BIO 101 Chapter 7b: Protein Sorting

signal sequence

a specific stretch of 15-60 amino acids that acts like a cellular “zip code” to direct a protein to its destination

Nuclear Localization Sequence (NLS)

A specific amino acid sequence that tags a protein for import into the nucleus

when ribosomes sometimes make a protein that doesn’t have a signal sequence

the protein remains in the cytosol

ER Import Signal Sequence

A specific sequence of amino acids at the N-terminus that directs a ribosome and its growing polypeptide chain to the rough endoplasmic reticulum.

post-translational transport

the movement of a protein to its destination AFTER it has been completely synthesized on a free ribosome in the cytosol

co-translational transport

The movement of a protein into the ER WHILE it is actively being synthesized by a ribosome attached to the ER membrane

final destinations of post-translational transport

nucleus, mitochondrion, chloroplast, or cytosol

final destination of co-translational transport

secretory vesicle, lysosome, plasma membrane, or ER

Nuclear Pore Complex

A macromolecular gateway in the nuclear envelope that actively controls the traffic of proteins, nucleotides, and mRNA

Nuclear import receptor

a cytosolic protein that binds to an NLS cargo protein and interacts with cytosolic fibrils to guide it through the nuclear pore

Nuclear localization signal (NLS)

Same thing as a nuclear signal sequence

Chaperone proteins

specialized proteins that bind to polypeptides to keep them unfolded during post-translational transport into its location

Signal recognition particle (SRP)

A cytosolic complex that binds to an ER signal sequence, temporarily halts translation, and delivers the ribosome to an SRP receptor on the ER membrane

Translocon

The membrane channel through which a growing polypeptide chain is threaded into the ER Lumen during co-translational transport

Glycosylation

The process in the RER where enzymes attach carbohydrate chains to a protein to form a glycoprotein

transport vesicles

Carry soluble proteins, membrane lipids and membrane proteins between compartments

Constitutive secretion

continuous, unregulated exocytosis that supplies the plasma membrane with newly synthesized lipids and proteins

regulated secretion

A pathway where secretory vesicles store proteins and only fuse with the plasma membrane in response to an extracellular signal.

receptor-mediated endocytosis

The selective uptake of macromolecules from outside the cell via membrane receptors, which mature into lysosomes for digestion

Phagocytosis

The process where a cell engulfs a large food particle or smaller cell into a phagosome, which then fuses with a lysosome.

Autophagy

The cellular recycling process in which a damaged organelle is enclosed in a membrane to form an autophagosome and delivered to a lysosome