Lecture 3D - Viruses

Question 1

What is the genetic structure of viruses?

Answer 1

they are acellular

they contain DNA and RNA

Question 2

How do viruses reproduce?

Answer 2

inside cells and rely upon the host cell machinery to survive and reproduce

Question 3

What are prions?

Answer 3

a novel form of infectious proteins which have no DNA at all

Question 4

Why can prions (and maybe viruses) not be considered as independent living organisms?

Answer 4

they do not possess the machinery to reproduce themselves, but require intracellular enzymes, metabolic pathways and organelles in order to reproduce

Question 5

What are viruses?

Answer 5

non living obligate intracellular parasites that need a host cell in order to replicate

Question 6

How do viruses contain genetic info?

Answer 6

they possess their own genetic info in the form of RNA or DNA

Question 7

What form do viruses also have?

Answer 7

an extracellular form

Question 8

What can viruses infect?

Answer 8

all types of cellular organisms including plants and animals

Question 9

What are some strains of virus associated with?

Answer 9

increased risk of cancer

Question 10

What happens if viruses have genetic information in the form of RNA?

Answer 10

usually it will have to be reverse transcribed back to DNA in order for the virus to replicate

Question 11

What are the aims of infectious virus particles?

Answer 11

to be able to invade a host cell to replicate and to be able to transmit from one host organism to another

Question 12

What are successful viruses?

Answer 12

they tend to not kill their host, as it does not help the survival of the viral strain

Question 13

How are polio and hepatitis A transmitted?

Answer 13

faecal-oral route

Question 14

How is rabies transmitted?

Answer 14

bite of an infected animal e.g. rabid dog or bat

Question 15

How is human papilloma virus (warts) transmitted?

Answer 15

skin contact

Question 16

How is herpes 1&2, HPV, hepatitis B and HIV transmitted?

Answer 16

sexual transmission

Question 17

How is ebola transmitted?

Answer 17

all body fluids and tissues

Question 18

How is influenza, colds, measles, mumps, rubella transmitted?

Answer 18

respiratory

Question 19

How is yellow fever, dengue fever, chikungunya virus transmitted?

Answer 19

insect vectors

Question 20

What is COVID-19?

Answer 20

a coronavirus which can cause severe acute respiratory syndrome

Question 21

Extracellular form viral structure?

Answer 21

diverse sizes, shapes and chemical composition

nucleic acid surrounded by protein coat (capsid)+/-lipid envelope

mainly rod shapes with a helical nucleic acid or icosahedral with spherical nucleic acid

Question 22

What do viruses have surrounding their icosahedral shape?

Answer 22

filamentous fibres

Question 23

What do viruses have at their core?

Answer 23

their genetic material, either DNA or RNA

and often some enzymes needed for cell entry during infectin and replication

Question 24

What are viruses with RNA?

Answer 24

retroviruses, the RNA needs to be reverse transcribed in order for the virus to replicate

Question 25

What is the lipoprotein bilayer on a virus?

Answer 25

envelope (some viruses) derived from the host

Question 26

What viruses have lipoprotein bilayer?

Answer 26

``` DNA = hepatitis B RNA = rabies, rubella ```

Question 27

What is the protein shell?

Answer 27

the capsid - nearly all viruses have this this encapsulates their genomic material

Question 28

Naked viruses?

Answer 28

``` DNA = papilloma RNA = hepatitis E ```

Question 29

What do the glycoprotein spikes do?

Answer 29

they bind to the target protein in the host and trigger the sequence of events which enables the virus to enter the cell

Question 30

Size of the largest viruses?

Answer 30

300-400nm across with a 100nm layer of filamentous fibres surrounding their icosahedral shape

Question 31

Size of COVID-19 virus?

Answer 31

50-150nm in diameter without the spikes

Question 32

DNA virus replication?

Answer 32

when the DNA is inserted into the host cell, it uses the host cells RNA polymerase to make mRNA, which is the translated by the ribosomes of the host cell

Question 33

RNA virus replication?

Answer 33

have several ways to replicate some carry their own RNA polymerase to produce mRNA some have to carry out an additional step so that the negative or antisense) RNA is converted to positive (sense) RNA, from which mRNA is made

Question 34

What do retroviruses have to do?

Answer 34

reverse transcribe their RNA into DNA which is then inserted into the host cell genome

Question 35

How does a virus with a lipid envelope leave the cell after replication?

Answer 35

it wraps itself in the membrane and buds off from the cell, to then travel onto the next target cell

Question 36

How does a virus without a lipid envelope leave the cell?

Answer 36

it escapes by rupturing the cell membrane (cytosis) as it is released, killing the host cell it is therefore cytopathic

Question 37

What are prion protein diseases?

Answer 37

rare, fatal neurodegenerative diseases belonging to amyloid group

Question 38

What do prion protein diseases affect?

Answer 38

Humans (Creutzfeld jacob disease) and agricultural, zoo and wild animals

Question 39

Examples of prion protein diseases?

Answer 39

scrapie in sheep bovine spongiform encephalopathy in cows chronic wasting disease in elk and deer

Question 40

Aetiology of prion protein diseases?

Answer 40

genetic, sporadic and infectious

Question 41

Incubation period of prion protein diseases?

Answer 41

they can have lengthy incubation periods >40 years!

Question 42

Clinical characteristics of prion protein diseases?

Answer 42

dementia and ataxia neuronal loss, gliosis and spongiform change in the brain

Question 43

Immune response to prion protein diseases?

Answer 43

no classical host immune response

Question 44

Treatment of prion protein diseases?

Answer 44

currently no treatments available for the disease, has to be managed by trying to eliminate the spread

Question 45

What is a marker of astrocytic gliosis?

Answer 45

glial fibrillary acidic protein

Question 46

What is detected by antibodies?

Answer 46

the prion protein

Question 47

What is one of the characteristic of prion diseases?

Answer 47

the accumulation of aggregates of abnormally folded prion protein (PrP)

Question 48

Structure of the normal prion protein PrPC?

Answer 48

3% beta sheet monomeric and soluble protease sensitive (PrPsen) neuroprotective

Question 49

Structure of infectious form of the prion protein (PrPSc)?

Answer 49

disease associated form 43% beta sheet aggregated and insoluble partially protease resistant (PrPres) infectious, toxic

Question 50

What is the infectious agent of prion disease not associated with?

Answer 50

any nucleic acids there is no detectable viral agent in the infectious particle

Question 51

Why is PrPC easy to break down?

Answer 51

it has a relatively open structure

Question 52

What happens when the aggregates of PrPSc are formed?

Answer 52

they are hard to break down and can induce normally folded prion protein to misfold, propagating the number of infectious particles

Question 53

Prion hypothesis?

Answer 53

prions are transmissable particles that are devoid of nucleic acid and seem to be composed entirely of a modified protein (PrPSc)

Question 54

How is PrPC converted to PrPSc?

Answer 54

through post translation process during which is acquires a high beta sheet content

Question 55

What do prions appear to encipher?

Answer 55

strain-specific properties in the tertiary structure of PrPSc

Question 56

How is PrPSc broken down?

Answer 56

it is protease resistant and can only be broken down at a very slow rate by the cell

Question 57

What does the misfolding of PrPC require?

Answer 57

the assistance of an additional unknown chaperone protein called protein X (stanley prusiner 1998)

Question 58

What does prion mean?

Answer 58

a protein only infectious agent