Organelles

nucleoid

The region in a prokaryotic cell where DNA is located

ribosomes

Small cellular structures made of RNA and protein that function to produce proteins (found free in the cytoplasm or bound to membranes)

cell wall

A protective layer external to the plasma membrane found in plants, prokaryotes, fungi, and some protists, constructed from polysaccharides such as cellulose, chitin, or peptidoglycan

flagella

Long microtubule extensions that project from certain cells and function to move the cell itself

cytoplasm

The contents of the cell enclosed within the plasma membrane; in eukaryotic cells, it refers to the region between the plasma membrane and the nucleus

nucleus

Membrane-bound organelle in eukaryotic cells that houses genetic material (chromatin)

nuclear envelope

The membrane that surrounds the nucleus

nuclear lamina

A network of intermediate filaments in animal cells that lines the inner surface of the nuclear envelope and imparts structural support

nuclear pore

Small holes in the nuclear envelope that allow the transport of materials into and out of the nucleus

chromatin

The DNA material contained within the nucleus

nucleolus

A condensed region in the center of the nucleus responsible for producing ribosomes

chromosome

Organized units into which cellular DNA is packaged

free ribosomes

float in the cytoplasm and synthesize soluble proteins that dissolve in water

bound ribosomes

attached to the endoplasmic reticulum and synthesize proteins destined for insertion into membranes, packaging in organelles, or secretion outside the cell

endoplasmic reticulum (ER)

An extensive membrane network in eukaryotic cells continuous with the outer nuclear membrane, functioning in protein and lipid synthesis and transport

rough ER (rER)

Endoplasmic reticulum studded with ribosomes on its outer surface; site where membrane and secreted proteins are synthesized and threaded into the ER lumen for folding and enzyme modification

secretory proteins

Proteins synthesized by ER bound ribosomes that enter the ER lumen, fold, undergo carbohydrate additions, and are segregated by ER membranes from cytosolic proteins before transport and secretion

smooth ER (sER)

Endoplasmic reticulum lacking surface ribosomes; serves as the site for lipid synthesis (including steroids), carbohydrate metabolism, and detoxification of drugs and poisons

Golgi apparatus

An organelle that functions in sorting, modifying, packaging, and dispatching cellular materials (such as ER products) via vesicles

vesicles

Small membrane-bound sacs used to transport materials between organelles

lysosomes

Membranous sacs of acidic digestive enzymes found in animal cells that function in intracellular digestion of macromolecules, engulfed material (phagocytosis), and cell component recycling (autophagy)

vacuoles

Fluid storage sacs found in plant, fungal, and animal cells that carry out storage, support, or specialized metabolic functions

contractile vacuoles

Specialized vacuoles that act as pumps to force excess water out of the cell as fast as it enters by osmosis

central vacuoles in plants

A large single vacuole in plant cells that absorbs water, stores ions (like K+ or C1-) and exerts turgor pressure against the cell wall to increase cell rigidity and support growth

mitochondria

double-membraned organelles common to all eukaryotes that serve as the sites of cellular respiration, using oxygen to extract energy from fuels and generate ATP

chloroplasts

green chlorophyll pigments found in plants and algae that serve as the sites of photosynthesis, absorbing sunlight to convert solar energy into chemical energy

semiautonomous

Act semi-independently; refers to organelles (mitochondria and chloroplasts) that contain their own small amounts of DNA and ribosomes, synthesize many of their own proteins, and divide independently within the cell

peroxisomes

Single membrane-bound sacs containing enzymes that transfer hydrogen atoms to oxygen to detoxify poisons (such as alcohol), producing hydrogen peroxide which is then converted into harmless water

cytoskeleton

A dynamic network of protein fibers (microtubules, microfilaments, intermediate filaments) extending throughout the cytoplasm that provides structural support, aids in cell movement, and facilitates intracellular transport

microtubules

(25 nm25 nm in diameter) constructed from tubulin dimers (αα-tubulin and ββ-tubulin) that resist compression, serve as tracks for motor proteins carrying organelles, and form centrioles, cilia, and flagella

tubulin

protein monomer (a tubulin and b tubulin) that forms dimers that assemble or disassemble at the plus (+) end of microtubules to control their growth and shrinkage

centrioles

Ring structures composed of 9 sets of triplet microtubules found in animal cells (absent in plants and fungi) that function during cell division

cilia

Short microtubule extensions projecting from cell surfaces that function to move fluid/substances relative to the cell or propel unicellular organisms

microfilaments

Solid protein rods (7 nm in diameter) consisting of two intertwined chains of actin monomers; function in bearing tension (pulling forces), cell motility, muscle contraction, and cytokinesis

actin

A globular protein monomer (G-actin) that polymerizes into long chains to build microfilaments

myosin

A motor protein that binds to actin filaments and utilizes ATP energy to walk along them, driving muscle cell contraction and amoeboid movement