Chapter 24 Viruses

Viral Structure & Replication Discovery of Viruses Virus: nonliving particle made up of nucleic acid and a protein coat or nucleic acid and a lipoprotein coat Cause many diseases in living organisms Useful tools for genetic research

Viral Structure & Replication Discovery of Viruses Late 1800s Living or nonliving? 1935, Wendell Stanley crystallized the tobacco mosaic virus (TMV) Concluded: infective agent that could be crystallized–––>not made of cells

Viral Structure & Replication Characteristics of Viruses Nonliving b/c: No cytoplasm or organelles No metabolism or homeostasis Do not grow by dividing in two Need other cells to reproduce

Viral Structure & Replication Viral Size & Structure Very small Shape is the result of genome or protein coat Helix Shape: capsid, protein coat, forms the helix TMV, Rabies, Measles Icosahedron: 20 triangular faces & 12 corners Adenovirus, herpes simplex, chickenpox, polio Spherical: circular Influenza Envelopes: bilipid membrane that surrounds membrane Helps new viruses to recognize host cells

Viral Structure & Replication Classification of Viruses RNA or DNA Genome single-stranded/double-stranded & linear OR circular Nature of capsid & presence or absence of an envelope

Viral Structure & Replication Replication in DNA Viruses Inserts DNA into host cell’s chromosome Provirus Transcribe mRNA  Translate viral proteins Use cell’s enzymes to make new viral DNA Assembled to make new viruses Replication in RNA Viruses Some: enter host cell & serve directly as mRNA Others: Transcribed & is a template for the synthesis of mRNA & more copies of viral genome

Viral Structure & Replication Replication in RNA Viruses, continued Retroviruses: use reverse transcriptase, which uses RNA as a template to make viral DNA, which then creates proteins that become part of the new viruses

Viral Structure & Replication Replication in Viruses that Infect Prokaryotes Lytic Cycle Invades a host cell, produces new viruses, and ruptures (lyses) the host cell when releasing newly formed viruses Virulent: viruses that reproduce only by the lytic cycle Destroy the cells that they infect Ex: T phages

Viral Structure & Replication Replication in Viruses that Infect Prokaryotes Lysogenic Cycle Hide in their host cell for days, months, or years Called Temperate Viruses

Viral Structure & Replication Viruses: Tools for Biotechnology Replace large pieces of the DNA of a phage with DNA of a particular interest, such as the human gene for cystic fibrosis Insert recombinant DNA into empty phage heads and allow them to infect bacteria Bacteria produces millions of copies Invaluable tools for medical research

Viral Structure & Replication The Origin of Viruses Evolved from early cells Naked pieces of nucleic acid that could travel from one cell to another Entered cells through damaged membranes Genes evolved to allow for protective protein coats and recognition proteins to attack healthy cells Example: Influenza virus and HIV

Viral Diseases Vectors of Viral Disease What is a vector? Intermediate host that transfers a pathogen or a parasite to another organism Include: humans, animals, mosquitoes, ticks, and fleas West Nile Virus: Mosquito---bird(WNV)---human, the virus can spread to human

Viral Diseases Human Viral Diseases Can affect: Brain Liver Heart Lungs Skin

Viral Diseases Viruses & Cancer What is cancer??? Cells divide at an uncontrolled rate and form a tumor that invades surrounding tissue Viruses contain viral oncogenes: genes that cause cancer by blocking the normal controls on cell reproduction Viral DNA inserts itself into a host’s chromosome near a proto-oncogene --- controls cell growth Converted to a oncogene HPV: cervical cancer Hep. B: liver cancer

Viral Diseases Emerging Viral Diseases Illnesses caused by new or reappearing infectious agents that typically exist in animal populations-- often in isolated habitats--and can infect humans who interact w/ these animals Ebola: hemorrhagic fever Hantavirus: caused outbreak of pneumonia SARS: avian flu

Viral Diseases Vaccinations Solution with a harmless version of a virus, bacterium, or toxin Causes an immune response  body forms an antibody Inactivated virus: not able to replicate in a host Attenuated virus: weakened form of the virus that cannot cause disease Attenuated viruses provide greater protection from disease

Viral Diseases Vector Control Drug Therapy Mosquito-control programs Rabies Vaccinations Drug Therapy Antiviral drugs interfere w/ viral nucleic acid synthesis Small number of these drugs, WHY?

Viral Diseases Viroids Prions Smallest know particles that can replicate Made of RNA Infect plants Prions Infectious protein particles that have no genome Abnormal forms of a natural brain protein, that convert normal brain proteins into prions Clump together inside of cells---death BSE: cattle Scrapie: sheep CJD/kuru: humans

Review CH 24: Viruses

Question #1 What are viruses made of? Enzymes and fats Carbohydrates & ATP Protein and nucleic acids Mitochondria & lysosomes

Question #2 How do viroids differ from viruses Viroids are larger in size Viroids do not have a capsid Viroids do not have nucleic acids Viroids can cause disease in plants

Question #3 During which of the following processes does a phage kill its host? Conjugation Transcription The lytic cycle The lysogenic cycle

Question #4 Which of the following is one reason why viruses are not considered living organisms? Viruses are able to grow Viruses do not metabolize Viruses can reproduce by splitting Viruses are too small to be easily observed

Question #5 Which of the following does the diagram represent? A virus A prion A virod A bacterium

Question #6 X To which of the following is label X pointing? Envelope Nucleic acid Protein coat Cell membrane X

Question #7 Complete the following analogy: Skin : Person :: Capsid : Virus Insect Fungi Bacterium

Question #8 Which of these four illnesses/diseases are caused by a virus? Malaria, West Nile, Yellow Fever, Lyme HPV, HIV, Influenza, Chickenpox Gang green, West Nile, Measles, Smallpox Heart disease, Tuberculosis, DMV, AIDS

Question #9 Genes that cause cancer by blocking the normal controls of cell reproduction are called Protease inhibitors Viroids Virulent Oncogenes