Viral Infection

EnvelopeProtein ShellCapsidNucleic AcidReceptorsDNA or RNAMembrane around virusProteins that help virus get into proper hostAttachmentThe virus attaches to receptors on the host cell.

The virus is able to get into the cell in one of three ways.Entry into the Cell

Fusion of the MembranesThe viral envelope and cell membrane fuse, allowing the virus to enter the cell.The virus is engulfed by the cell membrane.Endocytosis

InjectionE. coli

Bacteriophage T4What happens once the genetic material is inside the cell?One of two different processes may occur:

1.The virus takes over the cell and begins to replicate right away, killing the host cell in the process.

2.The virus doesnt take over or kill the host cell right away, but does begin to replicate.Lytic CycleThere are 5 steps in the Lytic Cycle

RELEASE (LYSIS)ATTACHMENTLytic Cycle1.Attachment the virus attaches to receptors on the host

ATTACHMENTLytic Cycle

2.Penetration the nucleic acid moves across the cell membrane into the host cellLytic Cycle

3.Replication and Synthesis the virus degrades the host nucleic acid and uses the host to make new viral components.Lytic Cycle

4.Assembly viral components are assembled into new viruses.Lytic Cycle

RELEASE / LYSIS5.Release / Lysis fully assembled viruses are released when the host cell burstsLytic CycleViruses that are in a lytic cycle are described as VIRULENT

RELEASE / LYSISATTACHMENT

T4 Bacteriophage Lysing E. coli Bacterium

Bacteriophage Lambda ()Lysogenic CycleThere are 4 steps in the Lysogenic Cycle

NNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNnnnnnnnnnnnnnnnnnddddATTACHMENTPENETRATIONINTEGRATIONREPLICATIONLysogenic CycleSteps 1 and 2 are identical to the first two steps in the lytic cycle.

NNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNnnnnnnnnnnnnnnnnnddddATTACHMENTPENETRATIONLysogenic Cycle

INTEGRATION3.Integration Phage DNA integrates into bacterial DNALysogenic Cycle

INTEGRATIONWhen it becomes integrated into the host DNA, the viral genome is referred to as a PROPHAGE.Lysogenic Cycle

REPLICATION4.Replication The integrated prophage replicates when bacterial DNA replicatesLysogenic Cycle

NNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNnnnnnnnnnnnnnnnnndViruses that enter into a lysogenic cycle are known as TEMPERATE VIRUSES

What is special about Bacteriophage ?ATTACHMENTPENETRATIONREPLICATION AND SYNTHESISASSEMBLYRELEASE / LYSISINTEGRATIONREPLICATION

Bacteriophage attached to an E. coli BacteriumReplication of Viral Nucleic AcidsDNA Viruses replication of viral DNA is similar to the process that the host cell uses to replicates its own DNADNA DNAReplication of Viral Nucleic AcidsMost RNA Viruses replication of viral RNA is dependent upon an enzyme that is encoded on the viral genomeRNA RNAReplication of Viral Nucleic Acids RNA viruses that convert their RNA into DNA using an enzyme that is included with the viral genomeRNA DNARetrovirusesReplication of Viral Nucleic AcidsRetroviruses This DNA is inserted into the host genome, where it can be transcribed back into viral RNA during normal cellular activity.Replication of Viral Nucleic AcidsRetroviruses Once the DNA is integrated into the host genome, some retroviruses may become LATENT, where they remain inactive for long periods of time.Replication of Viral Nucleic AcidsHuman Immunodeficiency Virus (HIV), the virus that causes AIDS, is an example of a retrovirus that can become latent.RetrovirusesVirus hijacks the host cell and keeps making more copies of itself until the host bursts openLytic CycleLysogenic CycleHIVVirus integrates into the host genome and replicates when the host divides. When triggered it can enter the lytic cycle.RNA viruses that convert their RNA to DNA which then integrates into the host genome.Retrovirus that infects humans which can remain latent for long periods of time.HIV Infection

When not active, the virus is described as being latent

Lytic and Lysogenic CyclesLytic and Lysogenic Cycles

ATTACHMENTPENETRATIONREPLICATION AND SYNTHESISASSEMBLYRELEASE / LYSISINTEGRATIONREPLICATION

dddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddLytic Cycle

dddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddLysogenic Cycle

Lytic and Lysogenic Cycles