Virus characteristics & structure

Question 1

Composition of virus

Answer 1

• genetic material
  
  • either RNA or DNA; never both
• Genetic surrounded by protein coat (capsid)
• Sometimes, there can be outer membrane or envelope

Question 2

primary objective of viruses

Answer 2

multiply & produce more progeny under selection pressure

Question 3

Nature of viruses

Answer 3

considered passive agents; have no intention to kill their host
Alive inside cells because they can reproduce, producing more progeny but they may not be alive outside the host cell

Question 4

describe the lack of organelles in viruses

Answer 4

• viruses do not have cellular organelles
• Specifically ribosomes
• Ribosomes are crucial for synthesising the necessary proteins in cells

Question 5

Describe viruses’ inability to synthesise proteins

Answer 5

• Lack ribosomes
• Virus cannot encode or synthesise their own proteins
• Must use host cell’s ribosomes to produce their necessary proteins

Question 6

Describe viruses’ reliance on host machinery

Answer 6

Virus need to hijack the host cellular synthesis machinery & force the host cell to produce their necessary protein as well as genomic material & other important things

Question 7

describe viruses’s inability to synthesise lipid

Answer 7

• virus do not encode the information for lipid synthesis in their genome
• They get envelope from host cell membrane or organelles

Question 8

What is a virus?

Answer 8

• described as infectious, obligate parasite
  
  • They must get inside the host cell for replication

Question 9

Is the virus a particle?

Answer 9

Invention of electron microscope, people able to visualise virus and confirmed its existence as a particle

Question 10

Dependency of living stems from several key limitations:

Answer 10

• lack of cellular organelles
• Inability to synthesise proteins
• reliance on host machinery
• no lipid synthesis

Question 11

How do viruses differ from other micro-organisms?

Answer 11

Replication method:
Cellular structure
Obligatory intracellular
Genomic integration

Question 12

How do viruses differ from other micro-organisms in replication method

Answer 12

• Virus does not multiply by binary fission
• Unlike bacteria & other organisms where one divides into 2 & then 4 …
• Multiplication strategy is distinct

Question 13

How do viruses differ from other micro-organisms in cellular structure

Answer 13

• virus do not have functional ribosomes or other cellular organelles
• Other microorganisms typically possess these structures

Question 14

How do viruses differ from other micro-organisms in obligatory intracellular property

Answer 14

completely reliant on living host cell for replication & protein synthesis

Question 15

How do viruses differ from other micro-organisms in size

Answer 15

• extremely small
• Requiring an electron microscope for visualisation
• Many can pass through filters that would trap bacteria
• e.g. 500 million rhinovirus could fit on the head of a pin
• not all are small, some like Pandora viruses can be bigger

Question 16

How do viruses differ from other micro-organisms in terms of genomic integration

Answer 16

• some viruses (i.e. retrovirus) can get into the host & integrate into the host genome
• approx 8.3% of the human genome consists of remnants or skeletons of retroviruses which is more than the functional gene contact ( 1.5% of the whole genome)

Question 17

Genome size of virus

Answer 17

• varies significantly from approx 2000 to 300k base pairs
• Most RNA viruses are typically 2000 to 20000bp

Question 18

Structure of genome of virus

Answer 18

• linear, circular, double-stranded, single stranded, segmented, non-segmented or gaped
• Flu virus has segmented genome with 8 segments
• Most cases, genomes are non-segmented

Question 19

virus genome function

Answer 19

• carries all necessary information for protein synthesis, replication, assembly & packaging of genome as well as timing of the processes
• does not contain information for lipid synthesis

Question 20

Virulence of viruses

Answer 20

• smaller genome viruses are often more infectious & cause most diseases
  
  • Particularly smaller sized RNA virus
• RNA virus often lack proofreading systems
  
  • High mutation rates which can cause population collapse or genetic bottleneck

Question 21

Functions of virus capsid

Answer 21

1. Protect genome
2. Assisting in attachment & entry into host cells
3. Facilitating the assembly & packaging of new viral particles
4. deliver the genome to the specific replication site within the host cell, navigating host defence mechanisms and unfavourable intracellular environments

Question 22

Property of capsid: metastable & non-covalently joined Allows what to occur

Answer 22

Allow them to open up & release the genome when they reach the replication site & receive favourable signal

Question 23

What is capsid made of

Answer 23

• Formed from protein subunits that combine to create structural units
  
  • Assemble to form the capsid

Question 24

What forms the nucleocapsid of virus

Answer 24

capsid & genome form the nucleocapsid or the core of the virus

Question 25

Capsid protects what

Answer 25

genomic material

Question 26

Envelope of viruses

Answer 26

present only in enveloped viruses

Question 27

What is an envelope in viruses

Answer 27

Lipid layer that surrounds the capsid in some viruses

Question 28

Where is the envelope derived from

Answer 28

host cell membrane or cellular organelles because viruses cannot synthesise lipids

Question 29

envelope function

Answer 29

protect capsid

Question 30

What does virus envelop contain

Answer 30

receptor proteins (glycoproteins or spike proteins ) embedded within it

Question 31

What does receptor proteins of virus envelop help with

Answer 31

Help the virus bind to host cells & are often the antigenic part of the virus that the host immune system recognises & produced antibodies against

Question 32

What are enveloped viruses susceptible to

Answer 32

detergents like soap because the lipoprotein envelope can be destroyed which also destroys the receptor, rendering the virus non-infectious

Question 33

Role of receptor proteins

Answer 33

crucial for attachment to host cells

Question 34

Where are receptor proteins located into enveloped viruses

Answer 34

typically found on the outside of the membrane

Question 35

Where are receptor proteins located into non enveloped viruses

Answer 35

they are located on the outer surface of the capsid

Question 36

properties of receptor proteins

Answer 36

- Primary antigenic parts of the virus that trigger an immune response from the host - Considered structural proteins

Question 37

What are non structural proteins

Answer 37

mainly different enzymes

Question 38

Roel of non structural proteins

Answer 38

enzymes vital for processes like replication & for interfering with the host immune system so that the virus can hijack cellular machinery effectively

Question 39

What are shapes of viruses

Answer 39

helical Icosahedral Complex

Question 40

E.g. of helical virus

Answer 40

tobacco mosaic virus

Question 41

e.g. of icosahedral virus

Answer 41

retrovirus, adenovirus

Question 42

Describe icosahedral virus

Answer 42

Specific number of proteins & structural units arranged in a precise fashion

Question 43

Describe complex virus

Answer 43

Viruses that do not have any specific helical or icosahedral shape

Question 44

e.g. complex virus

Answer 44

poxvirus, bacteriophage, pandora virus

Question 45

Species naming conventions often originate from:

Answer 45

Geographical location Significant clinical signs or disease Initial/acronyms

Question 46

What is the Baltimore scheme

Answer 46

categorised into 7 different Baltimore groups based on their genome structure & how their genome is converted into mRNA inside the host cell