Cytoplasmic Organelles

The cisternal maturation model states that cis-cisternae physically mature into medial and then trans-cisternae, receiving recycling enzymes from behind via COPI vesicles.

While N-linked glycosylation begins in the ER, O-linked glycosylation occurs exclusively within the compartments of the Golgi apparatus.

The trans-Golgi network is the sorting hub where exit vesicles are packaged and targeted to the plasma membrane, lysosomes, or extracellular space.

Without the mannose-6-phosphate (M6P) tag, lysosomal enzymes miss their sorting receptors in the trans-Golgi, routing into the default secretory pathway instead (I-cell disease).

The Golgi has a slightly lower pH than the ER. This acidic environment increases the affinity of KDEL receptors for ER proteins, facilitating their capture into retrograde COPI vesicles.

Rab GTPases serve as molecular tags on transport vesicles, interacting with specific tethering complexes on target membranes to ensure docking accuracy.

The sulfation of proteoglycans and proteins is a specialized maturation step carried out by sulfotransferase enzymes located in the trans-Golgi.

Cristae are folds of the inner mitochondrial membrane that house the respiratory chain and ATP synthase complexes.

The Golgi apparatus accepts vesicles from the ER, performs biochemical modifications, and targets them to their final cellular destinations.

The matrix is the gel-like central compartment of the mitochondrion where the Krebs cycle takes place. Stroma is found in chloroplasts.

Plant Golgi bodies are often referred to as dictyosomes because they exist as smaller, dispersed stacks within the plant cytoplasm.

The cis face, or forming face, is oriented toward the endoplasmic reticulum to intercept emerging transport vesicles.

As proteins move from the cis to the trans face, their attached sugar groups undergo sequential enzymatic modifications to form mature complex glycoproteins.

Lysosomal enzymes are specifically modified with a mannose-6-phosphate (M6P) tag in the cis-Golgi, which is recognized by M6P receptors in the trans-Golgi for sorting.

Primary lysosomes emerge as transport vesicles from the trans-Golgi network carrying concentrated mixtures of active hydrolytic enzymes.

COPI-coated vesicles handle retrograde vesicle transport, moving materials backward from the Golgi to the ER.

COPII coatomer proteins assemble transport vesicles moving anterograde from the ER toward the cis-Golgi. COPI tracks retrograde movements.

The Signal Recognition Particle halts translation temporarily to prevent premature protein folding in the cytosol before docking at the RER translocon.

New lipids are added to the cytosolic leaflet of the ER. Scramblases flip lipids randomly across leaflets without needing energy, balancing out the bilayer surface area.