Virus Structure and Function (Lecture 2)

Fill-in-the-blank flashcards covering key concepts from Lecture 2 on virus structure, capsid symmetry, genome packaging, envelopes, glycoproteins, staining techniques, and budding.

The primary function of the viral capsid is to __.

protect the genome

The fragile viral genome is composed of __ acids.

nucleic

The required balance of stability and flexibility in a capsid is called a __ structure.

metastable

The two common capsid symmetries are and .

helical; icosahedral

In negative staining, the __ is coloured, making the virion appear light on a dark background.

background

Positive staining makes viral structures appear __ on a light background.

dark

Crystallising virions and using __ yields very high-resolution structural data.

X-ray crystallography

An icosahedral capsid needs at least __ protein subunits to form a closed shell.

60

Helical symmetry is described by the equation __, where m = subunits/turn and r = axial rise.

P = m × r

A triangulation number of T = 4 requires __ subunits to build the capsid.

240

Each capsomere of tobacco mosaic virus binds __ nucleotides of RNA.

3

(−)-strand RNA viruses must package __ because their genomes cannot serve directly as mRNA.

RNA-dependent RNA polymerase (RDRP)

Rabies virus N protein attaches the nucleocapsid to the envelope through interaction with the __ protein.

matrix (M)

Viral envelopes are derived from __ membranes and contain many glycoproteins.

host

Envelope glycoproteins share three regions: __, __, and __ domains.

exterior; transmembrane; tegument (cytoplasmic)

Influenza haemagglutinin (HA) functions as a __ held together by disulfide bonds.

trimer

Sugars are added to viral glycoproteins as they pass through the __ apparatus.

Golgi

Myristylation and farnesylation attach __ groups to anchor proteins in membranes.

hydrophobic

For a T = 1 icosahedron, each triangular face contains __ identical capsomeres.

three

The lipid bilayer of the viral envelope is not permeable to __ compounds.

hydrophilic

Because helical capsids are open, increasing genome size can extend the __ of the virion.

length

Viral genomes maximise coding capacity by overlapping __ and using both strands for coding.

open reading frames (ORFs)

The electron-dense compound commonly used for negative staining is __.

uranyl acetate

The pitch of the TMV helix is __ nm.

2.3

Influenza virus budding is driven by interactions between nucleocapsid and the cytosolic tails of and proteins.

HA; NA

Integral membrane proteins usually span the membrane with a __ α-helix.

hydrophobic

Heavy metal such as __ is often adsorbed to virions to improve X-ray diffraction.

osmium tetroxide

Helical viruses face a smaller size constraint because they can form very __ filaments.

long

SV40 capsid proteins __ bind nucleosomes to aid further genome condensation during assembly.

VP2 and VP3