VirusesViruses

VirusVirus

A non living particle composed of a A non living particle composed of a nucleic acid and a protein coatnucleic acid and a protein coat

Causes many diseasesCauses many diseases Can change how a cell functionsCan change how a cell functions Study of viruses is called virologyStudy of viruses is called virology

CharacteristicsCharacteristics One of the smallest One of the smallest

biological particles capable biological particles capable of causing diseaseof causing disease

Range from 20 nm to 25 nmRange from 20 nm to 25 nm Nm (nanometers)Nm (nanometers) Not considered living Not considered living

organismsorganisms No nucleus, No nucleus,

cytoplasm, cytoplasm, organelles,or cell organelles,or cell membranemembrane

Replicate only by Replicate only by infecting other cells infecting other cells

Uses the organelles Uses the organelles and enzymes from and enzymes from the host cellsthe host cells

StructureStructure

Protein coat called a capsidProtein coat called a capsid May have DNA or RNAMay have DNA or RNA Envelope – membrane made mostly of Envelope – membrane made mostly of

lipids taken from the host cell. It lipids taken from the host cell. It allows new viruses to infect host cells allows new viruses to infect host cells during the first stage of viral during the first stage of viral replicationreplication

Glycoprotein's – projections that Glycoprotein's – projections that contain sugar chains that viruses use contain sugar chains that viruses use to attach to host cellsto attach to host cells

ShapeShape

Can be an Icosahedron – a geometric Can be an Icosahedron – a geometric shape that has 20 triangular faces.shape that has 20 triangular faces.

Helix – looks like a coiled springHelix – looks like a coiled spring

Virus TypesVirus Types

DNA virus – can directly produce RNA that DNA virus – can directly produce RNA that makes more viral proteins or it may join makes more viral proteins or it may join with the host cell DNA to direct synthesis with the host cell DNA to direct synthesis of new viruses.of new viruses.

RNA virus – Viral RNA is released into the RNA virus – Viral RNA is released into the host cells cytoplasm and uses the host cell host cells cytoplasm and uses the host cell ribosomes to produce new viral proteinsribosomes to produce new viral proteins

Retroviruses – a type of RNA virus that Retroviruses – a type of RNA virus that contains an enzyme called reverse contains an enzyme called reverse transcriptase which it uses to make DNAtranscriptase which it uses to make DNA

Bacteriophage infectionsBacteriophage infectionsLytic InfectionLytic Infection

In a lytic infection, a virus enters a In a lytic infection, a virus enters a cell, makes copies of itself, and cell, makes copies of itself, and causes the cell to burst burst = lysecauses the cell to burst burst = lyse

Lysogenic InfectionLysogenic Infection

In a lysogenic infection, a virus In a lysogenic infection, a virus integrates its DNA into the DNA of integrates its DNA into the DNA of the host cell, and the viral genetic the host cell, and the viral genetic information replicates along with the information replicates along with the host cell’s DNAhost cell’s DNA

Examples of Viruses Examples of Viruses

HIV VIRUSHANTA VIRUS

ViroidsViroids

Smallest known particles able to Smallest known particles able to replicate – consists of a short single replicate – consists of a short single strand of RNA and no capsidstrand of RNA and no capsid

Disrupts plant cell metabolism and Disrupts plant cell metabolism and can damage cropscan damage crops

PrionsPrions

Abnormal forms of proteins that Abnormal forms of proteins that clump together inside of a cellclump together inside of a cell

This clumping activity eventually This clumping activity eventually leads to the death of the cellleads to the death of the cell

Prevention and TreatmentPrevention and Treatment Antiviral Drugs – drugs that Antiviral Drugs – drugs that

interfere with viral nucleic interfere with viral nucleic acid synthesisacid synthesis

Vaccines – A preparation of Vaccines – A preparation of pathogens or other pathogens or other materials that stimulate materials that stimulate the bodys immune systemthe bodys immune system

2 types2 types Inactivated viruses – do not Inactivated viruses – do not

replicate in a host systemreplicate in a host system Attenuated viruses – Attenuated viruses –

viruses that have been viruses that have been genetically altered so that genetically altered so that they are incapable of they are incapable of causing disease.causing disease.