Viruses Biology 4C : compare the structures of viruses to cells, describe viral reproduction, and describe the role of viruses in causing diseases such as human immunodeficiency virus (HIV) and flu.

Viruses are not living organisms Viruses do not – Grow – Have homeostasis – Metabolize Viruses do – Infect cells and use the cell to make more viruses – Cause disease in many organisms

Viral Structure and Shape

compare the structures of viruses to cells

Parts of a Virion (a virus particle) Lipid Membrane – a membrane around the capsid in many viruses; helps the virus enter cells “enveloped” viruses; without the membrane, the virus is “naked”

Parts of a Virion (a virus particle) Capsid – protein coat that surrounds the DNA or RNA in a virus

Parts of a Virion (a virus particle) Viruses with RNA – Human immunodeficiency virus (HIV) – Influenza viruses – Rabies Viruses with DNA – Warts – Chickenpox – mononucleosis Nucleic Acid – RNA or DNA

Virus Shapes Helical Rodlike with capsid proteins winding around the core in a spiral Tobacco Mosaic Virus Polyhedral Has many sides Most polyhedral capsids have 20 sides and 12 corners

Virus Shapes Polyhedral capsid attached to a helical tail.

Viral Replication

How do viruses replicate? 2 methods of replication: 1.Lytic Cycle – the virus enters the cell, replicates itself hundreds of times, and then bursts out of the cell, destroying it.

1) Attachment – Virus attaches to the cell surface of the host cell

2) Entry – the virus or the virus’s DNA/RNA is inserted in the host cell and is place with the host DNA

3) Synthesis – the host cell will produce the viral DNA/RNA and parts

4) Assembly – the host cell will assemble the parts of the virus to get LOTS of new viruses

5) Release(lysis) – the new viruses will break open the cell, destroying the host cell and go off to infect new host cells.

How do viruses replicate? 2 methods of replication: 2.Lysogenic Cycle – the virus DNA integrates with the host DNA and the host’s cell helps create more virus DNA. An environmental change may cause the virus to enter the Lytic Cycle.

Virus attaches to the cell surface of the host cell 1) Attachment

the virus or the virus’s DNA/RNA is inserted in the host cell and is place with the host DNA 2) Entry

The Viral DNA/RNA integrates into the host cell’s DNA 3) Integration

The integrated DNA/RNA is replicated when the cell goes through normal division. 4) Replication

Viruses Enter Living Cells Viruses enter bacterial cells by punching a hole in the cells wall and injecting its DNA

Viruses Enter Living Cells Viruses enter plant cells through tiny rips in the cell wall. Viruses enter animal cells by endocytosis.

Viruses are host cell specific. Most viruses are restricted to certain kinds of cells (those that infect plants cannot infect animal cells). Why? Scientists think that viruses originated from escaped genetic material from host cells.

describe the role of viruses in causing diseases such as human immunodeficiency virus (HIV) and flu

The Flu ShQ ShQ

Human Immunodeficiency Virus (HIV) Acquired Immuno Deficiency Syndrome (AIDS)

Basic Structure Viral envelope – lipid bilayer; glycoproteins protrude from surface – Glycoproteins enable virus to recognize surface proteins of special immune cells and to enter the cell (like a key to the cell’s door) 2 strands RNA – only 9 genes; 3 are found in many viruses (structural proteins) Reverse Transcriptase – turns RNA into DNA (this makes HIV a retrovirus); DNA instructs cell to make more viruses

Virus enters cell through endocytosis Virus replicates RNA to DNA with reverse transcriptase HIV Making Factories

DNA enters nucleus & binds with host DNA New virions exit cell through exocytosis to infect other cells (notice cell isn’t destroyed) mRNA is created (carries instructions for making new viral proteins) and leaves nucleus Uses host cell’s enzymes to make new viruses

How Is HIV Spread? Sexual contact Sharing contaminated needles Blood transfusions Breast feeding (mother to baby) Mother to baby during pregnancy or birth

Think about it… In the US, there is better than a 1/1000 chance of contracting HIV during unprotected sex A person can be contagious for more than 10 years before any sign of the disease is apparent HIV becomes AIDS when the number of immune cells drops below a predetermined number No one dies from HIV or AIDS; people die from secondary infections (ranging from the common cold to cancer) More than 3 million people (size of Chicago) die each year There are approx. 14,000 new cases of HIV worldwide every day

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Mutating viruses Viruses can mutate when they copy the genetic material – Copy something wrong – Mistake proves useful – More powerful virus (more infectious) Viruses don’t mutate often, except… – Influenza – HIV

Viruses can be beneficial… Bacteriophages – attack & destroy bacteria Baculovirus – ebola-like virus that attacks insects – Could use for pest control in crops Cabbage loopers eat cabbage crops Virus can kill pests in days – (it’s really gross) … and then there are those that are not so good….

The spread of West Nile virus (1999 – 2002) – bird, horse, mosquito or human

Also important… Any agent (not just viruses) that causes disease is a pathogen. When a virus inserts its genetic material into a host’s DNA, it is called a provirus. Some viruses replicate very slowly and only cause damage when the conditions are “right”. (cold sores)

describe the role of viruses in causing diseases such as human immunodeficiency virus (HIV) and flu