Viruses

Are viruses living?  No! They are non-living but they depend on the living.

Can you think of any viruses?  H1N1  West Nile  Seasonal Influenza (the flu)  HIV  Chicken Pox  Rabies  Ebola

Char. Of LifeVIRUSCELL GrowthNoYes EnzymesLimited – uses host cell’s enzymes to cause reactions necessary for themselves Hundreds of enzymes present ATPCannot make ATP, uses host cell’s ATP Make own ATP MutationsYes Gene Make-upDNA or RNADNA ReproductionCalled replication, can only occur within host cell Called division by mitosis or fission, occurs independently StructureNucleic acid core, protein covering, some have envelope Cytoplasm, cell membrane, etc..

Viruses and Bacteria Size comparison size demonstration Viruses are very small particles and measured in nanometres (1000nm = 1μm)

*VIRUS*  Microscopic particles capable of reproducing only within living cells.

*2 main components*  1. Capsid  Protein outer coat  Covers the nucleic acid and protects it  2. Nucleic Acid Core  Genetic material consisting of either DNA or RNA Capsid Genetic material

 There are specific viruses which infect animal, plant or bacterial cells.  Those that infect bacteria are called bacteriophages.

*Bacteriophages Replicate in 2 ways…*  Virulent phages replicate actively and cause lysis.  Temperate phages lie dormant for varying periods of time, and can pass through generations attached to a chromosome. They cause lysogeneis.

Basic structure of a virus Some form of nucleic acid (DNA or RNA) Enclosed in a protein coat. (capsid) Bacteriophages helical

Viruses are specific to… a) organism - ex. Hanta virus - carried in mice (have no effect) but fatal to humans b) cell type - ex. human cold virus only attacks cells lining the respiratory tract. ans

 Viruses are able to reproduce ONLY inside living host cells.  They use the cell's genetic machinery (ribosomes, enzymes) to reproduce viral parts.  They are then assembled into many new viruses which may rupture the cell (destroying it), releasing these viruses to infect more cells.  Viruses can be considered to be intracellular parasites.

*Viruses may enter animal cells in 3 possible ways:* 1. Attachment and Injection 2. Endocytosis 3. Membrane fusion

1) Attachement and Injection  Capsid remains on outside of host cell Eg. Bacteriophage Virus attaches to the bacterial cell and injects its genetic material into the cell through a tiny syringe.

2) Endocytosis  The cell swallows up the virus through phagocytosis.  After entering the cell, the virus sheds its capsid (decapsidation), and the viral genetic material takes over the cell.

3) Membrane Fusion  Some viruses have a membrane (from a previous cell) that they fuse to the cell membrane and get inside the cell.  Once inside, decapsidation occurs and the virus takes over.

Viral Replication (2 possible cycles): Lytic and Lysogenic

1) Lytic Cycle cytoplasm  the replication process occurs in the cytoplasm of the host cell  1. the virus’s genetic material enters the host cell  2. the cell replicates the viral DNA or RNA  3. the host cell makes new capsids and assembles new viral particles  4. the host cell lyses (breaks open) and the new viruses leave the cell

2) Lysogenic Cycle chromosome  Virus’s genetic material enters the host cell nucleus and becomes part of the host cell’s chromosome (provirus)  In most cases the genes are not activated until later  Activation results in a continuation of the lytic cycle

Reproduction in Viruses UNIT 1 Chapter 2: Diversity: From Simple to Complex Section 2.1

Some Applications TechnologyApplication or possible application Using a virus capsule to deliver a drug This method may be used to deliver drugs to targeted cells in the body, for example, to deliver toxic chemotherapy to cancerous tumour cells Using a virus to insert a new copy of a gene This method may be used to insert corrective genes into individuals who suffer from a genetic disorder Using a virus to insert a gene taken from one species into another species This method can be used to create genetically modified organisms. It is widely used in the genetic engineering of plants.

Video Clip – Flu Attack! How a virus invades your body (3:39)  mEGShQ mEGShQ

23 Viral Replication