Chp 1

• Unikonts


  Eukaryotic organisms with a single flagellum
• Bikonts


  Eukaryotic organisms with two flagella
• Cavalier-Smith proposed the names 'unikonts' and 'bikonts' based on a scenario for the evolution of the flagellar apparatus
• Flagellar apparatus in eukaryotic cells

  • It is the centre of organization for the cytoskeleton
  • Its core is usually a single 'kinetid' consisting of one or more basal bodies
  • Basal bodies may either give rise to flagella, or be non-flagellated
• Cavalier-Smith argued that ancestral eukaryotes had a simple kinetid with one basal body anchoring one flagellum
• Unikonts had retained this ancestral organization, whereas the 'bikonts' descended from a common ancestor that had evolved a kinetid with two flagella, one anterior and one posterior
• Bikont


  Any of the eukaryotic organisms classified in the group Bikonta, many of which have two flagella
• Shared trait of bikonts

  • Fusion of two genes (thymidylate synthase and dihydrofolate reductase) into a single unit
  • The genes are separately translated in unikonts
• Some research suggests that a unikont was the ancestor of opisthokonts (Animals, Fungi, and related forms) and Amoebozoa, and a bikont was the ancestor of Archaeplastida (Plants and relatives), Excavata, Rhizaria, and Chromalveolata
• Six major eukaryotic groups are now recognized
• Alveolates


  • Include ciliates, dinoflagellates, and apicomplexans
  • United by the presence of cortical alveoli underlying their plasma membranes
• Ciliates


  • Highly speciose aquatic unicells
  • Characterized by an abundance of flagella and dimorphic nuclei (micro- and macronuclei)
  • Micronucleus is a transcriptionally inactive germ nucleus, while transcription occurs in the macronuclei
• Ciliates


  • Possess a cell mouth or cytostome
  • Covered with a pellicle
  • Reproduce asexually through transverse binary fission
• Unique organelles in ciliates

  • Trichocysts: for anchorage during feeding or for protection
  • Toxicysts: for defense or capturing preys by paralysis and cytolysis
  • Mucocysts: function in the formation of cysts or protective covering
• Ciliates


  • Paramecium
  • Vorticella
  • Balantidium
  • Stentor
  • Suctoria
• Apicomplexa


  • Characterized by an apical complex, which functions in the attachment and initial penetration of the host cell
  • Includes secretory organelles like micronemes, rhoptries, dense granules, polar rings, and in some species a conoid
• Life cycle of Plasmodium falciparum

  1. Infection of a human with sporozoites

  2. Asexual reproduction (pre-erythrocytic and erythrocytic phases)

  3. Sexual reproduction (gametogenesis, fertilization, sporogony)
• The human infection begins when an infected female anopheles mosquito bites a person and injects sporozoites
• Asexual reproduction of Plasmodium

  1. Sporozoites enter liver cells and divide into schizonts, which release merozoites into the bloodstream

  2. Merozoites invade red blood cells, develop into ring stages, trophozoites, and schizonts, which then release more merozoites
• Sexual reproduction of Plasmodium

  1. Gametocytes develop in red blood cells

  2. Gametocytes are taken up by mosquito during a blood meal

  3. Gametogenesis occurs in mosquito gut, forming zygote and ookinete

  4. Ookinete penetrates mosquito midgut wall and forms oocyst

  5. Oocyst releases sporozoites that migrate to mosquito salivary glands
• Rhizaria


  • Species-rich supergroup of mostly unicellular eukaryotes
  • Vary considerably in form, with no clear morphological distinctive characters
  • Most are biciliate amoeboflagellates, at least at some point in their life cycle
  • Produce shells or skeletons called tests, which make up the vast majority of protozoan fossils
  • Nearly all have mitochondria with tubular cristae
• Actinopods


  • Have a rigid and beautiful structure, often with a siliceous (glassy) shell
  • Are planktonic, floating in the water column
  • Have slender pseudopodia called axopodia that extend from the shell and capture small organisms
• Acantharia


  • Planktonic, free living, exclusively marine protozoa
  • Cell consists of a central endoplasm and a peripheral ectoplasm, separated by a central capsule
  • Skeleton of strontium sulfate (SrSO4), or celestite
  • Cell body covered with an outer pellicle and contractile filaments (myonemes) grouped around the spicule
  • Reproduce asexually by binary fission and sexually by isogamy
• Heliozoa


  • Spherical, predominantly freshwater organisms
  • Body consists of an outer cortex and an inner medulla
  • Frequently enveloped by a shell (or test) composed of silica or other materials
• Acantharian


  • Central capsule perforated by pores
  • Endoplasm contains nuclei and organelles, often brown, red, or black
  • Ectoplasm contains digestive vacuoles
  • Provided with axopodia stiffened by a central axis (axoneme)
  • Skeleton of strontium sulfate (SrSO4), or celestite
  • Cell body covered with an outer pellicle, the periplasmic cortex
  • Myonemes, contractile filaments grouped around the spicule
  • Contractile vacuoles absent
• Acantharian


  • Amphilonche
  • Acanthochiasma
• Heliozoa


  • Spherical and predominantly freshwater
  • Body consists of outer cortex containing food and contractile vacuoles, and inner medulla containing nuclei and axopod base
  • Frequently enveloped by a shell (or test) composed of silica or organic material
  • Radiating cytoplasmic masses called pseudopodia used for capturing food, not locomotion
• Heliozoa


  • Actinophrys sol
  • Acanthocystis turfacea
  • Actinosphaerium
• Radiolaria


  • Mostly spherically symmetrical
  • Complex and beautifully sculptured, minute skeletons (tests) composed of silica
  • Tests elaborately perforated in a variety of patterns
  • Pseudopodia extend through the perforated skeleton
  • Chitinous central capsule encloses nuclei and divides cytoplasm into two zones
  • Outer cytoplasm contains vacuoles that control buoyancy
• Radiolaria


  • Hexaconthium
  • Thalassicola
• Foraminifera


  • Marine
  • Shells are chalky calcium carbonate, often shaped like microscopic snail shells
  • Tend to live attached to the bottom or to objects in the water
  • Shells have tiny holes (Foraminifera means "hole bearer") for projection of reticulopods
  • Shells may be unilocular or multilocular
• Foraminifera


  • Globigerina
  • Elphidium
• Excavata


  • Unicellular organisms belonging to the domain Eukaryota
  • Many lack 'classical' mitochondria, have hydrogenosomes or mitosomes instead
  • Most have two, four, or more flagella
  • Many have a conspicuous ventral feeding groove with a characteristic ultrastructure
• Kinetoplastida


  • Flagellated protists characterized by presence of a kinetoplast (large massed DNA in mitochondrion)
  • Includes parasites responsible for serious diseases in humans and other animals, as well as free-living forms
  • Biflagellate bodonids and uniflagellate trypanosomatids
• Trypanosomatida


  • Parasitic kinetoplastids with complex life cycles progressing through multiple differentiation stages in two hosts
  • Dramatic morphological changes between lifecycle stages
• Kinetoplastida


  • Trypanosoma brucei (African sleeping sickness)
  • Trypanosoma cruzi (Chagas disease)
  • Leishmania (leishmaniasis)
• Life cycle of Trypanosoma brucei


  1. Metacyclic trypomastigotes delivered to mammalian bloodstream by tsetse fly bite

  2. Metacyclics differentiate into proliferating long slender forms

  3. Long slender forms penetrate blood vessel endothelium and invade tissues including CNS

  4. Long slender forms differentiate into short stumpy forms pre-adapted for tsetse fly

  5. Short stumpy forms taken up by tsetse fly, differentiate into procyclic trypomastigotes in midgut

  6. Procyclics migrate to proventriculus, undergo asymmetric division to generate epimastigotes

  7. Epimastigotes reach salivary glands, attach to epithelium and replicate

  8. Asymmetric division of attached epimastigotes generates free metacyclic trypomastigotes
• Metamonada


  • Large group of flagellate amitochondriate excavates
  • Lack mitochondria but retain mitochondrial relics like hydrogenosomes and mitosomes
  • Flagella or basal bodies in characteristic groups of four, often associated with nucleus (karyomastigont)
• Parabasalia


  • Found only in association with animals, some are pathogens
  • Characterized by axostyle composed of microtubules, 3-5 free flagella and a recurrent flagellum forming an undulating membrane
• Diplomonadida


  • Small heterotrophic protists with no mitochondria, mostly commensal in animal intestines
  • Have two sets of organelles: two nuclei, two sets of four flagella, two adhesive disks and a ventral groove