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Questions and Answers
What is the process called when cells engulf and internalize solid particles like bacteria?
What is the process called when cells engulf and internalize solid particles like bacteria?
Which of the following describes the process where cells internalize small dissolved particles?
Which of the following describes the process where cells internalize small dissolved particles?
What type of endocytosis allows cells to uptake specific molecules through receptor proteins?
What type of endocytosis allows cells to uptake specific molecules through receptor proteins?
In which process do cells release substances to the extracellular space?
In which process do cells release substances to the extracellular space?
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Which of the following correctly describes pinocytosis?
Which of the following correctly describes pinocytosis?
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What characterizes secretory proteins during their synthesis?
What characterizes secretory proteins during their synthesis?
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Which organelles are classified as having a double membrane?
Which organelles are classified as having a double membrane?
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What initiates the process of cotranslational targeting of secretory proteins?
What initiates the process of cotranslational targeting of secretory proteins?
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What is the role of the signal recognition particle (SRP)?
What is the role of the signal recognition particle (SRP)?
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Which component is NOT part of the SRP structure?
Which component is NOT part of the SRP structure?
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Where is the synthesis of cytosolic proteins completed?
Where is the synthesis of cytosolic proteins completed?
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Which of the following does the SRP NOT interact with?
Which of the following does the SRP NOT interact with?
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What happens after the SRP binds to the ribosome?
What happens after the SRP binds to the ribosome?
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What is the primary function of chaperones in the RER lumen?
What is the primary function of chaperones in the RER lumen?
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Which process involves the addition of a 14-sugar oligosaccharide to proteins in the ER?
Which process involves the addition of a 14-sugar oligosaccharide to proteins in the ER?
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What happens to the glucose residues during N-linked glycosylation in the ER?
What happens to the glucose residues during N-linked glycosylation in the ER?
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What is the role of protein di-sulphide isomerase?
What is the role of protein di-sulphide isomerase?
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In which environment can di-sulphide bonds form?
In which environment can di-sulphide bonds form?
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What is the role of chaperones in glycoprotein folding?
What is the role of chaperones in glycoprotein folding?
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What sequence is involved in the N-linked glycosylation process?
What sequence is involved in the N-linked glycosylation process?
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What occurs if a protein remains misfolded in the ER?
What occurs if a protein remains misfolded in the ER?
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What happens when RNA is mutated in the context of protein folding?
What happens when RNA is mutated in the context of protein folding?
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Which protein is known to help with the cis-trans isomerization of proline?
Which protein is known to help with the cis-trans isomerization of proline?
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How does glycosylation aid in protein folding?
How does glycosylation aid in protein folding?
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What is the function of the proteasome in the degradation process?
What is the function of the proteasome in the degradation process?
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Which component helps in the recognition of misfolded proteins in the ER lumen?
Which component helps in the recognition of misfolded proteins in the ER lumen?
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What initiates the signaling pathways of the Unfolded Protein Response (UPR)?
What initiates the signaling pathways of the Unfolded Protein Response (UPR)?
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What is one of the outcomes of the UPR signaling pathways?
What is one of the outcomes of the UPR signaling pathways?
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What is the role of UDP Glycosyl Transferase in the ER?
What is the role of UDP Glycosyl Transferase in the ER?
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What occurs to the signal sequence during the transport of a membrane protein?
What occurs to the signal sequence during the transport of a membrane protein?
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How is the orientation of a membrane-spanning protein determined during its insertion?
How is the orientation of a membrane-spanning protein determined during its insertion?
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What is exposed in the endoplasmic reticulum (ER) lumen upon cleavage of the signal sequence?
What is exposed in the endoplasmic reticulum (ER) lumen upon cleavage of the signal sequence?
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During polypeptide chain translocation, what happens when the translocon recognizes a transmembrane sequence?
During polypeptide chain translocation, what happens when the translocon recognizes a transmembrane sequence?
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What is the positioning of the amino terminus of a membrane protein that utilizes an internal transmembrane sequence?
What is the positioning of the amino terminus of a membrane protein that utilizes an internal transmembrane sequence?
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What happens to the carboxy (C) terminus of a protein that spans the ER membrane?
What happens to the carboxy (C) terminus of a protein that spans the ER membrane?
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During the translation of a protein that spans the membrane multiple times, what is true about the internal transmembrane sequences?
During the translation of a protein that spans the membrane multiple times, what is true about the internal transmembrane sequences?
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What does the topology of the secretory pathway represent?
What does the topology of the secretory pathway represent?
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Study Notes
Transport of Large Molecules
- Differentiation between cytosolic and secretory proteins based on location and function.
- Cytosolic proteins synthesized on free ribosomes; secretory proteins translated initially on free ribosomes, then completed on rough endoplasmic reticulum (RER) membrane.
- Signal peptide plays a crucial role in targeting proteins to the RER during translation.
Endocytosis and Exocytosis
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Endocytosis involves the uptake of materials, categorized into:
- Phagocytosis: Engulfment of solid particles (e.g., macrophages consuming pathogens).
- Pinocytosis: Uptake of liquid and dissolved substances.
- Receptor-mediated endocytosis: Specific molecules are internalized after binding to cellular receptors (e.g., uptake of LDL).
- Exocytosis refers to the process of vesicles fusing with the plasma membrane to release contents outside the cell.
Eukaryotic Cell Organelles
- Organelles classified based on membrane structure:
- Without Membrane: Ribosomes, centrioles.
- Single Membrane: Endoplasmic Reticulum (ER), Golgi apparatus, lysosomes, vacuoles, peroxisomes.
- Double Membrane: Mitochondria, chloroplasts, nucleus.
Protein Transport Mechanism
- Cotranslational targeting of secretory proteins occurs as they are synthesized, guided by the signal recognition particle (SRP).
- SRP halts translation temporarily until the ribosome-SRP complex binds to the SRP receptor on the RER membrane.
Protein Modification in the Endoplasmic Reticulum
- Signal peptidase cleaves the signal peptide, generating a new N-terminus for the protein.
- Chaperones in the RER lumen (e.g., Bip) prevent premature folding and assist in proper protein folding.
- N-linked glycosylation occurs, where a 14-sugar oligosaccharide is added to asparagine residues, enhancing stability and correct folding.
Quality Control Mechanisms
- Properly folded proteins exit the RER, while incorrectly folded proteins undergo ER-associated degradation:
- Misfolded proteins are recognized by chaperones and sent back to the cytosol for degradation via proteasomes.
- The unfolded protein response (UPR) is triggered during overwhelming misfolding, involving:
- Degradation of mutated RNA.
- Global translational inhibition.
- Increased expression of chaperone proteins.
Membrane Protein Insertion
- Membrane proteins can be inserted into the ER membrane through cleavable signal sequences or internal transmembrane sequences.
- Polypeptide chains can be anchored in the membrane with their N-terminus in the lumen and C-terminus facing the cytosol.
Pathways Overview
- The secretory and endocytic pathways demonstrate how proteins are processed, modified, and delivered across cell membranes, with clear routes for transport and processing of large molecules within eukaryotic cells.
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Description
This quiz covers key concepts related to the transport of large molecules within cell biology, focusing on cytosolic and secretory proteins, signal peptides, and their targeting to the rough endoplasmic reticulum (RER). Additionally, the roles of membrane protein signals, the unfolding protein response, and organelles such as the ER, Golgi, and lysosomes are explored.
