Viruses

Virus A non living particle composed of a nucleic acid and a protein coat A non living particle composed of a nucleic acid and a protein coat Causes many diseases Causes many diseases Can change how a cell functions Can change how a cell functions Study of viruses is called virology Study of viruses is called virology

Characteristics One of the smallest biological particles capable of causing disease One of the smallest biological particles capable of causing disease Range from 20 nm to 25 nm Range from 20 nm to 25 nm Nm (nanometers) Nm (nanometers) Not considered living organisms Not considered living organisms No nucleus, cytoplasm, organelles,or cell membrane No nucleus, cytoplasm, organelles,or cell membrane Replicate only by infecting other cells Replicate only by infecting other cells Uses the organelles and enzymes from the host cells Uses the organelles and enzymes from the host cells

Structure Protein coat called a capsid Protein coat called a capsid May have DNA or RNA May have DNA or RNA Envelope – membrane made mostly of lipids taken from the host cell. It allows new viruses to infect host cells during the first stage of viral replication Envelope – membrane made mostly of lipids taken from the host cell. It allows new viruses to infect host cells during the first stage of viral replication Glycoprotein's – projections that contain sugar chains that viruses use to attach to host cells Glycoprotein's – projections that contain sugar chains that viruses use to attach to host cells

Shape Can be an Icosahedron – a geometric shape that has 20 triangular faces. Can be an Icosahedron – a geometric shape that has 20 triangular faces. Helix – looks like a coiled spring Helix – looks like a coiled spring

Virus Types DNA virus – can directly produce RNA that makes more viral proteins or it may join with the host cell DNA to direct synthesis of new viruses. DNA virus – can directly produce RNA that makes more viral proteins or it may join with the host cell DNA to direct synthesis of new viruses. RNA virus – Viral RNA is released into the host cells cytoplasm and uses the host cell ribosomes to produce new viral proteins RNA virus – Viral RNA is released into the host cells cytoplasm and uses the host cell ribosomes to produce new viral proteins Retroviruses – a type of RNA virus that contains an enzyme called reverse transcriptase which it uses to make DNA Retroviruses – a type of RNA virus that contains an enzyme called reverse transcriptase which it uses to make DNA

Bacteriophage infections Lytic Infection In a lytic infection, a virus enters a cell, makes copies of itself, and causes the cell to burst burst = lyse In a lytic infection, a virus enters a cell, makes copies of itself, and causes the cell to burst burst = lyse

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

Examples of Viruses HIV VIRUS HANTA VIRUS

Viroids Smallest known particles able to replicate – consists of a short single strand of RNA and no capsid Smallest known particles able to replicate – consists of a short single strand of RNA and no capsid Disrupts plant cell metabolism and can damage crops Disrupts plant cell metabolism and can damage crops

Prions Abnormal forms of proteins that clump together inside of a cell Abnormal forms of proteins that clump together inside of a cell This clumping activity eventually leads to the death of the cell This clumping activity eventually leads to the death of the cell

Prevention and Treatment Antiviral Drugs – drugs that interfere with viral nucleic acid synthesis Antiviral Drugs – drugs that interfere with viral nucleic acid synthesis Vaccines – A preparation of pathogens or other materials that stimulate the bodys immune system Vaccines – A preparation of pathogens or other materials that stimulate the bodys immune system 2 types 2 types Inactivated viruses – do not replicate in a host system Inactivated viruses – do not replicate in a host system Attenuated viruses – viruses that have been genetically altered so that they are incapable of causing disease. Attenuated viruses – viruses that have been genetically altered so that they are incapable of causing disease.