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Flashcards in Morphology of Viruses Deck (68)
1

Smallest Viruses

Porcine Circovirus type-1 (17nm)

Parvovirus (18nm)

2

Largest Viruses

Pandoravirus (400nm)

Poxvirus (200x300nm)

3

Pleomorphism

Ability of some viruses to alter their shape or size

4

Most viruses are _______ or __________ shaped.

Most viruses are rod or spherical shaped.

5

Common methods used to deterime the morphology of viruses:

Electron Microscopy (EM)

Cryo-Electron Microscopy (Cryo-EM)

X-Ray Crystallographic Method

Nuclear Magnetic Resonance (NMR)

6

_____________ method requires negative staining with electron dense material such as Uranyl Acetate or Phosphotungstate.

Electron Microscopy (EM) method requires negative staining with electron dense material such as Uranyl Acetate or Phosphotungstate.

7

Resolution range for electron microscopy

50-75 angstroms

8

________________ method allows the observation of biological specimens in thier native environment (not fixed or stained in any way)

Cryo-Electron Microscopy (Cryo-EM) method allows the observation of biological specimens in thier native environment (not fixed or stained in any way)

9

Resolution range for Cryo-Electron Microscopy

3.3 to 20 angstroms

10

Explain the X-Ray Crystallographic method process

1. Virus or viral protein is crystalized

2. X-ray 

3. Deflection mesasured to form electron density map

4. Protein model created

5. Reconstruction of virus structure

11

Capsid

Protein shell of a virus that encases/ envelopes the viral nucleic acid or genome

12

The capsid is made up of ______ held together by covalent bonds

The capsid is made up of capsomeres held together by covalent bonds

13

Viruses have one capsid, except for _____________ which have a double layered capsid

Viruses have one capsid, except for Reoviruses which have a double layered capsid

14

Capsomere

Basic subunit protein in the capsid of a virus

15

Nucleocapsid

Capsid + Virus Nucleic Acid/Genome

16

Common capsid symmetries

Helical Symmetry

Cubic/ Icosahedral Symmetry

Complex

17

Incomplete virions cannot form ____________ symmetry.

Incomplete virions cannot form helical symmetry.

18

Helical nucleocapsids of animals are enclosed by ____________

Helical nucleocapsids of animals are enclosed by lipoprotein envelope

19

Naked helical nucleocapsids are common among _______ viruses.

Naked helical nucleocapsids are common among plant viruses.

20

Icosahedral viruses always have ________ corners

Icosahedral viruses always have 12 corners

21

Two types of capsomers present in icosahedral capsid

Pentagonal Capsomers

Hexagonal Capsomers

22

Pentons make up the (vertices/facets)

Pentons make up the (vertices/facets)

23

Hexons make up the (vertices/facets)

Hexons make up the (vertices/facets)​

24

Triangulation Number (T-Number)

Describes the relation between the number of pentagons and hexagons of the icosahedron.

25

The (larger/smaller) the T-Number the more hexagons are present relative to the pentagons.

The (larger/smaller) the T-Number the more hexagons are present relative to the pentagons.

26

T- Number Equation 

T = H+ h * k + k2

27

________ has a T = 1, simplest icosahedron

Parvovirus has a T = 1, simplest icosahedron

28

Functions of viral capsid

1. Structural symmetry

2.  Encase and protect viral nucleic acid 

3. Facilitate attachment of the virus to specific receptors on the susceptible host cells

4. Interact with host cell membrane to form envelope

5. Uncoat genome

6. Transport viral genome

7. Recognize and package nucleic acid genome

29

Viral envelope

Lipid bilayer with embedded proteins, facilitates virus entry into host cells and may also help the virus to adapt fast and evade host immune system

30

Explain how a virus acquires its envelope

Acquired by budding of viral nucleocapsid through a cellular membrane

31

Two kinds of viral proteins found in the envelope

Glycoprotein

Matrix Protein

32

Glycoprotein

Anchored in the lipid bilayer by hydrophobic bonds, spikes seen on the virus surface

33

External Glycoprotein

Anchored in the envelope by a single transmembrane domain and a shorter internal tail

Antigens of the virus and involved in hemagglutination, receptor binding, antigenicity and membrane fusion

34

Channel Proteins

Hydrophobic proteins that form a protein lined channel through the envelope

Alter permeability of the membrane and important in modifying the internal envrionment of the virus

35

Fusion proteins

Channel proteins that facilitate attachment and entrance of viral contents to enter host cell

36

Two kinds of fusion proteins

pH Independent

pH Dependent 

37

HIV and Measles are examples of pH (independent/dependent) fusion proteins.

HIV and Measles are examples of pH (independent/dependent) fusion proteins.

38

HA of the influenza virus is an example of pH (independent/dependent) fusion proteins.

HA of the influenza virus is an example of pH (independent/dependent) fusion proteins.

39

Matrix Protein

Proteins that lnk the internal nucleocapsid to the lipid membrane envelope

Recognition site of nucleocapsid at the plasma membrane and mediates the encapsidation of the RNA nucleoprotein cores into the membrane

40

________ proteins play a crucial role in virus assembly

Matrix proteins play a crucial role in virus assembly

41

(Enveloped/Non-Enveloped) viruses are easy to sterilze and cannot survive for long periods in the environment

(Enveloped/Non-Enveloped) viruses are easy to sterilze and cannot survive for long periods in the environment

42

(+/-) Sense RNA viruses have infectious genomes

(+/-) Sense RNA viruses have infectious genomes

43

+ Sense RNA Genome

Similar to mRNA and thus can be immediately translated by the host cell

44

- Sense RNA Genome

Complementary to mRNA and thus must be converted to + sense before translation

45

RNA Polymerase

Converts - Sense RNA to +Sense RNA

46

Antigenic Drift

Changes in the virus that arise from point mutations, may cause change in antigenicity

47

Processes of Antigenic Shift

Recombination

Reassortment

48

Recombination

Exchange of nucleotide sequences between different, but usually closely related, viruses during replication

49

Reassortment

Exchange of segmented genomic segments

50

Most important mechanism for high genetic diversity in viruses with segmented genome is _____________

Most important mechanism for high genetic diversity in viruses with segmented genome is Reassortment

51

Viral _________ constitute up to 50-70% of the virion

Viral protein constitute up to 50-70% of the virion

52

Two classes of virion proteins

Modified Proteins

Unmodified proteins

53

(Modified/Unmodified) viral proteins are obtained by post-translational proteolytic cleavage of polyprotein.

(Modified/Unmodified) viral proteins are obtained by post-translational proteolytic cleavage of polyprotein.

54

Lysins

Hydrolytic enzymes produced by bacteriophages to cleave the host cell wall

55

Retroviral Integrase (IN)

Enzyme produced by a retrovirus that enables its genetic material to be integrated into the DNA of the infected cell

56

Reverse Transcriptase (RT)

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

57

Nucleic Acid Polymerase

Responsible for viral genome replication

58

Structural Viral Proteins

Proteins the form the viral capsid

59

Nonstructural Viral Proteins

Encoded by viral genome that are produced in the organisms they infect, but not packed into the virus particles

Play role within the infected cell during virus replication or act in regulation of virus replication or virus assembly

60

Regulatory Proteins

Broad category of proteins that play indirect roles in the biological processes and activities of viruses

Regulate the expression of viral genes or are involved in modifying host cell functions

61

Incomplete virions

Virion without nucleic acid

62

Effective Virions

Virus that cannot replicate because it lacks full complement/ copy of viral genes

63

Defective Viral Particles

Result from mutations or errors in the production or assembly of virions

64

Replications of defective virions occurs only in mixed infection with a ___________.

Replications of defective virions occurs only in mixed infection with a helper virus.

65

Helper Virus

Supplement the genetic deficiency and make defective viruses replicate progeny virions when they simultaneously infect host cell and defective viruses

66

Defective Interfering Particle (DIP)

Defective virus can not replicate, but can interfere other congeneric mature virion enter the cells

67

Pseudovirion

Contains non-viral genome within the viral capsid, look like ordinary viral particles but do not replicate

68

Pseudotypes

Related viruses infect the same cell, the genome of one virus may be enclosed in the heterologous capsid of the second