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principle of virology إعداد مرتضى عبد المهدي محمد حسن المظفرمرتضى عبد المهدي محمد حسن المظفر E- mail : mail : 29/08/14352 مبادئ عِلْمِ الفيروساتمبادئ عِلْمِ الفيروسات

المقدمـــة : Introduction أول تحديد لعلم الأمراض المعدية كان مابين سنة حيث وضعوا مفهوم للأمراض المعدية سواء للإنسان و الحيوان, حيث تم اكتشاف أول إصابة فيروسية Tobacco Mosaic من قبل العالميين Beijerinck and Ivanovaski وأطلق اسم الرواشح لأول مرة على الفيروسات من قبل العالمين Loeffler and Frosch. الفيروسات عبارة عن كائنات حية فقط في الخلايا الحية, وتحتوي على المادة الوراثية وتكون أما DNA أو RNA محاطة بمحفظة وتسمى ب (genome) والتي بدورها تكون محاطة بمجموعة من البروتينات ولكل نوع وضيفة معينة ومنها يدخل في تركيب الفيروس. 29/08/14353

Characteristics of viruses They contain no ribosomes or other cellular organelles. They do not undergo binary fission. Replicate only within cells of the host they infect and are completely dependent upon the metabolic machinery of the cell They consist of a genome that is either RNA or DNA enclosed within a protective coat of protein molecules. In some viruses the nucleic acid may be infectious and if inserted into a host cell can initiate the infectious process and result in production of progeny virus. 29/08/14354

Morphological features of viruses 1.Isometric viruses particles The protein coat enclosing the nucleic acid genome assumes an isometric (icosahedral) configuration, and it may or may not be enclosed within a lipoprotein envelope An example of a non-enveloped isometric viruses – Adenovirus An example of an enveloped isometric viruses – herpesvirus 2.Tubular nucleocapsids with lipoprotein envelope This morphology is seen only in viruses with an RNA genome. – influenza virus – paramyxoviruses 29/08/14355

6 3.Complex viruses which contain additional structures Poxviruses -- have lateral bodies

Sequential steps in the replication of DNA viruses 1.Attachment or adsorption 2.Penetration 3.Uncoating of virus.. transport of genome to site of replication 4.Early transcription (mRNA) 5.Early translation and early proteins 6.Viral DNA synthesis 7.Late transcription of further mRNA 8.Late translation and synthesis of structural proteins 9.Assembly 10.Release 29/08/14357

The replication of RNA viruses 1. Positive-sense RNA viruses 29/08/ sense RNA is translated (late) Structural viral proteins Viral ss-RNA (+ sense) + sense RNA is translated (early) Early viral proteins eg. RNA polymerase + sense RNA forms an intermediate – sense RNA New viral + sense RNA Assembled together to form progeny virus No intravirion enzymes required Picornaviruses Coronaviruses

29/08/14359 mRNA (+ sense) Late viral proteins Structural viral proteins 2. Negative-sense RNA viruses Viral ss-RNA (- sense) mRNA (+sense) Early viral proteins eg. RNA polymerase Intermediate + sense RNA Progeny viral - sense RNA Assembled together to form progeny virus Intravirion transcriptase Intravirion transcriptase Intravirion transcriptase Does not act as mRNA – needs to be transcribed first to a positive sense mRNA-like product by a transcriptase within the virus Influenza viruses Paramyxoviruses

29/08/ Retroviruses Viral ssRNA (either of strands) ssDNA dsDNA mRNA Viral proteins Viral RNA Assembled to form progeny virus dsDNA enters nucleus and integrates into cellular DNA Reverse transcriptase – acts as an RNA-dependent DNA polymerase Reverse transcriptase (acts as DNA-dependent DNA polymerase Host cell transcriptase Early and late phases

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