviruses

Viruses associated with human cancers

Sometimes viruses carry oncogenes...

Accidentally

Retroviruses

RNA viruses that replicate through a DNA intermediate

Retroviruses are...

Enveloped viruses

Retroviruses are released by...

Budding

Retroviruses use...

Reverse transcriptase

Reverse transcriptase

RNA to DNA

Example of retroviruses

HIV

Characteristics of SARS-CoV-2

Enveloped with club-shaped spikes, helical capsid symmetry, positive sense, and single-stranded RNA genome