Viruses 16.5

Why are viruses considered non-living? Do they have organelles? Do they carry out life processes? –Grow, take in food, make waste? –How do they reproduce? Are they cells?

Viruses and bacteria can cause infection. Any disease-causing agent is called a pathogen. Let’s talk size- – viruses are 100x smaller than bacterial cells. viruses nm prokaryotics cells ,000 nm prion 2-10 nm viroids nm eukaryotics cells 10, ,000 nm 100 nm 1 nanometer (nm) = one billionth of a meter

Virus classification Type of nucleic acid –DNA or RNA but not both Their shape –Based on the structure of the capsid- outer protein coat. –Two basic shapes- Rod Spherical How they reproduce –Lytic ( lysis) cycle –Lysogenic ( latent) cycle What they infect- –Organisms/species –Type of cells

Viruses differ in shape and how they enter host cells. Viruses have a simple structure. –genetic material- DNA or RNA –Capsid- outer protein shell –maybe a lipid envelope, a protective outer coat capsid nucleic acid lipid envelope surface proteins capsid nucleic acid lipid envelope Surface proteins capsid surface proteins nucleic acid helical (rabies) polyhedral (foot-and-mouth disease) enveloped (influenza)

Basic Viral Structure- T-phage Bacteriophage- virus that infects bacteria capsid DNA tail sheath tail fiber

Viruses enter cells in various ways: bacteriophages pierce host cells- injecting their DNA colored SEM; magnifications: large photo 25,000; inset 38,000x

Viruses of eukaryotes -can fuse with cell membranes- endocytosis

host bacterium The bacterophage attaches and injects it DNA into a host bacterium. The host bacterium breaks apart, or lyses. Bacteriophages are able to infect new host cells. The viral DNA directs the host cell to produce new viral parts. The parts assemble into new bacteriophages. The viral DNA forms a circle. Viruses cause two types of infections. A lytic infection causes the host cell to burst. The virus may enter the lysogenic cycle, in which the host cell is not destroyed.

A lysogenic infection does no immediate harm- latent infection- examples: herpes, HIV The viral DNA ( a prophage) combines with the host cell’s DNA. Although the prophage is not active, it replicates along with the host cell’s DNA. Many cell divisions produce a colony of bacteria infected with prophage. At some point-the prophage leaves the host’s DNA and enter the lytic cycle.

Viruses such as a bacteriophage are capable of reproducing in two general ways, the lytic and lysogenic cycles..

Viruses cause many infectious diseases There are many examples of viral infections. –common cold

–influenza Viruses cause many infectious diseases There are many examples of viral infections. –common cold

–influenza Viruses cause many infectious diseases There are many examples of viral infections. –common cold – –Sars

–HIV HIV-infected white blood cell Viruses cause many infectious diseases There are many examples of viral infections. The body has natural defenses against viruses.

HIV-AIDS HIV =virus –Human Immunodeficiency Virus AIDS= disease- – Acquired Immune Deficiency Syndrome An immune disease- immune cells attacked- T4 white blood cells. Symptoms (damage of host immune cells) occurs when a switch from the lysogenic cycle to the lytic cycle occurs. –5-10 years later. HIV- retrovirus-RNA virus –Flow: RNA-DNA-RNA –How: they have reverse transcriptase An enzymes that synthesizes DNA from RNA

HIV HIV, a retrovirus, uses immune system cells to reproduce itself. These host cells are eventually destroyed, weakening the patient's immune system.

Prevention- Antibiotics have no effect Vaccines can be effective- Deactivated varieties or small pieces of pathogens that stimulate the immune system to respond by producing a memory response when the actual pathogen is met. Edward Jenner developed the first vaccine (cowpox) against smallpox. Not all viruses can be prevented with a vaccine because of the rapid mutation rates of these viruses.

Edward Jenner- Development of smallpox virus scheme. It worked because smallpox and cowpox are very similar –same antigens( cause an antibody response from the body smallpox was eradicated

Vaccines are made from weakened (attenuated) pathogens. A vaccine stimulates the body’s own immune response. Vaccines prepare the immune system for a future attack.- memory response Vaccines are the only way to control the spread of viral disease. What is herd mentality?

Antivirals? What are they?