Viruses

What to Know: Learning Objectives

Overview: What are some basic facts about viruses?

Structure: What are the shapes?

Reproduction: What is the lytic & lysogenic pathways?

Infection: How do they get into cells and then get reproduced?

Describe a few common or well-known virus. AIDS, the common cold, hepatitis, influenza What are viroids & prions?

Viruses

Infectious particles (not cells)

Contain Genetic information and protein coat (capsid) Some may contain RNA Grouping is determined by the type of

nucleic acid (DNA or RNA)

Typically named after the disease they cause or the tissues they infect

Virus Structure

Simple virus structure Genetics… this is the direction to make more virus Surrounded by proteins (capsid) May or may not have an additional covering (envelope)

Each have their own form but can be categorized: Helical Polyhedral Enveloped Other.

Helical Polyhedral Enveloped Others

Viruses: Living or Not?Considered to be non-living (debated) Does not meet all of the characteristics of life

Living Non-Living

-Contains genetic material (RNA/DNA)

-Reproduce (in host)

-Has organization

-Do not have cells

-Do not respond to stimuli

-Do not use energy

-Do not grow & develop

-Cannot reproduce on their own

Viral Reproduction

Viruses must have a living host cell to reproduce Example: Bacteriophages infect bacteria

Insert their genetic information inside the host cell and use the host cell to make more virus particles

Viral Replication

Lytic cycle Viral DNA is injected into host cell

Contains instructions needed to make more viruses

Host cell replicates viral DNA and makes the viral capsids (protein coats)

New viruses are assembled inside host cell Cell bursts open releasing new viruses

Lytic Cycle

Viral Replication

Lysogenic cycle Viral DNA is injected into the host cell Viral DNA inserts itself into the host’s DNA Remains inactive for days, months, or years As the cell reproduces, more cells are

produced that have the viral DNA in them Eventually, when the conditions are

favorable (like when your immune system is weakened) the virus will enter the lytic cycle

Lysogenic Cycle

A2 Chromosome and integrated viral DNA are replicated.E Lysis of host cell

lets new virus particles escape.

A Virus particle binds, injects genetic material.

Lytic Pathway

A1 Viral DNA is inserted into host chromosome by viral enzyme action.

Lysogenic Pathway

D Accessory parts are attached to viral coat. B Host replicates viral

genetic material, builds viral proteins.

A3 Cell divides; recombinant DNA in each daughter cell.

C Viral proteins self-assemble into a coat around viral DNA.

A4 Viral enzyme excises viral DNA from chromosome.

Transmission of Viral Disease

Virus are pathogenic and carcinogenic. They cannot

reproduce unless they attack another cell.

Once in the cell the have a tendency to cause irreparable damage that can lead to cancer.

HPV & Cervical cancer

Possible ways to become infected are Bites Physical contact Body fluid Mother to child Contact in the air Sexual contact

Video clip

Write 5 facts from the video

http://www.npr.org/blogs/krulwich/2011/06/01/114075029/flu-attack-how-a-virus-invades-your-body

Get into groups, divide the chapter up into sections, read through and gather information, answer the questions.

Here's a better, longer answer than the one in the video. First, some new viruses get caught in mucus and other fluids inside your body and are destroyed. Other viruses get expelled in coughs and sneezes. Second, lots of those new viruses are lemons. They don't work that well. Some don't have the right "keys" to invade healthy cells so they can't spread the infection. And third, as the animation shows, your immune system is busy attacking the viruses whenever and wherever possible.