Protein Transport and Signaling Flashcards

Vocabulary flashcards covering key concepts in protein transport, cellular signaling, and cytoskeleton dynamics.

Protein Localization

The process by which cells manage the specific placement of proteins to ensure proper function.

Targeting Signals

Specific sequences within proteins that dictate their destination within the cell.

Microsomes

ER-derived, membrane-enclosed spheres used to study protein synthesis in vitro.

Co-Translational Translocation

The process by which proteins are moved into the ER during translation.

N-Terminal Signal Peptide

A sequence of 16-30 amino acids at the beginning of secreted proteins, including a hydrophobic core, used for targeting to the ER.

SRP (Signal Recognition Particle)

A complex consisting of six proteins and one non-coding RNA that binds to signal peptides and directs the nascent polypeptide to the ER.

Translocon

A protein channel composed of sec61α, β, and γ proteins that facilitates the passage of nascent polypeptides into the ER lumen.

GPI Anchor

A glycosylphosphatidylinositol anchor that affects protein localization and membrane mobility.

Glycosylation

The addition of carbohydrates to proteins, which is often essential for proper folding, stability, and interaction with other proteins.

Protein Disulfide Isomerase

An enzyme that catalyzes the formation of disulfide bonds between cysteine residues, aiding in stabilizing protein structure.

Unfolded Protein Response (UPR)

A cellular stress response related to the endoplasmic reticulum. It is activated in response to an accumulation of unfolded or misfolded proteins in the lumen of the endoplasmic reticulum.

ERAD (ER-Associated Degradation)

The process by which misfolded proteins are dislocated to the cytosol, polyubiquitinated, and degraded by the proteasome.

TOM/TIM complexes

Protein complexes in the mitochondrial membranes that facilitate the translocation of proteins into the mitochondria.

Nuclear Localization Signal (NLS)

A sequence required for importing larger proteins (>40 kDa) into the nucleus, usually rich in basic amino acids.

Importin

A nuclear transport receptor that binds to NLSs and FG nucleoporins to facilitate import into the nucleus.

Exportin

Facilitates the transport of molecules out of the nucleus requiring a nuclear export signal (NES).

Autophagy

the natural process that removes unnecessary or dysfunctional components.

NXF1/NXT1 dimers

Directs mRNPs through nuclear pores via FG nucleoporins for mRNA export.

Constitutive Secretion

Continuous release of substances from a cell.

Regulated Secretion

Release of substances from a cell that occurs in response to specific signals.

Pulse-Chase Experiments

Experimental method involving short incubation with labeled amino acids followed by analysis after various intervals to study pancreatic acinar cells.

COPII Vesicles

Transport proteins from the ER to the cis-Golgi (anterograde transport).

COPI Vesicles

Responsible for retrograde transport, returning proteins back to the ER.

KDEL Sequence

A common sorting signal for soluble ER-resident proteins that ensures retrograde transport.

Rab GTPases

Serve as molecular addresses for targeting vesicles to appropriate membranes.

SNARE Proteins

Essential for the docking and fusion of vesicles with target membranes.

Cisternal Maturation Model

Theory that the Golgi apparatus matures from cis to trans, with retrograde transport driving organelle maturation.

Clathrin-Coated Vesicles

Vesicles with a two-layer coat consisting of clathrin triskelions and adapter protein (AP) complexes.

Dynamin

Polymerizes around the vesicle's neck during pinching off of clathrin-coated vesicles; GTP hydrolysis leads to constriction.

M6P (Mannose-6-Phosphate)

A crucial modification required for targeting lysosomal proteins; receptors bind modified proteins for delivery to late endosomes.

Proproteins

Enzymes and proteins synthesized in an inactive form that require proteolytic cleavage for activation.

Transcytosis

Proteins initially directed to the basolateral membrane are endocytosed, recycled, or delivered to apical membranes.

V-class Proton Pumps

Facilitate proton movement into endosomes, needing ATP hydrolysis to acidify the endosome.

Actin Cytoskeleton

Plays a crucial role in maintaining and altering the shape and structure of cells.

Nucleation (actin)

Involves assembling three G-actin subunits; it requires a critical concentration of G-actin and is a slow process.

Elongation (actin)

Characterized by fast addition of G-actin subunits, primarily at the plus end.

Steady State (actin)

The filament length remains constant, though there is a continuous exchange of subunits.

G-Actin

Globular actin, the monomeric form of actin.

F-Actin

Filamentous actin, formed by the polymerization of G-actin monomers.

Treadmilling

The dynamic process where ATP-G-actin is added to the plus end and ADP-G-actin is lost at the minus end, maintaining filament length.

Capping Proteins

Bind to either the plus or minus end of F-actin, regulating filament assembly and disassembly.

Formins

Dimeric proteins that stabilize G-actin at the plus end, allowing elongation and nucleation of actin filaments.

Arp2/3 complex

Promotes the formation of branched actin networks and is activated by Nucleation-Promoting Factors (NPFs).

Myosin II

A motor protein consisting of six subunits, including two heavy chains, two regulatory light chains, and two essential light chains.

Lamellipodia and Filopodia

Actin-rich structures produced at the leading edge of a migrating cell, pushing the membrane forward.

Small GTPases (Rho, Rac, Cdc42)

Govern the cytoskeletal architecture, activated by their GEFs and influenced by external signals.

Microtubules

Thicker, longer, and stronger than actin filaments and are essential for cellular transport and chromosome segregation.

αβ-Tubulin Dimers

Basic building blocks of microtubules; each type of tubulin has about 450 amino acids.

Microtubule Organizing Centers (MTOCs)

Structures where microtubules nucleate, primarily at the (-) end.

Centrosome

The main MTOC in interphase animal cells, consisting of two centrioles surrounded by pericentriolar material.

γ-Tubulin Ring Complexes (γ-TuRCs)

Facilitate microtubule nucleation in the pericentriolar material.

Dynamic Instability

Describes the processes regulating microtubule behavior: assembly rate, frequency of catastrophes, disassembly rate, and rescue frequency.

GTP Cap

GTP-bound β-tubulin that maintains the structural integrity of protofilaments, promoting growth.

MAPs (Microtubule-Associated Proteins)

Proteins that bind to microtubules, influencing their dynamics.

Kinesins

Motor proteins that transport towards the (+) end of microtubules (anterograde transport).

Dyneins

Motor proteins that transport towards the (-) end of microtubules (retrograde transport).

Cilia

Microtubule-based projections with a basal body acting as MTOC; contain an axoneme with a 9+2 arrangement of microtubules.

Interphase

That part of the cell cycle where a cell spends the majority of its life.

Intraflagellar Transport (IFT)

Anterograde transport via kinesin and retrograde transport via cytoplasmic dynein are crucial for cilium maintenance.

Mitosis

Process where a single cell divides to produce two daughter cells, each with identical genetic material.

Centrosome (Mitosis)

Acts as the main Microtubule-Organizing Center (MTOC) in non-dividing cells.

Kinetochore Microtubules

Connect to kinetochores at the centromeres for chromosome capture during mitosis.

Intermediate Filaments (IFs)

Provide structural support without intrinsic polarity and are comprised of proteins forming dimers, which aggregate into tetramers.

Keratins

Most diverse type of intermediate filament, involved in forming hair, nails, and structural support in epithelial cells.

Lamins

Intermediate filaments that form the nuclear lamina, interacting with chromatin and contributing to organizational structures within the nucleus.

Endocrine Signaling

Signaling molecules are transported via the circulatory system over long distances (e.g., hormones).

Paracrine Signaling

Cells are in close proximity; signaling molecules don't travel far (e.g., neuronal cells).

Autocrine Signaling

Cells respond to signals they produce themselves (e.g., tumor cells).

Signal Transduction Pathways

Relay signals detected by receptors, leading from initial detection to final cellular response.

Protein Kinases

Add phosphate groups to proteins, commonly used for activating/deactivating proteins.

Protein Phosphatases

Remove phosphate groups from proteins.

GPCRs (G Protein-Coupled Receptors)

Membrane receptors with 7 transmembrane helical regions that bind heterotrimeric G proteins.

G Proteins

Function as molecular switches; active (

Phototransduction

GPCRs (rhodopsin) used by rod cells to detect light, leading to changes to cGMP concentration, affecting ion channels and neurotransmitter release.

RTKs (Receptor Tyrosine Kinases)

Large class of receptors with intrinsic enzymatic activity, activated by various growth factors.

SH2 Domains

Bind phospho-tyrosines on RTKs, recruiting specific proteins for downstream signaling.

Ras/MAP Kinase Pathway

A signaling cascade where activated Ras triggers: Ras → Raf → MEK → MAP Kinase, leading to activation of transcription factors.

PI-3 Kinase Pathway

Activated by RTKs; phosphorylates lipids generating PI(3,4)P2 or PI(3,4,5)P3, leading to PKB activation.

TGF-β Signaling

Signaling molecules activated by their respective receptors (types I and II) that induce R-Smads signaling.

Notch/Delta Signaling

Contact-dependent pathway involving Notch (receptor) and Delta (ligand) in cell communication through receptor cleavage.

Wnt Signaling Pathways

Wnt proteins regulate various cellular processes including cell fate and proliferation; β-catenin accumulation leads to activation of gene transcription.