MIC462 Eukaryotic Microorganisms - Comprehensive Notes

Eukaryotic Microorganisms - MIC462

1.0 Kingdom Microbial Diversity

• Classification System:
  • Multicellular vs. Unicellular
  • Kingdoms: Protista, Algae, Fungi
• Taxonomy & Binomial Nomenclature
• Phylogenetic Tree
• Prokaryotic Microorganism VS
  • Cell Structure & Size
  • Genetic Materials
  • Replication Steps
• Endosymbiosis Theory
• Major Organelles

2.0 Classification

• Algae:
  • Red
  • Green
  • Brown

3.0 Unicellular Eukaryotes - Protista

• 2.1 Eukaryotes vs. Prokaryotes
• 2.2 Cell theory
• 2.3 Major organelles

Chapter 3 Topic Outlines

• Classification of Protozoa
• Morphology of Protozoa
• Reproduction in Protozoa
• Nutrient Acquisition
• Special Features - Locomotion
• Typical Species

Classification of Protozoa

• Protozoa are eukaryotic single-celled organisms within Kingdom Protista.
• Major classification is based on locomotion:
  • (1) Flagellates or Mastigophora (e.g., Giardia lamblia)
  • (2) Amoeba or Sarcodina (e.g., Entamoeba histolytica)
  • (3) Ciliates or Ciliophora (e.g., Balantidium coli)
  • (4) Sporozoa (e.g., Plasmodium knowlesi)
• Majority of protozoa species are:
  • Unicellular
  • Free-living
  • Pathogenic – Members of Sarcomastigophora sp, Apicomplexa sp.

Major Diseases Related to Protozoa Species

Examples of Protozoa

• Mastigophora: Chlamydomonas, Euglena (move via flagella)
• Sarcodina: Amoeba, Arcella (move via pseudopodia)
• Ciliophora: Paramecium, Vorticella (move via cilia)
• Apicomplexa: Plasmodium (undulating membrane; parasitic in red blood cells)

Classification - Mastigophora

• Mastigophora is a division of unicellular eukaryotic microorganisms belonging to protozoa.
• Most species are capable of self-propelled movement via flagella.
• Some species have pseudopodia (minor).
• Difference between flagella and pseudopodia: Flagella are permanent structures, while pseudopodia are temporary.
• Mastigophora are classified into Phytomastigophora and Zoomastigophora:
  • Phytomastigophora: Chloromonadida sp, Chrysomonadida sp, Coccolithophorida sp, Cryptomonadida sp, Dinoflagellida sp, etc.
  • Zoomastigophora: Choanoflagellida sp, Bicosoecida sp, Rhizomastigida sp, Kinetoplastida sp, etc.

Examples of Mastigophora Species

• Trachelomonas
• Oikomonas
• Astasiopis
• Mastigamoeba
• Dimorpha
• Dallingeria
• Tetramita
• Cryptomonas
• Diplomita
• Peranema
• Phacus
• Chlamydomonas
• Gonium
• Eudorina
• Pandorina
• Dinobryon
• Synura
• Ceratium
• Noctiluca
• Chilomonas
• Ptychodycus

Classification - Ciliophora

• Currently, there are at least 7,500 described species within the group.
• Ciliophora is Latin for eyelash (referring to cilia).
• They are the easiest protists to identify, characterized by cilia.
• Ciliates use cilia for locomotion and include some of the largest free-living protists.
• Examples of Ciliophora:
  • Spirostomum ambiguum, Strombidium lagenula, Paramecium caudatum, Paramecium aurelia, Spirostomum minus, etc.

Classification - Sarcodina

• Sarcodina or Amoeba is a unicellular eukaryotic microorganism.
• Phylum Sarcodina consists of amoeboid protozoa moving and feeding via cytoplasmic streaming (pseudopodia).
• Most species are free-living in aquatic environments, but some are parasitic.
• Phylum Sarcodina is divided into two major groups/classes:
  • Rhizopoda
  • Actinopoda
  • Superclass Rhizopoda: Classes Lobosa, Acarpomyxea, Eumycetozoea, Granuloreticulosea, Filosea, and Plasmodiophorea
  • Superclass Actinopoda: Classes Radiolaria, Heliozoea, and Phaeodarea.
• An estimated >12,000 species are in Phylum Sarcodina.

Typical Sarcodina/Amoeba

• Key structures:
  • Pseudopod
  • Contractile vacuole
  • Food vacuole
  • Nucleus
  • Endoplasm
  • Ectoplasm
  • Membrane

Classification - Apicomplexa

• Possess specialized organelles (apical complex) for penetrating host cells. The majority have an apical complex.
• Apicomplexa is the largest group of parasitic protists (>4000 identified species).
• The phylum is divided into two classes:
  • Aconoidasida (without conoid)
  • Conoidasida (with conoid)
• Conoidasida have a complete, hollow, truncated conoid.
• Apicomplexa (Sporozoa) is significant to humans and animals due to diseases caused by their infections.
• Sporozoa (parasitic protozoa) generally lack flagella, cilia, or pseudopods.
• Well-known parasites infect both animals and humans, causing benign or severe illnesses.
• Examples: Plasmodium sp. (malaria), Giardia duodenalis (coccidiosis).

Apicomplexa - Apical Complex Structure

• Key Structures:
  • Rhoptries
  • Apicoplast
  • Nucleus
  • Dense granules
  • Apical Ring 1 & 2
  • Conoid
  • Polar Ring I & II
  • Plasmalemma
  • Inner membrane
  • Micropore
  • Micronemes
  • Subpellicular microtubules

Morphology

• Unicellular Protista have characteristics similar to multicellular organisms.
• They aren't classified as animals, plants, or fungi.
• The presence of a nucleus means they are all eukaryotic.
  • Animal-like (Protozoan)
    • Ciliates (including planktonic subgroups)
    • Flagettes (Zooflagellates)
    • Sarcodines (amoebas belong to this group)
    • Sporozoans
  • Plant-like
    • Chlorophyta (green algae, mostly single-celled)
    • Rhodophyta (red algae or seaweed, multicellular)
  • Fungus-like
    • Decomposers
    • Molds (slime molds, mildew)

Morphology: Animal-Like Protista

• Characterized by method of movement:
  • Pseudopods or “false feet” - Amoeba (Phylum Sarcodina) has no true shape, moving via cytoplasm projections
  • Cilia - Paramecium and plankton (Ciliate Phylum) use tiny hairs lining the cell's exterior
  • Flagella – From Phylum Mastigophorans; Euglenoids whip a flagellum, Dinoflagettes use two flagella.
• Parasitic protists (e.g., sporozoan) are categorized by movement and disease in hosts.
• Animal-like protozoa are heterotrophic and contain organelles similar to other heterotrophs.

Morphology: Plant-Like Protista

• Foundation of aquatic food chains, responsible for >40% of photosynthesis in salt and fresh water, and essential for atmospheric oxygen production.
• Classified into three phyla:
  • Euglenophytes – One-celled Euglena in fresh water with chloroplasts; autotrophic when light is available and heterotrophic when dark.
  • Chrysophytes – Contain chlorophyll and are autotrophic via photosynthesis; examples include diatoms and green algae (fresh/salt water, sometimes moist land; many, like Volvox, form colonies).
  • Red Algae (seaweed) – Multicellular, in deep salt water; can cause ecological damage.
• Brown Algae - Seaweed with blades, root, and air sac structures; salt water; up to >100 feet; appear most plant-like.
• Dinoflagellates – Contain chlorophyll and use two flagella; create a porous glass (silicon) shell; sometimes glow in the dark ocean floor.

Morphology: Fungus-Like Protista

• Fungus-like protists have cell walls containing chitin but heterotrophic nutrition, like animals.
• They release spores to reproduce and can move (though this occurs only once during their lifespan).
• They require a moist environment to survive.
• Three types:
  • (1) Slime molds – Consume decaying materials, including microorganisms in soils.
  • (2) Water molds – Live in shallow/damp places.
  • (3) Downey mildews – Similar to water molds but harmful to vegetables.

Comparison of Morphology

• Mastigophora
  • Movement Equipment (Flagella): one or more flagella
  • Cellular Structure: Single nucleus, membrane-bound cell body (cytoplasm); photosynthetic species may have chloroplasts.
  • Cytoskeleton: well-developed (microtubules, microfilaments, flagellar apparatus).
• Sarcodina
  • Movement Equipment (Pseudopodia): temporary extensions of cell membrane
  • Cell Structure: Lack permanent organelles; may contain temporary food vacuoles and contractile vacuoles; nuclei.
  • Cytoskeleton: simple (microfilaments, myosin motor, intermediate filaments); flexible cell membrane.
• Ciliophora
  • Movement equipment (Cilia): numerous hair-like; locomotion, feeding, sensory functions
  • Cell structure
    • Oral groove and cytostome
    • Two types of nuclei: macronucleus (cell function) and micronucleus (reproduction).
  • Cytoskeleton: well-developed (microtubules, microfilaments, cilia apparatus).

Reproduction in Protozoa

• Protozoa reproduce sexually and asexually, depending on cell type.
• Sexual reproduction (conjugation in ciliates) requires the exchange of genetic information.
• Sexual reproduction occurs through syngamy, conjugation, and automixis.
• Asexual reproduction is more common (amoeba, flagellates) and involves a single cell producing offspring.
• Asexual reproduction includes binary fission, schizogamy, and budding.

Sexual Reproduction

• Two gametes unite to form a new individual via:
  • (1) Fusion of cytoplasm
  • (2) Fusion of nuclei.
• Protoplast fusion steps (microbial genetic engineering and biotechnology):
  • Preparation of parent protoplasts.
  • Fusion of protoplasts: using fusogens like PEG (Polyethylene Glycol).
  • Nuclear fusion: Combining nuclear contents
  • Formation of hybrid microbial cell: from both parent strains.

Mitotic Division

• A single eukaryotic cell divides to produce two genetically identical daughter cells.
• Maintains chromosome number, is a form of asexual reproduction form.
• Commonly used for rapid growth and population increase in unicellular eukaryotes.
• Occurs in both single-celled and multicellular eukaryotes.

Meiotic Division

• A specialized type of cell division that reduces chromosome number by half, resulting in four genetically diverse daughter cells.
• Produces four daughter cells with half the chromosome number of the parent (haploid cells)
• Leads to genetic diversity.
• Facilitates sexual reproduction by creating gametes or spores.
• Important in the life cycles of certain fungi, algae, and protozoa that can switch between haploid and diploid states.

Types of Meiotic Divisions

• Gametic meiosis
• Zygotic meiosis
• Sporic meiosis
• Zygotic meiosis involves meiosis directly after fertilization, with the diploid phase transient.
• Gametic meiosis involves meiosis occurring in specialized cells before fertilization, with the diploid phase dominating the life cycle.

Syngamy

• Syngamy is the fusion of gametes, typically from two different individuals, to form a zygote.
• It is classified into Isogamy, Heterogamy, and Oogamy.
  • Isogamy – Fusion between two gametes of similar size and shape. (e.g. Foraminifera, Phytomonadina and Gregarinda)
  • Heterogamy – Fusing gametes differ in size, shape, and behavior.
  • Oogamy – Fusion of gametes of different motility.

Conjugation

• In conjugation, temporary mating occurs between two mating types of individuals of the same species to transfer nuclear materials.
• They maintain distinct individuality and separate out after nuclear exchange.
• These two mating gametes are termed conjugants, they can be either isogamous (Paramecium) or anisogamous (Vorticella).

Automixis

• Automixis is the fusion of two gametic nuclei originating via division of the single nucleus of an individual.
• Self–fertilization or autogamy occurs in a single individual (Paramecium aurelia).
• Types:
  • Autogamy - (A → A2+A3 →A2 and A2 or A3 and A3 fuse together, fusing nuclei come from the same cell).
  • Paedogamy – A2 and A2 from different cells.
  • Cytogamy

Automixis -Autogamy

• The fusing nuclei come from the same cell, as in Paramecium.
• All nuclear changes are similar to conjugation, but the union occurs between pronuclei of the same individual.

Automixis - Paedogamy

• The fusion occurs between two nuclei coming from same parent cells.
• A single organism encysts and then divides into two or more gametocytes.
• The nuclei of these gametocytes undergo meiosis, and the gametes thus produced unite in pairs, forming the zygotes.
• Examples: Actinosphaerium, Actinophrys, myxosporidians, etc.

Nutrient Acquisition

• Nutrition in protozoa – a process of ingestion, assimilation, and egestion of food to release energy needed for various cell activity.
• General nutrition acquisition in Protozoa – autotrophic, heterotrophic, parasitism, etc.
• Methods:
  • 1. Holophytic nutrition,
  • 2. Holozoic nutrition,
  • 3. Saprozoic nutrition,
  • 4. Mixotrophic nutrition,
  • 5. Parasitic nutrition.

Specific Methods of Nutrition Acquisition

• 1. Holophytic Nutrition – Similar to plants, synthesizes organic compounds from sunlight.
• 2. Holozoic Nutrition – Ingests solid food particles, digests, and absorbs nutrients.
• 3. Saprozoic Nutrition – Absorbs soluble organic nutrients directly from the environment.
• 4. Mixotrophic Nutrition – Combines autotrophic and heterotrophic modes for versatility.
• 5. Parasitic Nutrition – Lives off a host, potentially causing harm while obtaining nutrients.

Nutrients Acquisition – Holophytic Nutrition

• Holophytic nutrition: microorganisms (autotroph) manufacture its own food with sunlight, $CO_2$ and water.
• Phytomastigophora with chloroplasts synthesizes food from $H<em>2O$ and $CO</em>2$ in sunlight.
• During this, carbon is retained in the cell and in combination with other inorganic salts and water to form complex organic compounds of protein and carbohydrate.
• Holophytic nutrition is mainly found in Amoeba sp., Giardia sp., Entamoeba sp, Euglena sp.

Nutrients Acquisition – Holozoic Nutrition

• Most free-living Protozoa obtain nutrition by the holozoic mechanism.
• It involves organelles for food capture, ingestion, digestion, assimilation, and egestion of undigested food materials.
• Three steps:
  • Capturing food or ingestion
  • Assimilation or digestion
  • Egestion

Mechanism of Holozoic Nutrition

• Ingestion: capturing food requires locomotory structures.
  • In Mastigophora, it occurs at a specialized region (mouth opening or cytostome) using flagellum.
  • Amoeba use the whole cell body to ingest food, pushing out pseudopodia to encircle and engulf food, forming a food vacuole (phagocytosis).
  • In Ciliophora, a specialized cytostome directs food into the oral groove.
  • Ingestion can also be done using suctorial tentacles.
• Digestion: an intracellular process inside food vacuoles, insoluble food molecules are broken down by digestive enzymes (Trypsin, pepsin, amylase) into its simplest form..
• pH of vacuole is first acidic, then alkaline.
• Adsorption + Assimilation: digested food is absorbed by living cell protozoa for energy production via diffusion.
• Egestion: undigested food material excretion process, cell membrane is ruptured or undigested food is left behind as the cell moves.
• In Paramecium, Euglena, and Ciliates - anal spot or cytopyge for egestion with permanent or temporary opening.

Nutrients Acquisition – Saprozoic Nutrition

• This involves the absorption of food by osmosis, through the general body surface (osmotrophy).
• The food is mainly dead organic matter decomposed by bacteria.
• This kind of nutrition is found in some species of Entamoeba and Euglena.

Nutrients Acquisition – Parasitic Nutrition

• Parasites are biologically and economically connected with the hosts throughout their lifetime.
• Parasitism is defined as an association between the parasites and their hosts.
• It is an association between two organisms whereby the parasite temporarily or permanently lives and feeds in or on the body of the host.
• Almost all the protozoan groups have parasitic species, and the Sporozoa group is exclusively parasitic.
• Two categories of parasitic protozoa:
  • 1. Food Robbers – feed upon the undigested foodstuffs of the host and they do not harm the host.
  • 2. Pathogenic – causing several dreadful diseases.

Nutrients Acquisition – Pinocytosis

• Cell drinking, involves ingestion of liquid food by invagination through the surface of the body.
• The pinocytosis channels formed at some parts of the body enclose the fluid from the surrounding medium.
• The lower ends of these channels are pinched as food vacuoles into the endoplasm.
• Pinocytosis is induced by certain active substances in the medium surrounding the cell, and high molecular compounds from the external medium are absorbed by this method.

Nutrients Acquisition – Myxotrophic

• This is a combination of more than one mode of nutrition.
• Many protozoa using photosynthesis also take in some part of their diet in dissolved form by osmotrophy or solid form by phagocytosis
• The best examples of this kind of nutrition are flagellates like Euglena and Peranema.

Locomotion Organelles

• Protozoa have diverse methods of movement → allow adaptation to various environments.
• Four major types:
  • Flagella (Mastigophora) – whip-like movement.
  • Pseudopodia (Sarcodina) – amoeboid movement.
  • Cilia (Ciliophora) – hair-like movement.
  • Myonemes (Sporozoa) – gliding movement; requires contact with a solid or semi-solid surface.

Locomotion Organelles - Flagella

• Flagella are long, whip-like structures that extend from the cell surface, facilitating locomotion in various microorganisms, including bacteria, archaea, and some eukaryotes.
• Main structures: Filament, Hook, Basal Body, Motor Proteins, and Regulatory Proteins.
• Functions: locomotion, cell feeding, reproduction, and detecting environmental changes like temperature and pH.

Main Structures - Flagella

• Filament
  • Rigid, elastic, surrounded by a protective contractile outer sheath.
  • Consists of 9 longitudinal paired peripheral fibers forming a cylinder and 2 longitudinal central fibers enclosed by a membranous inner sheath (9+2).
• Hook
  • Flexible coupling connect filament and basal body.
• Basal Body
  • Consists of a rod and a series of rings that anchor the flagellum to the cell wall and cytoplasmic membrane.
  • Its main function is to rotate the flagellum and propel the cell.
• Motor Protein
  • Molecular machine responsible for driving the rotation of flagella.
  • Basal body, Rotor, Stator (embedded in cell membrane).
  • LP-Ring and MS Ring (provide structural support).
• Regulatory Protein
  • Involved in the regulation of flagellar assembly, disassembly, and motor function.
  • Coordinate the expression and activity of flagellar genes and respond to environmental signals.

Movement Mechanism - Flagella

• Rotation Mechanisms Powered by ion flow across the membrane.
• The hook acts as a flexible coupling, enabling directional changes and smooth movement.
• Response to the Environment Flagella can detect and respond to external stimuli, adjusting their speed and direction to navigate toward favorable environments or away from harmful conditions.

Flagella Arrangement

• Monotrichous: A single flagellum at one end of the organism or the other.
• Lophotrichous: Several flagellum on one end of the organism or the other.
• Amphitrichous: A single flagellum on both ends of the organism.
• Peritrichous: Several flagellum attached all over the organism.

Type of Flagella

• Stichonematic
• Pantonematic
• Acronematic
• Pantacronematic
• Anematic

Intraflagellar Transport (IFT)

• IFT is the process by which protein complexes are transported along the axonemal microtubules within flagella and cilia, enabling their assembly, maintenance, and movement.
• General Mechanism:
  • IFT involves bidirectional movement along microtubules, utilizing motor proteins for transport in both directions.
  • Kinesin motor proteins facilitate movement towards the tip (anterograde transport), while dynein motor proteins enable movement back to the base (retrograde transport).
• Functions
  • IFT is essential for the length regulation of flagella.
  • Helps in signaling pathways that regulate flagellar functions and cellular responses.

Motor Proteins and Bidirectional Transport

• Kinesin-2: motor protein drives anterograde transport.
• Dynein-1b: motor protein is responsible for retrograde transport.

Locomotion Organelles - Pseudopodia Overview

• Pseudopodia, also known as "false feet," are temporary projections of the cell membrane and cytoplasm in amoeboid cells like Amoeba.
• These structures are essential for the locomotion, feeding, and engulfment of food particles by amoeba.
• Pseudopodia are composed from ectoplasm but also have a core of endoplasm.
• Main components: Actin filaments, Myosin Motor Proteins, Cell Membrane, Cytoplasm, Endoplasm and Ectoplasm.

Main Structure - Pseudopodia

• Actin Filaments
  • Protein filaments that provide the main structure and scaffold for the extension and retraction of pseudopodia.
  • They undergo dynamic assembly and disassembly to enable the protrusion and movement of the cell membrane.
• Myosin
  • A motor protein that interacts with actin filaments to generate force and facilitate movement.
  • In pseudopodia, myosin molecules help to propel the cytoplasm forward by sliding along actin filaments, leading to the extension of pseudopodia.
• Membrane cells
  • Cell membrane extends outward in the direction of movement, forming the leading edge of the pseudopodium.
• Cytoplasm
  • A gel-like substance that fills the interior of the cell. It flows into the pseudopodia during extension.
• Endoplasm and Ectoplasm
  • Endoplasm - denser and contains organelles and food vacuoles,
  • Ectoplasm - less dense and contains a higher concentration of actin filaments.
  • During pseudopodial movement, the ectoplasm undergoes rapid changes in viscosity and flow, allowing for the extension and retraction of pseudopodia.

Locomotion Organelles - Pseudopodia Characteristics

• Temporary Structures: They are formed dynamically as the cell moves towards nutrients or stimuli.
• Flexible and Adaptable: They adjust their shape quickly, allowing the cell to squeeze through tight spaces.
• Components: Pseudopodia consist of cytoplasm composed of outer ectoplasm and inner endoplasm that flow during formation.

Classification of Psuedopodia

1. Lobopodia
2. Filopodia
3. Reticulopodia
4. Axopodia

Locomotion Organelles - Pseudopodia Lobopodia

• Structure: Thick, blunt, and rounded (single/individual).
• Endoplasm & Ectoplasm: Contains both layers, and relatively large and suitable for phagocytosis.
• Actin Filaments: Dense network within the ectoplasmic layer.
• Actin polymerization and depolymerization drive lobopodia extension and retraction, effective for phagocytosis and movement.

Locomotion Organelles - Pseudopodia Filopodia

• Structure: Thin, long, and thread-like with pointed tips (single/individual)
• Endoplasm & Ectoplasm: Composed of ectoplasm (little or no endoplasm); act as sensory probes and attachment points.
• Actin filaments: Bundled and parallel fibers; suitable only for sensing and anchoring, lacking the capacity for engulfing particles.

Locomotion Organelles - Pseudopodia Axopodia

• Structure: Thin and radial symmetry, supported by microtubules (collective/non-individual).
• Endoplasm & Ectoplasm: Primarily ectoplasm (support from microtubules), rapid extension & retraction.
• Actin Filaments: Minor role. Advantageous for prey capture and maintaining buoyancy.

Locomotion Organelles - Pseudopodia Reticulopodia

• Structure: Reticulopodia form a net-like, interconnected network (collective form/non-individual).
• Endoplasm & Ectoplasm: consist of both, combination of endoplasmic streaming and ectoplasmic support.
• Actin filaments: A loosely organized network. Advantageous for prey capture.

Main Structure – Endoplasm & Ectoplasm

Movement Orientation

• Numbers of theories have been put forth to explain the movements of the Amoeba.
  • Actin Driven Motility​ Theory Sol-Gel-Sol Theory
  • Viscosity Theory
  • Amoeboid actions take place in amorphous structures i.e., bodies that do not have any shape or do not have a definite structure.
• Amoeboid movements occur due to cytoplasmic flow in the cells, forces the fluid in front of the cells to move forward by forming structures called pseudopodia.
• The cell undergoes many biochemical changes to alter the viscosity of the fluids in the cytoplasm.

Movement Orientation – Sol-Gel-Sol Theory

• Viscosity Theory consists of:
  • Ectoplasm: contains a thick viscous fluid called the plasma-gel (semi solid).
  • Endoplasm: less viscous liquid called the plasma-sol (liquid).
• Mechanism movement:
  • Transition between plasma gel (semi-solid) and plasma-sol (fluid).
  • Changes in viscosity of both ectoplasm and endoplasm.
  • With direction to move, one end of the cell becomes watery by forming a plasma-sol, and the other forms a plasma-gel.

Movement Orientation – Sol-Gel-Sol Theory

• Anterior (Advancing): Formation of plasma-gel, formation of hyaline cap
• Posterior (trailing): move through the inner region by shifting the liquid from posterior and then reach the gelation zone, and then formation of plasma gel from it.
  • Formation of plasma-sol (posterior).
  • Reaches gelation zone.
  • Forms new hyaline cap.

Movement Orientation - Actin Driven Motility

• Polymerization and depolymerization of actin filaments within the ectoplasm.

1. Actin Filaments Polymerize: Near the leading edge, actin monomers (G-actin) polymerize into filaments (F-actin).
2. Pushing the cell membrane outward and forming a pseudopodium (Cytoskeleton/Lamellipodium, proteins, and lipids of membrane​)
3. Lamellipodia are cytoskeletal protein actin projections at the leading edge of migratory cells.

Lamellipodium Assembly

• Extension: Polymerization of actin filaments leads to protrusive force.
• Adhesion: Binding of amoeba surface receptors to substratum components.
• Translocation: Tension/stress in the lamellipodium to pull the cell body forward.
• De-adhesion: Disassembly and retract the trailing cell edge of cells using contractile force that is generated by focal adhesion disassembly.

Locomotion Organelles - Cilia

• Cilia are short, hair-like projections on the cell surface, each made of microtubules arranged in a specific “9+2” structure.
• Function: Cilia provide locomotion by beating in coordinated waves, enabling ciliates to swim.

Axoneme Structure: main structre of Cilia is similar to flagella

• Components:
  • Axoneme
  • Basal Bodies
  • Motor Proteins (dynein)

Main Structure – Cilia (Axoneme)

• 9 + 2 organization of the peripheral doublet fibrils and central singlet fibrils are embedded in a matrix.
• The central fibrils are enclosed within a delicate sheath.

Movement Orientation - Ciliary Locomotion

• Paramecium moves using coordinated ciliary beating from anterior to posterior, cilia beat across its surface.
• effective stroke: propulsion; recovery stroke: smooth movement.
• This cycle helps with locomotion, fluid movement, and particle clearance from the cell surface.

Key Differences Between Flagella and Cilia