64 Questions
What is the role of the translocation channel in protein transport into mitochondria?
To facilitate import of unfolded proteins
What happens to the signal peptide in protein targeting the endoplasmic reticulum if it is not cleaved?
It becomes the first transmembrane domain
What is the main purpose of protein sorting in a cell?
To direct each protein to a specific organelle
Which organelles can proteins be directed to through the protein sorting process?
Mitochondria, lysosome, and nucleus
What does the term 'post codes' refer to in the context of protein targeting?
Specific sequences on proteins that signal their destination organelles
Why is protein sorting considered as critical as DNA replication and transcription?
Proper protein sorting is essential for cell function, organization, and survival
How does a cell determine the appropriate organelle for targeting a specific protein?
By recognizing specific signals or sequences on the protein
What role does the PEX-receptor play in protein transport into peroxisomes?
Binding to the PTS and targeting the cargo to the peroxisome membrane
How does a folded protein enter the nucleus?
Through gated pores
What is the role of the nuclear localisation sequence (NLS) in protein transport into the nucleus?
It guides proteins into the nucleus
What is the function of importin in protein transport into the nucleus?
Recognizing and binding to proteins with NLS
What is a common feature of proteins that are transported into mitochondria and peroxisomes?
They are translocated unfolded into the organelles
What characterizes one of the largest protein complexes in cells involved in protein transport in and out of the nucleus?
Binds to nuclear cytoskeleton for stability
What is the role of the TOM complex in protein translocation into mitochondria?
Insertion into membrane
What is the function of the TIM complex in protein translocation into mitochondria?
Translocation into matrix
What is the significance of ATP hydrolysis in the translocation process into mitochondria?
Complete translocation into matrix
What is the function of the mitochondrial signal sequence in protein translocation into mitochondria?
Targeting the precursor protein to the mitochondria
What is the role of the PEX receptor in protein translocation into peroxisomes?
PEX-receptor binds to the PTS and helps target the cargo to the peroxisome membrane.
Describe the role of importin in protein translocation into the nucleus.
Importin binds to the nuclear localization sequence (NLS) of the protein and facilitates its transport into the nucleus.
Why are proteins destined for mitochondria maintained in an unfolded state prior to translocation?
Maintaining proteins in an unfolded state helps them to be translocated more efficiently through the TOM complex.
What is the role of the Ran GTPase in nuclear transport and how does it provide directionality?
The Ran GTPase provides directionality to nuclear transport by hydrolyzing GTP. It binds to importin-cargo complex in the nucleus, leading to dissociation of the complex.
Explain how proteins are transported into mitochondria and what is the significance of the mitochondrial signal sequence?
Proteins are transported into mitochondria through the TOM complex. The mitochondrial signal sequence guides the protein to the correct location within the mitochondria.
Describe the process of translocation into peroxisomes and the role of the PEX-receptor in protein transport.
Proteins are translocated into peroxisomes through specific signals recognized by the PEX-receptor. The PEX-receptor facilitates the import of proteins into peroxisomes.
How do proteins shuttle between the cytosol and nucleus, and what signals are involved in this process?
Proteins shuttle between the cytosol and nucleus by possessing nuclear export signals (NES) and nuclear localization signals (NLS). Exportins recognize NES for export, while importins recognize NLS for import.
Explain the mechanism of translocation in and out of the nucleus, including the dissociation process of cargo complexes.
The receptor-cargo complex migrates through the nuclear pore, and the cargo complex dissociates in the nucleus during translocation into the nucleus. The same process happens in reverse for translocation out of the nucleus.
What is the function of the exportin in protein transport out of the nucleus, and how does it facilitate the process?
Exportin recognizes nuclear export signals (NES) in proteins and facilitates their transport out of the nucleus by associating with the nuclear pore complex. It helps in the dissociation of cargo complexes for export.
Match the following components with their role in protein translocation into mitochondria:
TOM complex = Insertion into membrane TIM complex = Translocation into matrix Mitochondrial signal sequence = Signal for translocation ATP hydrolysis = Complete translocation into matrix
Match the steps in protein translocation into mitochondria with their correct order:
Binding of precursor to membrane receptor = Step 1 Translocation into matrix via the TIM complex = Step 3 Cleavage of signal sequence by signal peptidase = Step 5 Complete translocation into matrix requires ATP hydrolysis = Step 4
Match the membrane components with their location in protein translocation into mitochondria:
Receptor outer membrane = TOM complex Inner membrane = TIM complex Outer membrane = TOM complex
Match the following terms with their association in protein translocation into mitochondria:
Translocase OUTER membrane = Signal for translocation Translocase INNER membrane = Translocation into matrix
Match the descriptions with the corresponding processes in protein translocation into mitochondria:
Poorly understood signal for entry into the matrix = Mitochondrial signal sequence ATP conversion to ADP + Pi for completion of translocation = ATP hydrolysis Insertion of precursor proteins into the membrane = TOM complex Cleavage of the signal peptide by an enzyme = Signal peptidase
Match the roles in protein translocation into mitochondria with their respective functions:
Directing proteins to enter the matrix via receptor binding = Binding of precursor to membrane receptor Facilitating the physical movement across membranes = Translocation into matrix Enabling energy release for translocation completion = ATP hydrolysis Removing the signal sequence after translocation is complete = Cleavage of signal sequence by signal peptidase
Match the following components with their roles in translocation into the nucleus:
Importin = Recognizes NLS Ran GTPase = Provides directionality to nuclear transport GTPase activating protein (GAP) = Leads to dissociation of importin-cargo complex Guanine nucleotide exchange factor (GEF) = Leads to dissociation of exportin-cargo-Ran complex
Match the following statements with the correct descriptions of protein transport into organelles:
Mitochondrial signal sequence = Guides proteins into mitochondria PEX-receptor = Recognizes proteins for translocation into peroxisomes TOM complex = Involved in protein translocation into mitochondria TIM complex = Facilitates translocation of proteins across mitochondrial inner membrane
Match the following steps in nuclear transport with their correct descriptions:
Receptor-cargo complex associates with FG repeats = Walks along nuclear pore complex filaments Receptor-cargo complex migrates through the pore = Dissociates in the nucleus Ran dependent GTP hydrolysis = Leads to dissociation of exportin-cargo-Ran complex Proteins possess nuclear export signals (NES) = Recognized by exportin for translocation out of the nucleus
Match the following terms with their significance in protein transport into organelles:
Unfolded state of proteins = Facilitates translocation into mitochondria and peroxisomes Post codes targeting proteins to organelles = Guide proteins to their specific locations Nuclear localisation sequence (NLS) = Aids in recognizing proteins for translocation into the nucleus FG (Phe-Gly) repeats in nuclear pore complex = Facilitate movement of cargo complexes through the pore
Match the following components with their role in translocation into peroxisomes:
PEX-receptor = Binds to the PTS Receptor-cargo complex = Targeted to the peroxisome membrane PEX translocon = Incorporates PEX-receptor Cargo = Translocated
Match the following statements with the correct process of translocation into the nucleus:
Folded protein enters nucleus through gated pores = Mechanism of translocation Nuclear pore complex is permeable to molecules ≤ 60 kDa = Permeability of the nuclear pore complex Proteins with signal >60 kDa are transported into nucleus sequence not cleaved = Criteria for transport into the nucleus Proteins are recognized and bound by importin in the cytoplasm = Initial step in nuclear import
Match the following descriptions with the correct process of translocation into the nucleus:
Protein sequence with signal >60 kDa transported into nucleus without cleavage = Nuclear localisation sequence (NLS) Proteins first recognized and bound by importin for transport = Role of importin in nuclear transport Longest lived protein complexes involved in nuclear transport = Complexity of nuclear transport protein complexes Importin binds to FG repeats on nuclear pore complex for migration through pore = Interaction with FG repeats during import
Match the following descriptions with their association to protein translocation into mitochondria:
Proteins destined for mitochondria maintained unfolded prior translocation = Preparation for mitochondrial import Role of TOM complex in protein transport into mitochondria = Function of TOM complex Significance of ATP hydrolysis in mitochondrial translocation process = Energy requirement for translocation Translocation channel function in mitochondrial protein transport = Channel involvement in translocation
Match the following components with their roles in protein translocation into the endoplasmic reticulum:
Signal recognition particle (SRP) = Binds to the signal sequence of the polypeptide Signal recognition particle receptor = Receives the SRP-polypeptide complex and initiates translocation ER signal sequence = Directs the polypeptide to the endoplasmic reticulum Translocation = Process of moving the polypeptide across the ER membrane
Match the following descriptions with their association in protein targeting to the endoplasmic reticulum:
Target post codes = Direct the polypeptide to the appropriate organelle Pre-sequences = Guide the protein to specific locations within the ER Internal targeting peptide = Aids in proper localization within the ER Cleavage site of a cleavable sequence = Marks where the signal sequence is cleaved during translocation
Match the steps in protein translocation into the endoplasmic reticulum with their correct order:
Recognition of signal sequence by SRP = First step in targeting to the ER Binding of SRP-polypeptide complex to SRP receptor = Initiates translocation process Translocation through ER membrane = Movement of polypeptide into the ER lumen Cleavage of signal sequence = Completion of translocation process
Match the membrane components with their location in protein translocation into the endoplasmic reticulum:
TOM complex = Outer membrane component involved in translocation TIM complex = Inner membrane component facilitating protein movement
Match the following terms with their significance in protein transport to the endoplasmic reticulum:
N-terminal pre-sequence = Directs proteins to specific compartments within the ER C-terminal continual patch = Aids in proper localization within the ER
What type of amino acids are typically found in the amphipathic helix of the pre-sequence targeting the mitochondria?
Basic amino acids
Which complex is responsible for the translocation of precursor proteins into the matrix of mitochondria?
TIM complex
What is the main function of pre-sequences in protein translocation into organelles?
Directing proteins to the appropriate organelle
What is the role of targeting peptides in the protein sorting process?
Direct proteins to specific organelles
Which organelle-specific complex is responsible for the insertion of proteins into the membrane during protein translocation into mitochondria?
TOM complex
Which component recognizes the amino terminal signal sequence on a protein for targeting to the endoplasmic reticulum?
Signal Recognition Particle (SRP)
If a signal peptide is not cleaved during protein targeting to the endoplasmic reticulum, what does it become?
A transmembrane domain
What is the function of Signal Recognition Particle (SRP) in protein translocation into the endoplasmic reticulum?
Recognition of signal sequences
What happens to the signal peptide in protein targeting the endoplasmic reticulum if it is not cleaved?
It becomes the first transmembrane domain of the protein.
What is the function of Signal Recognition Particle (SRP) in protein translocation into the endoplasmic reticulum?
SRP recognizes the amino terminal signal sequence on proteins and targets them to the ER membrane.
Explain how proteins are transported into mitochondria and what is the significance of the mitochondrial signal sequence?
Proteins are transported into mitochondria co-translationally, and the mitochondrial signal sequence guides them to the correct location within the mitochondria.
Explain the role of the PEX-receptor in the translocation process into peroxisomes.
The PEX-receptor binds to the PTS and is incorporated into the PEX translocon, facilitating the translocation of cargo into peroxisomes.
Describe the process of translocation into the nucleus, focusing on the role of the nuclear transport receptor.
The nuclear transport receptor recognizes the NLS on cargo, associates with cytoplasmic filaments, and facilitates the migration of the cargo complex through the nuclear pore.
What is the significance of the monopartite and bipartite signal sequences in targeting the nucleus?
Monopartite and bipartite signal sequences help in directing proteins into the nucleus by serving as recognition signals for the nuclear transport receptor.
How do proteins destined for mitochondria maintain their unfolded state prior to translocation?
Proteins destined for mitochondria are maintained in an unfolded state to facilitate their passage through the mitochondrial translocon.
Explain the significance of ATP hydrolysis in the translocation process into mitochondria.
ATP hydrolysis is required for the complete translocation of proteins into the matrix of mitochondria.
During translocation into peroxisomes, what happens after the cargo is translocated?
PEX-receptor dissociates from cargo
What is the role of the nuclear transport receptor (importin) in protein translocation into the nucleus?
Recognizes the NLS – cargo complex associates with cytoplasmic filaments
Which component recognizes the nuclear localization sequence (NLS) during protein translocation into the nucleus?
Nuclear transport receptor (importin)
Test your knowledge on protein sorting in cell biology with this quiz from the Foundations of Cell Biology course taught by Dr. Carl Mousley at Curtin University. Contact Dr. Mousley at [email protected] for more information.
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