1. Penetration through cellular membranes Intracellular transport
Virus Entry
Steps in virus entry
Penetration through cellular membranes
Intracellular transport

2. Steps in virus entry How do virions get into eukaryotic cells?
Enveloped and nonenveloped viruses have distinct penetration strategies
Some viruses can pass directly from cell to cell

3. Steps in virus entry
Fig. 4.1 Exit and entry of enveloped viruses occurs by vesicle transport.

4. Steps in virus entry
A variety of cell surface proteins can serve as specific virus receptors
Fig. 4.2 Cell surface glycoproteins used as virus receptors.

5. Steps in virus entry
Receptors interact with viral glycoproteins, surface protrusions, or “canyons” in the surface of the virion
Many viruses enter the cell via receptor-mediated endocytosis

6. Steps in virus entry
Passage from endosomes to the cytosol is often triggered by low pH

7. Steps in virus entry
Membrane fusion is mediated by specific viral “fusion proteins”
Fusion proteins undergo major conformational changes that lead to membrane fusion
Nonenveloped viruses penetrate by membrane lysis or pore formation

8. Steps in virus entry
Fig. 4.4 A model for influenza virus hemagglutinin mediated membrane fusion.

9. Intracellular transport
Virions and capsids are transported within the cell in vesicles or on microtubules
Import of viral genomes into the nucleus
The many ways in which viral genomes are uncoated and released

10. Intracellular transport
Virions and capsids are transported within the cell in vesicles or on microtubules
Import of viral genomes into the nucleus
The many ways in which viral genomes are uncoated and released

11. Virus Entry

12. Key Terms Glycolipid Glycoprotein Amantadine Bafilomycin A1 Hemifusion
Immunoglobulin family
Importin
Integrins
Karyopherin
Ligand
Lysosome
Lysosomotropic agent
Neuraminidase
Plasmodesmata
Proteoglycan
Receptor-mediated
endocytosis
Sialic acid
Syncytium (plural: synctia)
Type I transmembrane
protein
Vesicle transport
Amantadine
Bafilomycin A1
Budding
Carboxylic ionophors
Caveolae
Caveolin
Class I fusion proteins
Class II fusion proteins
Clathrin-Coated pits
Coiled-coil
Cytoplasm
Cytosol
Dynactin
Dynein
Early endosome
Endosome
Fission (Membrane)
Fusion (Membrane)
Fusion peptide