Presentation is loading. Please wait.

Presentation is loading. Please wait.

General Virology VIRUS STRUCTURE.

Similar presentations


Presentation on theme: "General Virology VIRUS STRUCTURE."— Presentation transcript:

1 General Virology VIRUS STRUCTURE

2 Virion vs virus Virion is the infectious particle
composed of nucleic acid, protein capsid, +/- envelope may be extracellular or intracellular Virus is any stage of infection

3 How do we know that NA is genetic material?
Hershey-Chase Fraenkel-Conrat Experiment TRANSFECTION EXPTS

4 TRANSFECTION FAILS FOR SOME VIRUSES
WHY?

5 Capsid Functions Protection of NA Attachment for naked viruses Enzyme
Helical vs Icosahedral Symmetry - Why do most viruses look alike? Tobacco mosaic virus is a ssRNA virus composed of 6000 nucleotides. The capsid is made of 2100 copies of a single protein subunit that contain 158 amino acids. Calculate the percentage of the genome that is used for structure.

6 How do helical viruses differ?
Helical- one axis of symmetry down center Multiple structural units

7 Icosahedral symmetry 20 identical equilateral triangles
Structural units on faces to give morphological capsomers Pentons (5 fold axis of symmetry) Hexons 3 fold through face 2 fold through edge How do spherical viruses differ?

8 Envelope Attachment Entry Assembly- matrix proteins Release
Proteins are viral Lipids are host Rare in plants or bacteria - why? If the membrane envelope is destroyed, the virus becomes noninfectious. Why?

9 Herpesvirus complexity
Tegument proteins - 12/84 viral proteins in HSV Potential role? Virion mRNA DNAase virion nucleic acids RT-PCR probe genome array

10 Genome - DNA or RNA strandedness - (single) (double)
How do we experimentally show that DNA or RNA is the virus genetic material? strandedness - (single) (double) linear or circular, partial double stranded circle number (single, segmented, multicomponent)

11 RNA Genomes sense (positive-sense, negative-sense, ambisense)
presence or absence of 5'-terminal cap or 5'-covalently-linked protein presence or absence of 3'-terminal poly (A) tract Retroviruses - replication strategy

12 Some viruses have high degree of secondary structure
Poliovirus - 5’ internal ribosome entry site (IRES) Guest et al J. Virol. 78:

13 SARS/coronaviruses have conserved 3’region
SARS s2m in red a - green = 530 loop of 16S RNA Similar binding properties: b - blue = S12 magenta = IF1 Possible role for s2m Hijacks protein synthesis from cell(binding cell factors) Needed to bind to similar viral protein for transcription Potential drug target in red tunnel Robertson et al PLOsBiology:3.

14 DNA Viruses may be large genomes
PolyDNAvirus (PDV) - contain many DNA segments Mimivirus - larger than small bacteria

15 Host-induced modification
Viral property that varies depending on the host Phage DNA hydroxymethyl cytosine (HMC) replaces C Viral enzymes: C to HMC Viral DNA polymerase: adds HMC not C What is advantage of HMC? Glucose is attached to HMC Host enzyme needed to prepare glucose Protects against host nuclease

16 What would happen if virus without glucose enters host with RE?
What would happen if virus with glucose enters host w/o enzyme to create UDP- glucose? Host enzyme makes

17 Proteins structural proteins non-structural virion proteins
transcriptase, protease integrase

18 How to identify virion proteins
Purify KSHV virions Run on SDS PAGE Excise bands, digest - get sequence and compare to database

19 Chemical synthesis of poliovirus: What are the implications?
Small genome positive strand RNA - sequence known Synthesized small DNA segments (~ 69 nucleotides) with overlapping complementary segments Added a T7 phage promotor to DNA Used DNA to make genome RNA in HeLa cell lysate with T7 polymerase Results: How do you show success?

20

21

22 International Congress on Taxonomy of Viruses http://www. ncbi. nlm
Morphology virion size enveloped or naked nucleocapsid capsid symmetry and structure Genome characteristics Replication strategy Antigenic Properties

23 Baltimore classification

24 WHY TRANSFECTION FAILS

25 ONE STEP GROWTH CURVE 1939- Ellis and Delbruck:
Infection with a high multiplicity of infection (MOI): ratio of virus to host cell Simultaneous infection Single replication cycle Sample at time intervals by plaque count for plaque-forming units (PFU), Identification of latent phase Determination of burst size/viral yield

26 Measuring Intracellular Events
Sample at time intervals after lysing cells ( Doermann) Chloroform Lysis from without Identification of eclipse and maturation phases Maturation phase

27

28 Strategy of replication
Lytic Temperate

29 Biologic Properties natural host range mode of transmission in nature
vector relationships geographic distribution pathogenicity, association with disease tissue tropisms, pathology, histopathology

30 How can you identify these viruses?


Download ppt "General Virology VIRUS STRUCTURE."

Similar presentations


Ads by Google