Protein monomer of microfilaments that functions in contraction, cell division, and reinforcing or reconfiguring the shape of a cell or its contents.
Complex of adhesion proteins that anchors cells to each other and to extracellular matrixes.
Domain of prokaryotic species; one of two lineages that evolved shortly after life originated. Archaeans have many unique molecular and biochemical traits but also share some traits with bacteria and other traits with eukaryotic species.
Domain of prokaryotic species; the first kinds of cells that formed after life originated. Collectively, bacteria are the most metabolically diverse organisms. Most kinds are chemoheterotrophs.
An organelle that started out as a centriole, the source of a 9+2 array of microtubules in a cilium or flagellum. It remains below the finished array.
Smallest unit that still displays the properties of life; it has the capacity to survive and reproduce on its own.
A dynamic mesh of crosslinked cytoskeletal elements just underneath the plasma membrane and attached to it.
Of a tissue, any molecular structure that connects adjoining cells physically, chemically, or both at their plasma membranes.
All organisms consist of one or more cells, the cell is the smallest unit of organization still displaying the properties of life, and life�s continuity arises directly from growth and division of single cells.
Of many cells (not animal cells), a semirigid but permeable structure that surrounds the plasma membrane; helps a cell retain its shape and resist rupturing.
In many mature, living plant cells, an organelle that stores amino acids, sugars, and some wastes; when it enlarges during growth, it forces the cell to enlarge and increase its surface area.
A barrel-shaped structure that arises from a centrosome and organizes newly forming microtubules into a 9+2 array inside a cilium or flagellum.
Organelle of photosynthesis in plants and algae. Two outer membranes enclose a semifluid interior, the stroma. A third membrane forms a compartment inside that functions in ATP and NADPH formation; sugars form in the stroma.
All of the DNA molecules and associated proteins in a nucleus.
In eukaryotic cells, a linear DNA double helix with many histones and other proteins attached. See also Bacterial chromosome.
A motile structure with a 9+2 array of microtubules that projects from the plasma membrane of certain eukaryotic cells. Modified cilia, such as those of hair cells, have sensory functions.
A type of single-celled photoautotroph; the first to use a noncyclic pathway of photosynthesis, which slowly enriched the early atmosphere with oxygen.
All cell parts, particles, and semifluid substances between the plasma membrane and the nucleus or nucleoid.
In a eukaryotic cell, the dynamic framework of diverse protein filaments that structurally support, organize, and move the cell and internal structures. Prokaryotic cells have a few similar protein filaments.
Endoplasmic reticulum, Golgi bodies, and transport vesicles concerned with modification of many new proteins, lipid assembly, and their transport within the cytoplasm or to the plasma membrane for export.
ER. Organelle that extends from the nuclear envelope through cytoplasm. Ribosomes coat the cytoplasmic side of rough ER, which modifes many new polypeptide chains in its lumen. Membrane lipids are assembled, fatty acids are broken down, and some toxins are inactivated in the lumen of smooth ER.
[Endo�, within + symbiosis, living together] An intimate, permanent ecological interaction in which one species lives and reproduces in the other�s body to the benefit of one or both.
Of many eukaryotic cells, a long, whip-like motile structure with an inner 9+2 array of microtubules. Prokaryotic flagella do not have this array and are not whiplike; they rotate like a propeller.
Cylindrical arrays of proteins in the plasma membrane of adjoining cells; they pair up as open channels for rapid flows of ions and small molecules.
Organelle of endomembrane system; its enzymes modify many new polypeptide chains, assemble lipids, and package both inside vesicles for secretion or for use inside cell.
Cytoskeletal element that mechanically strengthens some cells.
Gluelike polymer deposited in secondary cell walls; makes some plant parts stronger, more waterproof, and less vulnerable to attacks.
Structural basis of all cell membranes; mainly phospholipids arranged tail-to-tail in two layers, with hydrophilic heads of one dissolved in cytoplasmic fluid and heads of the other in extracellular fluid.
Vesicle filled with enzymes that functions in intracellular digestion.
The thinnest cytoskeletal element; consists of actin subunits that function in cell contraction, movement, and structural support.
Largest cytoskeletal element; a filament of tubulin subunits. Contributes to cell shape, growth, and motion.
A type of accessory protein that interacts with microfilaments or with microtubules to move cell structures or the whole cell; e.g., myosin.
An ATP-energized motor protein that moves cell components on cytoskeletal tracks. Interacts with actin in sarcomeres to bring about contraction.
A double membrane that is the outer boundary of the nucleus.
The portion of a prokaryotic cell where DNA is physically organized but not enclosed in a membrane.
[L. nucleolus, tiny kernel] In an interphase nucleus, a mass of material from which RNA and proteins are assembled into the subunits of ribosomes.
Large organelle with an outer envelope of two pore-ridden lipid bilayers that separates eukaryotic chromosomes from the cytoplasm.
One of the membrane-bound compartments that carry out specialized metabolic functions in eukaryotic cells; e.g., a nucleus, mitochondria.
Enzyme-filled vesicle that breaks down amino acids, fatty acids, and toxic substances such as ethanol.
A lipid with a phosphate group in its hydrophilic head. The main constituent of cell membranes.
Outer cell membrane; the structural and functional boundary between cytoplasm and extracellular fluid.
A plant cell junction that connects the cytoplasm of adjoining cells.
The first thin, pliable wall of young plant cells.
[L. pro, before, + Gk. karyon, kernel] A single-celled organism, often walled, that does not have the organelles characteristic of eukaryotic cells. Only bacteria and archaeans are prokaryotic.
A dynamic lobe of membraneenclosed cytoplasm; functions in motility and phagocytosis by amoebas, amoeboid cells, and many white blood cells.
The site of polypeptide chain synthesis in all cells. An intact ribosome has two subunits of rRNA and proteins.
A rigid, permeable wall inside the primary wall of many plant cells; forms after the first growing season.
The semifluid matrix between the thylakoid membrane system and two outer membranes of a chloroplast where sucrose, starch, cellulose, and other end products of photosynthesis are built.
A relationship in which the volume of an object increases with the cube of the diameter, but the surface area increases with the square.
An array of many strands of fibrous proteins collectively joining the sides of cells that make up an epithelium; the array prevents solutes from leaking between the cells.
A small, membrane-bound sac in the cytoplasm; different sacs transport or store substances or hold enzymes that digest their contents.