concept 19.2: viruses replicate only in host cells

what does it mean to be an obligate intracellular parasite

it means they can only replicate within a host cell

what cells are viruses capable of infecting

cells within their host range, a limited number of host cells they can infect

why can viruses only infect within their host range

host specificity results from evolution of viral recognition system of host cell receptor molecules, a lock and key fit between viral and host cell surface proteins

what occurs once a viral genome enters a cell

the cell begins manufacturing viral proteins and the virus begins using the hosts systems

what are the two alternative reproductive mechanisms of phages

the lytic cycle and the lysogenic cycle

what occurs during the lytic cycle

a phage replicative cycle that culminates in the death of a host cell, and this produces new phages and breaks opens the hosts cell wall a releases the progeny viruses

what does it mean to lyse

to break open

virulent phage

one that only reproduce by the lytic cycle

what do restriction enzymes do

recognize and cut up certain phage DNA

what occurs during the lysogenic cycle

replicated the phage genome without destroying the host, and the viral DNA molecule is incorporated into the host cells chromosome

prophage

the integrated viral DNA

what can environmental signals do to the virus genome

can trigger the virus genome to exit the bacteria chromosome and switch to the lytic mode

temperate phages

use both the lytic cycle and lysogenic cycles

what does natural selection favor inn bacterial mutants

they prefer surface proteins that cannot be recognized as receptors by a particular type of phage

restriction enzymes

identifies and cuts up foreign DNA

what are two key variables used to classify viruses that infect animals

they have an RNA or DNA genome and they have the presence or absence of a membranous envelope

what typically forms the viral envelope

the host cells nuclear envelop e

retrovirus

use the enzyme- reverse transcriptase- to copy their RNA genome into DNA

HIV

the retrovirus that causes AIDS, HIV targets T- lymphocytes (a type of white blood cell) in the immune system

provirus

the viral DNA that is integrated into the host genome

what is the difference between a prophage and a provirus

a provirus remains a permanent resident of the host cell while prophage does not

some ways a virus can damage or kill cells

by causing the release of hydrolytic enzymes from lysosomes

by having molecular components such as envelope proteins that are toxic

causing infected cells to produce toxins that lead to disease symptoms

how does a vaccine work

it is a harmless derivative of a pathogen that stimulates the immune system to mount defenses against the harmful pathogen

why cant antibiotics work the same as a vaccine

antibiotics target bacteria not viruses

how can antiviral help treat viral infections

by inhibiting synthesis of viral DNA and interfering with viral assembly