Anatomy of a Generalized Cell (Part 2: Cytoplasm & Organelles)

(pp. 63–75)

Cytoplasm

The cellular material outside the nucleus and inside the plasma membrane; the “factory area” of the cell and the site of most cellular activities.

Cytosol

Semitransparent fluid component of the cytoplasm that suspends the other elements.

Organelles

The metabolic machinery of the cell; specialized cellular compartments that carry out specific functions for the cell as a whole.

Inclusions

Chemical substances that may or may not be present; most are stored nutrients or cell products (e.g., lipid droplets, glycogen granules, melanin).

Mitochondria

The "powerhouses" of the cell; double-membrane structures (inner membrane folded into cristae) serving as the site of ATP synthesis.

Cristae

Shelflike protrusions formed by the folding of the inner mitochondrial membrane.

ATP

Adenosine triphosphate; provides the energy for all cellular work.

Ribosomes

Tiny, bilobed, dark bodies made of proteins and ribosomal RNA. They are the actual sites of protein synthesis in the cell.

Endoplasmic Reticulum (ER)

A system of fluid-filled cisterns (tubules/canals) serving as a minicirculatory system for carrying substances (primarily proteins).

Rough ER

ER studded with ribosomes. It is the cell’s membrane factory, where proteins are synthesized and folded, and phospholipids are synthesized on its external face.

Transport vesicles

Membranous sacs that bud from the rough ER carrying proteins and lipids to other cell areas, typically the Golgi apparatus.

Smooth ER

ER free of ribosomes. It functions in lipid metabolism (cholesterol and fat synthesis/breakdown) and detoxification of drugs and pesticides.

Golgi Apparatus

A stack of flattened membranous sacs that acts as the principal “traffic director” for cellular proteins. Its major function is to modify, package, and segregate proteins for secretion, lysosomes, or incorporation into the plasma membrane.

Secretory vesicles

Vesicles that pinch off the Golgi apparatus, filled with protein destined to be ejected to the outside of the cell (exocytosis).

Lysosomes

"Breakdown bodies"; membranous sacs containing powerful digestive enzymes (acid hydrolases) that function as the cell’s demolition sites, digesting worn-out structures and foreign substances.

Peroxisomes

Membranous sacs containing oxidase enzymes that use molecular oxygen to detoxify harmful substances (alcohol, formaldehyde) and convert dangerous free radicals to hydrogen peroxide.

Free radicals

Highly reactive chemicals with unpaired electrons that can scramble the structure of proteins and nucleic acids.

Catalase

An enzyme in peroxisomes that converts excess hydrogen peroxide to water.

Cytoskeleton

An elaborate network of protein structures that acts as a cell’s “bones and muscles,” furnishing an internal framework and machinery for movement and transport.

Microtubules

The largest elements of the cytoskeleton; tubelike structures that determine the overall shape of a cell and the distribution of organelles, and form centrioles, cilia, and flagella.

Intermediate filaments

Strong, stable, ropelike elements of the cytoskeleton that help form desmosomes and resist pulling forces on the cell.

Microfilaments

Fine filaments composed of actin protein; most involved in cell motility and producing changes in cell shape.

Centrioles

Paired, rod-shaped bodies made of microtubules that lie close to the nucleus and direct the formation of the mitotic spindle during cell division.

Cell Extensions

Obvious surface extensions on some cells.

Cilia

"Eyelashes"; whiplike cellular extensions (with microtubule cores) that move substances along the cell surface (e.g., move mucus away from the lungs).

Flagella

Substantially longer projections (with microtubule cores); the only human example is the sperm tail, which propels the cell itself.

Microvilli

"Little shaggy hairs"; tiny, fingerlike extensions of the plasma membrane (with actin filament cores) that tremendously increase the cell’s surface area for absorption