structure morphology_of_viruses

basic structure of virus, morphology, types,

1. WHAT IS A VIRUS 1

2. VIRUS INTRODUCTION BASIC STRUCTURE SYMMETRY Icosahedral Helical Binal Complex 2

3. INTRODUCTION TO VIRUSES Latin:   vīrus =   poison, term coined by Martinus Beijerinck U ltramicroscopic Acellular Intracellular obligate parasite Lack lipmann system (enzyme system) Specific to host Viruses are active inside host and inactive outside the host 3

4. INTRODUCTION TO VIRUSES Viruses either has DNA or RNA, not both (exception) Depending upon host interaction viruses are of 3 types: Animal viruses Plant viruses Bacterial viruses Viruses are nucleo-proteins Viruses are uniform in size and shape V iruses are sensitive to interferon Viruses ranges from 20 to 14,000 nm in length, 20-300 nm in diameter. 4

5. BASIC STRUCTURE OF VIRUSES Basic rules of virus architecture, structure, and assembly are the same for all families Some structures are much more complex than others, and require complex assembly and dissassembly The capsid (coat) protein is the basic unit of structure; functions that may be fulfilled by the capsid protein are to: Protect viral nucleic acid Interact specifically with the viral nucleic acid for packaging Interact with vector for specific transmission Interact with host receptors for entry to cell Allow for release of nucleic acid upon entry into new cell Assist in processes of viral and/or host gene regulation 5

6. BASIC STRUCTURE OF VIRUSES Virions are complete, fully developed viral particles composed of nucleic acid surrounded by a protein coat . Some viruses have an envelope composed of a phospholipid bilayer with viral glycoproteins (spikes). 6

7. BASIC STRUCTURE OF VIRUSES   1. Nucleic acid or Genome Viral genomes are either DNA or RNA (not both). Nucleic acid may be single- or double-stranded Nucleic acid may be circular or linear or separate molecules. Nucleic acid : protein ranges from about 1% - 50 %. 7

8. BASIC STRUCTURE OF VIRUSES 2. Capsid Capsid - protein coat Capsomeres are subunits of the capsid Protomeres are capsomere subunits 8

9. BASIC STRUCTURE OF VIRUSES 3.  Envelope The outer covering of some viruses, the envelope is derived from the host cell plasma membrane when the virus comes out. Some enveloped viruses have spikes . Influenza virus has two kinds of spikes, H ( Hemagglutinin ) and N (Neuraminidase): The H spike allows the virus to attach to host. T he N spike allows the mature viral particles to escape from the host cell. Non-enveloped or naked viruses are protected by their capsid alone . 9

10. 10

11. VIRUS SYMMETRY 1) Icosahedral or Polyhedral (nature’s favourite shape) In this nuclic acid is compact and folded. There are two types of capsid : a) Enveloped Eg . Herpes Virus b) Non-Enveloped Eg . Polio Virus, 11

12. VIRUS SYMMETRY 2) Helical or Spiral Virus contain genome enclosed in Helical capsid . About 12 to 812 Capsomeres are arranged on the surface of Nuclic acid. Eg . TMV 12

13. VIRUS SYMMETRY 3) Binal Symmetry (known as Best structure) Combination of Icosahedral and Helical. Head and tail are joined by collar . Tail is hollow tube, base plate contain tail fibers. Eg . Bacteriophage 13

14. VIRUS SYMMETRY 4) Complex Symmetry Viruses with asymmetrical structures are referred to as " complex" These viruses possess a  capsid  that is neither purely helical nor purely  icosahedral , and may possess extra structures such as  protein  tails or a complex outer walls . Eg . Pox virus family 14

15. VIRUS SYMMETRY 15