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Questions and Answers
What is the primary reason that biomolecular condensates are considered compartments?
What is the primary reason that biomolecular condensates are considered compartments?
What is the main distinction between "condensation" and "aggregation" in the context of biomolecular condensates?
What is the main distinction between "condensation" and "aggregation" in the context of biomolecular condensates?
Why are the interactions between molecules within biomolecular condensates referred to as "weak interactions"?
Why are the interactions between molecules within biomolecular condensates referred to as "weak interactions"?
What is the role of "client" molecules in relation to biomolecular condensates?
What is the role of "client" molecules in relation to biomolecular condensates?
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Which of the following is NOT a characteristic of biomolecular condensates?
Which of the following is NOT a characteristic of biomolecular condensates?
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What is a crucial requirement for the successful import of proteins during post-translational import?
What is a crucial requirement for the successful import of proteins during post-translational import?
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Which class of proteins plays a significant role in maintaining the unfolded state of proteins during import?
Which class of proteins plays a significant role in maintaining the unfolded state of proteins during import?
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What process occurs in the endoplasmic reticulum (ER) that contributes to membrane asymmetry?
What process occurs in the endoplasmic reticulum (ER) that contributes to membrane asymmetry?
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What role do chaperones play in post-translational protein import?
What role do chaperones play in post-translational protein import?
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What signifies the transport involved in the post-translational import process of proteins?
What signifies the transport involved in the post-translational import process of proteins?
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What occurs when a protein is not correctly folded during its interaction with calnexin?
What occurs when a protein is not correctly folded during its interaction with calnexin?
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What is the likely consequence if a protein accumulates excessively?
What is the likely consequence if a protein accumulates excessively?
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How does aggregation differ from forming condensates in proteins?
How does aggregation differ from forming condensates in proteins?
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What role does calnexin play during protein folding?
What role does calnexin play during protein folding?
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What is indicated by the presence of one glucose molecule bound to calnexin?
What is indicated by the presence of one glucose molecule bound to calnexin?
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What is the primary function of disulfide bonds formed in the endoplasmic reticulum (ER)?
What is the primary function of disulfide bonds formed in the endoplasmic reticulum (ER)?
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Which type of glycosylation predominantly occurs in the endoplasmic reticulum (ER)?
Which type of glycosylation predominantly occurs in the endoplasmic reticulum (ER)?
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What role does the chaperone protein calnexin serve in the ER?
What role does the chaperone protein calnexin serve in the ER?
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What is the significance of the sugar chains in N-glycosylation?
What is the significance of the sugar chains in N-glycosylation?
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Why is calnexin named as such?
Why is calnexin named as such?
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Flashcards
Calnexin Binding
Calnexin Binding
The interaction between calnexin and a protein indicating proper folding.
Unfolded Protein Response (UPR)
Unfolded Protein Response (UPR)
A cellular response triggered by misfolded proteins to restore normal function.
Chaperone Function
Chaperone Function
Proteins that assist in the proper folding of other proteins.
Protein Aggregation
Protein Aggregation
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Proteasome Activity
Proteasome Activity
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Biomolecular condensate
Biomolecular condensate
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Chemical reactions in condensates
Chemical reactions in condensates
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Weak interactions
Weak interactions
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Client molecules
Client molecules
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Dynamism of molecules
Dynamism of molecules
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Disulfide bonds
Disulfide bonds
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Glycosylation
Glycosylation
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N-glycosylation
N-glycosylation
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Calnexin
Calnexin
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ER functions
ER functions
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Post-Translational Import
Post-Translational Import
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Role of Chaperones
Role of Chaperones
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ATP-Dependent Transport
ATP-Dependent Transport
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GPI Anchors
GPI Anchors
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Compartmentalization in ER
Compartmentalization in ER
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Study Notes
Cell Compartments and Protein Sorting
- Cells compartmentalize to ensure materials reach the correct location at the right time, facilitated by transport systems
- Compartments restrict reactions by concentrating enzymes, substrates, and regulators
- Compartments increase membrane surface area for reactions like oxidative phosphorylation
- Membranes are generally impermeable so specialized transport mechanisms are essential for molecules to enter/interact with compartments
Intracellular Compartments
- Nucleus and cytosol (connected by pore complexes)
- Organelles in secretory/endocytic pathways (ER, Golgi, endosomes, lysosomes, peroxisomes)
- Mitochondria
Membrane Types in Cells
- Table 12-2: Shows relative amounts of membrane types in liver hepatocytes and pancreatic exocrine cells
- Plasma membrane
- Rough ER membrane
- Smooth ER membrane
- Golgi apparatus membrane
- Mitochondrial membranes (outer and inner)
- Nucleus membrane (outer/inner)
- Lysosome membrane
- Peroxisome membrane
- Endosome membrane
Compartmentalization within Cells
- Various organelles occupy different percentages of cell volume (cytosol, mitochondria, rough ER, smooth ER, Golgi, nucleus, peroxisomes, lysosomes, endosomes)
- The relationship between volume and surface area of different cell compartments is not always proportional, allowing for varied functions in different types of cells.
Electron Microscopy
- Electron microscopy images of organelles/cell structures can be misleading due to artifacts rather than actual structures.
- Electron-dense materials absorb more electrons in electron microscopy, showing up darker.
- Examples include lysosomes and other densely packed structures
Membrane-Bound Organelles and Biomolecular Condensates
- Organelles are primarily membrane-bound structures: mitochondria, nucleus, lysosomes
- Biomolecular condensates are compartments without membranes but still function as distinct cellular structures.
Vesicle Transport Principles
- Vesicle transport is highly regulated in both time and space, involving polarization of membranes.
- Orientation/polarity of membranes is crucial in vesicle transport (lumen of vesicle versus outer environment.)
- Polarization of membranes is critical for vesicle interactions during transport between organelles.
Protein Transport and Translocation
- Proteins destined for organelles have specific signal sequences (typically amino acid stretches).
- Co-translational transport: ribosomes attach to ER membrane as proteins synthesize, directly inserting nascent proteins into the ER lumen or membrane
- Post-translational transport: proteins are fully synthesized in the cytosol before being imported into the organelle such as ER or mitochondria utilizing distinct methods.
Endoplasmic Reticulum (ER)
- ER is involved in protein synthesis and processing (co-translational and post-translational)
- Contains translocon complexes essential for protein import.
- Contains chaperone proteins (e.g., calnexin) that assist in protein folding and quality control.
Signal Recognition Particle (SRP) and Protein Import
- SRP binds to signal sequence of nascent proteins, pausing translation until ribosome docks on the ER membrane.
- Receptor and ribosome facilitate protein import via the translocon (channel) into ER lumen.
- This process is dynamic and regulated to ensure efficient protein targeting.
Polyribosomes/Polysomes
- Clusters of ribosomes that simultaneously translate a single mRNA molecule.
- Efficient synthesis of multiple copies of protein.
Unfolded Protein Response (UPR)
- Cells respond to misfolded proteins in the ER by initiating UPR (three branches)
- UPR: aims to restore normal function but not necessarily exclude other mechanisms
- Misfolded proteins exit ER or are cleared via proteasomes for degradation (energy dependence).
- Proteasome: a protein complex not surrounded by membranes; it is a complex structure with specific functions for protein degradation.
Peroxisomes.
- Peroxisomes are membrane-bound organelles involved in detoxification (beta-oxidation, production of hydrogen peroxide-conversion to water), lipid metabolism and synthesis of certain lipids (e.g., plasmalogens).
- Peroxisomes form de novo through vesicle fusion (distinct from organelle division).
- Peroxin (PEX) proteins: transport essential fatty acids and enzymes.
Protein Transport: Mitochondria
- Mitochondria require substantial protein import due to their limited genome
- Use different translocator complexes (TOM, TIM, OXA) to import proteins, requiring energy.
- Protein import processes are selective due to signal sequences and translocator proteins.
Nuclear Transport
- Nuclear envelope has nuclear pores to allow selective transport of proteins/RNA/nucleotides between nucleus and cytosol.
- Gated regulated transport of materials (e.g., histones, RNA, proteins, nucleotides) through the nuclear pores
- Signal sequences/import receptors guide proteins through nuclear pores.
- Nuclear transport is energy-dependent (using small GTPase Ran).
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Description
Explore the intricate structures and functions of cell compartments and their role in protein sorting. This quiz covers intracellular compartment structures, membrane types, and the essential transport mechanisms that maintain cellular integrity. Test your knowledge on how cells compartmentalize processes to optimize their functions.
