Viruses

Viruses

Which Kingdom?

VirusesThey are considered “lifeless”…why?

They can NOT carry out metabolic and reproductive functions alone.

They require a host organism

They lack cytoplasm, organelles, and a cell membrane

5000 influenza viruses can be found on the head of a pin.

Viral Infections • Are they all deadly?

• No, viruses range from mild to deadly

• Ex. Herpes simplex I, West Nile Virus, cold/flu viruses, Cancer, HIV/AIDS.

• Each virus is specific to a host

• The host range describes all of the hosts a virus can infect

• E.g. swine flu virus infects both pigs and humans

Scientists classify viruses based on their unique characteristics, including:

size and shape of the capsid (protein coat surrounding genetic material)

shape and structure of the virustype(s) of diseases the virus causestype of genetic material (RNA or DNA)method of reproduction

Virus Shape and Structure:

There are different shapes for viruses:

1) Helical (Spiral)

2) Polyhedral

Enveloped Non-enveloped

3) Complex/Phage (many sides with a tail)

E.g. Bacteriophage (bacteria eating virus)

An inner genetic material (nucleic acid - DNA or RNA)

Capsid – outer protein coat

VIRUS TYPESThere are many virus types

including:RetrovirusesReovirusesAdenovirusesRhabdovirusesOrthomyxoviruses, etcEach has a different inner nucleic acid, coat and structure

Methods of Reproduction

Incubation period = the time it takes between when the virus infects a cell and when symptoms appear (when the virus ruptures the cell).

There are two types of reproduction/replication: The LYTIC cycle – shorter incubation period The LYSOGENIC cycle – longer incubation period

How Do Viruses Replicate?

Viruses replicate through a cycle known as the lytic cycle

Some viruses, such as cancer causing viruses and bacteriophages, go through a lysogenic cycle

Occurs without the host being aware and the host may not be aware until years later (e.g. HIV)

Lytic Cycle

The lytic cycle occurs through four steps:

1. Attachment and entrance: the virus recognizes the host cell and then enters into the cell’s cytoplasm

2. Synthesis of protein and nucleic acid: The virus tricks the cell into copying the virus DNA (or RNA)

Virus replicates through four steps:

3. Assembly of the virus: All the virus components (i.e. DNA (or RNA), enzymes, capsid proteins, and other proteins are brought together

4. Release of new viruses: the new viruses burst out of the cell in a process known as lysis

How Do Viruses Replicate?

Lysogenic Cycle

The virus enters the cell just as the lytic cycle, but instead of it replicating, its nucleic acid becomes part of the cell’s nucleic acid

When the cell replicates, so does the virus nucleic acid

https://www.youtube.com/watch?v=3vSRfVC4OIo

Viruses and Human HealthViruses destroys cells as they replicate This causes the symptoms

Vaccines are used to prevent virus infection

Vaccines: are made of dead virus or virus components to activate the body’s immune cells to prepare them for battle

VIRUSES AND CANCER

Some viruses can cause cancer by adding specific genes to an infected cell transforming it into a cancer cell

Virus Cancer Type

Human papillomavirus

Cervical, skin, etc.

Hepatitis B/C Liver cancer, lymphomas

Epstein-Barr virus Burkitt’s lymphoma, Hodgkin’s lymphoma

INFLUENZA VIRUS

Various strands of the flu virus exist in the environment

Flu Vaccines only treat the most common strain of the season

Virus destroys cells in upper respiratory tract so there is no sweeping of foreign particles

Symptoms – sore throat, congested lungs

Human Immunodeficiency

Virus (HIV)Virus that causes AIDS (Aquired Immunodeficiency Syndrome)Retrovirus is transmitted through variety of bodily fluids: blood, semen, vaginal fluid, breast milkHIV attacks the immune systemSince 1981, almost 25 million people have died from AIDS

Other Viral Diseases

Varicella zoster virus: chickenpox (children) and shingles (adults)

Variola major virus: smallpox

Poliovirus - Polio

SARS coronovirus: Severe Acute Respiratory Syndrome (SARS)

Ebola: https://www.youtube.com/watch?v=sRv19gkZ4E0

Homework

Read pages 52-57#1-3, 5, 7, 8, 11-14 (p.58)