lecture 10: viral life cycles

Question 1

what is a virus?

Answer 1

viral genome enclosed in a protective coat

Question 2

what is the viral genome?

Answer 2

-single or double strand DNA or RNA
-linear or circular

Question 3

what is the protective coat of the virus?

Answer 3

-capsid
-rod shaped or polyhedral
-comprised of protein subunits called capsomeres

Question 4

true or false, all viruses have envelopes

Answer 4

false, only some

Question 5

what is the viral envelope? what does it consist of?

Answer 5

-found in certain viruses
-membrane that covers capsid and is derived from the host membrane
-contains viral proteins and glycoproteins

Question 6

wha type of parasites are viruses?

Answer 6

obligate

Question 7

true or false? virus cells are host specific.

Answer 7

true! (example: influenza virus infects cells of the respiratory tract

Question 8

how do viruses infect specific cells?

Answer 8

specific interactions between viral glycoproteins and host-cell receptors

Question 9

what are the steps to infection with viruses?

Answer 9

Question 10

how do viral glycoproteins get into the viral envelope if the envelope is a piece of the host cell’s membrane?

Answer 10

viral glycoproteins are synthesized at ER, and will travel in vesicle to plasma membrane to be picked up by the budding virus. basically, through cell budding

Question 11

what are the 2 types of bacteriophage life cycles?

Answer 11

1) lytic life cycle (cell lyses)
2) lysogenic life cycle (cell does not lyse)

Question 12

what type of cells do bacteriophages infect?

Answer 12

bacteria cells

Question 13

during the lytic life cycle, what is the enzyme produced from the viral genome that digests the bacterial cell wall?

Answer 13

lysozyme

Question 14

during the lytic life cycle, what destroys the host’s DNA?

Answer 14

the first viral proteins produced destroy the host’s DNA

Question 15

what are the steps to the lytic cycle?

Answer 15

Question 16

true or false, the phage DNA circularizes in the lytic and lysogenic cycle

Answer 16

true!

Question 17

what are the steps to the lysogenic life cycle?

Answer 17

Question 18

what is the link between the lytic and lysogenic cycle?

Answer 18

During lysogenic cycle, if prophage exists bacterial chromosome, lytic cycle is initiated

Question 19

what are the bacterial defences against phages?

Answer 19

restriction endonucleases

Question 20

what do restriction endonucleases do?

Answer 20

they cut foreign DNA that enters the cell

Question 21

how is the host cell DNA protected from restriction endonucleases?

Answer 21

protected from degradation by methylation

Question 22

what are retroviruses?

Answer 22

enveloped viruses with a single stranded RNA genome

Question 23

by what enzyme does the single stranded RNA genome of a retrovirus serve as a template for DNA synthesis

Answer 23

reverse transcriptase

Question 24

explain the retroviral life cycle

Answer 24

Question 25

what is a provirus?

Answer 25

when viral DNA is inserted into host cell’s chromosomes for retroviruses

Question 26

what is an example of a retrovirus?

Answer 26

covid

Question 27

true or false, prions are viruses

Answer 27

false!

Question 28

what is a prion?

Answer 28

-a prion is a misfolded form of a protein normally found in brain cells
-once in a cell, prions convert the normal form of the protein to the misfolded prion form (prion causes other normal proteins to fold)
-prions form aggregates (clusters) that disrupt normal cell functions in the brain
-prions act slowly (10+year incubation) and are virtually indestructible