Endomembrane Pathway Overview

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Questions and Answers

Which organelle is primarily responsible for the synthesis of lipids?

  • Transport vesicles
  • Rough endoplasmic reticulum
  • Golgi apparatus
  • Smooth endoplasmic reticulum (correct)

What process occurs when vesicles release their contents to the extracellular environment?

  • Phagocytosis
  • Transcytosis
  • Endocytosis
  • Exocytosis (correct)

Which part of the endomembrane pathway involves sorting and packaging of proteins and lipids?

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

In the secretory pathway, which sequence correctly describes the transport of proteins?

<p>Rough ER → Golgi → secretory vesicles → cell exterior (D)</p> Signup and view all the answers

What is the initial step in the synthesis of proteins destined for secretion?

<p>Synthesis on ribosomes attached to the rough ER (D)</p> Signup and view all the answers

Which vesicles contain modified proteins after they leave the Golgi apparatus?

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

Which of the following is NOT a component of the endomembrane pathway?

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

What role do transport vesicles play in the endomembrane pathway?

<p>They move molecules between organelles. (C)</p> Signup and view all the answers

Which of the following describes the PM pathway accurately?

<p>Rough ER → Golgi → membrane vesicles → PM (D)</p> Signup and view all the answers

What distinguishes rough ER from smooth ER?

<p>Attachment of ribosomes (B)</p> Signup and view all the answers

What happens to proteins after being synthesized on ribosomes of the rough ER?

<p>They undergo folding and modifications in the ER lumen (C)</p> Signup and view all the answers

Which type of ribosomes synthesizes proteins intended for the cytoplasm?

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

Which modification is commonly performed on proteins within the rough ER?

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

What is the main function of the rough ER?

<p>Production of proteins for export or secretion (C)</p> Signup and view all the answers

Which coat protein is primarily responsible for forming vesicles that transport materials from the Golgi apparatus back to the ER?

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

What is the primary direction of vesicle movement in the endomembrane trafficking process?

<p>ER to Golgi (B)</p> Signup and view all the answers

Which motor proteins are responsible for transporting vesicles along microtubules?

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

Which stage in vesicular trafficking involves the formation of vesicles required for exocytosis?

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

What is the role of COPII coat proteins in vesicular trafficking?

<p>Form vesicles moving from ER to Golgi (B)</p> Signup and view all the answers

During vesicular transport, what happens once a vesicle reaches its destination?

<p>It docks and then undergoes a fusing process (D)</p> Signup and view all the answers

Which of the following accurately describes the movement of vesicles during vesicular trafficking?

<p>Vesicles can move in multiple directions depending on the proteins (D)</p> Signup and view all the answers

What is the primary function of the Golgi apparatus regarding proteins?

<p>Modification and packaging for transport (A)</p> Signup and view all the answers

Which process primarily occurs in the Golgi apparatus to modify proteins?

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

How does the Golgi apparatus 'tag' proteins for their final destination?

<p>By adding specific modifications (B)</p> Signup and view all the answers

In which compartment of the Golgi apparatus do proteins primarily undergo modifications?

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

What types of groups can the Golgi apparatus add to proteins aside from sugar chains?

<p>Phosphate groups and sulfate groups (B)</p> Signup and view all the answers

Which face of the Golgi apparatus is responsible for packaging proteins into transport vesicles?

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

What is the primary function of COPI coat proteins in vesicular transport?

<p>Forming vesicles that move between the Golgi apparatus (B)</p> Signup and view all the answers

Which motor proteins are primarily involved in the transport of vesicles along microtubules?

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

During which stage of vesicular transport does a vesicle merge with its target membrane?

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

What is the main role of clathrin in vesicular transport?

<p>To form vesicles for both endocytosis and exocytosis (D)</p> Signup and view all the answers

Which statement accurately describes vesicle budding?

<p>It requires the presence of coat proteins for vesicle formation. (D)</p> Signup and view all the answers

In which direction do vesicles typically move from the Golgi apparatus?

<p>From the cis Golgi to the plasma membrane (C)</p> Signup and view all the answers

What happens to proteins that are mistakenly included in vesicles during the transport process?

<p>They return to the ER if they were meant to stay there. (D)</p> Signup and view all the answers

How are lysosomes formed within a cell?

<p>From vesicles that bud off from the trans-Golgi network (B)</p> Signup and view all the answers

What is the primary function of lysosomal enzymes?

<p>To break down worn-out cell parts and debris (D)</p> Signup and view all the answers

What is the significance of the acidic environment within lysosomes?

<p>It enhances the ability of enzymes to break down materials (C)</p> Signup and view all the answers

Which organelle is involved in producing proteins that are later modified for lysosomes?

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

What mechanism allows lysosomes to access their cargo for degradation?

<p>Fusion with vesicles containing materials (C)</p> Signup and view all the answers

What is the primary function of microtubules in a eukaryotic animal cell?

<p>Organizing the positions of organelles and directing intracellular transport (D)</p> Signup and view all the answers

Which cytoskeletal filament type is primarily responsible for mechanical strength in animal cells?

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

Where are microfilaments most concentrated within an animal cell?

<p>Right beneath the plasma membrane (C)</p> Signup and view all the answers

What role do intermediate filaments primarily play in the context of epithelial cells?

<p>Building networks that connect epithelial cells (A)</p> Signup and view all the answers

Which of the following correctly describes microfilaments?

<p>Actin-based filaments concentrated beneath the plasma membrane (D)</p> Signup and view all the answers

What is the primary role of keratin in epithelial cells?

<p>Holding skin cells together and resisting mechanical tension (A)</p> Signup and view all the answers

Which type of intermediate filament is associated with neurons?

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

What is the function of vimentin in connective tissue cells?

<p>Holding tissues together and providing strength (C)</p> Signup and view all the answers

What is the primary role of lamins in the nuclear envelope?

<p>Maintaining the integrity of the nuclear envelope (C)</p> Signup and view all the answers

In which part of the body would you primarily find keratin?

<p>Epithelial cells, hair, and nails (C)</p> Signup and view all the answers

What is the primary function of the nuclear lamina?

<p>Maintaining structural integrity of the nuclear envelope (D)</p> Signup and view all the answers

What are the two types of lamins associated with the nuclear lamina?

<p>A-type and B-type lamins (B)</p> Signup and view all the answers

Which of the following diseases is associated with mutations in lamin genes?

<p>Hutchinson–Gilford progeria syndrome (B)</p> Signup and view all the answers

What is a key characteristic of the proteins that make up the nuclear lamina?

<p>They possess strength and elasticity (D)</p> Signup and view all the answers

What critical roles does the nuclear lamina play in cellular processes?

<p>Facilitates chromosome organization and mitosis (C)</p> Signup and view all the answers

What is the primary function of neurofilaments in neurons?

<p>To provide structural support and maintain shape (C)</p> Signup and view all the answers

Which types of neurofilaments are classified based on their chain composition?

<p>Heavy chain, medium chain, and light chain (B)</p> Signup and view all the answers

What happens to neurons if neurofilaments or microtubules are disrupted?

<p>Neurons lose their integrity and may die (B)</p> Signup and view all the answers

Neurofilaments release into which fluids can indicate neuronal damage?

<p>Blood and cerebrospinal fluid (D)</p> Signup and view all the answers

What impact do neurofilaments have during axon development?

<p>They regulate the length and diameter of axons (C)</p> Signup and view all the answers

In which type of cells would neurofilaments primarily be found?

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

Which condition could result from the disruption of neurofilaments?

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

What is the arrangement of microtubules found in most eukaryotic cilia and flagella?

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

Which protein is primarily responsible for mediating movement along microtubules?

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

What role do microtubule rails play in a cell?

<p>Facilitate guided transport of vesicles (C)</p> Signup and view all the answers

What is the role of the centrosome in eukaryotic cell division?

<p>Organize microtubules and form chromosome pairs (B)</p> Signup and view all the answers

During which processes do microtubules undergo polymerization and depolymerization?

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

What is a primary function of microfilaments in muscle cells?

<p>Facilitation of muscle contractions (D)</p> Signup and view all the answers

How do microfilaments enable phagocytosis in white blood cells?

<p>By changing cell shape through polymerization (B)</p> Signup and view all the answers

In which process do microfilaments play a critical role regarding the movement of organelles within a cell?

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

What specific role do microfilaments have during cell division?

<p>Creating a cleavage furrow (A)</p> Signup and view all the answers

Microfilaments are made from which type of protein monomer?

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

Flashcards

Endomembrane Pathway

A complex network of internal membranes within eukaryotic cells used for the synthesis, modification, packaging, and transport of biomolecules.

Transport Vesicles

Small membrane-bound sacs within eukaryotic cells that transport molecules between organelles.

Rough Endoplasmic Reticulum (RER)

Organelle responsible for the synthesis of proteins, particularly those destined for secretion or other cellular compartments.

Smooth Endoplasmic Reticulum (SER)

Organelle responsible for the synthesis of lipids, including steroids and phospholipids.

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Golgi Apparatus

Organelle responsible for further processing, sorting, and packaging of proteins and lipids received from the ER.

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Exocytosis

The process of releasing substances from a cell by fusion of a vesicle with the plasma membrane.

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Secretory Pathway

The pathway where proteins are synthesized in the rough ER, modified in the Golgi, packaged into vesicles, and secreted outside the cell.

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Plasma Membrane Pathway

The pathway where proteins synthesized in the rough ER, modified in the Golgi, are packaged into vesicles and incorporated into the plasma membrane .

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Protein Synthesis

The process by which proteins are assembled on ribosomes attached to the RER.

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What is rough ER?

A network of flattened sacs called cisternae, with ribosomes attached to its membrane. These ribosomes distinguish it from the smooth ER.

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What is the main function of RER?

Proteins destined for the cell membrane, other organelles, or secretion outside the cell are synthesized here.

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What happens to proteins synthesized on the RER?

After being synthesized on ribosomes, proteins are transported into the ER lumen where they undergo folding, modifications like glycosylation, and quality control checks.

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Where are proteins destined for the cytoplasm synthesized?

Proteins destined for the cytoplasm are synthesized by cytoplasmic ribosomes, not by the RER.

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What is the relationship between the RER and nuclear membrane?

The rough ER is continuous with the outer nuclear membrane, forming a interconnected network of membranes.

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What role do clathrin proteins play in vesicular trafficking?

Clathrin coat proteins form vesicles that transport materials from the Golgi apparatus for release outside the cell (exocytosis) or for internalization into the cell (endocytosis).

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What is the function of COPI coat proteins in vesicle trafficking?

COPI coat proteins are involved in the movement of vesicles between different compartments of the Golgi apparatus and in the retrieval of proteins from the Golgi back to the ER.

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What is the function of COPII coat proteins in vesicle trafficking?

COPII coat proteins play a crucial role in transporting vesicles from the endoplasmic reticulum (ER) to the Golgi apparatus.

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How do vesicles move within the cell?

Kinesin and Dynein motor proteins attach to vesicles and move them along microtubule tracks within the cell.

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What is vesicle budding?

Vesicles bud off from one compartment (e.g., ER, Golgi) and carry their contents to another compartment.

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What is vesicle docking?

Vesicles fuse with the membrane of their target compartment, delivering their contents.

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What is vesicular trafficking?

The process of vesicle budding, transport, and fusion with a target membrane, allowing for the movement of materials within a cell.

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What are the compartments of the Golgi apparatus?

The Golgi apparatus is a stack of flattened sacs called cisternae, which are divided into three compartments: cis, medial, and trans. Proteins travel through these compartments, undergoing modifications as they progress.

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What is the main function of the Golgi apparatus?

The most common function of the Golgi is glycosylation, adding sugar chains to proteins to create glycoproteins. It can also perform other modifications like phosphorylation and sulfation.

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How does the Golgi sort and package proteins?

The Golgi tags proteins for their final destination by adding specific modifications, packing them into transport vesicles, and sending them to the correct location within the cell.

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What is the difference between the cis, medial, and trans faces of the Golgi?

The cis face of the Golgi is located near the ER and receives proteins from the ER via transport vesicles. The medial face is the middle region where further modifications happen. The trans face is the exit point where modified proteins are packaged and shipped out.

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What is glycosylation?

Glycosylation is the process of adding sugar chains (glycans) to proteins, creating glycoproteins. This is the most common Golgi modification.

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What are the primary modifications that occur in the Golgi?

The Golgi modifies proteins by adding sugar chains, phosphate groups, or sulfate groups. These modifications help determine what proteins are and where they should go.

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Vesicle Budding?

Vesicles pinch off from a donor membrane, forming small sacs carrying molecules.

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What role do coat proteins play in vesicle transport?

Coat proteins, like COPII, COPI, and clathrin, help vesicles form and are specific to different transport routes.

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How are vesicles transported?

Vesicles travel along microtubules within the cell using motor proteins like kinesin and dynein.

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Vesicle Docking?

A vesicle attaches to its target membrane before fusing with it.

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Vesicle Fusion?

The vesicle membrane merges with the target membrane, releasing its contents.

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What's the general direction of vesicle movement?

Vesicles typically move from the ER to the Golgi and then to the plasma membrane or other compartments.

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Why might vesicles move backwards?

Some vesicles return to the ER from the Golgi to bring back proteins that were mistakenly transported.

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What are lysosomes?

Lysosomes are membrane-bound organelles that act as the cellular recycling center, containing enzymes capable of breaking down various materials within the cell.

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Where do lysosomes come from?

Lysosomes originate from vesicles that bud off from the trans-Golgi network, the final processing stage of the Golgi apparatus.

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What do lysosomes contain?

Lysosomes contain hydrolytic enzymes, which are specialized for breaking down a variety of molecules, including proteins, nucleic acids, lipids, and carbohydrates.

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Why is the lysosomal environment acidic?

Lysosomes maintain a highly acidic pH (around 4-5) within their interiors, necessary for the optimal activity of their digestive enzymes.

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How do lysosomes break down materials?

Lysosomes fuse with other vesicles containing materials destined for degradation, allowing the enzymes to access and break down the cargo.

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Cytoskeleton

A network of protein fibers that provides support, shape, and movement to eukaryotic cells.

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Microtubules

Hollow tubes made of tubulin protein, responsible for organizing organelles, directing intracellular transport, and forming structures like cilia and flagella.

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Intermediate filaments

Rope-like fibers made of various proteins, providing mechanical strength and connecting cells in tissues.

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Microfilaments (Actin filaments)

Thin filaments made of actin protein, responsible for cell shape, movement, and muscle contraction.

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Plasma membrane

The outer boundary of the cell, composed of a phospholipid bilayer, regulating what enters and exits the cell.

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Keratin

A type of intermediate filament found in epithelial cells, hair, nails, and horn, providing strength and resistance to mechanical tension.

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Vimentin

A type of intermediate filament found in connective tissue cells, including muscle, contributing to tissue cohesion and strength.

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Neurofilaments

A type of intermediate filament found in neurons, supporting the unique and complex structure of nerve cells.

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Lamins

A type of intermediate filament that forms a meshwork beneath the nuclear envelope, helping maintain the integrity of the nucleus.

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What is the nuclear lamina?

A network of protein fibers located beneath the inner nuclear membrane, providing structural support and regulating the shape of the nucleus.

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What are lamins?

Lamins are intermediate filament proteins characterized by their strength and elasticity, playing a crucial role in maintaining the integrity of the nuclear envelope.

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How can mutations in lamin genes affect health?

Mutations in lamin genes can lead to a wide range of diseases, including Hutchinson-Gilford progeria syndrome (HGPS), which causes premature aging, and Emery-Dreifuss muscular dystrophy, a muscle-weakening disorder.

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What are the types of lamins?

A-type lamins and B-type lamins are the two types of lamins found in cells. They have both structural and regulatory roles in the nucleus.

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Why is the nuclear lamina important?

The nuclear lamina is essential for essential nuclear activities like mitosis (cell division) and chromosome organization, ensuring proper cell function.

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What are neurofilaments?

A type of intermediate filament found in the cytoplasm of nerve cells, providing structural support and helping maintain the neuron's unique shape.

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What is the role of neurofilaments in axon development?

Neurofilaments are crucial for maintaining the length and diameter of axons, helping them grow and stabilize.

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What happens when neurofilaments are damaged?

If neurofilaments are disrupted, the axon loses structural integrity and may retract, leading to neuron death. This can contribute to various neurodegenerative diseases.

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How can neurofilaments be used as biomarkers?

When neurons are damaged, neurofilaments can be released into the blood and cerebrospinal fluid (CSF), serving as a potential biomarker for neuro-axonal injury.

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What happens when lamin genes are mutated?

Mutations in lamin genes can lead to various diseases, including Hutchinson-Gilford progeria syndrome (HGPS), which causes premature aging, and Emery-Dreifuss muscular dystrophy, a muscle-weakening disorder.

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What is the significance of intermediate filaments?

They are an important component of the cytoskeleton, providing structural support and helping to maintain the shape and integrity of the cell.

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What are microtubules?

Microtubules are long, hollow tubes made of tubulin proteins. They are found in eukaryotic cells and play a crucial role in various cellular processes.

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What is the '9+2' arrangement?

The arrangement of microtubules in cilia and flagella is known as the "9+2" structure. It involves nine pairs of microtubules surrounding a central pair.

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How do motor proteins move things?

Motor proteins such as dynein move along microtubules, transporting vesicles and organelles within cells.

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What is the centrosome?

The centrosome is a microtubule organizing center (MTOC) located near the nucleus. During cell division, it plays a vital role in forming the spindle fibers that separate chromosomes.

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How do microtubules grow and shrink?

Microtubules can change in length by adding or removing tubulin monomers. This dynamic process called 'polymerization' and 'depolymerization' is essential for various cellular functions, including cell division.

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How are microfilaments involved in muscle contractions?

One of the main functions of microfilaments is in muscle contractions by interacting with myosin. The sliding filament model explains this process.

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How do microfilaments help with cell movement and phagocytosis?

By quickly assembling and disassembling, microfilaments allow some cells to form temporary extensions called pseudopods. This enables them to move and capture prey.

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What role do microfilaments have in cytoplasmic streaming?

Microfilaments are responsible for the movement of organelles within the cytoplasm, much like tiny tracks for transport.

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How are microfilaments involved in cytokinesis?

During cell division, microfilaments form a band called the cleavage furrow, which pinches the cell in two, creating daughter cells.

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Study Notes

Endomembrane Pathway Overview

  • The endomembrane pathway describes the synthesis, modification, packaging, and transport of biomolecules (proteins and lipids) within a cell.
  • It's crucial for delivering molecules to their final destinations, which might be within the cell or secreted outside.

Components of the Pathway

  • Rough Endoplasmic Reticulum (RER): Site of protein synthesis. Continuous with the outer nuclear membrane; a network of flattened sacs (cisternae) with ribosomes attached to the cytosolic face of the membrane; primarily produces proteins destined for the plasma membrane, other organelles, and secretion. Proteins destined for the cytoplasm are synthesized by cytoplasmic ribosomes, not ER ribosomes.
  • Smooth Endoplasmic Reticulum (SER): Site of lipid synthesis.
  • Golgi Apparatus: Modifies, sorts, and packages proteins and lipids. Contains different compartments (cis, medial, trans).
  • Transport Vesicles: Move molecules between organelles.
  • Lysosomes: Contain hydrolytic enzymes to break down worn-out cellular parts. Originate from the trans-Golgi network.

Protein Synthesis Process

  • Proteins destined for other cellular parts or secretion are made on ribosomes attached to the RER.

ER to Golgi Transport

  • Newly synthesized proteins are packaged into transport vesicles that bud from the ER.
  • These vesicles fuse with the cis face of the Golgi. This movement is driven by COPII coat proteins.

Protein Processing in the ER

  • Once synthesized on ribosomes, proteins are transported into the ER lumen where they undergo folding, modifications like glycosylation, and quality control checks.

Golgi Processing and Sorting

  • Inside the Golgi, proteins are further modified and sorted.
  • The Golgi apparatus is composed of flattened sacs called cisternae, arranged in a stack called a Golgi stack.
  • The Golgi stack has distinct compartments: cis face (closest to the ER), medial, and trans face (closest to the plasma membrane). Each compartment contains specific enzymes for different modifications.
  • The most common Golgi modification is the addition of complex sugar chains (glycans) to proteins, creating glycoproteins, through a process called glycosylation.
  • Other modifications include adding phosphate groups (phosphorylation) or sulfate groups (sulfation) to proteins, depending on the specific protein and its destination.
  • By adding specific modifications, the Golgi "tags" proteins for their final destination, allowing them to be packaged into transport vesicles that bud off from the trans face and deliver the molecules to their correct location within the cell.
  • Proteins are sorted into vesicles based on their final destination, using various coat proteins.
  • Vesicles can move between different Golgi compartments (cis, medial, trans) as well as back to the ER (COPI coat proteins).

Lysosome Function and Origin

  • Lysosomes are formed from vesicles that bud off the trans-Golgi network.
  • They contain hydrolytic enzymes that break down worn-out cell parts, cellular debris, and ingested particles.
  • The interior of a lysosome is acidic (pH 4-5), optimal for its digestive enzymes.
  • Lysosomal enzymes include proteases, nucleases, lipases, and glycosidases, each specific to different molecules.
  • Lysosomes fuse with other vesicles to access their cargo, for degradation.
  • ER produced proteins destined for lysosomes are modified and packaged in the Golgi before transport.

Vesicle Transport and Exocytosis

  • Modified proteins are packaged into Golgi vesicles, using different coat proteins (clathrin, for instance).
  • These vesicles fuse with the cell membrane, releasing their contents via exocytosis.

Key Pathways

  • Secretory Pathway: RER → Golgi → secretory vesicles → cell exterior
  • Plasma Membrane (PM) Pathway: RER → Golgi → membrane vesicles → PM
  • Lysosomal Pathway: Trans-Golgi Network → Lysosome

Vesicular Trafficking

  • Vesicle movement is a multi-step process with four main stages:
    • Vesicle budding: A vesicle pinches off from a donor membrane, dependent on coat proteins (COPII, COPI, clathrin).
    • Vesicle transport: Vesicles use motor proteins (kinesin and dynein) to travel along microtubules to their destinations.
      • COPII coat proteins form vesicles that move from ER to Golgi.
      • COPI coat proteins form vesicles that move between Golgi apparatus and from Golgi back to ER.
      • Clathrin is involved in vesicle formation from Golgi for exocytosis and for endocytosis at PM.
    • Vesicle docking: Vesicles align with the target membrane.
    • Vesicle fusion: The vesicle membrane merges with the target membrane.
  • Movement generally follows ER → cis Golgi → medial → trans → PM and to lysosomes
  • Retrograde transport (Golgi to ER) also occurs using COPI coat proteins, carrying proteins that were mis-sorted into vesicles.

Cytoskeleton

  • Animal cells have three types of cytoskeletal filaments: microtubules, intermediate filaments, and microfilaments (actin filaments).
  • Microtubules: Are polymers made from Tubulin protein monomers. Organize organelles and direct intracellular transport.
  • Microtubules play a role in motility (flagella & cilia) and vesicle transport.
  • Microtubules in cilia and flagella are arranged in a 9 + 2 pattern (nine outer doublets surrounding two central microtubules).
  • Motor proteins like Dynein mediate movement along microtubules.
  • Centrosomes (Microtubule Organizing Centers) are outside the nuclear envelope and organize microtubules. They play a role in chromosome separation during eukaryotic cell division.
  • Microtubules go through polymerization and depolymerization during cell division.
  • Intermediate filaments: Rope-like fibers supporting the nuclear envelope and forming cable networks in epithelial cells; provide mechanical strength. Types include:
    • Keratin: Found in epithelial cells, hair, nails, and horn. Resist tension
    • Vimentin: Found in intracellular fibers of connective tissue cells, including muscle. Provide tissue strength.
    • Neurofilaments: Found in the cytoplasm of neurons in both the central and peripheral nervous systems. Are a key part of the neuronal cytoskeleton, providing structural support and maintaining structure. Neurofilaments regulate axon length and diameter during development and stabilize mature axons. Types include heavy, medium, and light chains. Disruption of neurofilaments or microtubules can cause axon loss, retraction, and neuronal death, leading to dementia. Neurofilaments can be released into blood and cerebrospinal fluid (CSF) after neuronal damage, serving as biomarkers for neuro-axonal injury or loss.
    • Lamins: Components of the nuclear lamina, located beneath the inner nuclear membrane. Characterized by strength and elasticity; play a critical role in regulating the shape and structural integrity of the nuclear envelope, and are essential for many nuclear activities, including mitosis, chromosome organization. Two types: A-type and B-type lamins. Mutations in lamin genes can cause various heritable human diseases, including Hutchinson–Gilford progeria syndrome (HGPS) and Emery-Dreifuss muscular dystrophy.

Microfilaments

  • Microfilaments are polymers made from Actin protein monomers.
  • Cellular muscle: Microfilaments play a crucial role in muscle contractions.
  • Cell Movement & Phagocytosis: Rapid polymerization and depolymerization of microfilaments in white blood cells and amoebas enables pseudopod formation and movement for prey capture.
  • Cytoplasmic Streaming: Microfilaments are essential for the movement of organelles within cells.
  • Cytokinesis: Microfilaments aid in the formation of the cleavage furrow during cell division into two daughter cells.

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