lec 4

Question 1

what are viruses

Answer 1

viruses are obligate intracellular parasites, they can replicate only inside the cell

Question 2

host cells of viruses include:

Answer 2

all types of organisms

Question 3

virons

Answer 3

outside of the host cells, viruses exist as inert infectious particles

Question 4

structure of virons

Answer 4

1) capsid: made of proteins called capsomeres
- nucleocapsid: nucleic acid + capsid
2) enveloped viruses also contain an envelope composed of phospholipid bi layer, it also had additional proteins on the envelope that are virus specific

Question 5

only —- type of nucleic acid is found in irons of a given virus

Answer 5

1

Question 6

using —- , —- and —- viruses insert and replicate their genomes side of the host cell

Answer 6

amino acids, ribosomes, nucleic acids

Question 7

RNA virus vs DNA virus

Answer 7

genome made of RNA vs. genome made of DNA

Question 8

simple viruses vs. complex viruses

Answer 8

3 proteins vs. more than 100 proteins

Question 9

the envelope is typically seen in —– viruses, and the —— is steel from the cell.

Answer 9

animal, membrane

Question 10

function of envelope viruses

Answer 10

they are involved in the attachment of the virus to the next host cell

Question 11

shape of virons is influenced by:

Answer 11

the nature of the capsomeres, but also the genome as well. e.g. if you have a large genome, you would need a large capsid

Question 12

name the 3 major shapes of virons

Answer 12

1) helical
2) polyhedral viruses
3) complex viruses

Question 13

helical viruses
typical in:
number of capsomeres:
tobacco:

Answer 13

• plant viruses
• specific number of capsomeres that package the genome inside a rod
• 2130 identical capsomeres

Question 14

polyhedral viruses

• shapes:
• number of capsomeres:
• human papilloma virus:

Answer 14

• all shapes are possible but the most common one is icosahedron , a regular polyhedral with 20 triangular faces
• because of the geometry some capsomere numbers are possible
  it contain 72 clusters of 5 capsomeres

Question 15

complex viruses

• composition
• in what terms is it complicated
• viruses of —-, causes the cell —–
• how do they function

Answer 15

• head, collar, tail, tail pins, tail fibres, end plate
• in terms of structure NOT necessarily genome organization
• bacteria (bacteriophages), explode
• tail fibres and tail pins drill through the cell wall of the bacteria

Question 16

what are viroids

Answer 16

viroids are closed circles of single stranded RNA containing 240-380 nucleotide

Question 17

how do viroids cause diseases

Answer 17

their replication is dependent on the host machinery, disease is caused by the overtaking of this machinery

Question 18

viroids are only known to infect —– cells

Answer 18

plant

Question 19

structure of viroids

Answer 19

just a piece of nucleic acid

Question 20

how stable are viroids

Answer 20

very stable - can survive outside the host cell

Question 21

viruses infect plant cells by:

Answer 21

entering the plasmodesmata of each cell and eventually infecting the whole vascular system ** its very small

Question 22

transmission of viroids is done as a —-

Answer 22

vector

Question 23

how many proteins do prions have

Answer 23

1

Question 24

what do prions result in

Answer 24

neurological disorders

• scrapie (sheep)
• bone spongiform encephalopathy - BSE
• jakob disease: human
• vCJD: transmitted by inception of BSE
• Kuru: mostly elder women, brain degeneration

Question 25

rate of transmission of prions

Answer 25

very low

Question 26

prions - misfiled proteins

Answer 26

prions are normal to have in the brain as PrPC

abnormal: PrPSc