Viruses

Brain Tap What do we already know about Viruses?

Virus Research Project With your lab partner, you will work together to create a “Virus Wanted Poster” With your partner, pick a Virus you are interested in researching (first come, first serve) Tentative due date:Monday Oct 26

The impact of Viruses https://www.youtube.com/watch?v=d- YXx3jRPCI

So what are viruses? Are they living? Characteristic of Life Virus Cell Growth NO YES Homeostasis Metabolism Mutation Nucleic Acid DNA or RNA DNA Reproduction Within Host Cell Cell Division Structure Nucleic acid core, protein covering. Cytosol, cell membrane, organelles

Viruses Submicroscopic obligate, intracellular parasites… but are typically considered NON-LIVING (do not meet all the requirements that make life) Submicroscopic: Extremely small particles, unable to view using light microscope Can sometimes be seen using powerful electron microscopes Range in size from 20nm to 250nm (the size of a bacterium)

Viral Structure All Viruses have two essential features: A nucleic acid, and a protein coat surrounding it. Nucleic acids: Can be either DNA or RNA Nucleic acid: Can be helical, closed loop, or long strand, depending on the virus. The Protein Coat surrounding the virus is known as the capsid.

Viral Structure Cont’d Some viruses have a membrane-like structure on the outside, known as an envelope. Envelope is made mostly of lipids (fats) from the host cell, and aids in the infection of host cells. On the surface of the envelope, are projections made of Glycoproteins Projections made of sugar chains, which help the virus attach to the host cell

Not listed: Spherical viruses (e.g. Influenza)

Grouping Viruses The grouping of viruses is based on the presence of a capsid structure, envelope, and the nucleic acid type they contain. Table 25-2 In your textbook

DNA Viruses Directly produce RNA, then make Viral proteins Viral DNA joins host cell DNA, and directs protein synthesis from there (More on this during Viral Replication)

RNA Viruses Viral RNA is released into the host cytoplasm, where it directly links up with ribosomes, to produce Viral proteins

Retrovirus Example: HIV Contain an enzyme known as Reverse Transcriptase Reverse Transcriptase – Uses Viral RNA as a template to make DNA, which is then integrated into the host genome, replicates like a DNA virus. Named so because it reverses the transcription process (RNA  DNA) Example: HIV

Viroids and Prions Simpler forms of Viruses Viroids – Smallest known particles capable of replicating, consisting of a short, single strand of RNA. Prions – Abnormal clumps of proteins, blocks normal cell traffic, killing the cell. Mad Cow disease is caused by a Prion virus.

To Do Now Work on 25.1 Review