BIOL 251 Microbiology Week 12 Lecture Notes

Microbiology: An Introduction 13th Edition - Ch. 13

Virus

Genetic element that cannot replicate independently of a living host cell

Virology

Study of viruses

Virus Particle

Extracellular form of virus

• Facilitates transmission from one host to another

Virion

Infectious virus particle

Obligate

_____ Intracellular Parasites: Require living host to replicate

• Contain DNA or RNA

• Contain a protein coat

• NO Ribosomes

Host range

The spectrum of host cells a virus can infect

• Determined by specific host attachment sites and cellular factors

• Classification based on host: bacterial, animal, plant viruses

Nucleic Acid

_____ _____

DNA or RNA

Single- or Double-stranded

Linear or circular

Capsid

_____

Protein coat made up of capsomeres (subunits)

Capsomere

A protein subunit that makes up the capsid of a virus

Envelope

Spikes

A lipid, carbohydrate, or protein coat on some viruses

• Enveloped vs Nonenveloped viruses

_____: Projections from outer surface

Helical

_____ Viruses: Shaped like long rods

• Capsids are hollow cylinders with a helical structure

Polyhedral

_____ Viruses: Capsids are many-sided.

Enveloped

_____ Viruses: Has an outer envelope (derived from the host cell's membrane) surrounding its core structure. These viruses often have spikes on their surface.

Complex

_____ Viruses: Have irregular shapes and structures, often consisting of multiple types of proteins and sometimes other components. They can include bacteriophages and some animal viruses.

Order

Family

Subfamily

Genus

International Committee on Taxonomy of Viruses (ICTV)

____: ends in -ase

____: ends in -viridae

____: ends in -virinae

____: ends in -virus

Species designated by common designated name and number

living

Viruses must be grown on _____ cells. One method is embryonated eggs

• Bacteriophages form plaques on a lawn of bacteria

  • Plaque Forming Unit (PFU)

Cytopathic

Continuous

Testing Viruses in Cell Cultures

• Tissues treated with enzymes - separate cells

• Infected cells detected - deterioration - _____ Effect (CPE)

• _____ Cell lines are used

host

metabolic

For a virus to multiple;

1. It must invade a _____ cell

2. Must take over host’s _____ machinery

Eclipse

Viral One-Step growth curve

• _____ period: The time when a virus is replicating within a host cell, but is not yet producing any new infectious virions

Lytic

Lysogenic

Multiplication of Bacteriophages

• _____ Cycle: Phage causes lysis and death of host cell

• _____ Cycle: Phage DNA is incorporated in the host DNA

  • No cell death

Oncogenic

_____ Viruses: a virus that can cause cancer

• DNA Viruses - HPV, HBV

• RNA Viruses - T-cell Leukemia, Lymphoma

Viroids

Short pieces of naked RNA

• Small, circular, single stranded

Prions

Infectious agents composed of misfolded proteins that cause neurodegenerative diseases. They propagate by inducing normal proteins to misfold.

• PrP^c: Normal cellular protein, on cell surface

• PrP^Sc: Scrapie protein; accumulates in brain cells to form plaques

Budding

The mechanism whereby an enveloped virus leaves a host cell

Transduction

The process by which viruses transfer genetic material from one bacterium to another

Lysogeny

A viral life cycle in which the viral genome integrates into the host DNA and replicates along with it without immediately destroying the host

Absorption

The initial step in viral infection where the virus attaches to specific receptors on the surface of a host cell

Viruses are not composed of cells

How do ALL viruses differ from bacteria?

Cannot reproduce by themselves

Viruses are not considered living organisms because they…?

is read by ribosomes during the process of translation

DNA does all but which of the following?

Serves as the genetic material passed from parent to offspring

Provides the instructions for the synthesis of messenger RNA

Is read by ribosomes during the process of translation

DNA to RNA to protein

According to the central dogma, which of the following represents the flow of genetic information in cells?

Protein to DNA to RNA

DNA to RNA to protein

RNA to DNA to protein

DNA to protein to RNA

ligase

Which of the following is not involved in the initiation of replication?

Ligase

DNA gyrase

Helicase

Primase

True

More primers are used in lagging strand synthesis than in leading strand synthesis.

True

False

3′-GTCAAGCCT-5′

Which of the following would be synthesized using 5′-CAGTTCGGA-3′ as a template?

3′-AGGCTTGAC-4′

3′-TCCGAACTG-5′

3′-GTCAAGCCT-5′

3′-CAGTTCGGA-5′

The polypeptide is released

When the ribosome reaches a nonsense codon, which of the following occurs?

A methionine is incorporated

The polypeptide is released

A peptide bond forms

promotor

Which of the following components is involved in the initiation of transcription?

Primer

Origin

Promotor

Start codon

mRNA

What is the final product of transcription?

nonsense mutation

Which of the following is a change in the sequence that leads to formation of a stop codon?

Missense mutation

Nonsense mutation

Silent mutation

Deletion mutation

Deletion of one nucleotide

Which of the following is an example of a frameshift mutation?

Deletion of a codon

Missense mutation

Silent mutation

Deletion of one nucleotide

Direct repair

Which of the following is the type of DNA repair in which thymine dimers are directly broken down by the enzyme photolyase?

Direct repair

Nucleotide excision repair

Mismatch repair

Proofreading

Plasmids

What are transferred by conjugation?

Transformation

Which of the following refers to the uptake of naked DNA from the surrounding environment?

Conjugation

Generalized transduction

Specialized transduction

Transformation

Conjugation

Which of the following refers to the mechanism of horizontal gene transfer naturally responsible for the spread of antibiotic resistance genes within a bacterial population?

Conjugation

Generalized transduction

Specialized transduction

Transformation

Vector

A DNA molecule that transports foreign DNA into a cell is called a

Clone

Vector

Nanosphere

Mutagen

Tryptophan

Indole is from the enzymatic hydrolysis of what biomolecule?