Protein Sorting and Delivery Mechanisms
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Questions and Answers

What mechanism is used by organelles to import proteins?

  • Fusion with the plasma membrane
  • Endocytosis only
  • Passive diffusion
  • Three mechanisms (correct)

    • Proteins with a signal sequence are directed to the wrong organelle.

    False

    What feature is commonly found in signal sequences for organelle targeting?

    Rich in hydrophobic amino acids

    Proteins that lack a signal sequence are typically ________.

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

    Match the following protein signal sequences with their corresponding features:

    <p>N-terminus = Amphipathic helix with basic aa C-terminus = SKL sequence</p> Signup and view all the answers

    What is the primary function of nuclear pores?

    <p>Allowing the passage of proteins between the nucleus and cytoplasm</p> Signup and view all the answers

    Proteins can only enter the nucleus when they are in their unfolded state.

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

    What does NLS stand for and what is its role?

    <p>Nuclear Localization Signal; it is an encoded part of the protein that directs proteins to the nucleus.</p> Signup and view all the answers

    Small proteins and molecules can pass through nuclear pores by ________.

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

    What drives the nuclear transport cycle?

    <p>GTP hydrolysis</p> Signup and view all the answers

    Match the following with their descriptions:

    <p>Nuclear import receptors = Proteins that bind to cargo and NLS Ran-GTP = Disrupts interaction with NLS on cargo Nuclear export = Transporting proteins out of the nucleus Hydrogel pore interior = Facilitates passage of small proteins</p> Signup and view all the answers

    Nuclear export operates in a manner similar to nuclear import.

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

    What is the size threshold for proteins to require active transport through nuclear pores?

    <p>40 kDa</p> Signup and view all the answers

    Which process is involved in the nuclear import of NFκB during an infection?

    <p>Ubiquitination of IκB</p> Signup and view all the answers

    The endosymbiont genome is enhanced through gene transfer from the host organism.

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

    What is the function of NFκB in response to infection?

    <p>To turn on genes that fight infection.</p> Signup and view all the answers

    The cellular stress signal that dictates the nuclear localization of NFκB is _____.

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

    What would result in decreased nuclear localization of NFκB after interleukin stimulation?

    <p>Ubiquitination of IκB is altered</p> Signup and view all the answers

    What is the main role of the import receptor (R) in peroxisome protein import?

    <p>To recognize and shuttle soluble proteins into the peroxisome</p> Signup and view all the answers

    Mitochondrial precursor proteins are folded during import.

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

    What type of helix is the signal sequence for mitochondrial import?

    <p>Amphipathic α-helix</p> Signup and view all the answers

    Catalase cannot be located in cells that lack peroxisomes.

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

    Match the protein transport components to their respective functions:

    <p>NLS = Directs proteins to the nucleus IκB = Inhibits NFκB localization to the nucleus Ran-GTP = Facilitates transport through the nuclear pore Signal sequence = Targets proteins for mitochondrial import</p> Signup and view all the answers

    What is observed when catalase is detected in normal cells using fluorescent microscopy?

    <p>Small dots of fluorescence</p> Signup and view all the answers

    The import of soluble proteins into peroxisomes requires _____ hydrolysis by a complex in the peroxisome membrane.

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

    Match the processes with their respective features:

    <p>Peroxisome import = Uses a receptor that recognizes SKL signals Mitochondrial import = Involves ATP hydrolysis Nuclear transport = Imports proteins in a folded state Immunofluorescence microscopy = Detects specific proteins with antibodies</p> Signup and view all the answers

    What is the main function of the TOM complex?

    <p>Importing proteins into the mitochondria</p> Signup and view all the answers

    Changing hydrophobic amino acids in a mitochondrial signal sequence to other hydrophobic amino acids will affect the protein's import into the mitochondria.

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

    What role does TIM22 play in mitochondrial protein import?

    <p>TIM22 facilitates the insertion of multi-pass transmembrane proteins into the inner mitochondrial membrane.</p> Signup and view all the answers

    Mitochondrial proteins are imported via the _______ and _______ complexes.

    <p>TOM, TIM</p> Signup and view all the answers

    What is a consequence of adding a mitochondrial signal sequence to the amino-terminal end of a normally cytosolic protein?

    <p>The protein will be imported into the mitochondria</p> Signup and view all the answers

    Peroxisomes solely rely on the mitochondria for their protein import.

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

    What is produced during oxidation reactions in peroxisomes?

    <p>Hydrogen peroxide (H2O2)</p> Signup and view all the answers

    Match the following terms with their functions:

    <p>TOM = Translocator of the outer membrane TIM = Translocator of the inner membrane Catalase = Recycles H2O2 into H2O and O2 Peroxisome = Site of oxidation reactions</p> Signup and view all the answers

    Study Notes

    Protein Sorting I

    • Eukaryotic cells are complex with many membrane-bound compartments
    • Organelles include: nucleus, mitochondria, chloroplasts, endoplasmic reticulum, Golgi apparatus, lysosomes, endosomes and peroxisomes
    • These compartments have different functions.
    • Proteins are targeted to specific organelles.
    • Intracellular compartment percentages:
      • Cytosol - 54%
      • Mitochondria - 22%
      • Endoplasmic reticulum - 12%
      • Nucleus - 6%
      • Golgi apparatus - 3%
      • Peroxisomes - 1%
      • Lysosomes - 1%
      • Endosomes - 1%

    Protein Delivery Mechanisms

    • Organelles import proteins via three mechanisms:
      • Transport through nuclear pores
      • Transport across membranes
      • Transport by vesicles
    • Proteins destined for specific organelles have specific signals that act like addresses.

    Nuclear Import

    • Nuclear pores are the only gateways between the nucleus & cytoplasm.
    • Proteins pass in their folded state.
    • Protein import receptors attach to the NLS and transport the cargo into the nucleus
    • Two ways to pass through a pore: diffusion or active transport. Small proteins (<40kDa) and RNA diffuse, while larger proteins use active transport mechanisms
    • Protein transport in and out of the nucleus is driven by GTP hydrolysis of Ran-GTP and Ran-GDP

    Mitochondrial Import

    • Precursor proteins unfold to be imported into mitochondria.
    • Import occurs across two mitochondrial membranes via TOM (outer membrane) TIM23 (inner membrane) complexes
    • Protein targeting signals (often at the N-terminus) are recognized by receptors in the TOM and TIM complexes.
    • The N-terminal Signal peptide is cleaved within the mitochondria.
    • The process requires energy (ATP hydrolysis) and involves chaperone proteins to help with unfolding and folding.

    Peroxisome Import

    • Peroxisomes bud off from the ER as vesicles via fission
    • Import of peroxisomal proteins is a process involving signal sequences and receptors.
    • SKL sequences are involved in peroxisome targeting, and receptors are involved in binding and transport of cargo into the peroxisome.
    • Protein import is in a folded state, similar to nuclear transport in these aspects but unlike mitochondria
    • Peroxisomes are involved in oxidation reactions involving H2O2 and catalase.

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    Protein Sorting Lecture 13 PDF

    Description

    Explore the complex world of eukaryotic cell organelles and protein sorting mechanisms in this quiz. Learn about the various compartments, their functions, and the specific transport methods for proteins. Test your knowledge of how proteins are directed to their respective organelles!

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