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Introduction to Protozoa


LESSON LEARNING OUTCOMES

1 Able to EXPLAIN various forms of parasite: * Nucleus & cytoplasm * Locomotor organelles

2 Able to EXPLAIN various functions of parasite: * Life cycle & Reproduction * Encystment * Feeding & Metabolism * Excretion & Osmoregulation


1. History begins.. •A. Van Leeuwenhoek observed G. duodenalis in his own diarrheic stools, and he discovered Opalina and Nyctotherus species in frogs intestines. •Other species were being reported since the middle of 18th century at a rapid rate and the discoveries have continued unabated to the present.


2. Overview •The word “protozoa” originated from Greek • Proto (Greek) – first • Zoa (Greek) – animals •Protozoon (singular), Protozoa/ Protozoans (plural) - are microorganisms classified under unicellular eukaryotes (cells contain complex structures enclosed within membranes).


Eukaryotic cells contain membranebound organelles, such as the nucleus, while prokaryotic cells do not.

https://upload.wikimedia.org/wikipedia/commons/thumb/d/d8/Plant_cell _structure-en.svg/1280px-Plant_cell_structure-en.svg.png

https://upload.wikimedia.org/wikipedia/commons/thumb/9/99/Prokaryote _cell_diagram.svg/1024px-Prokaryote_cell_diagram.svg.png


3. Form & Function •

The protozoans cell carries out all of the processes to sustain and propagate life • Form: • Nucleus & cytoplasm • Locomotor organelles • Function: • Reproduction & Life Cycle • Encystment • Feeding & Metabolism • Excretion & Osmoregulation


3. Form & Function 1. Nucleus & Cytoplasm • Bodies are covered by a plasma membrane (PM). • Possess a thick glycocalyx (or glycoprotein surface coat) that has immunological importance. • Undulating membranes in trypanosomes and trichomonads. • Mitochondria : • single large body (in flagellates). • elongated • sausage-shaped structures (in ciliates)


https://upload.wikimedia.org/wikipedia/commons/e/ea/Euglena_diagram.jpg


Undulating membrane

https://c2.staticflickr.com/8/7037/6939384913_ac9d441c84_b.jpg


3. Form & Function


3. Form & Function 1. Nucleus & Cytoplasm – cont… • Microbodies: • spherical structures. • contain oxidase and catalase (in animal & plant cell). • Peroxisomes (in aerobic protozoa): • biochemical activity. • Hydrogenosomes (in anaerobic protozoa- Trichomonas sp): • Glycosomes (in Kinetoplastida)


3. Form & Function 1. Nucleus & Cytoplasm – cont… • Extrusomes: • lie beneath the cell membrane. • will release their contents to the exterior when fuse with the cell membrane: • Toxosomes – release toxic substances that act as a defensive mechanism. • Kinetocysts – to capture food. • Haptocysts – to paralyze prey. • Trichocysts – mechanical resistance to predators. • Mucocysts – to provide a protecting coating against osmotic shock.


3. Form & Function 1. Nucleus & Cytoplasm – cont… • Cytoplasm (central & peripheral zone) can be distinguished as: • Endoplasm : • sol state (fluid/granular) • it bears the nucleus, mitochondria, Golgi bodies. • Ectoplasm: • gel state (solid/ transparent ) • maintain cell shape • more transparent under LM. • where bases of flagella or cilia embedded in.


https://upload.wikimedia.org/wikipedia/commons/thumb/9/9c/Amoeba_%28PSF%29.svg/2000pxAmoeba_%28PSF%29.svg.png


3. Form & Function 1. Nucleus & Cytoplasm – cont… • Membrane –bound nucleus. • Protozoan nuclei are typically oval, discoid, or round, vesicular, irregular distribution of chromatin material and ‘clear’ areas in nuclear sap. • BUT in ciliates: • Micronuclei – reproductive nuclei (meiosis prior to sexual reproduction (conjugation). • Macronuclei – dense, elongated, chainlike or branched. Considered ‘somatic’; function in cell metabolism & growth (do not undergo meiosis) Somatic cells or body cells have a diploid or full set of chromosomes. Gametes or sex cells, also called germ cells, have a haploid number of chromosomes or half the number.


3. Form & Function 1. Nucleus & Cytoplasm – cont… • Endosomes (vesicle arising by endocytosis): • are nucleoli • in parasitic amebas & trypanosomes. •

Nuclear envelope is similar to that of most eukaryotic cells, consisting of two membranes that fuse in the region of pores but the envelope may be thickened.

The nucleolus (plural nucleoli) is a non-membrane bound structure composed of proteins and nucleic acids found within the nucleus


3. Form & Function 2. Locomotor organelles •

Move by three basic organelles • Flagella undulipodia • Cilia • Pseudopodia


3. Form & Function 2a. Locomotor organelles – Flagella (undulipodia) • • •

Slender Whiplike structure Heterokont – a flagellate has at least two flagella with differing structures/ shapes.

Entire unit: flagellum, kinetosome & associated organelles is called mastigont/ mastigont system.


3. Form & Function 2a. Locomotor organelles – Flagella – cont.. •

How about ‘finlike’ undulating membrane ? • kinetosomes are more or less fixed in position relative to other organelles, thus flagella may be directed anteriorly, laterally, or posteriorly, independent of their movements. • flagellum that are bent back along and loosely attached to the lateral cell surface. • Let’s observe


3. Form & Function 2a. Locomotor organelles – Flagella – cont.. • How about their movement? • Beat irregularly, turning-and-coiling in a 3 dimensional space. • body movement may be slow or fast, forward, backward, lateral or spiral. • Let’s see -


3. Form & Function 2b. Locomotor organelles – Cilia (also undulipodia) • •

Structurally similar to flagella How do they move? • Beat regularly, with a back-and-forth stroke in a two dimensional plane. • Let see


3. Form & Function 2c. Locomotor organelles – Pseudopodia in amoebas • temporary extensions of cell membrane and are found in amoebas (an other cell types in other organisms). • function in locomotion and feeding. • Let’s see – lobopodia


3. Form & Function 2c. Locomotor organelles –Pseudopodia – cont… • Four general types in amoebas: Lobopodia

•Finger-shaped, round-tipped, contain both ecto & endoplasm. •e.g. Free living soil, freshwater & ALL parasitic & commensal amebas of human.

Filopodia

•Slender, sharp-pointed, ONLY ectoplasm •e.g Globigerina sp

Rhizopodia (reticulose pseudopod) Axopodia (or actinopodia)

•Branching that may fuse to form netlike meshes. •e.g. Foraminefera Like filopodia, but each contain a slender axial filament composed of microtubules that extent to the cell interior. e.g. Helizoan


http://i.vimeocdn.com/video/564212794_1280x720.jpg


3. Form & Function 2d. • • •

WITHOUT the locomotor organelles glide through fluids with NO subcellular motion. in Apicomplexans (gregarines, coccidia, malarial parasites (Plasmodium), the merozoites, ookinetes and sporozoites. Let see the ‘snakelike’ movement by Gregarines accomplished through the use of an actin & myosin complex.


4. Reproduction & Life cycle •

Either asexual reproduction.

ASEXUAL: i) Binary fission (one divides into two).  plane of fission (amoebas)  longitudinal (flagellates)  homothetogenic – transverse in ciliates

or

sexual

http://cdn.biologydiscussion.com/wp-content/uploads/2016/03/clip_image002_thumb2-6.jpg


4. Reproduction & Life cycle •

ASEXUAL – cont… ii) Multiple fission Merogony (a.k.a schizogony) – multiple fission to produce merozoites (daughter cell from merogony)  in amoebas & Apicomplexa  Nucleus and essential organelles divide repeatedly BEFORE cytokinesis to produce large number of daughter cells.  Cells undergoing schizogony are called: https://s3mn.mnimgs.com/img/shared/discuss_editlive/1350613/2013_01_29_21_53_40/  schizonts kzgfdsgf5690287729533656388.jpg  meronts  segmenter


4. Reproduction & Life cycle •

ASEXUAL – cont ii) Multiple fission – cont… 

Sporogony – Multiple fission of a zygote (sporont)  Sporont – undifferentiated cell mass within an unsporulated oocyst

http://www.tulane.edu/~wiser/protozoology/notes/images/SARCO_LC.gif


4. Reproduction & Life cycle •

ASEXUAL – cont iii) Budding  Plasmotomy – division of a multinucleate cell into multinucleate daughter cell, without accompanying mitosis  External budding – in some ciliates

https://s3mn.mnimgs.com/img/shared/discuss_editlive/4080797/2012_12_24_ 13_15_27/jhj.PNG

http://www.studyandscore.com/images_all/1_Study%20material/Life %20sciences/Zoology/Protozoa/Plasmotomy.png


4. Reproduction & Life cycle •

ASEXUAL – cont iii) Budding – cont…  Internal budding (endopolyogeny) – asexual reproduction in protozoa in which new progeny are produced by budding within the parent cell.  Endododygeny is endopolyogeny in which two daughter cells are formed. (e.g in Toxoplasma gondii).


4. Reproduction & Life cycle •

SEXUAL • involves reductional division in meiosis, resulting changing in from diploidy to haploidy. • involving the union of gametes from two parents (amphimictic) OR, • one parent give rise to both gametes (automictic) • gametes will unite either by the entire cells (called syngamy) or only nuclei.  the larger, more quiescent of the pair – macrogametes  The smaller, more active partner – microgametes  Fusion of macro & microgametes produces a zygote.


4. Reproduction & Life cycle • in conjugation (nuclei unite):  only among ciliates  Cytogamy – two individuals fuse but do not change pronuclei.  Autogamy – haploid pronuclei from the same cell fuse but there is no cytoplasmic fusion with another individual. http://image1.slideserve.com/2202908/paramecium-conjugation-n.jpg


5. Encystment •

the process of forming or becoming enclosed in a cyst or capsule.

resting stage or protection against unfavorable conditions: • food deficiency • desiccation • decreased [O2] • pH and temperature change http://cdn.biologydiscussion.com/wp-content/uploads/2016/05/clip_image002-139.jpg


5. Encystment


5. Encystment • It is important to understand : • the factors that induce cyst formation within the host. • the role in completing of a parasite’s life cycle. • factors to disseminate the cysts. • e.g. amoebiasis is spread by persons who often have no clinical symptoms but pass cysts in their feces. • The composition of the cyst wall (not CELL WALL) varies in different organisms. • What really happen during encystment? •secretion of cyst wall •food reserves are stored (starch & glycogen) •projection of locomotor organelles are partially/wholly re-absorbed.


5. Encystment • a return of favorable conditions will stimulate excystation (escape from a cyst) that occur in the life cycle of parasites after the cystic form has been swallowed by the host. •

Mechanisms for excystation include (in host gut): • water absorption -> cyst swelling • secreting of lytic enzymes by protozoan • action of host digestive enzyme on cyst wall • reactivation of enzyme pathway that were ‘turned off’ during resting stage • internal reorganization • redifferentiation of cytoplasmic and locomotor organelles


6. Feeding & Metabolism • Parasitic protozoans are heterotrophics (organisms that cannot fix carbon and uses organic carbon for growth). • They are generally particles feeders (grazers & predators). • Some show temporary mouth feeding (in amoebas). • Others have permanent cytostomes (cell mouth) (in most ciliates).

http://www.microscopyuk.org.uk/mag/imagsmall/amoebafeeding3.jpg

https://image.slidesharecdn.com/lecture5-150923063458-lva1app6891/95/balantidium-coli-4-638.jpg?cb=1442990146


6. Feeding & Metabolism • sub-microscopic micropore in present Eimeria and Plasmodium species (certain stage involved in taking nutrients). • Food taken into food vacuole (digestive organelle). • Indigestible material is voided through: • temporary opening • permanent opening (cytopyge, in ciliates)

http://www.assignmentpoint.com/wpcontent/uploads/2017/05/Apicomplexa.jpg


6. Feeding & Metabolism •Endocytosis is an important activity in many protozoa: • pinocytosis – deals with droplets of fluid (cell drinking) • phagocytosis – process of internalizing particulate matter (cell eating). •Carry out reactions of glycolysis, the Krebs cycle, nucleic acid metabolism, lipid oxidation etc. •Ammoniotelic – excrete most of their nitrogen to ammonia. •Common waste products are CO2, pyruvate & short-chain fatty acid. •After waste secretion, it will accumulate within their host cell or on the death infected cell that will bring toxic effects on the host. •Contractile vacuoles – probably involved in osmoregulation


LESSON LEARNING OUTCOMES

1 Able to EXPLAIN various forms of parasite: * Nucleus & cytoplasm * Locomotor organelles

2 Able to EXPLAIN various functions of parasite: * Life cycle & Reproduction * Encystment * Feeding & Metabolism * Excretion & Osmoregulation

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