Bio 2- Tes 2- Chapter 24
What kind of virus infects bacteria?
Bacteriophages
The five stages of a lyric infection are attachment, penetration, ______, assembly, and release.
Replication
Why is the lytic cycle more dangerous than the lysogenic?
The host will not have any symptoms at first until the viral cells explode; this cycle can cause death
True/False: Some viruses are DNA while others are RNA
True
True of false: Viruses can manufacture proteins
False
True/ False: Viruses can penetrate plant cell walls when they are healthy.
False! Viruses cannot penetrate cell walls unless they are damaged
What is an enveloped virus?
A virus that is surrounded by an outer envelope of plasma membrane derived from the host cell
What kind of organisms do viruses infect?
ALL; bacteria, archaea, protists, plants, fungi, and animals
What is a verion?
Capsid protein and everything in a virus before it attaches to something
How are bacteriophages used?
Clinically used to treat infection for close to a century, but now replaced by antibiotics
Viroids appear to interfere with gene regulation in _____.
Plants
What can prions do?
Prions can aggregate and accumulate in the brain and certain other tissues and cause fatal diseases
How are viral genes transcribed?
Transcribed by host RNA polymerases, synthesizing copies of viral RNA
What are subviral agents?
Infective agents that are smaller and simpler than viruses
What was the first virus to be found?
Tobacco Mosaic Virus
What does reverse transcriptase do?
Transcribes viral RNA genome into DNA, which is integrated into the host DNA by a viral enzyme
What are the two classification systems of a virus?
ICTV and the Baltimore classification system
What can human viruses cause?
Chickenpox, herpes simplex, mumps, rubella, rubeola, rabies, warts, infectious mononucleosis, influenza, viral hepatitis, certain caners, and AIDS
A virus contains wither ___ or ___, which can be ________ or ______
DNA;RNA // Single-Stranded; Double-Stranded
Are viruses smaller than prokaryotes?
Yes
Do mutations make some viruses less virulent?
Yes
What is the virus-first hypothesis?
Viruses predate or coevolved with their current cellular hosts even before the lifeforms assigned to the three domains diverged
Pathogens:
Viruses responsible for serious diseases, such as rabies, influenza, and AIDS
Most plant viruses have _____ , but not _____.
Capsids; Envelopes
How do viruses that do not have an outer envelope exit?
Cell Lysis
How can viruses be transferred from one host cell to the next?
Via fluids (Sweat, blood, saliva, etc)
What are the three capsid shapes?
1. Helical 2. Polyhedral 3. Combination
What stage of a lytic infection are phage components put together to make new viruses?
Assembly
What is an example of a virus that goes through the lytic cycle?
Ebola
What factors can spread a disease?
Living conditions, including sanitation, nutrition, physical stress, level of health care, and sexual practices
The ____ cycle destroys the host cell.
Lytic
Which type of reproduction is more dangerous/worse?
Lytic
What are the two types of viral reproductive cycles?
Lytic and Lysogenic
Reverse Transcription:
RNA is read backwards into DNA and then replicated
What kind of parasite is a virus considered as?
Obligate Intracellular
Steps of Lytic cycle:
1. Attachment 2. Injection 3. Replication 4. Growth 5. Explosion of viral cells
Why do most scientists view viruses as nonliving particles?
1. They are not composed of cells 2. They cannot carry on metabolic activities or reproduce on their own
Viroid:
A very short, circular, single strand of naked RNA with no protective protein coat and no associated proteins to assist in duplication
Tamiflu:
Inhibits neuraminidase, a viral enzyme necessary for the virus to leave the host cell
What are vectors for viral plant diseases?
Insects
At what stage of the lysogenic cycle would a prop have appear?
Integration
Can viruses live a long time outside of a host cell?
No; they must be transmitted from one host cell to the other
What are re-emerging diseases?
Those that has been almost eradicated and then strike unpredictably, causing an epidemic
What surrounds the virus?
A capsid: Protein coat
How can viruses be classified?
By host range and characteristics such as size and shape, presence of an envelope, and method of transmission, and if they are a DNA or RNA virus.
How do bacteria protect themselves?
By producing restriction enzymes that cut up the foreign DNA of the phage
Protein coat of a virus
Capsid
What do polydnaviruses consist of?
Consist of multiple circles of double-stranded DNA encased in capsid proteins and an envelope
The Capsid
Contains protein subunits called capsomers, which determine the shape of the virus
What is an example of an enveloped virus?
HIV
Why does your immune system not recognize HIV?
HIV uses your own membrane to envelope itself
What can some animal viruses cause?
Hog cholera, foot-and-mouth disease, canine distemper, and certain types of cancer
What can contribute to epidemics of infectious diseases?
Human activity, such as urbanization, global travel, and war
Who discovered viruses and when?
Martinus Beijerinck (1898)
What are prions?
Normally harmless proteins that can sometimes fold into a different shape that causes a disease
Lysogenic Cycle:
Not the deadly kind of virus; stays with the DNA of the host cell and does not cause harm right away.
According to the progressive hypothesis, viruses may have originated as mobile genetic elements such as:
Plasmids
Once a plant is infected, the virus spreads through the plant body by passing through ___________.
Plasmodesmata
What do restriction enzymes do?
Prevent the phage DNA from duplicating
Mad cow disease is an example of an infection caused by a _____.
Prion
What kind of viruses are the majority of pathogenic viruses?
RNA through reverse transcriptase
What are retroviruses?
RNA viruses that have a DNA polymerase
What do subviral agents include?
Satellites, viroids, and prions
Most plants are ___________ __________ RNA
Single stranded
What happens during the viral infection of animals?
Some enveloped viruses fuse with the animal cell's plasma membrane. Other viruses enter the host cell by endocytosis
What effects can viral infections cause in plants?
Stunted growth, changes in the shape of the foliage, cause sports, streaks, or mottled patterns on the leaves, flowers, or fruits
How does the viral DNA replicate in the lysogenic cycle?
The viral genome becomes integrated into the host bacterial DNA: a prophage or provirus. When the bacterial DNA replicates, the prophage also replicates
In the lysogenic cycle, what happens as DNA is replicated?
The virus is replicated as well
What does an enveloped virus do while inside the host cell?
The virus synthesizes with certain proteins and inserts them into the host's plasma membrane
How can plants pass their virus once they are infected?
Through their seeds
What does TSE stand for?
Transmissible spongiform encephalopathies
What is the regressive hypothesis?
Viruses may have evolved fro mall, independent cells that were parasites in larger cells, and unneeded genes were gradually lost through evolution
What is the progressive hypothesis?
Viruses may have originated as mobile genetic elements (transposons and plasmids) that could have moved from one cell to another through damaged cell membranes
How big are viruses?
Viruses range from 20 to 300 nm
What is the only place polydnaviruses can replicate?
Wasp ovary cells
How many base pairs does the virus genome contain?
5000 to more than 100,000
Amantadine:
A drug that inhibits penetration or uncoating of viral nucleic acids
What are TSEs?
A group of fatal degenerative brain diseases in birds and mammals
What is the proteinaceous infectious particle?
A new biological principle of infection
What is an obligate intracellular parasite?
A parasite that depends on a living host to survive and replicate
What is the correct unit of measurement for the size of most viruses?
Nanometers
Do viral infections kill plants?
No, not normally
The specificity of viruses to different types of cells is due to ____ sites in the host cell.
Receptor
