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Many viruses cana be purified and crystallized.
Each type of virus always has at least two parts: _____________
The capsid of a virus is composed of ________________.
composed of protein subunits
The capsid is always surrounded by an outer membraneous envelope.
- Not all viruses contain an outer membraneous envelope.
- If it does not contain, the virus is said to be 'naked.'
- ***The envelope is actually a piece of the host's plasma membrane that also contains viral glycoprotein spikes.
The classification of viruses is based on 3 criteria:
- 1. their type of nucleic acid (single stranded, or double stranded)
- 2. their size and shape
- 3. presence/absence of an outer envelope
The nucleic acid of viruses contain:
B. either DNA or RNA
B. either DNA or RNA, but never both.
(this multiple choice question has been scrambled)
Viruses cannot reproduce outside a living cell. What is the scientific term for this?
Obligate intracellular parasites.
Viruses are able to evolve and reproduce.
True..However, they are only able to inside host cells
How do viruses gain entry to a particular host cell?
Viruses gain entry into and are specific to a particular host cell because portions of the capsid (or the spikes of the envelope) adhere in a lock and key manner with a receptor on the host cell outer surface.
What are bacteriophages?
Bacteriophages are viruses that parasitize bacteria.
What are the two types of bacteriophage life cycles called?
- Lytic Cycle
- Lysogenic Cycle
In which of the bacteriophage life cycles does the phage remain dormant or latent for a period of time?
What are the 5 Stages of the Lytic Cycle?
- 1. Attachment
- 2. Penetration
- 3. Biosynthesis
- 4. Maturation
- 5. Release
In the lytic cycle, what happens during the attachment stage?
Capsid combines with receptor on the bacterial cell wall in a lock and key manner
In which stage of the Lytic cycle does the viral DNA enter the host cell?
In which stage of the Lytic Cycle are the viral components being synthesized?
- -Biosynthesis stage begins after the virus brings about inactivation of host genes
- -Virus takes over machinery of the cell in order to carry out viral DNA replication
- -production of multiple copies of capsid protein subunits.
In which stage of the Lytic Cycle are the viral components being assembled together?
- Maturation Stage
- -Viral DNA and capsids are assembled to produce several hundred viral particles.
In which stage of the lytic cycle are the new viruses released out of the host cell?
- Release stage
- -Lysosomes coded by the viral particles are produced to break down the cell wall of the host.
- This allows the new viruses to be released.
- -Bacterial cell (host cell) dies as a result of the disruption of the cell wall.
What is the difference between Lytic and Lysogenic cycles?
- After Attachment and Penetration stages, Integration Stage occurs in Lysogenic Cycles.
- Viral DNA becomes incorporated into bacterial DNA with no destruction of host DNA.
- While latent, the viral DNA (only the portion that is viral DNA) called a prophage.
- All subsequent cells called lysogenic cells carry a copy of the prophage.
- Environmental factors such as UV radiation can use the prophage to enter the lytic stage of biosynthesis, maturation, and release stages.
In Animal Viruses, new viral particles are released out of the host cell by ____________.
- During Budding, the virus picks up its envelope consisting of lipids, proteins, and carbohydrates from the plasma membrane.
- Envelope markers, such as glycoproteins that allow the virus to enter a host cell are coded for by the viral genes.
Retroviruses contain a special enzyme that carries out RNA -------> cDNA transcription (Reverse transcription)
What is the enzyme called?
- Retroviruses are RNA animal viruses (animal virus--> so viral replication is same as animal viruses)
- The DNA is called cDNA because it is a DNA copy of the viral genome.
Unlike bacteriophages who enter the host cell by penetration, animal viruses enter the host cell by what means?
- By fusion.
- Capsid and envelope fuse with host cell.
How are some viruses cancer-producing?
- Some viruses are cancer-producing because they bring with them oncogenes.
- Oncogenes are normal genes that have been transformed and that can cause the cell to repeatedly undergo the cell cycle.
What are viroids?
Viroids are naked strands of RNA (not covered by a capsid)
*Viroids mainly infect plants.
Like viruses, viroids direct the cell to produce more viroids.
What are prions?
- Prions are made up of protein molecules.
- may have a misshapen tertiary structure that can cause other proteins of their own to convert to this structure also.
- -Linked to mad cow disease
- -causes CJD (Creutzfeldt-Jakob), mental disorder that can lead to loss of vision and special before paralysis/death can occur.
Viruses, viroids, and prions are all known to cause diseases in humans.