Almost Living

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Almost Living

• Viroids, Prions, and Viruses

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Non-Living Disease Agents

• Viroid- small naked molecules of RNA that can
  cause disease in plants.
• Prion-proteins that can cause disease in animals,
  degenerative diseases of nervous system
• Virus-nucleic acid surrounded by protein

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Viral Characteristics

• Nucleic Acid- DNA or RNA single or double
  stranded rings of DNA
• Capsid Protein- surrounds nucleic acid
• Obligate Parasite- must invade host cell to
  complete cycle
• Accessory Structures- ex. envelope protein- in
  some(retro) viruses acts as a receptor ( spiky
  outer protein)

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Viral Types are host specific

• Plant ex.Tobacco mosaic
• Bacteria ex. T4 phage
• Animal ex. Papovirus-warts, Adenovirus-respiratory
  infections, Herpesvirus-chicken pox cold sores
  genital herpes, Reovirus-diarrhea,
  Picornovirus-colds, Retrovirus-HIV

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T4 PHAGE VIRUS
RECEPTOR PROTEIN
NUCLEIC ACID
CAPSID PROTEIN
ANIMAL VIRUS
ENVELOPE
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• Lytic- a reproductive cycle culminating in death
  of the host cell
• virulent virus depends on this type of cycle
• 1. Attachment
• 2. Inject nucleic acid
• 3. Host DNA is hydrolyzed and viral genome is
  incorporated (REPLICATE NUCLEIC ACID)
• 4. Hosts metabolic machinery is directed to
  manufacture new virus particles(ASSEMBLY)
• 5. Host cell lyses

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Virulent

• Virus that is only capable of a lytic cycle

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Lysogenic Cycle

• Viral genome is incorporated into the host cell
  without destruction
• viral DNA can remain dormant for an extended
  period-PROPHAGE
• temperate virus- viruses that are capable of both
  types of cycles

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Genome of RETROVIRUSES

• 1. Consists of RNA
• Capsid gene
• Envelope gene
• Reverse Transcriptase gene- causes the host to
  make DNA from viral RNA

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VACCINE

• Dead or weakened form of pathogen is injected or
  introduced into the host cell
• Attenuated virus
• Outer protein molecules are most important
• Stimulate host to produce an immune response
• represent an ANTIGEN/ causing ANTIBODIES to be
  produced

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Antigen- any substance which stimulates the
production of Antibodies
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Genetic Variation

• Transduction- viral transfer of DNA from one
  bacteria to another
• Transformation- exchange of naked DNA by a
  bacteria from environment Competence (Ca ions
  in environment)

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Eukaryotic Expression

• Lac Operon Hypothesis OPERON(pg.345)
• Regulatory
• Promoter
• Operator
• Structural

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Genetic Variation Cont.

• Conjugation- exchange via pili
• Plasmids are often exchanged via pili
• Transposons- DNA that can move from one location
  on the genome to another- can cut and seal DNA
  by making ligase enzymes

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Bacterial Reproduction

• Prokaryotic- no nucleus
• DNA double stranded large single ring
• makes up main genome-NUCLEOID
• Plasmids- secondary smaller rings outside main
  genome

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Reproduction

• Fission- replicate genome and divide
• Pili- conjugation exchange of DNA
• Fast reproductive rate results in relatively high
  rate of recombination and mutation