DTT 17 - Viruses, Viroids, Prions and Diseases

Question 1

virus definition

Answer 1

‘A tiny, infectious particle, consisting of a nucleic acid core surrounded by a protein coat called a capsid’.

Question 2

smallest and largest virus and size

Answer 2

250Å (yellow fever)
2,500Å = 0.25µm (Vaccinia, Smallpox);
Å = angstrom = 0.1 nanometre

Question 3

who discovered first virus and what virus did they discover

Answer 3

1892 by the Russian botanist Dmitri Iwanowski who was looking at ‘Tobacco Mozaic Virus’

Question 4

properties of a virus

Answer 4

not cellular
don't respire
have no metabolism
don't break down carbon compounds
don't die

Question 5

3 morphological classification

Answer 5

helical
icosahedral
combined or complex

Question 6

how else can they be classified

Answer 6

based on nucleic acid

Question 7

what additional property do some viruses have

Answer 7

Some viruses have a lipoprotein envelope in addition, which is derived from the membrane of the host cell.

Question 8

how does virus propagate

Answer 8

The virus enters via sent into cytoplasm in a vacuole via the cell membrane
protein capsule left on cell’s surface
Viral nucleic acid is then released to take over the genetic machinery of the host cell
Viral DNA becomes incorporated into the DNA of the host, assuming command of genetic control.
The host synthesises viral proteins rather than its own so that new virus particles
are generated and eventually released, completing the life cycle.

Question 9

examples of viral infection in human body other than COVID

Answer 9

meningitis
pharyngitis
Hepatitis
Smallpox

Question 10

6 stages of viral propagation

Answer 10

1. attachment - interaction of virion w/ specific receptor site on host cell’s surface
2. penetration - viral particle enters cell via endocytosis look like endosomes
3. uncoating - viral nucleic acid is removed from capsid
4. eclipse/replication - viral particles are now small non-infective subunits in host cell
5. assembly - new viral genomes is formed
6. release - non enveloped viruses cause cell of host to burst and leave the host cell

Question 11

describe process of endocytosis when host cell uptakes virus

Answer 11

virus meets plasma membrane of host cell
binds to receptors and plasma membrane surrounds virus
endosomal vesicle surrounds virus as it moves in to cytoplasm
vesicle is released from vesicle but virus leaves behind capsid

Question 12

DNA viruses

Answer 12

DNA viruses - enter host cell’s nucleus and are replicated and transcribed in nucleus except retroviruses

Question 13

RNA viruses

Answer 13

replicated and transcribed in cytoplasm except retroviruses

Question 14

RNA Virus replication

Answer 14

viral nucleic acid alters genetic expression of host and instructs it to synthesize the building blocks for new viruses

Question 15

RNA virus protein synthesis

Answer 15

RNA virus used for synthesis of viral proteins (translation0

Question 16

polarity of RNA virus

Answer 16

whether or not it can be used directly by ribosomes to make proteins

Question 17

what does polarity of RNA virus determine

Answer 17

determines the

replicative mechanism;

Question 18

what other factor determines polarity of RNA virus

Answer 18

the other major criterion is whether the genetic material is single-stranded or double-stranded.

Question 19

what enzymes do RNA viruses use to create copies of their genomes

Answer 19

their own RNA replicase

Question 20

How does rubella virus propagate into host cell

Answer 20

virus binds to specific receptors of host cells plasma membrane
membrane surrounds virus
virus enters cytoplasm of host cell
viral nucleic acid is released from capsid and enters nucleus of host cell and replicates
it is then transcribed into mRNA
Viral mRNA directs ribosomes to synthesise viral proteins
vesicles transport glycoproteins to host cell membrane
virus is fully assembled and released

Question 21

describe shape of rubella virus

Answer 21

icosahedral shaped vorus

Question 22

symptoms of rubella measles

Answer 22

red rash and fever and cause heart failure

Question 23

effects of viral propagation on their host

Answer 23

benign or malignant growths

asymptomatic

Question 24

lytic infection

Answer 24

enzymes produced which erode the cell wall
(bacteria)/ cell membrane and cause the cell to
rupture;

Question 25

lysogenic infection

Answer 25

here viral DNA/RNA becomes incorporated into the genome of the cell and coexists with the cell;

Question 26

treatment of virus infection

Answer 26

viral chemotherapy
acyclovir - cold sore creams on Herpes virus
Interferon - used to treat AIDS

Question 27

what viruses can cause human cancers

Answer 27

Papilloma wart virus and cervical cancer (Barton, 1994)

Epstein-Barr virus - Burkitt’s lymphoma

Question 28

human papillomavirus

Answer 28

DNA virus

causes warts and non-malignant tumours

Question 29

examples of subviral particles

Answer 29

viroids

prions

Question 30

definition of subviral particles

Answer 30

Infectious agents smaller by an order of magnitude than viruses have been identified in recent years

Question 31

describe viroids

Answer 31

Short single strands of RNA;
• Circular structures of 250-400 nucleotides
• Don’t code for any proteins;
• No protective coat (unlike viruses)
• Copied by the host RNA polymerase;
• Infect plant cells.

Question 32

what are prions short for

Answer 32

‘Proteinaceous infectious particle’

Question 33

what year were prions discovered

Answer 33

1982

Question 34

describe prions

Answer 34

Even smaller than a viroid and consisting of just a protein of 208 Amino Acids;
• Only infectious agent without nucleic acid;
• Induces normal PrP proteins to misfold thus forming
another prion

Question 35

what disease are prions involved in humans

Answer 35

spongioform encephalopathies
long incubation periods
usually fatal outcomes

Question 36

another example of prions in humans

Answer 36

kuru - transmitted by eating corpses

consumption of infected human brain tissue

Question 37

where is kuru found

Answer 37

new guinea

Question 38

what organs does kuru affect

Answer 38

nerves and brain