A capsid is the protein shell of a virus. It consists of several oligomeric structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or may not correspond to individual proteins, are called capsomeres. The capsid encloses the genetic material of the virus.

Capsids are broadly classified according to their structure. The majority of viruses have capsids with either helical or icosahedral structure. Some viruses, such as bacteriophages, have developed more complicated structures due to constraints of elasticity and electrostatics. The icosahedral shape, which has 20 equilateral triangular faces, approximates a sphere, while the helical shape is cylindrical. The capsid faces may consist of one or more proteins. For example, the foot-and-mouth disease virus capsid has faces consisting of three proteins named VP1–3.

Some viruses are enveloped, meaning that the capsid is coated with a lipid membrane known as the viral envelope. The envelope is acquired by the capsid from an intracellular membrane in the virus' host; some examples would include the inner nuclear membrane, the golgi membrane, and the cell's outer membrane.

Once the virus has infected the cell, it will start replicating itself, using the mechanisms of the infected host cell. During this process, new capsid subunits are synthesized according to the genetic material of the virus, using the protein biosynthesis mechanism of the cell. During the assembly process, a portal subunit is assembled at one vertex of the capsid. Through this portal, viral DNA or RNA is transported into the capsid.

Structural analyses of major capsid protein (MCP) architectures have been used to categorise viruses into families. For example, the bacteriophage PRD1, Paramecium bursaria Chlorella algal virus, and mammalian adenovirus have been placed in the same family.

Read more about Capsid:  Triangulation Number

Other articles related to "capsid, capsids":

Corticovirus - Virology
... The virons consist of a round, icosahedral, non-enveloped capsid of a diameter of 60 nm and an internal lipid membrane located between outer and inner protein shell ... The icosahedral capsid (T = 21) is 56 nanometers (nm) in diameter and is composed of 1200 P1 (spike) and 60 P2 (capsid) proteins ... The capsid encloses an internal lipid core containing the structural proteins P3 to P10 ...
Late Protein
... In Human papillomavirus, two late proteins are involved in capsid formation a major (L1) and a minor (L2) protein, in the approximate proportion 955% ... Intermolecular disulphide bonding holds the L1 capsid proteins together ... L1 capsid proteins can bind via its nuclear localisation signal (NLS) to karyopherins Kapbeta(2) and Kapbeta(3) and inhibit the Kapbeta(2) and Kapbeta(3) nuclear import pathways ...
Capsid - Triangulation Number
... Icosahedral virus capsids are typically assigned a triangulation number (T-number) to describe the relation between the number of pentagons and hexagons i.e ... their quasi-symmetry in the capsid shell ... Representation of Viral Capsid T-numbers up to (6,6) capsid parameters hexagon/pentagon system triangle system (h,k) T # hex Conway notation image geometric name # tri Conway notation image ...
... The capsomere is a basic subunit of the capsid, an outer covering of protein that protects the genetic material of a virus ... Capsomeres self-assemble to form the capsid ... aggregate to form capsomeres which in turn aggregate to form capsid ...
Alfalfa Mosaic Virus - Structure and Genome
... The virion has a capsid (coat protein) but no envelope ... The icosahedral symmetry of the capsid is round to elongated ... RNA 4 encodes the capsid ...