L12 - Intracellular Transport 1

UNT Biol 3510

Endomembrane system

" A network of membranes within eukaryotic cells that are involved in the synthesis, modification, and transport of proteins and lipids."

Endosymbiont

" A cell that lives within another cell, with both cells benefiting from the relationship."

Gated transport

The selective movement of proteins and RNA molecules between the cytoplasm and the nucleus through nuclear pore complexes.

Transport

across membranes The movement of proteins across membranes via protein translocators.

Vesicular transport

The movement of proteins and lipids between membrane-bound compartments via membrane-enclosed transport vesicles.

Signal sequence

A short stretch of amino acids that directs a protein to a specific cellular location.

Necessary and sufficient

A criterion for demonstrating that a signal sequence is both required and adequate for targeting a protein to a specific location.

Co-translational protein translocation

The transport of a protein across the ER membrane while it is being synthesized by a ribosome.

Post-translational protein translocation

The transport of a protein across a membrane after its synthesis is complete.

Protein chaperones

" Proteins that assist in the folding or unfolding of other proteins, and indirectly in protein translocation mechanisms."

Nuclear envelope

The double membrane that surrounds the nucleus in eukaryotic cells.

Nuclear lamina

" A network of intermediate filaments that lines the inner surface of the nuclear envelope, providing structural support."

Perinuclear space

The space between the inner and outer nuclear membranes.

Nuclear pore complex

" A large protein complex that spans the nuclear envelope, regulating the passage of molecules between the nucleus and cytoplasm."

Nucleoporins

Proteins that make up the nuclear pore complex.

Daltons

A unit of mass used to express the molecular weight of proteins and other molecules.

Nuclear fibrils

Protein filaments that extend from the nuclear pore complex into the cytoplasm and nucleoplasm.

Nuclear localization signal

A signal sequence that directs proteins to the nucleus.

Nuclear import receptor

A protein that binds to nuclear localization signals and facilitates the import of proteins into the nucleus.

Ran-GDP

" The inactive form of the Ran GTPase, bound to GDP, with a weak affinity for nuclear import receptor."

Ran-GTP

" The active form of the Ran GTPase, bound to GTP, with a strong affinity for nuclear import receptor."

Ran GAP

" Ran GTPase-activating protein, which triggers GTP hydrolysis by Ran, converting it to Ran-GDP."

Ran GEF

" Ran guanine nucleotide exchange factor, which promotes the exchange of GDP for GTP on Ran, converting it to Ran-GTP."

Signal peptidase

An enzyme that removes the signal sequence from a protein after it has been translocated across a membrane.

Signal-recognition particle (SRP)

A ribonucleoprotein complex that binds to signal sequences and targets ribosomes to the ER membrane.

SRP Receptor

A protein on the ER membrane that binds to SRP and the ribosome assisting with protein import to the ER.

ER-bound ribosome

A ribosome that is attached to the endoplasmic reticulum membrane.

Free ribosome

A ribosome that is not attached to the endoplasmic reticulum membrane.

Polyribosome (polysome)

A cluster of ribosomes simultaneously translating a single mRNA molecule.

Endoplasmic reticulum lumen

The interior space of the endoplasmic reticulum.

Endoplasmic reticulum membrane

The membrane that surrounds the endoplasmic reticulum.

Start and stop signals

Signal sequences that initiate and terminate the translocation of a protein across the ER membrane.

Single-pass transmembrane

A protein that spans the membrane only once.

Multi-pass transmembrane

A protein that spans the membrane multiple times.

Sec complex

" A protein complex that forms a channel in the ER membrane, allowing the translocation of proteins."

BiP (hsp70-like chaperone protein)

A chaperone protein in the ER lumen that assists in protein folding.

Molecular ratchet model

A model explaining how proteins are pulled through the ER membrane using BiP and ATP hydrolysis.

Mitochondrial envelope

The double membrane surrounding the mitochondrion.

Mitochondrial intermembrane space

The space between the outer and inner mitochondrial membranes.

Mitochondrial cristae

The folds of the inner mitochondrial membrane.

Mitochondrial matrix

The innermost compartment of the mitochondrion.

TIM complex

" Translocase of the inner mitochondrial membrane, a protein complex that mediates the import of proteins into the mitochondrial matrix."

TOM complex

" Translocase of the outer mitochondrial membrane, a protein complex that mediates the import of the proteins into the mitochondrial intermembrane space."

Peroxisome

" A membrane-bound organelle that contains enzymes involved in various metabolic reactions, including the breakdown of fatty acids. "

Peroxisome signal sequence

A signal sequence that directs proteins to the peroxisome.

Peroxin

Proteins that mediate the import of proteins into peroxisomes.