Viruses - notes

Viruses are not cells! What is a virus?

•An agent that causes ______in plants and animals

•Segments of nucleic acids (genetic material like ______or RNA)contained in a protein coat

Viruses are generally considered to be ______-living becausethey DO ______have all the characteristics of life.

Viruses are different from living things in 3 ways:

1.DO NOT ______

2.CANNOT maintain ______

3.DO NOT metabolize

Viruses are similar to living things in 2 ways:

1.They contain nucleic acid (______or RNA)

2.They contain proteins (the capsid)

Vocabulary

pathogen- agent that causes ______

host- an organism that shelters and nourishes a virus or another organism

capsid- the ______coat of a virus

envelope- surrounds the capsid and helps viruses ______cells

bacteriophage- a virus that attacks a bacteria (word parts! phage – to ______)

prophage/provirus- a viral DNA segment inserted into a bacterial cell

retrovirus- a virus that replicates by first transcribing RNA into DNA (HIV)

lysis- the ______apart of the cell to release new viruses (word parts! lyse – to burst)

viroid- a single strand of viral RNA that causes ______diseases

prion – protein that infects ______

Characteristics of a Virus

When trying to find the cause of tobacco mosaic disease (disease that stunts the growth of tobacco plants) scientists discovered something other than bacteria was causing TMD

Concluded it was ______than a bacterium and named it virus

after the Latin word meaning “______”

1935, Wendell Stanley concluded that the cause of TMD was a chemical rather than an organism/cell. Today we know that Stanley had discovered the first virus.

Viruses have the following characteristics:

•______than prokaryotic cells (like bacteria)

•not normally classified (debate over living vs. nonliving)

•live and reproduce ______inside other living cells

•cause diseases such as ______, influenza, AIDS, smallpox, measles, chicken pox, rabies, mumps, and mononucleosis

How are Viruses Structured?

•Viruses have an outer layer called a capsid that is made of ______

•Inside the capsid is genetic material such as ______or ______(but it never contains both as the same time)

•Some viruses have an envelope outside of their capsid as well as proteins that stick out to aid in entering host cells (similar to marker or receptor proteins on cells)

5 basic shapes of a virus: (draw an example of each below, next to the description)

–helical

–spherical

–polyhedral

–binal

–filovirus

•Helical:

–RNA or DNA is coiled in a long narrow capsid

Ex. tobacco mosaic virus

•Spherical:

–typically studded with receptors, may be enveloped

Ex. influenza virus (flu)

•Polyhedral:

–geometric in appearance

Ex. adenovirus (causes the common cold)

•Binal:

–polyhedral capsid

–helical tail

Ex. bacteriophage

•Filovirus:

–no distinct uniform shape

–threadlike loops

Ex. Ebola virus

HIV is a Retrovirus

HIV- human immunodeficiency virus

Structure:

•spherical

•contains RNA

•retrovirus

•exterior wall made of glycoprotein

Function:

  • causes ______(acquired immune deficiency syndrome)
  • binds to human immune cells at specific receptor sites
  • is a special type of virus called a retrovirus

–virus that getsits genetic information copied ______fromRNA to DNA

•when aretrovirus infects a cell, it produces a DNA copy of its RNA

•retroviruses are responsible for some types of cancer in animals, including humans

Human Diseases Caused by Viruses

Category / Disease
Sexually transmitted disease / ______ (caused by HIV), genital herpes, HPV (causes cancers)
Childhood diseases / measles, mumps, chicken pox
Respiratory diseases / common cold, ______ (flu)
Skin diseases / warts, shingles
Digestive tract diseases / gastroenteritis
Nervous System diseases / polio, viral meningitis, rabies
Other diseases / smallpox, hepatitis, avian “bird” flu, Ebola, SARS, West Nile

Viruses are transmitted from one host organism to another by many different vectors.

transmit – to pass along

vector – the substance or path used to pass the virus along

Viruses, like other pathogens, are commonly transmitted through body fluids, including the spittle in your sneezes and coughs, mucus produced by many parts of your body such as your nose and lungs, and even the ear wax in your ears. They can be transmitted through contaminated food and drinks as well. Some require contact with body fluids such as blood, semen, or vaginal secretions that you do not usually encounter.

SOME viral infections can be prevented through vaccines, such as the flu vaccine available each year and the HPV vaccine available from your doctor. A vaccine is often a weakened form of the virus injected to prevent infection. Children in the United States are also commonly vaccinated against measles, mumps, chicken pox, and polio. There are vaccines available for some forms of meningitis, rabies, smallpox, and some forms of hepatitis, but they are only given to people at risk of getting the diseases such as first responders, medical personnel, soldiers, and even some teachers.

Unfortunately, viruses mutate rapidly and vaccines lose their ability to be 100% effective in preventing disease. This is why we have a new flu vaccine every year. It takes over a year to manufacture flu vaccine, therefore scientists have to predict what will be most effective in the future. Sometimes they have excellent predictions and almost everyone who gets the vaccine stays well. Sometimes, they don’t have excellent predictions and many people get sick. It’s still important to get the vaccine because there is often more than one flu virus going around and protection against at least some of the virus is better than none at all.

Once we do get sick with a viral infection, we don’t have many effective ways to “cure” the infection. We do have some antiviral medications which help prevent viruses from replicating as rapidly as they would without it, and interferons which mimic molecules naturally produced by your body in response to viral infections. Antibiotics DO NOT have any effect on viruses and should never be given or taken for an infection such as influenza (which is a respiratory illness, NOT a digestive system illness) or a cold.

Our inability to vaccinate against and to cure viral infections is why it is so important that you always cover your mouth when you sneeze or cough, don’t share drinks or eat after someone else, wash your hands frequently, and even avoid sharing earbuds!