protea

• Protists


  • Algae
  • Protozoa
  • Slime molds
  • Water molds
• Protists


  • Diverse: unicellular and multicellular
  • Lack the level of tissue organization present in higher eukaryotes
  • No common ancestor
  • Widespread, aquatic and terrestrial
  • Parasites of plants and animals including humans
  • Moist environments
• Nutrition in Protists


  • Protozoa are chemoorganoheterotrophic protists - saprophytes, nutrients obtained from dead organic matter through enzymatic degradation, osmotrophy - absorb soluble products, holozoic nutrition - solid nutrients acquired by phagocytosis
  • Photolithoautotrophic protists - strict aerobes, use photosystems I and II for oxygenic photosynthesis
  • Mixotrophic protists - use organic and inorganic carbon compounds
• Protist Morphology


  • Plasma membrane structure similar to multicellular plants/animals
  • Pellicle structure provides support in protozoa
  • Cell wall in algae
  • Motility - Pseudopodia in amoeboids, Flagella, Cilia, Some with no motility
• Encystment


  1. Protists simplify in structure and become dormant (cyst) with a cell wall and very low metabolic activity

  2. Protects against environmental changes

  3. Can assist in nuclear reorganization/reproduction (schizogony and plasmotomy)

  4. Serve as a means of host to host transfer for species
• Excystment


  1. A return to favourable conditions may stimulate a cyst form to return to its original state

  2. In parasitic protists, this may occur following ingestion of a cyst by a new host organism
• Protist Reproductive Cells and Structures


  • Asexual stage - usually binary fission but can be multiple fission or budding
  • Sexual stages use fusion of gametes in syngamy process within a single org (autogamy) or between (conjugation)
• Protists Taxonomy


  • Difficult to define due to vast differences in protists
  • Still an area of active research
  • New classification scheme is based on that of the International Society of Protistologists - doesn't utilize hierarchical ranks (class and order)
  • 5 Super Groups - Excavata, Amoebozoa, Chromoaveolata, Archaeplastida, Rhizaria
• Chromoaveolata


  • A diverse group including autotrophic, mixotrophic, and heterotrophic protists
  • Some of the most significant parasitic protists: Balantidium coli causes diarrhoea and dysentery, Plasmodium species cause Malaria (P. vivax, P. ovale, P. malariae and P. falciparum)
• Adl et al.: 'Diversity, Nomenclature, and Taxonomy of Protists. (2007) Systematic Biology, Volume 56, Issue 4, Pages 684–689, https://doi.org/10.1080/10635150701494127'
• Virion


  Complete virus particle
• Virology


  Study of viruses
• Virologists


  Scientists who study viruses
• Characteristics of viruses


  • Acellular
  • Exist intracellularly and extracellularly
  • Cannot reproduce independent of living cells nor carry out cell division
  • Major cause of disease
  • Important members of aquatic world
  • Important in evolution
  • Important model systems in molecular biology
• Viruses


  • Need electron microscope to view
  • Viral size
• Host Range


  Variety of host cells that a virus can infect
• Specific viruses often have narrow host range
• Hosts that viruses can infect


  • Plants
  • Fungi
  • Bacteria- bacteriophages\phages
  • Animals
• Host\Virus interaction


  • Host range determined by interaction of virus with host cell
  • Receptors on host cell membrane
  • Binding sites on viral structure
• Virion size range


  • ~10–400 nm in diameter
• Components of a virion


  • Nucleic acid (DNA or RNA)
  • Protein coat (capsid)
  • Envelope (some viruses)
• Capsids


  • Large macromolecular structures which serve as protein coat of virus
  • Protect viral genetic material and aids in its transfer between host cells
• Protomers


  Protein subunits that make up capsids
• Types of capsid symmetry


  • Helical
  • Icosahedral
  • Complex
• Helical capsids


  • Shaped like hollow tubes with protein walls
  • Protomers self assemble
  • Size of capsid is a function of nucleic acid
• Icosahedral capsids


  • An icosahedron is a regular polyhedron with 20 equilateral faces and 12 vertices
  • Capsomers - ring or knob-shaped units made of 5 or 6 protomers
  • Pentamers (pentons) - 5 subunit capsomers
  • Hexamers (hexons) - 6 subunit capsomers
• Capsids of Complex Symmetry


  • Some viruses do not fit into the category of having helical or icosahedral capsids
  • Poxviruses - largest animal virus
  • Large bacteriophages - binal symmetry, head resembles icosahedral, tail is helical
• Viral Envelopes


  • Many viruses are bound by an outer, flexible, membranous layer called the envelope
  • Animal virus envelopes (lipids and carbohydrates) usually arise from host cell plasma or nuclear membranes
• Viral Envelope Proteins


  • Envelope proteins, which are viral encoded, may project from the envelope surface as spikes or peplomers
  • Involved in viral attachment to host cell e.g., hemagglutinin of influenza virus
  • Used for identification of virus
  • May have enzymatic or other activity e.g., neuraminidase of influenza virus
  • May play a role in nucleic acid replication
• Virion Enzymes


  • A variety of virions have enzymes
  • Some are associated with the envelope or capsid but most are within the capsid
• Diversity of viral genomes


  • Single or double stranded DNA or RNA
  • Genomes can be segmented or circular
• Viral Multiplication


  1. Attachment to host cell

  2. Entry

  3. Uncoating of genome

  4. Synthesis

  5. Assembly

  6. Release
• Attachment (Adsorption)


  • Specific receptor attachment
  • Receptor determines host preference
  • May be specific tissue (tropism)
  • May be more than one host
  • May be more than one receptor
  • May be in lipid rafts providing entry of virus
• Viral Entry and Uncoating


  • Entire genome or nucleocapsid enters
  • Varies between naked or enveloped virus
  • Fusion of the viral envelope with host membrane; nucleocapsid enters
  • Endocytosis in vesicle; endosome aids in viral uncoating
  • Injection of nucleic acid
• Synthesis Stage


  1. Genome dictates the events

  2. ds DNA typical flow

  3. RNA viruses must carry in or synthesize the proteins necessary to complete synthesis

  4. Stages may occur, e.g., early and late
• Assembly


  1. Late proteins are important in assembly

  2. Assembly is complicated but varies

  3. Bacteriophages - stages

  4. Some are assembled in nucleus

  5. Some are assembled in cytoplasm

  6. May be seen as paracrystalline structures in cell
• Virion Release


  1. Nonenveloped viruses lyse the host cell, viral proteins may attack peptidoglycan or membrane

  2. Enveloped viruses use budding, viral proteins are placed into host membrane, nucleocapsid may bind to viral proteins, envelope derived from host cell membrane, but may be Golgi, ER, or other, virus may use host actin tails to propel through host membrane
• Types of Viral Infections


  • Infections in Bacteria and Archaea
  • Infections in eukaryotic cells
  • Viruses and cancer
• Virulent phage


  One reproductive choice, multiplies immediately upon entry, lyse bacterial host cell
• Temperate phages


  Have two reproductive options, reproduce lytically as virulent phages do, or remain within host cell without destroying it