introduction to viruses, classification and structure.
- 1. Introduction to Viruses Viruses are small infectious agents that can only replicate inside the living cells of organisms. They can infect all types of life forms, from animals and plants to microorganisms like bacteria. Despite being simple in structure, viruses play a significant role in various diseases, including the common cold, flu, and COVID-19. Understanding their characteristics and behavior is crucial for developing effective treatments and preventive measures. ks by kanchan sharma
- 2. Classification of Bacterial Viruses 1 Bacteriophages Bacteriophages are viruses that infect and replicate within bacteria. They have complex structures with tail fibers that attach to the bacterial cell wall, injecting their genetic material for replication. 2 Plasmaviruses Plasmaviruses are viruses that are associated with plasmids, which are small, circular DNA molecules found in bacteria. They are known for their ability to replicate independently within the host cell. 3 Satellite Viruses Satellite viruses are dependent on other viruses for replication. They can either enclose their nucleic acid in a capsid protein provided by a helper virus or utilize the replication machinery of the helper virus for their own replication.
- 3. Structure of Bacterial Viruses Tail Fibers and Baseplate Bacteriophages possess tail fibers and a baseplate, which are essential for attachment to the bacterial cell wall and the injection of genetic material. Nucleic Acid and Capsid The genetic material of bacterial viruses is enclosed within a protein shell called a capsid, protecting the viral DNA or RNA during the infection and replication process.
- 4. Classification of Plant Viruses RNA Viruses Plant RNA viruses have RNA as their genetic material. They can cause various symptoms in infected plants, including mosaic patterns, stunting, and discoloration of leaves. DNA Viruses Plant DNA viruses contain DNA as their genetic material. They can lead to symptoms such as leaf curling, mottling, and abnormal growth in infected plants.
- 5. RNA Viruses RNA viruses are a type of virus that have ribonucleic acid (RNA) as their genetic material . They are classified into three distinct groups based on their genome and mode of replication . Animal RNA viruses are classified by the International Committee on Taxonomy of Viruses (ICTV) . The nucleic acid in RNA viruses is usually single- stranded RNA (ssRNA), but it may be double- stranded RNA (dsRNA) . RNA viruses can be further classified according to the sense or polarity of their RNA into negative-sense and positive-sense, or ambisense RNA viruses . Some examples of RNA animal viruses include the common cold, influenza, SARS, MERS, COVID-19, Dengue Virus, hepatitis C, hepatitis E, West Nile fever, Ebola virus disease, rabies, polio, mumps, and measles . DNA Viruses The genome of DNA viruses is made of deoxyribonucleic acid. They can be either dsDNA (double- stranded DNA) viruses or ssDNA (single-stranded DNA) viruses. In dsDNA viruses, the deoxyribonucleic acid is distributed into two strands. In ssDNA, it is just one strand of DNA. Both dsDNA and ssDNA have almost the same manner of transcription. DNA viruses are present everywhere, especially in the marine ecosystem. Also, they infect both eukaryotes and prokaryotes. Examples – Poxviruses, Herpesviruses and Papillomaviruses.
- 6. Structure of Plant Viruses 1 Viral Particles Plant viruses consist of protein capsids that encapsulate their genetic material. The capsids protect the viral genome and aid in the transmission of the virus to new host plants. 2 Viral Genome The genetic material of plant viruses can be either DNA or RNA, packed within the capsid. This genomic material carries information for the infection and replication processes.
- 7. Structure of Plant Viruses Plant viruses are viruses that affect plants. They are obligate intracellular parasites that do not have the molecular machinery to replicate without a host1. Most plant viruses are rod-shaped or isometric particles1. The structure of a virus is given by its coat of proteins, which surround the viral genome1. Over 50% of known plant viruses are rod- shaped (flexuous or rigid). The length of the particle is normally dependent on the genome but it is usually between 300 and 500 nm with a diameter of 15–20 nm1. The great majority of plant viruses have an RNA genome, which is usually small and single stranded (ss), but some viruses have double-stranded (ds) RNA, ssDNA or dsDNA genomes1. The nucleic acid makes up 5 to 40% of the virus, protein making up the remaining 60 to 95%2.
- 8. Classification of Animal Viruses 1 Enveloped Viruses Enveloped animal viruses possess an outer lipid bilayer obtained from the host cell membrane. This envelope aids in the entry of the virus into host cells. 2 Non-Enveloped Viruses Non-enveloped animal viruses lack an outer lipid bilayer. They enter host cells through mechanisms such as endocytosis or direct fusion with the cell membrane.
- 9. Structure of Animal Viruses Capsid Proteins Animal viruses have capsid proteins that enclose the viral genetic material, providing protection and facilitating the entry of the virus into host cells. Enveloped Membrane Enveloped animal viruses are covered with a lipid bilayer derived from the host cell membrane, enabling them to evade detection by the immune system. Genetic Material The genetic material of animal viruses can be DNA or RNA, containing instructions for viral replication and protein synthesis within host cells.
- 10. Satellite Viruses, Viroids, and Classification of Fungi Satellite Viruses Satellite viruses are subviral agents that depend on helper viruses for replication and encapsidation. They can influence the pathogenicity and symptoms caused by the helper viruses. Viroids Viroids are small circular RNA molecules that can infect plants, causing diseases by interfering with the regulation of gene expression. They do not code for proteins but can replicate autonomously within host cells. Classification of Fungi Fungi are eukaryotic organisms classified into various taxonomic groups based on characteristics like spore type, morphology, and reproductive structures. They play critical roles in ecosystems and as pathogens of plants and animals.
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