BIOL 206 Exam 2 - Donna Janes

T/F: Viruses are cells

False, viruses are NOT cells

Viruses are obligate intracellular parasites. What does this mean?

They must be living in a host and must be grown in a host

Viruses ______________ (do/do not) divide and grow

do not

T/F: viruses contain DNA and RNA

False, they contain DNA OR RNA (very few exceptions)

Which two viruses are unique in that they have both DNA and RNA?

Cytomegalovirus and mimivirus

List the four types of genomes a virus can have

dsDNA

ssDNA

dsRNA

ssRNA

Most DNA viruses are __________ (ds/ss) while most RNA viruses are ___________ (ds/ss)

ds, ss

What's the range in size for viruses?

10nm-500nm

How do viruses impact their host's ribosomes?

they steal the ribosomes from the host to replicate

_____________ + ____________ (protein coat) = nucleocapsid

nucleic acid, capsid

T/F: viruses have ribosomes

False

T/F: viruses have no ATP-generating mechanism

True

T/F: viruses are infectious

True

Viruses are medically ______________ (important/insignificant)

important

Herpes is a ___________ (small/large) family of viruses and includes what three relevant types for BIOL 206?

large family; includes cold sores, genital herpes, chicken pox

HPV is the cause of most _______________ in humans, but is most known for causing __________________ in women and __________________ in men

warts; cervical cancer, throat cancer

HPV affects ____________ (what type?) tissue

epithelial

T/F: there are many strains of HPV

True

Define virion

virus particle

T/F: viruses can be seen with a light microscope

False; requires a Electron Microscope

RBCs are __________ nm, E. coli is ______________ nm, virophages are ________________ nm

10,000, 1,000x3,000, 70

mamavirus is _____________ nm, poliovirus is___________ nm, smallpox virus is ______________ nm

390, 30, 200x300

_______________ (most/all/no) viruses have capsids

all

define a capsid in relation to viruses

a protein coat that encloses and protects the virus's nucleic acid

Capsids are constructed from ________________________________ (3 words) called __________________

identical protein subunits; capsomeres

What about the capsid triggers the human immune system to recognize the virus as foreign?

The repeating pattern of capsomeres which is foreign to the human body

List the four shapes of viruses

1) filamentous/helical (rigid or flexible)

2) icosahedral (soccer ball shaped with spikes coming off)

3) enveloped

4) complex morphology (includes a head and tail)

List two types of filamentous shaped viruses

tubulovirus (rigid), ebola (flexible)

Adenovirus is ____________ (what shape?)

icosahedral

Herpes virus is __________________ (what shape?)

enveloped

List two types of complex morphology/head and tail viruses and explain their effect on the host

T2 bacteriophage, T4 bacteriophage;

infect bacteria which can cause the human gut to become sterile resulting in diarrhea

_________________ (shape) is a continuous helix of capsomers forming a cylindrical nucelocapsid

helical

Polyhedral/icosahedral viruses are ___________ sided with ____________ corners (number) and vary in number of __________________

20, 12, capsomers

Some polyhedral viruses are enveloped meaning what?

their membrane is external to the capsid

Rabies virus is ________________ shaped

bullet

This virus is an example of Ebola virus or ______________ shaped virus

helical

From where is the viral envelope derived?

host cell membrane

Why can't an enveloped virus get its envelope from a bacterial cell membrane?

Bacterial cells have cell walls protecting them from enveloped viruses

When does an enveloped virus acquire its envelope?

When it leaves or buds through the host cell

The exposed proteins on the outside of a viral envelope are called _________________ and are essential for what?

spikes/peplomers; essential for binding to the host receptor and for the infectivity of the host cell

What are viruses without an envelope called?

Naked viruses

COVID vaccines are made to attack what part of a virus?

the peplomers thus preventing the virus from binding to the host cell

An envelope is ________________ (required/optional) for the survival of enveloped viruses

required

List an advantage and a disadvantage of the viral envelope

Advantage: disguises the virus from the immune system because it is coated in the host cell membrane (molecular mimicry)

Disadvantage: soap and water dissolve the envelope thus killing the virus bc the envelope is required for survival

List the two functions of a viral envelope

1) protects the nucleic acid when the virion is outside the host cell

2) is used to bind to the receptor and infect the host cell

T/F: a naked cell can still infect a host cell

false; no envelope = no infectivity

Naked viruses bind to the host cell via ______________

its capsid

The viral envelope ____________________ with the host cell membrane allowing for its infectivity

fuses

Anything that damages the _________________ will damage the viral envelope

cell membrane

List factors which damage the viral envelope

Environmental conditions (temp, pH, pressure, toxins, detergents, etc);

Naked viruses are ___________________ (more/less) resistant to damaging environmental factors;

Advantage __________(in/out) of the body;

Disadvantage ____________ (in/out) of the body

more resistant, advantage in the body, disadvantage out of the body

Why is resistance to environmental conditions important?

Naked viruses can persist because it does not have a damaged/destroyed envelope

Why can't a virus with a damaged/destroyed envelope persist in the host?

it cannot interact with the complementary molecule/host cell receptor

T/F: viruses only grow in living cells

true; they are obligate intracellular pathogens

Animal viruses are grown in what three hosts?

1) living animals

2) embryonated eggs

3) cell cultures

Which is most commonly used to grow viruses in the lab?

a) living animals

b) embryonated eggs

c) cell cultures

Cell cultures

Explain what determines if a virus is "chosen for" and how this relates to COVID

viruses that best fit into the host receptor are chosen for; COVID mutates allowing it to continue to fit into the host receptor as the immune system becomes resistant to the current strain

Bacteriophages form plaques on a _________________ (3 words) bc they infect bacteria

lawn of bacteria

All viruses must do what to gain entry into the host

interact with a complementary host cell receptor

T/F: viruses are motile

false; they are nonmotile

How are viruses moved around/spread?

normal kinetic energy of air molecules moves the virus around

How does a virus know that it is near a host cell?

Chemical attraction allows the virus to sense the presence of the host cell

T/F: enveloped viruses infect bacteria

false; bacteria have a cell wall preventing the enveloped virus from getting through and coating itself in the bacterial cell membrane

List and explain the three mechanisms by which animal viruses enter a cell

Direct penetration: only the nucleic acid enters the host cell

Membrane fusion: only the nucleocapsid enters

Endocytosis: the entire enveloped virus or naked virus enters the cell

Direct penetration is only a mechanism of entry for which type of virus?

naked viruses

Membrane fusion is only a mechanism of entry for which type of virus and why?

enveloped viruses because they are made of the same stuff as the cell membrane and can thus be undetected

Explain endocytosis in relation to viral entry into a host cell. How and why does it work?

Some complementary receptors trigger endocytosis; viruses may also use an amino acid shape to bind to the receptor and trigger endocytosis because the cell thinks it is taking in a protein molecule

Why are viruses species specific?

the host must have a complementary receptor to bind to viruses

Why are viruses tissue specific?

not every tissue expresses the same genomes which prevents the complementary receptor for the virus from being present on certain tissues

Why is rabies transmittable to any mammal if viruses are species specific?

Mammals have shared receptors for rabies

What is required to release the genome/nucleic acid (NA) into the cytoplasm? Why does the genome/NA need to be released into the cytoplasm?

Enzymes are needed to release the genome/NA into the cytoplasm for viral replication

List and explain the two ways in which a virus leaves the host cell

Budding/blebbing: exocytosis; nucleocapsid binds to the membrane which pinches off and sheds the virus gradually;

Lysis: viruses are released when the cell dies and ruptured

Lysis is only a mechanism of release for which type of virus?

Naked viruses

The number of viruses released during lysis ______________ (remains the same/varies) among different viruses

varies

Budding is an exit mechanism of ___________ viruses (all, naked, enveloped)

enveloped

Define molecular mimicry. How does the immune system react?

The enveloped virus looks like the host cell due to the presence of host cell membrane, but the immune response will eventually recognize the viral components

T/F: virus budding will kill the host cell

true; eventually kills the host cell

Some bacteriophages have a______ along with a_____and_____ (in relation to shape and structure)

polyhedral nucleocapsid; helical tail; attachment fibers

Bacteriophages are also referred to as what? Define what a bacteriophage is.

phages; bacterial viruses

Which bacteriophages are the most widely studied?

Those that infect escherichia coli

Describe the multiplication process of bacteriophages in relation to animal viruses

Bacteriophages go through similar stages as animal viruses

What part of the bacteriophage enters the cytoplasm?

only the nucleic acid

Release due to cell lysis is called what?

The lytic cycle

How do bacteriophages exit the host cell? Why is this?

Lysis; bacteriophages must be naked cells because bacterial cells have cell walls that would prevent enveloped viruses from getting through

The __________________ of the viral surface proteins for __________________ proteins (_______________) is responsible for the ability to infect the host cell

affinity; complementary; receptors

If the cell surface does not possess a receptor that interacts with the viral surface, what happens?

Nothing; no host receptor = no binding = no infectivity

The host range is determined by the presence of what?

the receptor/complementary molecule/protein

T4 bacteriophage infects what?

only E coli

List and explain the 5 steps of phage replication in order

Attachment: binding of a virus to a specific molecule/receptor;

Penetration: genome/nucleic acid (NA) enters the host cell;

Biosynthesis: viral components are produced;

Maturation: assembly and completion of viral formation;

Release: viruses leave the cell via lysis to infect other cells

List some products of biosynthesis

making of enzymes that are needed to release the NA into the cytoplasm, makes nucleic acids for progeny (viral babies)

What component of the host cell do viruses use during biosynthesis?

ribosomes

Define burst time in relation to viruses

the time from attachment to lysis

Define burst size as it relates to viruses

the number of viral particles released

Bacteriophages release ________ to _________ visions. T4 bacteriophage specifically releases ____________ visions (numbers). This is a _____________ (large/small) quantity compared to bacteria size

50-300 virions; ~ 200 virions; large quantity

_______________ on the _____________ is the receptor for T4 on e coli meaning that T4 is a ______________ (gram positive/gram negative) stain

LPS on the outer membrane; gram negative

T4 produces ______________ which weakens the e coli's _____________ allowing for ______________ (part of the T4 cell) penetration

lysozyme; cell wall; allowing for viral tail penetration

Maturation is a _______________ reaction but always occurs in the same __________________

spontaneous; order

What kind of virus has two life cycles?

temperate virus

Describe the lytic phase of a virus. When does it occur and give examples? What is its purpose?

Happens when the cell conditions are unfavorable for the virus such as in UV radiation, extreme heat, etc;

Signals the bacteria to hurry up to have babies (progeny) and get out of the host cell

Describe the lysogenic phase of a virus. When does it occur? Describe the process

Occurs when the host cell conditions are favorable AND the virus has invaded the immune system (required for the virus to stick around);

The viral chromosome implants itself in the bacterial chromosome so that every time the cell divides, so does the virus thus causing it to multiply and infect more cells