Viruses

Question 1

What are viruses?

Answer 1

Acellular microorganisms that cannot survive without a host : no metabolic abilities of their own
Rely completely on bio synthetic machinery of infected cell to multiply

Question 2

What is the composition of a virus?

Answer 2

Genetic material : made from either DNA or RNA
Capsid : a protein coat that surrounds and protects the genetic material
Envelope of lipids : surround the protein coat when they’re outside a cell

Question 3

What is a viral capsid?

Answer 3

Capsids are made of multiple units of the same protein building block known as capsomers

Question 4

What are capsomers?

Answer 4

Subunit of the capsid arranged in a precise and highly receptive pattern around the nuclei acid

Question 5

What are the three types of symmetry capsomers can be arranged in?

Answer 5

Helical e.g. TMV = rod shaped
Icosahedral e.g. Adenovirus = 3D shape
Complex e.g. Bacteriophage = head is icosahedral and tail is helical

Question 6

What is the viral genome made up of?

Answer 6

Made up of nucleic acid (DNA and RNA)
Could be linear, circular or segmented
Size can vary from 4,000 to > 1 million nucleotides
All four possible forms of RNA and DNA are found in viruses

Question 7

Eukaryotic Virus Diversity process

Answer 7

Nucleic acid -> capsid symmetry -> naked envelope -> genome architecture
Nucleic acid : DNA or RNA?
Capsid symmetry: icosahedral, helical or complex? - (only DNA)
Envelope : naked or enveloped?
Genome architecture : segmented or nonsegmented
+mRNA already been transcribed
-mRNA hasn’t been transcribed

Question 8

Positive RNA vs Negative RNA

Answer 8

Positive : mRNA already transcribed
Negative : mRNA needs to be transcribed

Question 9

What do viruses infect?

Answer 9

Viruses infect all cell types and all forms of life
An organism a virus infects is called a “host organism”
A cell a virus multiplies in is called a “Host cell”

Question 10

What are bacteriophages?

Answer 10

Viruses that infect and replicate in bacteria
Used to treat bacteria as it ‘eats’ bacteria

Question 11

Cycle of bacteriophage infection

Answer 11

1. Attach - must attach before attacking
2. Penetrate
3. Uncoat - inserts DNA into cell
4. Genome replication and gene expression
5. Assembly - proteins assembled into varients
6. Release
   APUGAR

Question 12

What is SARS-CoV-2

Answer 12

Enveloped, +ssRNA, linear, non-segmented
Includes RNA polymerase to copy the genome
Limited proof-reading so makes some errors developing variants which allows for tracking and leads to new strains

Question 13

What is the spike in the genome process?

Answer 13

Critical for attachment and cell entry
A major target for neutralising immunity
Viruses must bind to a receptor protein to infect a cell
Vaccines target the spike (can cover receptor so viruses can’t bind)

Question 14

SARS-CoV-2 Replication Cycle

Answer 14

1. Spike binds to ACE2 receptor
2. Cell entry
3. Fusion
4. Genome translation, viral RNA synthesis, viral mRNAs and genome
5. Assembly
6. Exocytosis
   SCFGAE

Question 15

Replication of an RNA Enveloped Virus (HIV)

Answer 15

HIV fuses with host cell membrane, effects T cell CD4
Reverse transcriptase occurs
Viral integrate chops up our DNA and inserts HIV into genome
Vesicles transport the glycoproteins into the plasma membrane
New viruses with viral envelope glycoproteins bud from host cell