multiplication of tmv
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Multiplication of tmv
1. Prof. Suraj Dipak Gabale Assistant professor Vivekanand College, Kolhapur
2. Tobacco mosaic virus TMV is a plant virus which infects a wide range of plants, especially tobacco and other members of the family Solanaceae. The infection causes characteristic patterns, such as "mosaic"-like mottling(spots) and discoloration on the leaves (hence the name). TMV was the first virus ever to be discovered.
3. Rod shaped- 300nm x 180nm No. of Capsomers- 2130 Molecular wt. of virion 40x106 d. Each capsomer is made up of 158 amino acids. Capsomers arranged in helix around central hole of 4nm radius.
4. Genome: Single stranded, unsegmented, positive sense RNA. Contains 6400 nucleotides Mol. Wt.- 2.1x106 The RNA encodes 3 essential proteins- a) RNA dependent RNA polymerase (Replicase) b) Movement protein c) Coat Protein
5. Mechanical- i) Contaminated hands, ii) Clothing or tools in farm Biological- i) Seeds from infected plants ii) Pollen grains iii) Insects (aphids) Physical- i) Wind ii) Water
6. The reproductive cycle of TMV consists of Five steps as- 1. Entry into host cell 2. Uncoating 3. Intracellular Development 4. Assembly (Maturation) 5. Release
7. TMV can not directly enter the host cell. It requires damage to plant cells. It enters through breaches (Gap) in the cell wall.
8. It is a process in which capsid is removed and nucleic acid is released into the cell cytoplasm. Nucleic acid of plant viruses enters the host cell cytoplasm along with capsid. In the cytoplasm capsid is removed and nucleic acid is freed. It requires assistment of host enzymes to remove capsids.
9. In order to produce disease, the virus must relpicate and spread to neighbouring cells and then systematically throughout the plant. Spreads of virus to neighbouring cells occurs through microscopic channels in the cell walls called plasmodesmata. Plasmodesmata- These are slender structures extending from cell wall which connects adjacent plant cells.
10. Spread to other parts of the plant by vasculature system ( Xylem and phloem). The cell to cell movement of virus requires one or more protein called as “Movement protein”. Most plant viruses uses coat/capsid proteins for transfer.
11. TMV contains SS Positive sense RNA as its genome. Replication of virion RNA thus involves synthesis of negative strand RNA using positive strand RNA as a template. Thus, replication completes in 2 steps- 1) Synthesis of negative strand RNA using positive strand RNA as a template which forms doubles stranded intermediate termed as “Replicative form (RF)”. 2) Synthesis of positive strand RNA using negative strand RNA as a template using virus coded RNA dependent RNA polymerase.
12. Also called Maturation. After intracellular synthesis of enough no. of capsid proteins and Virion RNA, virion assembly begins. It is highly organized process. Initially Capsid assembly begins when capsomers associate with 3I end of the RNA. TMV assembly will occur in vitro when capsid proteins and nucleic acids are mixed.
13. Capsomers binds to each other to form disks. Each disk contains 2 layers each with17 subunits. Then helical capsid grows by addition of disks to one end of rod. Mechanism: At neutral pH carboxylic groups of adjacent capsomers have normal pK’s values. But at acidic pH (high H+ conc.) repulsion between adjacent carboxylic group occurs due to increse in pk’s. This results in Lock “Washer formation”.
14. Man plant viruses kills their hosts in which they multiply. They releases by autolysis of host cell which causes death of cell.
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