Lysosomes and Vacuoles: Structure, Types, and Functions

Vocabulary flashcards covering the structure, polymorphism, functions, and plant equivalent organelles of lysosomes and vacuoles based on lecture notes.

Primary Lysosome

A newly formed organelle (~100 nm in diameter), also known as a protolysosome or virgin lysosome, bounded by a single unit membrane and containing acid hydrolases.

Heterophagosome

A secondary lysosome (also called a heterolysosome or phagolysosome) formed by the fusion of a primary lysosome with cytoplasmic vacuoles containing extracellular material acquired through endocytosis.

Autophagosome

A secondary lysosome (also called a cytolysosome or autolysosome) formed when a primary lysosome engulfs and digests the cell's own intracellular structures, such as mitochondria or ribosomes.

Microautophagy

A form of autophagy in which lysosomes flow directly around cytoplasmic structures and fuse to enclose them in a double-membrane sac prior to enzymatic degradation.

Macroautophagy

A form of autophagy where an organelle targeted for digestion is first wrapped by the smooth endoplasmic reticulum (SER) to form a vesicle that subsequently fuses with a primary lysosome.

Digestive Vacuole

A secondary lysosome in an advanced stage of digestion where the original nature (heterophagosome or autophagosome) can no longer be easily identified.

Residual Body

A telolysosome or dense body formed when digestion inside a vacuole remains incomplete due to the absence of specific lysosomal enzymes.

Lipofuscin Granules

Age pigments consisting of accumulated residual bodies that remain in long-lived cells, such as nerve cells of old animals.

Spherosome

A spherical, membrane-bound plant cell organelle with a fine granular interior rich in lipids and proteins that functions similarly to a lysosome.

Aleurone Grain

A spherical, membrane-bound storage particle (protein body) in seed endosperm and cotyledon cells that stores proteins for germination.

Tonoplast

The membrane that bounds a plant cell's central vacuole, separating the internal cell sap from the surrounding cytoplasm.

Central Vacuole

A large vacuole occupying up to 80–90% of the volume in mature plant cells that maintains turgor pressure, stores nutrients, and detoxifies waste.

Contractile Vacuole

A specialized vacuole found in freshwater protists (e.g., Amoeba, Paramecium) that regulates osmoregulation by pumping out excess water to prevent cell lysis.

Food Vacuole

A phagocytic vacuole formed by endocytosis or phagocytosis in protozoa and phagocytes that digests engulfed food using lysosomal enzymes.

Sap Vacuole

A plant vacuole filled with cell sap (water, sugars, salts, organic acids, and pigments) that maintains osmotic balance within the cell.

Gas Vacuole

A pneumatocyst structure in cyanobacteria, algae, and aquatic plants that provides buoyancy for floating near the water surface to perform photosynthesis.

Air Vacuole

A vacuolar structure found in certain prokaryotic bacteria that provides buoyancy and protects the cell from harmful radiation.

Autolysis

The self-digestion of a dead or damaged cell caused by the rupture of lysosomal membranes and the release of hydrolytic enzymes into the cytoplasm.

Lysosomal Proton Pump

An ATP-driven membrane transporter that pumps $H^+$ ions into the lysosomal lumen to maintain an acidic pH (~5).

Lysosomal Membrane Glycosylation

The heavy attachment of carbohydrates to lysosomal membrane proteins, protecting them from degradation by luminal proteases.