Arianna K. Olivia J. Willow G. Virus Structure

Overview What is a virus? Characteristics of a virus Viral Reproduction  RNA Viruses Lytic infections Lytic Cycle vs. Lysogenic Cycle

What is a Virus?  particles made of proteins, nucleic acids, and sometimes lipids non-living organisms crystalize unlike organisms that are living AK

How do they differ from Each other? Specific to one cell: plant, animal, etc. Size: large, complex or small and simple Some have additional membranes AK

Structures Within a Virus Capsid: protein surrounding virus Capsids bind to receptor proteins on cell DNA or RNA: store genetic information for virus AK

Characteristics of a virus Same as living cells Different from living cells Changes over time Contain genetic info Reproduction only inside host Does not grow No energy needed needed AK

What does a virus need to reproduce? Grow and reproduce by infecting living cells Nutrients and cellular machinery of their hosts OJ

What types of cells do viruses infect? Plant viruses -> plant cells Animal viruses -> animal cells Bacteriophages -> virus that infects bacteria      OJ

The common cold Virus enters -> invades -> replicates Virus Mistaken identity of viral RNA Host assembles virus particles -> infects cells All within 8 hours Virus OJ

HIV Group of RNA -> Retroviruses Contains RNA as its genetic info RNA -> DNA not DNA -> RNA Replication of RNA -> DNA  copy of viral RNA is made Remains dormant -> once activated (can be many years)  Before destruction of the immune system OJ

Lytic Infections Virus enters a bacterial cell Makes copies of itself Causes the cell to burst WG

Lytic Cycle Virus injects its DNA into host cell Cell uses virus' information Makes mRNA from viral info. Viral mRNA makes viral protein Viral protein chops up host cell's DNA WG

Lysogenic Cycle Prophage: bacteriophage embedded in host DNA Virus injects DNA into bacterium Viral DNA in bacterial chromosome WG

Lysogenic CYcle (continued) Prophage replicates w/ bacterium for generations Prophage exits chromosome Enters Lytic Cycle WG

Lytic vs. Lysogenic Cycle Lytic Cycle Lysogenic Cycle Virus injects DNA into bacterium Protein synthesis with viral info. Viral nucleic acids       new viruses Viral enzymes lyse the cell wall Viruses escape       infect new cells Virus injects DNA into bacterium Viral DNA      bacterial chromosome Viral DNA is now called a prophage Prophage replicates with bacterium for generatons Prophage exits bacterial chromosome (enters Lytic Cycle) WG

How can you tell that a virus is not living? They do not breath A virus uses sunlight for energy Viruses crystalize They are made of proteins C Ak

What makes Virus Cells different from Living cells? The cell does not need energy Energy is needed for reproduction Reproduction occurs outside the host Does not contain genetic information A AK

HOW IS THE GENETIC INFORMATION OF A RETROVIRUS COPIED? A.) DNA -> RNA B.) RNA -> DNA C.) Complementary DNA -> DNA D.) No replication B OJ

A.) 9 hours B.) 6 hours C.) 8 hours D.) One day How many hours does it take for the host cell to release the virus particles and to infect other cells? C OJ

WHAT INFECTION CAUSES THE CELL TO BURST? A.) Prophage Infection B.) Lytic Infection C.) Capsid Infection D.) Lysogenic Infection B WG

WHat infection takes generations to set in? A.) Lysogenic Infection B.) Lytic Infection C.) Viral Infection D.) Bacteriophagal Infection A WG

Overview What is a virus? Characteristics of a virus Viral Reproduction  RNA Viruses Lytic infections Lytic Cycle vs. Lysogenic Cycle