Living or Nonliving

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Living or Non-living

• Growth
• Homeostasis
• Metabolism
• Mutation
• Nucleic Acid
• Reproduction
• Structure

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Viruses

• Non-living particle composed of a nucleic acid
  and a protein coat
• Some of the smallest biological particles capable
  of causing disease

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Structure of a Virus

• A Nucleic Acid DNA or RNA
• Capsid- protein coat surrounding the nucleic acid

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Structure of a Virus

• Envelope- Membrane like structure surrounding the
  capsid, made of lipids
• Glycoproteins- Protein and sugar projections on
  the surface of the envelope

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Structure of a Virus

• Shape may be determined by the capsid or nucleic
  acid
• Icosahedron a geometric shape with 20 triangular
  faces
• Helix Spring-like coil

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Grouping of Viruses

• Based on shape and structure
• Presence of capsid and/or envelope
• Shape of capsid
• RNA or DNA

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Producing new Viruses

• DNA and RNA viruses differ in the way they use
  the host cells machinery to produce new viruses
• DNA Directly make RNA or join host cells
• RNA Uses host cells ribosomes or it is a
  retrovirus

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Retroviruses

• Contain the enzyme Reverse Transcriptase as well
  as RNA
• Uses RNA as a template to make DNA
• The DNA is integrated into the hosts genome
• DNA makes an RNA transcript of itself
• The new RNA is translated into proteins and new
  viruses are made

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Viroids

• The smallest known disease causing agent, simpler
  than viruses
• Consists of a short single strand of RNA and no
  capsid
• Able to disrupt plant cell metabolism

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Prions

• Abnormal forms of proteins that clump together
  inside a cell
• Composed of about 250 amino acids and no
  associated nucleic acids
• Linked to certain disease of the brain
• Ex Scrapie, Mad Cow Disease, Creutzfeld Jakob
  Disease

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Viral Replication

• Viruses are Obligate intracellular parasites
  because they depend on host cells for replication
• There are two different replication cycles of
  bacteriophages the lytic cycle and lysogenic
  cycle

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Bacteriophage

• Viruses that infect bacteria

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Lytic Cycle

• Viruses are called virulent because they cause
  disease
• There are 5 phases of the cycle
• Attaches to susceptible bacterium by attaching to
  receptor sites
• The phage releases an enzyme that weakens the
  cell wall

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Lytic Cycle

• 3. The phage then injects its DNA into the cell
  wall through weakend cell wall
• Newly generated capsids enclose newly replicated
  viral DNA
• The newly generated Viruses leave the cell
  through lysis

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Lysogenic Cycle

• Viruses are called temperate because they do not
  kill the host immediately
• The phage inserts its DNA in the same way as
  lytic cycle but the DNA is incorperated into the
  host cells DNA

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Lysogenic Cycle

• The DNA that integrates at a specific site is
  known as a prophage
• When the host DNA replicates, the viral DNA does
  also and each new cell has new viruses
• Does not harm the host but can eventually enter
  the lytic cycle