VirusesChapter 19

A Borrowed LifeVirus: an infections particle incapable of replicating outside of a cell, which consists of an RNA or DNA genome enclosed in a protein coat (______)

________________ parasites

Arguments for describing viruses as non-living Can not ________ outside of host cell Can not carry out ________________

outside of outside of host cell Lack _________ and enzymes

Structure of Viruses

Capsids are made up of protein subunits called __________.

Viral envelopes: membranous envelope made up of phospholipids and membrane proteins that surrounds the capsids of some viruses

Virus Classification

Virus Reproduction1. Virus enters host cell

after host cell recognition 2. Host enzymes replicate

virus DNA3. Host enzymes transcribe

viral DNA into viral mRNA, which is used to make capsid proteins

4. New virus particles assemble and leave host cell

Replication of PhagesLytic cycle: host cell ____ when releasing phages = cell death

Surface proteins Restriction enzymes

CRISPR

Lysogenic cycle: ________ of phage genome ≠ cell death

Prophage

Replication of Animal Viruses1.Glycoproteins on viral envelope

bind to receptors on host cell2.Cellular enzymes digest capsid3.Viral genome copied by viral RNA

polymerase to make mRNA4.Viral RNA functions as mRNA,

which is translated to make capsid proteins and glycoproteins

5.Vesicles transport viral envelope to plasma membrane

6.Capsid assembles around viral genome

7.New virus buds from host cell

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Replication of Retroviruses1. Glycoproteins on viral envelope bind to

____________ on immune cell then fusing with plasma membrane and releasing capsid proteins and RNA into the host cell

2. ___________________ synthesizes DNA from viral RNA then subsequent DNA strands complementary to the first

3. Double stranded viral DNA incorporated into host cells DNA (_______)

4. Proviral genes transcribed to make RNA genome for progeny viruses and mRNA for translation into viral proteins

5. Capsids assembled around viral genomes

6. New viruses with viral envelope glycoproteins bud from host cell

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Human Immunodeficiency Virus (HIV) Description:

ssRNA that is template for DNA synthesis

________ Infects vital human immune system

cells Helper T cells, macrophages

Treatment: Azidothymidine (AZT)

Blocks _________________ Protease inhibitors

Blocks building of capsid

Ebola virusDescription: Class V: ssRNA that is template for

mRNA synthesis Infects human _______ system cells Causes hemorrhagic fever

Small blood clots throughout body Fever, vomiting, bleeding, organ

failure

Treatment: No known treatment

Vaccines currently being tested

Influenza virusDescription: Class V: ssRNA that is template for mRNA

synthesis Infects epithelial cells of _________ system H1N1 refers to surface proteins of virus

Hemagglutinin (H) and Neuraminidase (N)

Treatment: Rest and wait for immune response

Shortened and less severe when vaccinated Antiviral drugs

Neuraminidase inhibitors block budding from host cell M2 proton inhibitors block virus from entering host cell

H1N1 influenza A virus

Nucleoprotein(RNA)

Lipidenvelope

Capsid Hemagglutinin

Neuraminidase

HepatitisDescription: At least five different unrelated viruses Causes ______________

Hep A ssRNA ________ envelope Ingestion of contaminated food or water Vaccination

Hep C ssRNA ____ envelope Transmitted through contact with blood Antiviral drugs

PoliomyelitisDescription: Class IV: ssRNA that can serve as mRNA _% of infections target human nerve

cells Do not divide and cannot be replaced

Infected feces entering the mouth

Treatment: Few people show symptoms Iron lung __________ developed vaccine No cure for polio

Vaccination1. Antigen-Presenting Cell (APC) finds and ingests vaccine antigen then presents

antigen on the cell surface. APCs travel to lymph nodes where other immune cells are congregated

2. T helper cells recognize the foreign antigen and alert other immune system cells

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Vaccination3. B-cells recognize the antigen and then divide into antigen specific Plasma B-

cells which produce antibodies. Some B-cells become Memory B-cells

4. T cells recognize the foreign antigen and mature into Killer T-cells which find and destroy cells infected with the virus. Some T-cells become memory T helper cells and Memory Killer T-cells

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Using Viruses Gene transfer in gene therapy

https://youtu.be/2pp17E4E-O8