Page 92 - MNU microbiology theoritical 2025

General Microbiology & Immunology (PM 401) Second level Semester 4 2024/2025

Structure of viruses

Three parts

• Capsid (protein coat)

• Nucleic acid core

• Envelope

1- Capsid (protein

coat)
• The viral genomes are externally coated by a shell of proteins called capsid.

• Capsid is a polymeric structure made of structural subunits called capsomers.

• Capsid together with enclosed nucleic acid is termed as nucleocapsid.

• The number and arrangement of the capsomers are useful in identification and

classification of viruses

Functions:

1- Capsid protects the viral genome from any

physical or chemical stresses

2- Capsid contains attachment sites to adhere

to the host cell and helps to penetrate the host

cell.

3- Give the virus its geometrical symmetry:

General Microbiology & Immunology (PM 401) theoretical handbook Page 81