Protein Sorting and Eukaryotic Organelles

Vocabulary flashcards covering organelles, the endomembrane system, cotranslational and post-translational protein sorting pathways, and the endosymbiotic theory.

Central Dogma

The cellular process of converting genetic information from DNA to RNA via transcription, and from RNA to protein via translation utilizing ribosomes.

Endomembrane System

An interconnected network of eukaryotic membranes consisting of the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes in animals, vacuoles in plants, and plasma membrane.

Nuclear Envelope

A double membrane surrounding the nucleus that contains nuclear pores and is continuous with the endoplasmic reticulum.

Nuclear Pores

Structures within the nuclear envelope that control what can enter and exit the nucleus.

Rough Endoplasmic Reticulum

A region of the endoplasmic reticulum studded with ribosomes that plays a key role in synthesizing proteins and starting the protein sorting process.

Bound Ribosome

A ribosome that is attached directly to the membrane of the rough endoplasmic reticulum.

Unbound Ribosome

A ribosome that floats freely within the cytoplasm.

Smooth Endoplasmic Reticulum

A region of the endoplasmic reticulum that functions in calcium buildup and detoxification of drugs and toxins.

Golgi Apparatus

An organelle composed of stacked membranes organized from cis, medial, to trans compartments that processes, packages, and routes proteins to their proper destinations.

Acid Hydrolases

Enzymes located inside lysosomes that break down macromolecular bonds and function specifically at an acidic pH.

Central Vacuole

A prominent organelle in plant cells that functions primarily in storage, regulation of cell volume, and degradation.

Plasma Membrane

A phospholipid bilayer surrounding the cell that controls what can enter and leave the cytoplasm.

Nucleolus

The specific region within the nucleus where ribosomal subunits are formed prior to being shipped into the cytoplasm.

Peroxisome

An organelle present in all eukaryotes that uses the enzyme catalase to break down toxic hydrogen peroxide into water and oxygen.

Catalase

An enzyme present inside peroxisomes that breaks down toxic hydrogen peroxide into non-toxic water and oxygen.

Sorting Signals

Short amino acid sequences approximately $10$ to $15$ amino acids in length that direct a polypeptide chain to its proper destination inside or outside the cell.

Cotranslational Sorting

A protein sorting pathway used for proteins destined for the endomembrane system or secretion, characterized by a temporary pause in translation while the ribosome complex docks at the endoplasmic reticulum.

Post-translational Sorting

A protein sorting pathway used for proteins targeted to the nucleus, mitochondria, chloroplasts, or peroxisomes, occurring after translation is fully completed in the cytoplasm.

Signal Recognition Particle (SRP)

A protein that binds to an ER sorting signal, pauses translation, and guides the ribosome complex to a channel on the endoplasmic reticulum membrane.

Signal Peptidase

A specific enzyme that cleaves the signal sequence from the polypeptide chain once it enters the lumen of the endoplasmic reticulum.

Chaperone Proteins

Proteins that guide polypeptide chains during post-translational sorting and keep them unfolded in a linear primary structure until import is complete.

Matrix Targeting Sequence

A specific signal sequence that targets an unfolded polypeptide chain for transport into the mitochondrial matrix.

Cristae

The highly folded structures of the inner mitochondrial membrane that vastly increase surface area to volume ratio.

Matrix

The innermost compartment of a mitochondrion enclosed by the inner membrane.

Thylakoids

Stacked, pancake-like membrane structures located inside chloroplasts that carry out photosynthesis.

Endosymbiotic Theory

The theory proposing that mitochondria originated from purple bacteria and chloroplasts originated from cyanobacteria that were engulfed by an ancestral eukaryotic cell.

Cyanobacteria

A type of photosynthetic blue-green algae from which chloroplasts are believed to have derived according to the endosymbiotic theory.