Eukaryotic Microorganisms and Cell Features

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Questions and Answers

What distinguishes eukaryotic microorganisms from prokaryotic microorganisms?

  • Eukaryotic microorganisms have membrane-bound organelles. (correct)
  • Eukaryotic microorganisms cannot be human pathogens.
  • Eukaryotic microorganisms do not have DNA.
  • Eukaryotic microorganisms lack a defined cellular structure.

Which cellular component is responsible for the synthesis of secreted proteins in eukaryotic cells?

  • Golgi apparatus
  • Rough endoplasmic reticulum (correct)
  • Lysosomes
  • Smooth endoplasmic reticulum

Which of the following is a primary function of the Golgi apparatus?

  • Protein synthesis
  • Lipid synthesis
  • ATP production
  • Protein modification and packaging (correct)

What is the main purpose of lysosomes within a eukaryotic cell?

<p>To perform intracellular digestion (C)</p> Signup and view all the answers

How do materials typically move between the endoplasmic reticulum and the Golgi apparatus?

<p>Via transport vesicles (C)</p> Signup and view all the answers

Which of the following is a key component of the eukaryotic cytoskeleton, providing structural support and facilitating movement?

<p>Microfilaments, microtubules, and intermediate filaments (C)</p> Signup and view all the answers

What lipid is a key component of eukaryotic plasma membranes, contributing to membrane strength?

<p>Cholesterol (C)</p> Signup and view all the answers

In eukaryotic cells, what material primarily forms the cell walls of photosynthetic algae?

<p>Pectin (D)</p> Signup and view all the answers

What is the primary function of the nucleolus inside the nucleus?

<p>Ribosome construction (A)</p> Signup and view all the answers

How do eukaryotic flagella facilitate cell movement?

<p>By undulating in a wave-like motion (A)</p> Signup and view all the answers

Which diameter is generally observed for microfilaments?

<p>Approximately 4-7 nm (A)</p> Signup and view all the answers

Which of the following best describes the function of intermediate filaments?

<p>Providing structural support and linking cells (B)</p> Signup and view all the answers

What role do microtubules play within eukaryotic cells?

<p>Maintaining cell shape and participating in intracellular transport (D)</p> Signup and view all the answers

What is the name given to the process where unfolded or misfolded proteins are targeted for destruction in the Secretory Pathway?

<p>Quality assurance mechanism (C)</p> Signup and view all the answers

Why do lysosomes maintain an acidic internal environment?

<p>To activate their hydrolytic enzymes (A)</p> Signup and view all the answers

Which process enables eukaryotic cells to bring materials into the cell?

<p>Endocytosis (D)</p> Signup and view all the answers

What is the function of autophagy in eukaryotic cells?

<p>Digestion and recycling of cytoplasmic components (A)</p> Signup and view all the answers

Which eukaryotic organelles likely originated from bacterial cells according to the endosymbiotic theory?

<p>Mitochondria and chloroplasts (A)</p> Signup and view all the answers

What is the main function of mitochondria in eukaryotic cells?

<p>ATP production through cellular respiration (C)</p> Signup and view all the answers

What is an identifying feature of a hydrogenosome compared to a mitochondrion?

<p>ATP production via fermentation rather than respiration (A)</p> Signup and view all the answers

What role do porins play in the structure of mitochondria?

<p>They are channels in the outer membrane. (B)</p> Signup and view all the answers

What is the primary function of the grana found inside chloroplasts?

<p>To trap light energy and generate ATP, NADPH, and oxygen (B)</p> Signup and view all the answers

Which arrangement refers to the structure of microtubules in eukaryotic flagella and cilia?

<p>9+2 (C)</p> Signup and view all the answers

Where are proteins destined for the cell membrane, endosomes and lysosomes synthesized?

<p>Ribosomes on rough endoplasmic reticulum (B)</p> Signup and view all the answers

How is an autophagosome formed?

<p>Double membrane surrounds cell component (D)</p> Signup and view all the answers

What happens to a lysosome once its contents are digested?

<p>It is called a residual body. (D)</p> Signup and view all the answers

The following are functions of the ER, except:

<p>Synthesising proteins. (B)</p> Signup and view all the answers

What role does the cytoplasm play in eukaryotic cells?

<p>Serves as the location for many metabolic processes (A)</p> Signup and view all the answers

Which of the following components are found in the matrix enclosed by the inner membrane of the Mitochondria? (Select all that apply)

<p>Ribosomes (A), Mitochondrial DNA (C), Enzymes of the tricarboxylic acid cycle (D)</p> Signup and view all the answers

The type of vescicle that delivers proteins to the cell membrane are:

<p>Transport vesicles (C)</p> Signup and view all the answers

Which factor differentiates eukaryotic microorganisms from prokaryotic microorganisms?

<p>Presence of membrane-bound organelles (C)</p> Signup and view all the answers

What is the direct result of the ribosomes being 'attached' to the Rough ER?

<p>Synthesising proteins destined for secretion (D)</p> Signup and view all the answers

Which is the following structures of the Mitochondria has an analogous structure to that of gram-negative bacteria?

<p>Outer membrane (C)</p> Signup and view all the answers

What is the purpose of the nuclear envelope?

<p>To contain DNA (C)</p> Signup and view all the answers

Match the Eukaryotic cell structure to function: Cilia

<p>Cell movement. (C)</p> Signup and view all the answers

Match the Eukaryotic cell structure to function: Nucleus

<p>Repository for genetic information. (C)</p> Signup and view all the answers

Complete the following statement: After release, some vesicles deliver their contents to...

<p>endosomes and lysosomes (C)</p> Signup and view all the answers

Chloroplasts are mostly located in what type of organism? (Select all that apply)

<p>Algae (C), Plants (D)</p> Signup and view all the answers

Through which action is the strength of the plasma membrane reinforced?

<p>Cholesterol (A)</p> Signup and view all the answers

True or False: The Cytoskeleton provides cell structure and movements.

<p>True (B)</p> Signup and view all the answers

Flashcards

Eukaryotic Microorganisms

Prominent members of ecosystems, useful as model systems, and major human pathogens.

Membrane-bound Organelles

Membrane-bound structures within eukaryotic cells that perform specific functions.

Intracytoplasmic Membrane

A complex of internal membranes that acts as a transport system in eukaryotic cells.

Eukaryotic Cell Envelope

The outer boundary of a eukaryotic cell that consists of the plasma membrane and external coverings. It is a lipid bilayer composed of lipids including phosphoglycerides, sphingolipids and cholesterol.

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Cytoskeleton

A vast network of interconnected filaments within the cytoplasmic matrix of eukaryotic cells. Provides structure and movement.

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Microfilaments

Small protein filaments (4-7 nm diameter) in the cytoskeleton involved in cell motion and shape changes.

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Intermediate Filaments

Elements of the cytoskeleton (~10 nm diameter) with structural roles.

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Microtubules

Thin cylinders (~25 nm diameter) involved in maintaining cell shape, movement, and intracellular transport.

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Secretory Endocytic Pathway

An intricate complex of membranous organelles and vesicles that move materials into, out of, and within the cell.

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Endoplasmic Reticulum (ER)

An irregular network of branching and fusing membranous tubules and flattened sacs involved in transport, lipid synthesis and protein synthesis.

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Golgi Apparatus

Organelle made of cisternae involved in modification, packaging, and secretion of materials.

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Lysosomes

Membrane-bound vesicles containing hydrolases for intracellular digestion. Maintain an acidic environment.

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The Secretory Pathway

A pathway used to move materials to various sites within the cell or to the plasma membrane or cell exterior.

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Endocytosis

A process used by all eukaryotic cells to bring materials into the cell.

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Autophagy

Degradation of materials in the cell by a route that does not involve endocytosis.

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Nucleus

The membrane-bound spherical structure that houses genetic material in eukaryotic cells.

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Nuclear Envelope

A double membrane structure in the nucleus that delimits the nucleus, continuous with ER, and penetrated by pores.

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Nucleolus

Organelle within the nucleus, not membrane enclosed, important in ribosome synthesis.

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Eukaryotic Ribosomes

Larger than bacterial ribosomes; may be attached to the ER or free in the cytoplasmic matrix. 80S in size.

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Endosymbiotic Hypothesis

Proposed origin of the mitochondria, hydrogenosomes and chloroplasts organelles.

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Mitochondria

Known as the “power houses of the cell”. Involved in tricarboxylic acid cycle activity, ATP generation, electron transport and oxidative phosphorylation.

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Hydrogenosomes

Small energy conservation organelles in some anaerobic protists. Descended from common mitochondrial ancestor.

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Chloroplasts

Organelle involved in photosynthetic reactions and surrounded by a double membrane.

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Flagella

Used for motility, usually 100-200 µm move in undulating fashion.

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Cilia

Used for motility, usually 5-20µm long, working like oars.

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Ultrastructure of Flagella and Cilia

Membrane-bound cylinders that are ∼2 µm in diameter.

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Study Notes

  • Eukaryotic microorganisms are crucial ecosystem members.
  • They are valuable for model systems and industry applications.
  • They can be significant human pathogens.
  • Protists and fungi are the two eukaryotic groups commonly possessing microbial members.

Features of Eukaryotic Cells

  • Eukaryotic cells have membrane-delimited nuclei.
  • They also have membrane-bound organelles performing specific functions.
  • Eukaryotic cells feature an intracytoplasmic membrane complex that serves as a transport system.
  • Eukaryotic cells are structurally more complex and generally larger than bacterial or archaeal cells.

Eukaryotic Cell Envelopes

  • The eukaryotic cell envelope includes the plasma membrane and external coverings.
  • The plasma membrane is a lipid bilayer with major lipids like phosphoglycerides, sphingolipids, and cholesterol.
  • These lipids contribute to the membrane's strength.
  • Unlike the peptidoglycan in bacterial and archaeal cell walls, many eukaryotes lack or have chemically distinct cell walls.
  • Photosynthetic algae cell walls are composed of cellulose, pectin, and silica.
  • Fungi cell walls are made of cellulose, chitin, or glucan.

The Cytoplasm of Eukaryotes

  • The cytoplasm comprises liquid cytosol and organelles.
  • The cytoskeleton is a network of interconnected filaments in the cytoplasmic matrix.
  • Filaments forming the cytoskeleton include microfilaments (actin), microtubules, intermediate filaments, and motor proteins.
  • The cytoskeleton plays a role in cell shape and movement.

Microfilaments

  • Microfilaments are small protein filaments with a diameter of 4 to 7 nm.
  • They are scattered within the cytoplasmic matrix or organized into networks and parallel arrays.
  • Actine is the protein that composes microfilaments
  • Microfilaments participate in cell motion and shape changes.

Intermediate Filaments

  • Intermediate filaments are heterogeneous elements of the cytoskeleton.
  • They are approximately 10 nm in diameter.
  • Keratin and vimentin are examples of intermediate filaments.
  • The role of intermediate filaments in the cell includes structural support, nuclear lamina formation, and linking cells into tissues.

Microtubules

  • Microtubules are shaped like thin cylinders, about 25 nm in diameter.
  • They are made of σ and ẞ-tubulin.
  • Microtubules help maintain cell shape.
  • They are involved with microfilaments in cell movements and participate in intracellular transport processes.

Secretory Endocytic Pathway

  • The secretory endocytic pathway is an intricate complex of membranous organelles and vesicles that move materials into the cell, from inside to outside, and within the cell.
  • It includes the endoplasmic reticulum (ER), Golgi apparatus, and lysosomes.

Endoplasmic Reticulum (ER)

  • The ER is an irregular network of branching and fusing membranous tubules and flattened sacs known as cisternae.
  • Rough ER has attached ribosomes that synthesize secreted proteins.
  • Smooth ER lacks ribosomes and facilitates lipid synthesis.

ER Functions

  • The ER transports proteins, lipids, and other materials within the cell.
  • The ER serves as a major site of cell membrane synthesis.

The Golgi Apparatus

  • The Golgi apparatus is made of stacked cisternae.
  • It has cis and trans faces.
  • Dictyosomes are stacks of cisternae, central to this organelle.
  • It is involved in the modification, packaging, and secretion of materials.

Lysosomes

  • Lysosomes are membrane-bound vesicles found in most eukaryotes.
  • They participate in intracellular digestion.
  • Lysosomes contain hydrolases, enzymes that hydrolyze molecules and function best under slightly acidic conditions.
  • They maintain an acidic environment by pumping protons into their interior.

The Secretory Pathway

  • The secretory pathway is used to move materials to various sites within the cell and either the plasma membrane or cell exterior.
  • Proteins for the cell membrane, endosomes, lysosomes, or secretion are synthesized by ribosomes on rough endoplasmic reticulum (RER).
  • These proteins are targeted to the RER lumen and released in small budding vesicles from RER.

Secretory Pathway - Continued

  • Small vesicles release the proteins at the cis face of the Golgi apparatus, with modifications occurring there before being released at the trans face.
  • Transport vesicles, modified proteins, are released from the trans face of the Golgi.
  • Some vesicles after release deliver their protein contents to endosomes and lysosomes.
  • Two types of vesicles deliver proteins to the cell membrane.
    • Constitutive delivery, and special secretory vesicles only release proteins when a signal is present in multicellular eukaryotes.

Secretory Pathway - Quality Assurance

  • During synthesis, quality assurance mechanisms identify unfolded or misfolded proteins.
  • These proteins are secreted into the cytosol, targeted for destruction by ubiquitin polypeptides, and destroyed by proteasomes.

The Endocytic Pathway

  • Endocytosis is used by all eukaryotic cells to bring materials into the cell.
  • Solutes or particles are taken up and enclosed in vesicles pinched from the plasma membrane.
  • In most cases, materials are then delivered to the lysosome and destroyed.

Types of Endocytosis

  • Phagocytosis uses cell surface protrusions to surround and engulf particles.
  • In clathrin-dependent endocytosis, clathrin protein-coated pits have external receptors that specifically bind macromolecules.
  • Caveolae-dependent endocytosis may play a role in signal transduction and transporting small and macromolecules.

Endocytosis Process

  • Clathrin-coated vesicles, along with some caveolin-coated vesicles, transport the contents to endosomes.
  • Early endosomes mature into endosomes that eventually fuse with lysosomes.
  • Caveosomes also fuse with early endosomes.

Autophagy

  • Autophagy delivers materials by a route that does not involve endocytosis for digestion.
  • Macroautophagy involves digestion and recycling cytoplasmic components.
  • A double membrane forms an autophagosome around the cell component.
  • The autophagosome then fuses with a lysosome.

Once Lysosome is Formed

  • Digestion occurs without any lysosome enzymes releasing into the matrix.
  • Once the contents inside have been completely digested, the products are used as nutrients.
  • A residual body forms (resulting lysosome) and releases its contents outside by lysosome secretion.

Genetic Control Organelles

  • The nucleus and ribosomes are involved in genetic control of the cell.

The Nucleus

  • The nucleus is a membrane-bound spherical structure that houses the genetic material of a eukaryotic cell.
  • Chromatin, a dense fibrous material, is within the nucleus.
    • Composed of DNA, histones, and other proteins.
    • Five types of histones form nucleosomes: H1, H2A, H2B, H3, and H4.
    • Chromatin condenses into chromosomes during division.

Nuclear Envelope

  • The nuclear envelope is a double membrane that delimits the nucleus
  • It is continuous with the ER.
  • The nuclear envelope is penetrated by nuclear pores.
    • Associated proteins make up the nuclear pore complex.
    • These pores allow materials to be transported into or out of the nucleus.

The Nucleolus

  • Eukaryotic cells usually have more than one nucleolus per nucleus.
  • This organelle lacks a membrane enclosure.
  • It is important in ribosome synthesis.
    • Directs synthesis and processing of rRNA.
    • Directs the assembly of rRNA to form partial ribosomal subunits.
    • Ribosomes mature in the cytoplasm.

Eukaryotic Ribosomes

  • Eukaryotic ribosomes are larger in mass than 70S bacterial and archaeal ribosomes.
  • They are 80S in size, containing 60S and 40S subunits.
  • They may be attached to the ER or free in the cytoplasmic matrix.
  • The 60S subunit is bound to the ER.
  • Proteins made on ribosomes of RER are secreted or inserted into the ER membrane as integral membrane proteins.
  • Free ribosomes synthesize nonsecretory and nonmembrane proteins.
    • Some proteins are inserted into organelles.

Organelles Involved in Energy Conservation

  • Mitochondria, hydrogenosomes, and chloroplasts are organelles involved in energy conservation.
  • The Endosymbiotic Hypothesis states that all these organelles likely evolved from bacterial cells that were ingested by early eukaryotic cells.

Mitochondria

  • Mitochondria, the cell's "power houses," are found in most eukaryotic cells.
  • They are the site of tricarboxylic acid cycle activity and where ATP is generated by electron transport and oxidative phosphorylation.
  • Mitochondria are about the same size as bacterial cells and reproduce by binary fission.

Mitochondrial Structure

  • The outer membrane contains porins similar to the outer membrane of Gram-negative bacteria.
  • The inner membrane is highly folded to form cristae, containing location of enzymes and electron carriers for electron transport and oxidative phosphorylation.
  • The matrix enclosed by the inner membrane contains ribosomes (same size as bacterial), mitochondrial DNA (may be closed circular like bacteria DNA), and enzymes of the tricarboxylic acid cycle and enzymes involved in catabolism of fatty acids.

Hydrogenosomes

  • Hydrogenosomes are energy conservation organelles in anaerobic protists.
  • These organelles descended from a common mitochondrial ancestor.
    • They have a double membrane, lack cristae, and usually lack DNA.
    • ATP is generated by fermentation rather than respiration.
    • Products include CO2, H2, and acetate.

Chloroplasts

  • Chloroplasts are a type of plastid observed in plants and algae.
  • This is the site of photosynthetic reactions. It is surrounded by a double membrane.
  • The stroma (matrix) is within the inner membrane and contains DNA, ribosomes, lipid droplets, starch granules, and thylakoids.
  • Thylakoids are flattened, membrane-delimited sacs.
    • Grana (s., granum) are stacks of thylakoids, and are the site of light reactions (trapping of light energy to generate ATP, NADPH, and oxygen).
  • The stroma is the site of the dark reactions of photosynthesis. Formation of carbohydrates from water and carbon dioxide
  • Algal chloroplasts contain a pyrenoid, which participates in polysaccharide synthesis.

External Cell Coverings

  • Cilia and flagella are external cell coverings.
  • Flagella (singular: flagellum) are 100–200 µm long and move in an undulating fashion.
  • Cilia (singular: cilium) are 5-20 µm long and beat with two phases, working like oars.
  • Membrane-bound cylinders are about 2 µm in diameter.
  • The axoneme contains microtubules in a 9+2 arrangement.
  • The basal body is at the base of the flagellum or cilium and directs synthesis of flagella and cilia.

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