Viruses 16 5 Why are viruses considered nonliving

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- 1 nanometer (nm) = one billionth of a meter – viruses are 100 x smaller than bacterial cells. 100 nm eukaryotics cells 10, 000 -100, 000 nm viruses 50 -200 nm prokaryotics cells 200 -10, 000 nm viroids 5 -150 nm prion 2 -10 nm

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 enveloped (influenza) capsid nucleic acid lipid envelope helical (rabies) Surface proteins capsid nucleic acid surface proteins lipid envelope polyhedral (foot-and-mouth disease) surface proteins capsid nucleic acid

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 cellsinjecting their DNA colored SEM; magnifications: large photo 25, 000; inset 38, 000 x

Viruses of eukaryotes -can fuse with cell membranes- endocytosis

Viruses cause two types of infections. • A lytic infection causes the host cell to burst. 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 forms a circle. The viral DNA directs the host cell to produce new viral parts. The parts assemble into new bacteriophages. The virus may enter the lysogenic cycle, in which the host cell is not destroyed.

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

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

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 – influenza

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

HIV-AIDS • HIV =virus – Human Immunodeficiency Virus • AIDS= disease– Acquired Immune Deficiency Syndrome • An immune disease- immune cells attacked- T 4 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. 1979 - 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?