Viruses
Warts are a skin virus!
Herpes mouth virus:
Other Viral Diseases Measles Polio Smallpox Influenza
Hepatitis B Virus Viruses & Cancer Human Papilloma Virus HPV
Tree Man - HPV
Is a Virus a Living Organism? Properties of life Cellular Respiration Reproduction Metabolism Homeostasis Heredity Responsiveness Growth and development
Are viruses living or non-living? Nonliving Not cells No respiration No growth No development No metabolism Can be crystalline, dormant Living Replicate using a host Contain DNA,RNA Contain protein coat
Virus Characteristics Non-living: Do not grow Do not develop Do not carry out respiration All they can do is replicate but they can t to that without a host cell
Viruses are very small, even compared to bacteria, and they can only be viewed with the electron microscope. The smallest viruses are about 20nm and the largest about 300nm.
Virus means Poison in Latin Composed of nucleic acids (DNA or RNA) wrapped in a protein coat called a capsid Some viruses have an extra layer of protection called an envelope Virus Structure
Viral Structure Nucleic Acid RNA or DNA Capsid protein coat that surrounds the DNA or RNA in a virus Lipid Membrane a membrane around the capsid in many kinds of viruses; helps the virus enter cells ( enveloped viruses; without the membrane, the virus is naked ) Made of proteins, lipids, and glycoproteins
Origin of Viruses Scientists suggest viruses might have originated from their host cells May be nucleic acids that broke away from their host but maintain the ability to replicate parasitically within the host cell
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.
Plant peach virus Viruses can infect Plants Animals Bacteria
Differences in Viruses Species Specific Viruses: Ex. Smallpox (eradicated) Non-species specific: Flu & West Nile Cell-type Specific: Ex. Polio only infects intestinal & nerve cells
Viruses are named after the diseases they cause or the tissues or organs they infect Ex. Bacteriophage Infects a bacterium Naming Viruses
Virus Categories DNA viruses stable, do not mutate rapidly Single-stranded or double-stranded Smallpox, Hepatitis B Warts Chickenpox mononucleosis RNA viruses mutate rapidly, unstable Single-stranded or double-stranded Rhinovirus Human immunodeficiency virus (HIV) Influenza viruses Rabies
Virus Shapes Helical Rodlike with capsid proteins winding around the core in a spiral Tobacco Mosaic Virus
Virus Shapes Polyhedral Has many sides Most polyhedral capsids have 20 sides and 12 corners
Virus Shapes Polyhedral capsid attached to a helical tail.
Chicken Pox & Polio Virus
Rabies virus Hepatitis B (Liver)
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. 2. Lysogenic Cycle the virus DNA integrates with the host DNA and the host s cell helps create more virus DNA when it divides. An environmental change may cause the virus to enter the Lytic Cycle.
Attachment proteins on virus recognize & attach to the receptor site on the plasma membrane of the host cell Puzzle pieces http://www.slic2.wsu.e du:82/hurlbert/micro1 01/images/101VirusF usionan.gif Attachment
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.
Virus Cycles Once a virus enters a cell it either enters into the Lytic or Lyosogenic Cycle Lytic Cycle takes over host cell immediately & kills cells by (bursting or lysis) http://whyfiles.org/132aid s2/images/virus_movie.gif
Viral Replication: Lytic Cycle
Lysogenic Cycle Viral DNA becomes incorporated into host cells DNA & becomes a Provirus Provirus is replicated with host cells chromosome http://goldiesroom.org /video_archive.htm At any time a provirus can be activated & enter into a lytic cycle Physical Stress Sunburn Emotional Stressanxiety Immuno-depressed
Provirus Examples Cold sores (Herpes simplex I) Genital Herpes (Herpes simplex II) Hepatitis B Chicken Pox (Varicella zoster) Shingles painful infection of some nerve cells
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)
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
Retroviruses Have RNA as their nucleic acid most complex replication cycle Ex. HIV Make DNA from RNA using the enzyme reverse transcriptase
HIV Double-stranded DNA enters into host cells chromosome & becomes a Provirus Can test for the enzyme reverse transcriptase to see if you have the virus
The spread of West Nile virus (1999 2002) bird, horse, mosquito or human
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.
Viroids Infectious particles of naked RNA. Similar to viruses, but lack a capsid. Ex: Coconut Blight Chrysanthemum Wilt
Viroids Composed of a single circular strand of RNA with no protein coat Diseases in Plants Enter through wounds or insect bites Don t use surface recognition Doesn t undergo lytic or lysogenic phases May cause stunted growth & yield losses Mosaic viruses are not harmful cause beautiful patterns
What is a prion? Prions have recently been implicated in diseases called Encephalopathies which affect the brain. The most common ones that are know today are Bovine Spongiform Encephalopathy or BSE in cattle, Scrapie in sheep and new variant Creutzfeldt-Jakob disease in humans. Prions are infectious agents but they are not like bacteria or viruses. Prions are pieces of protein that can transfer the disease from one organism to another. IT is simply a protein where the chains have folded incorrectly. (secondary structure) The chains have the same amino acid sequence as the normal protein. It is not known how the malfunction in protein folding occurs
Prion Action
Prions Proteins but no nucleic acids Cause proteins to fold incorrectly Animal diseases: Mad Cow Disease Creutzfeldt-Jacob disease
Treatments for Viruses Vaccines (preventative). Some Drugs Ex: Ara-A Acyclovin Comment - some treatments are working on the reverse transcriptase.
Cow pox vaccination 1749 Acquired Immunization Artificial injection of a small amount of virus Body s immune response makes antibodies
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
HIV Virus
HIV virus infects T-cells HIV virus Weakens the immune system AIDS patients die of common diseases when T cell (WBC) count falls
AIDS = break down of the immune system & death due to common diseases versus death by AIDS virus
B Memory cells..
Activation of the Immune Response
AIDS Virus on a T Cell
Activation of the Immune Response AIDS virus destroys Helper T cells!
Loss of T Cells makes the patient susceptible to common infections
Prevent attachment Prevent Replication Prevent Coat formation
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
VIRUSES Review Viruses are not usually included in classification systems as they are non-cellular and they are dependent on a host cell for their replication and metabolic processes.
What is a virus? Viruses have very simple structures - Most of them are simply a protein coat surrounding a core of nucleic acids. Could be DNA or RNA
LIVING or NOT LIVING? Viruses are not capable of living as free entities; in fact they are generally inert and inactive outside of their host cells, which are needed only for the virus to replicate. Viruses can infect all types of cells animals, plants and bacteria, but each different type of virus is specific to its particular type of host cell.
Bacterial Viruses Best understood of all viruses. May show two types of virus life cycles: Lytic Cycle Lysogenic Cycle
VIRUS REPLICATION Once inside the host cell the virus hijacks the cells genetic machinery and uses it to make more viruses. The lytic cycle short, replicates quickly, destroys host cell when releasing thousands of new viruses. Cold, flu, Ebola.
The lysogenic cycle virus enters cell, replicates DNA, and WAITS. Herpes, wart, HIV Your immune system responds to the infection, and in the process of fighting, it produces chemicals called pyrogens that cause your body temperature to increase.
Lytic Mode Triggers Switches the host from Lysogenic to Lytic Cycles ex: radiation, chemicals, stress
Herpes Viruses Use nuclear membrane. Viral DNA integrated into Host DNA as a provirus. Shows both lytic and lysogenic life cycles.
RNA Viruses Classes III - VI Class VI - Retrovirus - use Reverse Transcriptase to make DNA from an RNA template.
Human Immunodeficiency Virus HIV - causes AIDS. Retrovirus from chimps. Destroys the body s immune system, allowing other diseases to kill.
Plant Viruses Can be an important agricultural problem. Ex: Tobacco Mosaic Virus Tulip Flower Breakage