Protein Transport Mechanisms

What determines the specificity of protein transport into membrane-enclosed organelles?

Proteins can only be transported into organelles while they are being synthesized.

Describe the role of topological similarity in protein movement between organelles.

Proteins are targeted to specific organelles via the recognition of ________ by protein sorting receptors.

Match each type of protein transport with its corresponding mechanism:

Which of the following best describes the function of nuclear pore complexes (NPCs) in gated transport?

Nuclear pore complexes permit the free diffusion of all molecules smaller than 40 kDa.

What modifications to a protein can result in the regulation of nuclear localization and export signals and why is this important?

To initiate nuclear import, nuclear localization signals (NLS) within the cargo must be recognized by ________.

Match the following proteins with their roles in nuclear transport:

How does Ran-GTP affect nuclear import receptor cargo proteins inside the nucleus?

The activity of some gene regulatory proteins is controlled by permanently localizing them within the nuclear compartment.

Describe the role of calcineurin in the nuclear transport of NFAT, during T cell activation.

Mitochondrial proteins are first synthesized as ________ in the cytosol and then translocated into mitochondria.

Match the following mitochondrial protein complexes with their locations:

What structural feature is commonly found within the signal sequence of mitochondrial precursor proteins?

Mitochondria and chloroplasts encode all the proteins they need for their function.

Why is ATP hydrolysis required for the import of proteins into mitochondria?

Transmembrane proteins with a beta-barrel structure are transferred to the ________ for proper folding in the mitochondrial outer membrane.

Match the following components with the order their processes occur for protein import into mitochondria:

What structural feature in proteins, is required, for proteins to undergo co-translational translocation into the ER?

All proteins that enter the ER lumen are ultimately secreted from the cell.

What are the defining characteristics of an ER signal sequence?

The ________ pauses translation when it binds to the ER signal sequence, and then delivers the ribosome to the ER membrane.

Match the components of SRP with their functions in protein targeting and translocation:

Where does cleavage of ER signal sequences, from water soluble proteins, typically occur?

A single protein can only contain either a start-transfer sequence or a stop-transfer sequence but not both.

What determines whether the N-terminus or the C-terminus of a single-pass transmembrane protein ends up in the ER lumen, when is it not known?

In multipass transmembrane proteins, the first start-transfer sequence typically functions as the ________ sequence.

Match the following characteristics with the correct protein transport mechanisms:

Where are proteins synthesized and what must happen to those proteins for them to eventually reside inside of a membrane-enclosed organelle?

Transport does not rely on any specific type of sequences within the protein itself.

Briefly describe the functionality of gated transport.

Proteins are transported into the mitochondria via transmembrane transport through the ________ and ________ complexes.

Match the following organelles of the cell to their descriptions:

What are the names of the 3 main types of organelle transport?

Mitochondria's outer membrane will only accept topologically equivalent proteins from the golgi.

Why do proteins need a signal sequence?

Proteins traffic between the ________ and ________ through gated transport.

Match the following protein processes with their description:

What is the significance of topological similarities in the context of protein movement between organelles?

Nuclear import receptors release their cargo proteins in the nucleus because RAN-GDP binds to them.

Describe how a gradient of RAN-GTP is established across the nuclear pore and explain its importance in nuclear transport.

Proteins destined for the mitochondrial matrix are first fully synthesized in the ______ as precursor proteins.

Match the following mitochondrial protein complexes with their primary function:

What role do chaperones like Hsp70 play in mitochondrial protein import?

In the context of ER protein import, the signal recognition particle (SRP) binds to the ER signal sequence and immediately directs the ribosome to the translocon on the ER membrane, without pausing translation.

Describe the key features of an ER signal sequence and explain how it functions in directing proteins to the endoplasmic reticulum.

For a single-pass transmembrane protein with its N-terminus in the ER lumen and its C-terminus in the cytosol, the translocation process involves a ______ sequence that halts the transfer process, resulting in the protein being anchored in the membrane.

What determines whether the N-terminus or the C-terminus of a single-pass transmembrane protein ends up in the cytosol during ER translocation?

Why is it essential for proteins synthesized in the cytosol to be transported into membrane-enclosed organelles?

How do cells ensure that proteins reach the correct cellular compartment?

Describe the mechanism of gated transport and name the cellular location where it occurs.

What is the role of TOM and TIM complexes in protein transport?

Explain co-translational transport, specifying the organelle it is associated with.

What does it mean for organelles to have 'topological similarities' and how does it relate to protein movement?

What role do sorting signals and receptors play in protein transport between organelles?

Name the three fundamental mechanisms of protein transport between cellular compartments.

Describe how nuclear pore complexes regulate the movement of molecules into and out of the nucleus.

What is the size restriction for molecules that can freely diffuse through nuclear pore complexes?

What is the role of nuclear localization signals (NLS) in protein import?

Why does nuclear protein import increase order in the cell?

What provides the energy for nuclear transport?

Describe the two states in which RAN exists, and explain how they are regulated.

Explain the roles of RAN-GTP in nuclear import and export.

How can nuclear transport be a means of gene regulation?

Explain how NFAT is regulated by nuclear transport in T-cells.

Where are mitochondrial proteins synthesized, and how do they reach the mitochondria?

What is the role of an amphipathic alpha helix in mitochondrial import signal sequences?

Name two protein complexes involved in translocation across mitochondrial membranes, and specify which membrane each complex functions across.

What is the role of the SAM complex in mitochondrial protein import?

What is the function of the TIM23 complex?

What role do chaperones play in mitochondrial protein import?

Why is mitochondrial protein import not energetically favorable, and how is this overcome?

Describe co-translational translocation.

Name two types of proteins that require co-translational translocation.

Describe a typical ER signal sequence.

What role does the Signal Recognition Particle (SRP) play in protein translocation to the ER?

What are the two components of SRPs, and what is the function of each?

What happens to the ER signal sequence after a water-soluble protein has been translocated into the ER lumen?

How is a single-pass transmembrane protein inserted into the ER membrane?

What determines whether the C-terminus or the N-terminus of a single-pass transmembrane protein will be located in the cytosol?

Explain how multi-pass integral membrane proteins are synthesized and inserted into the ER membrane.

What is a hydropathy plot, and how is it used to analyze membrane proteins?

Differentiate between gated transport, transmembrane transport, and vesicular transport, providing an example of each.

What role do chaperones play in the context of protein translocation and folding?

How does the cell ensure that proteins destined for different organelles are sorted correctly in the ER?

Many mitochondrial and chloroplast proteins are encoded by the nuclear genome. What implications does this have for protein targeting and transport?

How could a mutation in a nuclear localization signal (NLS) affect a protein's function?

Explain how post-translational modifications, such as phosphorylation, can regulate nuclear protein import.

How does the diameter of the nuclear pore complex (NPC) change, and what triggers this change?

Describe the role of Ran-GTP in the release of cargo proteins during nuclear import.

How do nuclear localization and export signals regulate gene expression?

Outline the role of calcineurin in NFAT activation during T-cell activation.

Why is it essential for mitochondrial precursor proteins to be surrounded by chaperones in the cytosol?

Describe how the electrochemical gradient across the inner mitochondrial membrane contributes to protein import.

What distinguishes co-translational translocation into the ER from the protein transport mechanisms used for mitochondria and nuclei?

What common structural feature do ER signal sequences share, and how does this feature contribute to their function?

How does transmembrane protein orientation during ER translocation contribute to the protein's final function?

What is the role of hydropathy plots in predicting the structure of multi-pass transmembrane proteins?