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Questions and Answers
Where do nearly all proteins begin their synthesis?
Where do nearly all proteins begin their synthesis?
What contains the active site of the ribosome for creating new peptide bonds?
What contains the active site of the ribosome for creating new peptide bonds?
What is the main pathway for protein secretion in cells?
What is the main pathway for protein secretion in cells?
Where do new proteins go from the ribosome in the cytosol to reach the organelle where they function?
Where do new proteins go from the ribosome in the cytosol to reach the organelle where they function?
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Which organelle has a netlike labyrinth of branching tubules and flattened sacs?
Which organelle has a netlike labyrinth of branching tubules and flattened sacs?
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What is the main function of the smooth endoplasmic reticulum?
What is the main function of the smooth endoplasmic reticulum?
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Which proteins are responsible for preventing protein misfolding and aggregation in the ER?
Which proteins are responsible for preventing protein misfolding and aggregation in the ER?
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What is the role of calnexin in protein folding in the ER?
What is the role of calnexin in protein folding in the ER?
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What is the function of OST (oligosaccharyltransferase) in N-linked glycosylation?
What is the function of OST (oligosaccharyltransferase) in N-linked glycosylation?
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Which component guides the ER signal sequence to the ER membrane?
Which component guides the ER signal sequence to the ER membrane?
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Which organelle is responsible for protein glycosylation by adding a common N-linked oligosaccharide?
Which organelle is responsible for protein glycosylation by adding a common N-linked oligosaccharide?
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What is the core of the translocator in the ER called?
What is the core of the translocator in the ER called?
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Which enzyme removes the final glucose residue if protein folding is good?
Which enzyme removes the final glucose residue if protein folding is good?
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What is the role of ERp57 in protein folding in the ER?
What is the role of ERp57 in protein folding in the ER?
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What is the function of PDI (Protein disulfide-isomerase) in the ER?
What is the function of PDI (Protein disulfide-isomerase) in the ER?
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What is the main function of the rough endoplasmic reticulum?
What is the main function of the rough endoplasmic reticulum?
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Where do nearly all proteins, except a few inside mitochondria and plastids, begin their synthesis?
Where do nearly all proteins, except a few inside mitochondria and plastids, begin their synthesis?
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What is the main pathway for protein secretion in cells?
What is the main pathway for protein secretion in cells?
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What organelle is responsible for protein glycosylation by adding a common N-linked oligosaccharide?
What organelle is responsible for protein glycosylation by adding a common N-linked oligosaccharide?
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What is the function of OST (oligosaccharyltransferase) in N-linked glycosylation?
What is the function of OST (oligosaccharyltransferase) in N-linked glycosylation?
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Which component guides the ER signal sequence to the ER membrane?
Which component guides the ER signal sequence to the ER membrane?
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What is the main function of calnexin in protein folding in the ER?
What is the main function of calnexin in protein folding in the ER?
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What is the function of OST (oligosaccharyltransferase) in N-linked glycosylation?
What is the function of OST (oligosaccharyltransferase) in N-linked glycosylation?
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What is the role of ERp57 in protein folding in the ER?
What is the role of ERp57 in protein folding in the ER?
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What is the main function of the smooth endoplasmic reticulum?
What is the main function of the smooth endoplasmic reticulum?
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Where do nearly all proteins begin their synthesis?
Where do nearly all proteins begin their synthesis?
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What contains the active site of the ribosome for creating new peptide bonds?
What contains the active site of the ribosome for creating new peptide bonds?
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What is the core of the translocator in the ER called?
What is the core of the translocator in the ER called?
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What is the main pathway for protein secretion in cells?
What is the main pathway for protein secretion in cells?
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What is the role of PDI (Protein disulfide-isomerase) in the ER?
What is the role of PDI (Protein disulfide-isomerase) in the ER?
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What is the function of Hsp70/BiP in protein folding in the ER?
What is the function of Hsp70/BiP in protein folding in the ER?
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What is the function of Gls (Glucosidase) in N-linked glycosylation?
What is the function of Gls (Glucosidase) in N-linked glycosylation?
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Study Notes
Protein Synthesis and Pathways
- Nearly all proteins begin their synthesis in the ribosome, with the exception of some proteins synthesized in mitochondria and plastids.
- The ribosome's active site is responsible for forming new peptide bonds during protein synthesis.
Protein Secretion
- The main pathway for protein secretion in cells is the secretory pathway, where proteins are transported from the ribosome to the endoplasmic reticulum (ER) and then to their final destination.
Endoplasmic Reticulum Structure
- The smooth endoplasmic reticulum (SER) features a netlike labyrinth of branching tubules and flattened sacs.
Endoplasmic Reticulum Functions
- The primary function of the SER is lipid synthesis and metabolism, as well as detoxification processes.
- The rough endoplasmic reticulum (RER) is involved in the synthesis of proteins destined for secretion, incorporation into membranes, or for organelles.
Protein Folding and Quality Control
- Chaperone proteins, such as Hsp70/BiP, play critical roles in preventing misfolding and aggregation of proteins in the ER.
- Calnexin assists in the proper folding of glycoproteins by retaining them in the ER until they achieve correct conformation.
- ERp57 is another chaperone that facilitates protein folding by assisting in the formation of disulfide bonds within polypeptides.
- Protein disulfide-isomerase (PDI) catalyzes the formation and rearrangement of disulfide bonds, essential for proper protein structure.
Glycosylation Process
- Oligosaccharyltransferase (OST) is responsible for catalyzing the transfer of oligosaccharides to asparagine residues during N-linked glycosylation.
- The glycosylation process involves adding a common N-linked oligosaccharide, primarily taking place in the rough ER.
- Glucosidase (Gls) removes glucose residues from glycoproteins, aiding in protein maturation and quality control.
ER Signal Sequence and Translocators
- A signal recognition particle guides the ER signal sequence to the ER membrane, facilitating the import of nascent proteins into the ER.
- The core of the translocator in the ER is known as the Sec61 complex, which forms a channel for polypeptide translocation.
Protein Quality Control
- If a protein folds correctly, the final glucose residue is removed from its glycan by glucosidase, a crucial step for determining whether the protein will proceed to the next stage in the secretory pathway.
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Description
Test your knowledge of protein sorting in the endoplasmic reticulum with this quiz. Explore the processes involved in protein synthesis and the role of ribosomes in ensuring accurate pairing of codons and anticodons. Challenge yourself with questions related to the structure and function of ribosomal subunits and the catalytic site.
