Biomedical Sciences I - Endomembrane System
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Questions and Answers

Which of the following organelles is NOT part of the endomembrane system?

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

    • What is the primary function of the rough endoplasmic reticulum?

  • Modification of incoming proteins
  • Synthesis of lipids
  • Synthesis of proteins (correct)
  • Storage of calcium ions

    • What role do motor proteins play in the endomembrane system?

  • They form membranes around the endosomes.
  • They modify proteins during their passage through the ER.
  • They synthesize proteins within the Golgi apparatus.
  • They assist in moving transport vesicles. (correct)

    • Which statement accurately describes the dynamic nature of the endomembrane system?

    <p>Transport vesicles facilitate movement back and forth between compartments.</p> Signup and view all the answers

    What type of proteins are typically secreted from the cell through the secretory pathway?

    <p>Hormones and neurotransmitters</p> Signup and view all the answers

    Which feature is common to all organelles within the endomembrane system?

    <p>They are bounded by membranes.</p> Signup and view all the answers

    What is primarily synthesized in the endoplasmic reticulum?

    <p>Proteins</p> Signup and view all the answers

    What type of pathway involves transporting proteins to be modified in the Golgi apparatus?

    <p>Biosynthetic pathway</p> Signup and view all the answers

    How are transport vesicles moved within the cell?

    <p>Through the action of motor proteins and cytoskeletal elements</p> Signup and view all the answers

    Which pathway describes proteins destined to remain inside the cell?

    <p>Lysosomal pathway</p> Signup and view all the answers

    What differentiates the Rough Endoplasmic Reticulum (RER) from the Smooth Endoplasmic Reticulum (SER)?

    <p>RER has ribosomes attached to its cytoplasmic surface.</p> Signup and view all the answers

    What is the primary function of Protein Disulfide Isomerase (PDI) in the RER?

    <p>Facilitation of correct protein folding.</p> Signup and view all the answers

    Which of the following proteins is synthesized in the cytosol?

    <p>Proteins intended for mitochondria.</p> Signup and view all the answers

    Where is the lumen of the Endoplasmic Reticulum located?

    <p>Surrounded by the ER membrane and separated from the cytosol.</p> Signup and view all the answers

    What typically characterizes the sorting signals on proteins for their transport?

    <p>They can be identified by specific receptors in the cellular membranes.</p> Signup and view all the answers

    What role does glycosylation play in protein maturation?

    <p>It modifies proteins for correct sorting and transport.</p> Signup and view all the answers

    Which component of the Endoplasmic Reticulum is primarily involved in lipid synthesis?

    <p>Smooth Endoplasmic Reticulum (SER)</p> Signup and view all the answers

    The perinuclear cavity is defined as what?

    <p>The space between the inner and outer nuclear membranes that is continuous with the ER lumen.</p> Signup and view all the answers

    What process occurs primarily in the Rough Endoplasmic Reticulum?

    <p>Synthesis and quality control of proteins.</p> Signup and view all the answers

    How do sorting signals contribute to protein transport in cells?

    <p>They ensure proteins are delivered to the correct cellular compartment.</p> Signup and view all the answers

    What percentage of proteins in mammals are synthesized on ribosomes attached to the rough endoplasmic reticulum (RER)?

    <p>One-third</p> Signup and view all the answers

    Which type of protein is fully translocated across the ER membrane and released into the ER lumen?

    <p>Water-soluble proteins</p> Signup and view all the answers

    What is the role of glycosylation in the rough endoplasmic reticulum?

    <p>To add carbohydrates and prevent degradation</p> Signup and view all the answers

    Which organelle is primarily responsible for the synthesis of lipoprotein particles in liver cells?

    <p>Smooth Endoplasmic Reticulum</p> Signup and view all the answers

    What happens to oligosaccharides once they are attached to nascent proteins in the ER?

    <p>They are modified by removing glucose and mannose</p> Signup and view all the answers

    Which sequence is recognized by the signal recognition particle (SRP) during protein translocation to the rough endoplasmic reticulum?

    <p>N-terminal hydrophobic signal sequence</p> Signup and view all the answers

    How does the endoplasmic reticulum participate in the folding and quality control of proteins?

    <p>Through molecular chaperones that assist in proper folding</p> Signup and view all the answers

    Which of the following is NOT a function of the smooth endoplasmic reticulum?

    <p>Protein synthesis</p> Signup and view all the answers

    Where are the carbohydrate chains of glycoproteins typically located after vesicles fuse with the plasma membrane?

    <p>On the external side of the plasma membrane</p> Signup and view all the answers

    What is a key characteristic of congenital diseases of glycosylation?

    <p>Lack of an enzyme required for glycosylation</p> Signup and view all the answers

    What process is responsible for removing excess Smooth Endoplasmic Reticulum membrane after detoxification is no longer needed?

    <p>Autophagocytosis</p> Signup and view all the answers

    Which component of muscle cells is specialized for sequestering calcium ions?

    <p>Smooth Endoplasmic Reticulum</p> Signup and view all the answers

    What is the main function of the Golgi complex regarding proteins?

    <p>Modification and sorting of proteins</p> Signup and view all the answers

    Which face of the Golgi complex is responsible for receiving vesicles from the Endoplasmic Reticulum?

    <p>Cis face</p> Signup and view all the answers

    Which of the following processes modifies the N-linked oligosaccharides on proteins?

    <p>Glycosylation</p> Signup and view all the answers

    What is the role of mannose-6-phosphate in the Golgi complex?

    <p>It directs transport of proteins to lysosomes</p> Signup and view all the answers

    What type of lipids does the Golgi complex synthesize from ceramide?

    <p>Sphingomyelin and glycolipids</p> Signup and view all the answers

    Which proteins play an important role in regulating the movement of vesicles and tubules in the Golgi complex?

    <p>Motor proteins</p> Signup and view all the answers

    Which structure within the Golgi complex is involved in handling and packaging cellular constituents?

    <p>Cisternae</p> Signup and view all the answers

    What happens to the excessive Smooth Endoplasmic Reticulum after the detoxification process is complete?

    <p>It is removed via autophagocytosis</p> Signup and view all the answers

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    Biomedical Sciences I - Cellular Biology I

    The Endomembrane System

    • Present in all eukaryotic cells
    • Consists of distinct compartments bounded by membranes
    • Forms an extensive network of interconnected tubules and flattened sacs

    Endomembrane System - Components

    • Rough endoplasmic reticulum (RER)
    • Smooth endoplasmic reticulum (SER)
    • Golgi apparatus
    • Lysosomes
    • Endosomes

    The Endomembrane System - Function

    • The organelles are part of a dynamic network.
    • Materials are shuttled back and forth between the different compartments.
    • Transport vesicles move materials between organelles in a directed manner.
    • Motor proteins and cytoskeletal elements are key to transport vesicle movement.

    Endomembrane System - Pathways

    • Biosynthetic pathway: proteins are synthesized in the ER, modified in the Golgi, and transported to various destinations.
    • Example destinations include membrane proteins, and lysosomal enzymes.
    • Secretory pathway: proteins destined to be secreted from the cell (e.g., extracellular matrix proteins, hormones, neurotransmitters).
    • Endocytic pathway: materials move from the cell surface to the intracellular space

    The Endoplasmic Reticulum (ER)

    • The widest subcellular structure in eukaryotic cells
    • Network of membranous tubules and sacs called cisternae.
    • Contains an extensive lumen that is separated from the cytosol by the ER membrane
    • The outer nuclear membrane is continuous with the ER membrane; therefore, the perinuclear cavity is also continuous with the ER lumen.
    • The ER is a dynamic structure with a changeable shape and size.

    Rough Endoplasmic Reticulum (RER)

    • Continuous with the outer nuclear membrane
    • Ribosomes are attached to the cytoplasmic surface of the membrane.
    • Under electron microscope it appears as rough.

    Rough Endoplasmic Reticulum (RER) - Functions

    • Synthesis of proteins
    • Protein folding
    • Initiation of glycosylation
    • Quality control of proteins

    Protein Synthesis

    • Proteins destined for cytosol, nucleus, mitochondria, peroxisomes are made by free ribosomes in the cytosol.
    • Proteins destined for ER, Golgi, lysosomes, plasma membranes, or secretion are made by bound ribosomes attached to the RER and move into the ER for further modifications

    Protein Maturation

    • Proteins are addressed to their correct location by specialized sorting signals.
    • Sorting signals are encoded within the amino acid sequence.
    • Sorting signals are recognized by specific receptors on the cellular membranes.
    • Signal sequences are often removed after the protein has been sorted.
    • There are 3 different ways proteins move between compartments: gated transport, protein translocation, and vesicular transport.

    Rough Endoplasmic Reticulum - functions

    • One-third of the mammals' proteins are synthesized on ribosomes attached to the RER.
    • Proteins enter RER lumen and are translocated through, where they are either secreted or become integral membrane proteins.
    • These proteins are further modified in RER lumen.

    Rough Endoplasmic Reticulum - functions (continued)

    • Synthesis of secreted proteins
    • Integral membrane proteins
    • Soluble proteins
    • Glycosylation
    • Protein folding
    • Quality control

    Rough Endoplasmic Reticulum - Protein Folding and Quality Control

    • Newly synthesized proteins are screened by a quality control system composed of molecular chaperones.
    • These components determine if the protein is properly folded and ready to move to the next cellular compartment.
    • Misfolded proteins are recognized, moved to the cytosol, and degraded

    Congenital Diseases of Glycosylation

    • Inherited metabolic disorders that impact organ systems.
    • These disorders arise when crucial enzymes for glycosylation are missing or dysfunctional.
    • Mutations impede the glycosylation pathways in the ER.
    • Cystic fibrosis is caused by mutations in the CFTR gene.
    • This gene encodes a plasma membrane protein and transport channel, responsible for chloride regulation.
    • The ER's quality control system often degrades mutant CFTR proteins, even if they might function effectively elsewhere.

    Smooth Endoplasmic Reticulum (SER)

    • Lacks ribosomes
    • Usually smaller than RER
    • Located farther from the nucleus
    • Tubular cavities in continuous with RER

    Smooth Endoplasmic Reticulum (SER) - Functions

    • Sequestering calcium ions within the cytoplasm of cells.
    • Synthesis of steroid hormones in endocrine cells (gonads and adrenal cortex).
    • Detoxification of drugs and harmful compounds in liver cells.
    • Principal site of production of lipoprotein particles in liver cells.
    • Synthesis of phospholipids and cholesterol.

    Golgi Complex

    • Stack of flattened cisternae with thickened borders.
    • Associated tubules and vesicles.
    • Contains from a few to several thousands per cell.
    • It's a polarized organelle with distinct faces.
    • The cis face is closer to the ER and receives vesicles.
    • The trans face is opposite to the cis face and releases vesicles.

    Golgi Complex - Functions

    • Handling/packaging center of the cell
    • Modification and synthesis of carbohydrate portions of glycoproteins.
    • Synthesis of glycolipids and sphingomyelin
    • Lipid metabolism (e.g., sphingomyelin synthesis from ceramide).
    • Glycosylation of proteins

    Golgi Complex - Functions (continued)

    • Glycosylation of lysosomal proteins (e.g., addition of mannose-6-phosphate).
    • Modification of N-linked oligosaccharides.
    • Sorting and transport, e.g., proteins to lysosomes.

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    Cellular Biology I - Endomembrane System (PDF)

    Description

    This quiz focuses on the endomembrane system, an essential component in all eukaryotic cells. It covers the structure, components like the rough and smooth endoplasmic reticulum, Golgi apparatus, and their functions. Test your knowledge on this intricate network of organelles.

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