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What is a virus?
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Viruses
An agent that causes _______________ in plants and animals
Segments of nucleic acids (genetic material like ________ or RNA) contained in a protein coat
They are __________ cells
Viruses are generally considered to be non-living because they DO NOT have all the characteristics of
life.
They:
1. DO _______ grow
2. CANNOT maintain homeostasis
3. DO ______ metabolize
Viruses are similar to living things in 2 ways:
1. They contain nucleic acid (DNA or RNA)
2. They contain ______________ (in the form of a capsid)
Terminology
 Pathogen- agent that causes disease
 Host- an organism that _____________ and nourishes something
 Capsid- the _____________ coat of a virus
 Envelope- surrounds the capsid and helps viruses enter cells
 Bacteriophage- a virus that attacks a _____________
 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 breaking ____________ of the cell to release new viruses
 Viroid- a single strand of viral RNA that causes __________ diseases
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 TMV
Concluded it was _________________ than a bacterium and named it virus after the Latin word
meaning “__________________”
1935, Wendell Stanley concluded that TMV was a chemical rather than an organism/cell
• Smaller than prokaryotic cells (like bacteria)
• Not normally classified (debate over living vs. nonliving)
• Live and reproduce ____________ inside other living cells
• Cause diseases such as colds, flu, AIDS, smallpox, measles, chicken pox, rabies, mumps, and
mononucleosis
How are Viruses Structured?
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Viruses have an outer layer called a capsid that is made of ____________
Inside the capsid is ______________ material such as DNA or RNA (but it never contains both
as the same time)
Structure and Shapes
2 parts to a virus:
–Core of nucleic acid (DNA or __________)
–Protein coat (capsid) that encases the core of nucleic acid
5 basic shapes of a virus: (draw an example of each below, next to the description)
– Helical
– Binal
– Spherical
– Filovirus
– Polyhedral
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Helical:
– RNA or DNA is coiled in a long narrow capsid
Ex. Tobacco Mosaic Virus
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Spherical:
– Typically studded with receptors, may be enveloped
Ex. Influenza Virus (Flu)
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Polyhedral:
– Geometric in appearance
Ex. Adenovirus (causes the common cold)
Draw:
Draw:
Draw:
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Binal:
– Polyhedral capsid
– Helical tail
Ex. Bacteriophage
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Filovirus:
– No distinct uniform shape
– Threadlike loops
Ex. Ebola virus
Draw:
Draw:
HIV a Retrovirus
HIV- Human immunodeficiency virus
Structure:
• ___________________
• Contains RNA
• Retrovirus
• Exterior wall made of glycoprotein
• Binds to human ______________ cells at
specific receptor sites
Retrovirus
• HIV is a special type of virus called a retrovirus
• Viruses that get their genetic information copied ________________…
– From RNA to DNA
• Virus that contains RNA
• When the virus infects the cell, they produce a DNA copy of their RNA
• Responsible for some types of _________________ in animals
Human Diseases Caused by Viruses
Category
Disease
Sexually transmitted disease
AIDS (__________), genital herpes
Childhood diseases
Measles, _____________, chicken pox
Respiratory diseases
Common cold, influenza (flu)
Skin diseases
_____________, shingles
Digestive tract diseases
Gastroenteritis
Nervous System diseases
Polio, viral meningitis, ___________
Other diseases
Smallpox, hepatitis, Avian Bird flu, Ebola, SARS, West Nile
What is a Prion?
A prion is a ________________ that can cause infection or disease
Prions are different from viruses in their composition:
- prions consist of protein _____________ while viruses contain nucleic acids and a protein coat
And how they replicate:
– When mutated prions comes in contact with normal prion it causes the normal prion to
change its shape to that of a infected prion.
– Like a domino effect
Disease Caused by Prions
• Abnormal prions infect and burst nerve cells in the brain leaving spaces that make the brain
look like a ____________
• Prions cause diseases such as “mad cow.”
– Abnormal prions are found in the brains and spinal cords of cattle. Scientists think that
spinal cords might be cut during butchering, infecting the meat, and then infecting
humans that eat the meat.