54 Questions
What is the purpose of treating cells with [35S]methionine for 0.5h?
To label all newly synthesized proteins
How are proteins visualized after being fractionated from the ER, Golgi, and membrane?
Using autoradiography
In the context of protein sorting and secretion, what is the role of membrane-bound vesicles?
Transporting protein cargo into, out-of, and within the cell
What is responsible for sending out proteins to the correct place inside or outside the cell?
Endoplasmic Reticulum
Which organelle is involved in sorting proteins to the plasma membrane or to lysozymes?
Golgi Apparatus
What is the purpose of the N-terminal signal sequence in proteins?
Guides the ribosome to the Endoplasmic Reticulum
Which step involves opening of the translocon to allow insertion of the signal sequence and the growing peptide chain?
Protein synthesis and translocation across the ER membrane
Where are carbohydrate chains added to proteins in glycosylation of proteins?
Carboxyl groups of serine/threonine
Which type of glycosylation involves adding 1 - 4 carbohydrate residues?
O-linked glycosylation
What is the function of protein disulfide isomerase (PDI) in the ER?
Assisting in Cys-Cys bond formation
Which enzyme is responsible for adding the first sugar to Dolicol phosphate in N-linked glycan biosynthesis?
Pyrophosphatase
What triggers the unfolded protein response in the ER?
Accumulation of unfolded proteins
What is the role of Ire1 in the unfolded protein response?
RNA endonuclease
Which structure is transferred to an Asp residue in the ER lumen during N-linked core glycan biosynthesis?
14-residue precursor
What assists proteins in folding into their native conformation in the ER lumen?
Chaperones
Which lipid is involved in the addition of sugars during N-linked core glycan biosynthesis?
Dolicol phosphate
What happens when a protein receives a 'stop transfer' signal during insertion into the ER membrane?
The protein is left inserted in the ER membrane.
In the secretory pathway, where do proteins destined for lysosomes go?
Trans-golgi network (TGN)
How are proteins moved from the golgi apparatus back to the ER during the secretory pathway?
Transport by retrograde vesicles
Where are proteins that are destined for regulated secretion sent by the trans-golgi network (TGN)?
Plasma membrane
Which vesicles are responsible for transporting golgi resident proteins back to an earlier portion of the golgi?
Retrograde vesicles
What is the main function of the golgi complex in the secretory pathway?
Sorting proteins to the plasma membrane or lysosomes
Which structure is responsible for directing ribosomes with N-terminal signal sequences to the endoplasmic reticulum?
Signal Recognition Particle (SRP)
In the co-translational translocation of proteins, what is required for SRP to target the ribosome to the ER membrane?
GTP
Which step in protein secretion involves the insertion of the signal sequence and the growing peptide chain into the translocon?
Protein synthesis and translocation across the ER membrane
What is the specific function of the N-terminal signal sequence in proteins that need to be sorted within the cell?
Guide ribosomes to endoplasmic reticulum
What is the unifying principle of both the secretory and endocytic pathways?
Use of membrane-bound vesicles
In vesicle docking, what proteins are responsible for the fusion of a vesicle with its target membrane?
SNAP Receptor proteins
Which type of vesicle is responsible for transporting proteins from the rough ER to the Golgi?
COP II
What initiates vesicle budding in the process of vesicle formation?
Recruitment of small GTP-binding proteins
Which proteins ensure that a vesicle fuses with the correct target membrane during vesicle docking?
v-SNARE proteins
Which technique is used to label all newly synthesized proteins in cells?
Autoradiography
In the context of studying genetic secretory mutants, what can one investigate using genetic engineering and mutagenesis?
Effects of clinically relevant mutations or therapeutic molecules on the secretory pathway
What is the main purpose of treating cells with non-isotopic methionine after labeling with [35S]methionine?
Label newly synthesized proteins for further analysis
Which organelles are proteins fractionated from after being labeled with [35S]methionine?
Endoplasmic reticulum, Golgi, and membrane
What is the significance of using membrane-bound vesicles in protein transport within the cell?
To transport protein cargo into, out-of, and within the cell
What is the main function of the rough ER in protein sorting and secretion?
Completion of translation for secretory proteins
In the context of the secretory pathway, what is the significance of transport vesicles?
Facilitate movement of proteins from rough ER to Golgi complex
How are non-secreted cytosolic proteins distinguished from secretory proteins in terms of their generation?
Non-secreted proteins are generated on cytosolic ribosomes without any specific signaling sequence.
What is the fate of secretory proteins after passing through the Golgi complex?
Secretory proteins are released outside the cell
In protein sorting, what would be the consequence if a protein lacks an ER signal sequence?
The protein will not be secreted and will complete translation in the cytosol.
What is the role of Sar1 in vesicle formation during the secretory pathway?
Anchors into the membrane via a hydrophobic tail
Which protein is responsible for the stable docking and membrane fusion of vesicles in the secretory pathway?
VAMP
How do ER luminal proteins get retrieved from the golgi back to the ER in the secretory pathway?
Incorporated into COP II vesicles and transported back
Which protein is involved in dissociating the SNARE complex during membrane fusion in the secretory pathway?
NSF
What is the function of the KDEL receptor in protein trafficking?
Retrieving ER resident proteins from the golgi
What is the role of Ero1 in the ER lumen?
Forming and rearranging disulfide bonds
Which protein is responsible for catalyzing Cys-Cys bond formation in secretory or membrane-bound proteins?
PDI
In the context of glycosylation of proteins, which amino acid residue is involved in O-linked carbohydrate chain addition?
Threonine
What is the primary function of Ire1 in protein quality control in the ER?
Activating translation of Hac1 protein
What is the significance of Dolicol phosphate (DP) in N-linked core glycan biosynthesis?
It adds the first sugar via pyrophosphate linkage
Which process is visualized by fluorescence microscopy using GFP-tagged proteins?
Protein transport through the secretory pathway
What is the primary function of chaperones in the ER lumen?
Helping fold proteins into their native conformation
In N-linked glycan biosynthesis, what is the role of the 7 residue intermediate that is 'flipped' across the ER membrane?
'Flips' to transfer sugars to Asp residue in the ER lumen
Study Notes
Protein Synthesis and Sorting
- Treating cells with [35S]methionine for 0.5h labels all newly synthesized proteins.
- The purpose of this treatment is to visualize proteins after fractionation from the ER, Golgi, and membrane.
Protein Trafficking and Secretion
- Membrane-bound vesicles play a crucial role in protein sorting and secretion.
- They are responsible for sending proteins to the correct place inside or outside the cell.
- The Golgi apparatus is involved in sorting proteins to the plasma membrane or to lysosomes.
- The N-terminal signal sequence is responsible for directing proteins to the correct location.
Protein Modification and Folding
- The N-terminal signal sequence is inserted into the translocon during protein synthesis.
- Carbohydrate chains are added to proteins in the Golgi apparatus during glycosylation.
- O-linked glycosylation involves adding 1-4 carbohydrate residues.
- Protein disulfide isomerase (PDI) helps proteins fold into their native conformation in the ER lumen.
ER Quality Control
- The unfolded protein response (UPR) is triggered by the accumulation of unfolded proteins in the ER.
- Ire1 plays a key role in the UPR, helping to maintain ER homeostasis.
- Protein disulfide isomerase (PDI) also helps to correct protein folding in the ER.
Vesicle Formation and Transport
- Vesicle budding is initiated by the formation of a bud on the ER membrane.
- Sar1 is involved in vesicle formation during the secretory pathway.
- SNARE proteins are responsible for the fusion of vesicles with their target membrane.
- Rab proteins ensure that vesicles fuse with the correct target membrane.
Golgi Apparatus and Protein Secretion
- The Golgi apparatus is responsible for sorting and modifying proteins for secretion.
- Proteins destined for regulated secretion are sent to the trans-Golgi network (TGN).
- Vesicles that transport proteins from the rough ER to the Golgi are called COPII vesicles.
- The main function of the Golgi apparatus is to modify and sort proteins for secretion.
Protein Quality Control and Retrieval
- The KDEL receptor is involved in protein retrieval from the Golgi back to the ER.
- Ero1 is responsible for catalyzing Cys-Cys bond formation in secretory or membrane-bound proteins.
- Chaperones in the ER lumen help proteins fold into their native conformation.
- The 7-residue intermediate is involved in N-linked core glycan biosynthesis.
Visualization and Analysis
- Fluorescence microscopy using GFP-tagged proteins can visualize protein trafficking and secretion.
- Genetic engineering and mutagenesis can be used to investigate protein secretion and sorting in genetic secretory mutants.
- Treating cells with non-isotopic methionine after labeling with [35S]methionine can be used to analyze protein synthesis and secretion.
Test your knowledge on protein post-translational modifications such as glycosylation and covalent stabilization through Cys-Cys bond formation. Learn about the assembly of multi-subunit conformations and cleavage into active forms. Understand the different types of glycosylation involving serine, threonine, and asparagine residues.
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