Structural and Chemical Composition of Viruses - Ghosh

Question 1

What is the smallest virus?

Answer 1

Porcine circovirus type 1

Question 2

What is the largest virus?

Answer 2

Poxvirus in animals, humans and birds

200nm diameter
300 nm length

Question 3

What shape is the rabies virus?

Answer 3

Bullet-shaped

Question 4

What shape is ebola virus?

Answer 4

Filament shaped

Question 5

What shape is the tobacco mosaic virus?

Answer 5

Rod shaped

Question 6

What shape is pox virus?

Answer 6

Brick shaped

** largest virus

Question 7

What shape is rota virus?

Answer 7

Spherical

Question 8

What shape is a bacteriophage?

Answer 8

Tadpole- shaped

Question 9

___________ is the ability of some viruses to alter their shape or size

Answer 9

Pleomorphism

Question 10

What common methods are used to visualize and determine morphology of a virus?

Answer 10

1. Electron microscopy
2. Cryo-Electron microscopy
3. X-ray Crystallographic method
4. Nuclear Magnetic Resonance (NMR)

Question 11

What is a capsid?

Answer 11

protein shell of a virus that encases the viral nucleic acid or genome

made of capsomeres

*** most viruses have 1 capsid EXECPT Reoviruses which have a double capsid

Question 12

________ is the basic subunit protein in the capsid of a virus

Answer 12

Capsomere

Question 13

What makes up a nucleocapsid?

Answer 13

Capsid + nucleic acid (RNA or DNA)/genome

Question 14

Which virus has a double layered capsid?

Answer 14

Reoviruses

Question 15

What is the formula to calculate the triangulation number?

Answer 15

T = h2 + h×k + k2

Question 16

In all animal viruses, the helical nucleocapsid is enclosed within a __________

Answer 16

Lipoprotein envelope

Question 17

Naked helical nucleocapsids are common among _________-

Answer 17

Plant viruses

Ex: tobacco mosaic virus

Question 18

What does the T number describe?

Answer 18

The relation between the # of pentagons and hexagons of the icosahedron

Question 19

Describe the capsid symmetry and virus architecture of parvovirus

Answer 19

T=1

** simplest icosahedron

Question 20

Describe the capsid symmetry and virus architecture of reoviridae

Answer 20

Outer capsid has a T=13 icosahedral symmetry

Inner capsid has a T=2 icosahedral symmetry

Question 21

Give an example of a virus with a complex capsid symmetry and virus architecture

Answer 21

Poxvirus

** also bacteriophage but its not a virus

Question 22

What is the function of the viral capsid?

Answer 22

1. Structural symmetry of virus particle
2. Encases + protects viral nucleic acid from enzymes, chemicals, pH, temp
3. Receptor attachment proteins on capsid helps attach virus to host cells
4. Determines antigenicity of virus

Question 23

What is the envelope made of?

Answer 23

Lipid bilayer with embedded proteins

Question 24

How is the viral envelope acquired?

Answer 24

By budding of nucleocapsid through cytoplasmic membrane, golgi membrane, or nucleus membrane

Question 25

What viral proteins are found in the envelope?

Answer 25

1. Glycoproteins (External glycoprotein and channel protein) 2. Matrix protein

Question 26

Describe the external glycoprotein found in the viral envelope

Answer 26

- Major antigens of the virus involved in 1. Hemagglutination 2. receptor binding 3. antigenicity 4. membrane fusion

Question 27

Describe channel proteins found in the viral envelope

Answer 27

** mostly hydrophobic proteins that form a channel through the envelope - alters permeability of membrane -modifies internal enviro of the virus

Question 28

Describe the matrix protein found in the viral envelope

Answer 28

*** IMPT for budding - Links internal nucleocapsid to lipid membrane envelope - Plays a role in viral assembly -Stabilizes lipid envelope

Question 29

Which survives longer: a non-enveloped virus or an enveloped virus?

Answer 29

Non enveloped virus survives longer. Enveloped viruses are easy to sterilize + dont survive long

Question 30

Which solvents can inactivate an enveloped virus?

Answer 30

1. Ether 2. Chloroform 3. Sodium deoxycholate, detergents, etc

Question 31

True or false: The viral matrix protein is located between the viral nucleic acid (DNA/RNA) and the capsid

Answer 31

FALSE. Matrix is between envelope and capsid

Question 32

What causes antigenic drift in viruses?

Answer 32

Mutations

Question 33

What causes antigenic shift in viruses?

Answer 33

Recombination or reassortment

Question 34

What is recombination?

Answer 34

Involves exchange of nucleotide sequences between different but closely related viruses during replication ** occurs in a single gene segment Ex: You have a blue shirt and a red shirt and combine them to make 1 red and blue striped shirt *** = antigenic shift

Question 35

What is reassortment?

Answer 35

MOST IMPT mechanism for genetic diversity of viruses with SEGMENTED GENOME *** = antigenic shift ** only in viruses with segmented genome/ more than 1 gene segment

Question 36

What are important viral enzymes that are critical to infection?

Answer 36

1. Lysins 2. Retroviral integrase 3. Reverse transcriptase 4. Nucleic acid polymerases

Question 37

What are lysins?

Answer 37

Hydrolytic enzymes produced by bacteriophages to cleave host cell wall

Question 38

What are retroviral integrases?

Answer 38

Enzymes made by REOVIRUSES (Ex: HIV) that allows genetic material to be integrated into the DNA of the infected cell

Question 39

What is reverse transcriptase?

Answer 39

Enzyme used to generate complementary DNA (cDNA) from RNA template

Question 40

What are nucleic acid polymerases?

Answer 40

IMPT for viral replication

Question 41

What is the function of viral nonstructural proteins?

Answer 41

Plays a role within infected cells during virus REPLICATION Acts in regulation of virus replication or virus assembly

Question 42

Non structural proteins are seen in extracellular virions

Answer 42

FALSE

Question 43

What is an incomplete virion?

Answer 43

Lacks nucleic acid , empty capsid ** like a hollow egg shell with no egg inside ** Only contains capsid! no nucleic acid

Question 44

What is a defective virion?

Answer 44

Virus that cant replicate bc it lacks a full copy of viral genes Results from mutations or errors in assembly of virions

Question 45

What is a pseudovirion?

Answer 45

Contains non viral genome within the viral capsid Ex: host nucleic acid instead of viral nucleic acid

Question 46

Define a pseudotype

Answer 46

When related viruses infect the same cell, the genome of 1 virus may be enclosed in the heterologous capsid of the 2nd virus