Lecture 12: Chapter 17

Viruses

what is the relationship between viruses and host cells

viruses cannot reproduce or carry out metabolism outside of a host cell

are viruses cells?

viruses are not cells

what does a virus consist of?

nucleic acid (linear or circular) enclosed in a protein coat, sometimes a membranous envelope

how many genes does a virus encode?

3-2000 genes

what are the two ways a nucliec acid can be arranged?

double/single stranded DNA= DNA virus

double/single stranded RNA=RNA virus

capsid

protein shell that encloses the viral genome built from protein subunits called capsomeres

viral envelope

derived from membranes of host cells and surround the capsids of many viruses found in animals

what are the four virus forms

filamentous (aka, helical, rod shaped), isosahedral, enveloped, head and tail (bacteriophages)

what form of virus includes plant viruses, such as tobacco mosaic virus (TMV)

filamentous (helical/rod shaped)

whats the structure of icosahedral virus

polyhedron with 20 triangular faces

protein spikes: aid in infection

causation of virus: cold, sore throat, pink eye

rarely causes serious illness or death

what virus is derived from the host cell’s membrane? What is it’s structure and what sickness does it include?

the “viral envelope”

combination of viral and host cell molecules, including glycoprotein spikes that aid in infection

includes: influenza, measles, coronavirus, HIV

bacteriophages (head and tail)

viruses that infect bacteria

most complex capsids found among viruses

where does replication occur for viruses?

viruses replicate ONLY in host cells

what does the term “obligate intracellular parasites” mean?

organisms that must live and reproduce inside the cells of the host

each virus has a ___ range

“host” range: limited number of host cells that it can infect

how does a viral replicative cycle begin?

virus binds to a host cell and the genome enters the cells

what is the relation of viral nucliec acid molecules and capsomeres?

.they both spontaneously self assemble into new viruses

.capsomeres come together to form the capsid & the capsid surrounds and protects the viral nucleic acid

what are the two replicative cycles of phages

lytic cycle & lysogenic cycle

what is the function of the lytic cycle (phages)?

produces new phages and lyses (breaks open) the host’s cell wall, releasing the progeny viruses

a phage that reproduces ONLY by the lytic cycle is called a ___

virulent phage

The viral DNA molecule becomes incorporated into the host cell’s chromosome, once integrated, the viral DNA is known as a ___

prophage

what are the two phages that use both the lytic and lysogenic cycles?

temperate phages

what is the process of a “retrovirus”?

RNA serves as template for synthesis of DNA that gets integrated into the host genome DNA

What enzyme do retroviruses use to copy their RNA to DNA

reverse transcriptase

What retrovirus causes aids?

HIV

What does provirus mean?

reverse transcribed viral DNA that integrates into the host genome

why can’t antibiotics treat viral infections?

antibiotics target parts of bacteria that viruses don’t even have

what can help treat, though not cure, viral infections?

antiviral drugs

what are epidemics and pandemics caused by?

new strains of influenza or other viruses to which people have little immunity

what are the 3 ways epidemics/ pandemics can arise?

-mutation of existing RNA viruses (=seasonal flue)

-dissemination from small, isolated populations (HIV)

-spread from other animals (zoonotic: swine flue=75% of new human diseases

what are the two major routed plant viruses spread their disease?

-horizontal transmission: external source entering through damaged cell walls (herbivores or pruning)

-vertical transmission: inheriting the virus through a parent