Eukaryotic Cell Anatomy

Plasma membrane

Double layer of lipids (mainly phospholipids and cholesterol) with embedded proteins; some proteins span the membrane while others are on one side; outer surface may have attached sugar groups; functions as a selective barrier, controls transport, maintains electrical potential, and enables cell signaling and recognition

Cytoplasm

Region between the nuclear and plasma membranes containing cytosol, inclusions (stored nutrients, pigments, secretory products), and organelles; site of most cellular metabolic activity

Centrioles

Paired cylindrical structures made of nine triplets of microtubules; organize the spindle and asters during mitosis and form the bases of cilia and flagella

Cilia

Short cell-surface projections made of nine pairs of microtubules surrounding a central pair; move substances across the cell surface in a coordinated manner

Flagella

Long cell-surface projections similar to cilia; in humans found only on sperm cells; function in cell movement

Tonoplast

Specialized membrane surrounding the central vacuole in plant cells; regulates movement of ions, nutrients, and wastes into and out of the vacuole and helps maintain turgor pressure and cellular homeostasis

Plasmodesmata

Microscopic cytoplasmic channels that pass through plant cell walls; connect adjacent cells and allow direct transport of water, ions, small molecules, and signaling substances for cell-to-cell communication

Golgi apparatus

Stack of flattened membrane sacs near the nucleus; modifies, packages, and sorts proteins for secretion, lysosomes, or membrane insertion

Intermediate filaments

Protein fibers of varying composition; provide mechanical strength, stabilize cell structure, and help anchor chromatin to the nuclear membrane

Lysosomes

Membrane-bound sacs containing digestive enzymes (hydrolases); responsible for intracellular digestion and recycling

Microfilaments

Thin actin filaments; involved in muscle contraction, cell movement, and maintaining cell shape

Microtubules

Hollow tubes made of tubulin; maintain cell shape, assist in movement, and form structures such as centrioles and spindle fibers

Mitochondria

Double-membraned organelles with folded inner membranes (cristae) and circular DNA; site of ATP production and involved in signaling, cell death, and differentiation

Peroxisomes

Membrane-bound sacs containing oxidase enzymes; detoxify harmful substances and break down hydrogen peroxide using catalase

Ribosomes

Small particles made of rRNA and proteins; free in cytoplasm or attached to rough ER; sites of protein synthesis

Rough endoplasmic reticulum

Membranous network studded with ribosomes; modifies proteins, attaches sugar groups, packages proteins into vesicles, and synthesizes phospholipids and cholesterol

Smooth endoplasmic reticulum

Membranous sacs and tubules without ribosomes; site of lipid and steroid synthesis, lipid metabolism, and drug detoxification

Vesicles

Small membrane-bound structures including transport vesicles, lysosomes, and peroxisomes; involved in transport and metabolism

Nucleus

Largest organelle surrounded by a nuclear envelope; contains nucleoplasm, nucleoli, and chromatin; control center that stores genetic information and directs protein synthesis

Chromatin

Thread-like material made of DNA and histone proteins; contains genes

Nuclear envelope

Double membrane with pores; separates nucleus from cytoplasm, regulates molecular transport, and anchors chromatin

Nucleoli

Dense, non-membrane-bound regions inside the nucleus; sites of ribosome subunit production

Central vacuole (plant cells)

Large membrane-bound compartment; stores ions, wastes, pigments, and protective compounds

Chloroplasts (plant cells)

Membrane-bound organelles containing thylakoids arranged in grana and surrounded by stroma; site of photosynthesis