Virus Basics
These infectious agents are considered obligate intracellular parasites because they must reproduce inside a living cell.
Viruses.
The protein coat that surrounds and protects a virus's genetic material.
Capsid.
The first step required before a virus can enter a host cell.
Attachment to the host cell.
Viruses that infect bacteria.
Bacteriophages (phages)
The usual entry point for plant viruses.
Damaged Tissues (wounds)
Viruses are classified as this because they are not made of cells.
Noncellular.
The two possible types of genetic material found inside a virus.
DNA or RNA.
The host cell system viruses take over to make more viruses.
Metabolic machinery.
The viral reproductive cycle in which viruses immediately being reproducing.
Lytic cycle.
Tiny channels that allow plant viruses to spread from cell to cell.
Plasmodesmata.
Scientists debate whether viruses belong in this category because they reproduce only inside living cells.
Living organisms (alive)
Specialized structures that help certain viruses attach to host cells.
Spikes.
The small DNA or RNA molecule inside a virus.
Viral genome.
The viral reproductive cycle in which viral DNA remains dormant until activated.
Lysogenic Cycle
A well-known virus that infects tobacco plants.
Tobacco mosaic virus (TMV)
Viruses cannot perform this essential life process without infecting another organism.
Independent reproduction.
The outer membrane found on some viruses outside the capsid.
Viral envelope.
The host cell functions viruses depend on because they cannot perform them themselves.
Metabolic processes.
An event that causes a virus in the lysogenic cycle to begin the lytic cycle.
A trigger, such as stress or an environmental change.
Organisms that were commonly controlled to reduce the spread of plant viruses.
Insect vectors.
Name two reasons viruses are generally not considered living organisms.
- They are noncellular.
- They lack metabolism.
- They cannot reproduce independently.
- They require a host cell to reproduce.
Compare the functions of the capsid and the envelope.
Capsid: Protects the viral genome and gives the virus its shape.
Envelope: Helps the virus enter host cells and may help it avoid the immune system.
Explain why viruses infect only certain organisms or specific cells.
Their attachment proteins (spikes) bind only to matching receptors on specific host cells.
Compare the lytic and lysogenic cycles.
Lysogenic cycle: Viral DNA remains dormant inside the host cell until activated, then enters the lytic cycle.
The virus that genetically engineered Hawaiian papaya plants were designed to resist.
Papaya ringspot virus (PRSV)