Biol 251 Chapter 13

Viruses that infect bacteria are called bacteriophages or phage

A virus needs live host cells but must stop synthesis of host protein so that the viral genes are translated

• Attachment
• Entry
• Uncoating
• Biosynthesis of DNA virus
• Late translation
• Maturation
• Release

• Animal viruses have attachment sites that attach to complementary receptor sites on the host cell's surface. However, the receptor sites of animal cells are proteins and glycoproteins of the plasma membrane
• Many of the enveloped viruses, such as influenza virus, the attachment sites are spikes located on the surface of the envelope
• Receptor sites are proteins of the host cell
• Virus' attachment site or the cell's receptor site may soon be used to treat some viral infections

• Many viruses enter into eukaryotic cells by receptor-mediated endocytosis; cell's plasma membrane continuously fold inward to form vesicles
• Enveloped viruses can enter by an alternative method called fusion in which the viral envelope fuses with the plasma membrane and releases the capsid into the cell's cytoplasm

• Separation of the nucleic acid from its protein coat
• uncoating by the action of lysomomal enzymes of the host cell. These enzymes degrade the proteins of the viral capsid
• A portion of viral DNA is transcribed, producing mRNA that encodes "early" viral prteins

• DNA containing viruses replicate their DNA in the nucleus of the host cell by using viral enzymes
• Proteins migrate into the nucleus and are joined with the newly synthesized DNA to form virons

Capsid proteins are synthesized

• Viron matures
• First step of viral maturation is the assembly of the protein capsid; this assembly usually spontaneous process

• Envelope actually develops around he capsid by a process call budding 
• Budding doesn't kill the host cell immediately, and in some cases the host cell survive
• None enveloped viruses are release through ruptures in the hos cell plasma membrane. In contrasts to budding, this type of release usually results in the death of the host cell

DNA or RNA but never both

Not covered by envelope

Each capsid is composed of capsomere

• Can be single stranded or double stranded
• Double stranded DNA, Single stranded DNA, Double stranded RNA, Single straned RNA

• Protect nucleic acid from nuclease enzymes
• The nucleic acid of a virus is protected a protein coat
• Structure of capsid is ultimately determined by the viral nucleic acid accounts for most of mass of a virus

• Envelope covers capsid
• composed of lipid, protein, and carbohydrates
• Spikes

• Envelopes may or may not have covered by spikes. 
• Which are carbohydrate-protein complexes that project from the surface of the envelope
• attach to the host cells
• means of identification