Chapter 2 Flashcards
What makes a virus unique?
Viruses occupy a position between non living and living matter
What is a virus?
A microscopic particle capable of reproducing only within living cells
What is the size range for viruses?
20 to 400 nm. One nanometer is one billionth of a meter
Name and explain two parts that make up most viruses
A virus consists of an inner nucleus acid core, or strand, surrounded by an outer protective protein coat called a capsid.
There are 3 shapes of viruses: irregular, spherical, and rod-shaped. Give an example of each and what type of organism do they infect.
A rod shaped virus called the tobacco mosaic virus, infects the leaves of the tobacco plant.
A spherical shaped virus called the adenovirus infects animals.
A irregular virus called the bacteriophage infects bacteria.
Referring to viruses, what is an envelope?
An extra protective coat of protein and fat
5 examples of living characteristics of viruses:
- Has nucleus acid core-RNA or DNA
- Able to reproduce-in host cell only
- Able to invade a host cell and take over it’s reproductive machinery
- Causes a contagious disease
- Able to mutate
Non-living characteristics of Viruses:
- No metabolic needs-doesn’t need to eat, sleep, breathe
- Not made up of cells
- Able to be crystallized-when liquid evaporates-can await a new host in this form-length of time varies
Finish the sentence: because viruses have characteristics like living and non living things they are considered:
To be transitional between life and non-life
Finish the sentence: viruses evolve and reproduce but they…
are obligate intercellular parasites
What are the four main steps to viral reproduction?
- Virus attaches to cell and nucleic acid enters cell-either injects RNA or DNA or whole virus enters cell
- Replicate parts-nucleic acid, capsid, envelope…=synthesis
- Assemble new virus from parts
- Cell lysis or viral release from infected cell
Viruses infect bacteria by which two cycles?
Lytic cycle and lysogenic cycle
Explain the lyric cycle (viral reproduction)
Virus attacks cell, kills it and releases more viruses right away- follows 4 steps of viral reproduction. It caused the disease right away and is more virulent
Define virulent
How quickly a virus reproduces and is spread. More virulent viruses tend to follow lytic cycle.
Explain lysogenic cycle
Sometimes a virus doesn’t kill host cell right away or immediately cause disease-coexist with host. Virus stays dormant as a prophase in the cell for several generations. Viral DNA gets copied at each replication of host cell-passed on to offspring. Later, the virus is triggered or activated and causes the disease by entering the cell. A trigger may be time, stress, or other illness.
What is a prophage?
Host DNA and virus DNA
What is a retrovirus?
Has RNA as the genetic material. RNA is converted into DNA copy inside the host cell by an enzyme called reverse transcriptase. Follows the lysogenic pathway. Can mutate easily-hard to make vaccines for these ones. Infects mainly animal cells.
Examples: HIV, influenza
What is a pathogen?
Disease-causing agents
Name the system that defends the body against pathogens.
The immune system
Explain the Non-Specific response and the specific response of the body
The immune system comprises two main components: non-specific defenses, which are the body’s first line of defense against disease, and specific defenses, which invoke a specific immune response once a particular pathogen gets past the body’s generalized defense.
What is the body’s primary line of defense?
Skin, mucous, membranes, tears, digestive enzymes (Non-specific response)
What is the body’s second line of defense?
Phagocytic white blood cells which engulf and destroy the pathogens like viruses, bacteria, etc…. (Non-specific response)
What is the body’s tertiary line of defense?
Lymphocytes-white blood cells that produce antibodies (active immunity) specific response
What are interferons?
When viruses succeed in invading an animal cell, small protein substances called interferons are produced. When released from virus-infected cells, they make it difficult for the virus to infect other cells. This occurs no matter what virus invades the body cells.
What is an antigen?
A substance, usually protein in nature, that stimulates the formation of antibodies.
What is an antibody?
Protein formed within the blood that reacts with antigens. They can flag pathogens for destruction and can change the virus shape so the virus can’t enter the cell.
What is a host range?
The number of species a virus can infect.
How many species does a narrow host range infect?
1-3 species. Example: human cold virus
What is a broad host range?
Infects many different species. Example: rabies infects mammals and birds
How does a virus identify the host cell?
By a “lock and key” system. Antigens on the outside of the virus fit into a specific receptor site on the host cells surface.
What is a vaccine?
A weakened, diluted, or dead form of the virus that is infected (because saliva and stomach enzymes would destroy it) into the body to produce immunity. The body reacts to the shape of the virus and produces antibodies so immune system can fight off the disease. However, vaccines can also weaken your immune system as you can not fight off other diseases because your immune system is busy.
What do vaccines prevent?
Outbreaks, infection, and death
What are 4 harmful effects of viruses?
- Causes disease, cancer
- Causes brain damage (ex.measles)
- Destroys organs (ex. Hepatitis-liver, heart)
- Can be fatal
What are 3 beneficial effects of viruses?
- Vector for gene splicing (to replace the bad gene)
- Biological control (control or eliminate other organisms)
- Make vaccines
How can you avoid viruses?
Vaccinations. Good hygiene. Abstinence. Boil water where cleanliness is in question. Eat healthy.
Explain virus evolution.
Viruses were once just fragments of genetic material that came from cellular organisms (left over parts). This is why viruses are specific to certain cells (because they come from them).
Explain the steps of the scientific method.
Observations Question Hypothesis Experiment Analyze and interpret data Hypyothesis supported Further experimentation Hypothesis continues to be supported Report results (publish)
What is the depth of field?
Distance in front or behind the specimen which appears to be in focus.
How do you calculate the actual size of a specimen?
Number of times object crosses field
How do you calculate the drawing size?
Drawing size (mm) ---------------------- Actual size (mm)
What is the diameter of field?
How much of the slide you can see.
What is the diameter of field on low power?
4mm or 4000 um
What is the diameter of field on medium power?
2 mm or 2000 um
What is the diameter of field on high power?
0.4 mm or 400 um
What is the diameter of field with the oil lens?
0.2 mm or 200 um
