Bio Ch 4 Glossary

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Chapter 4

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Glossary

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BASAL BODY

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A centriole that, after giving rise to microtubules of a flagellum or cilium, remains attached to its base in the cytoplasm.

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CELL

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[L. cella, small room] Smallest living unit; organized unit with a capacity to survive and reproduce on its own given DNA instructions, energy sources, and raw materials.

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CELL JUNCTION

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Site where cells are interacting physically, functionally, or both.

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CELL THEORY

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All organisms consist of one or more cells, the smallest units with a capacity for independent life that no longer spontaneously arise under existing conditions on Earth.

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CELL WALL

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A semirigid, permeable structure external to the plasma membrane; helps many cells retain their shape and resist rupturing.

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CENTRAL VACUOLE

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Fluid-filled storage organelle of plant cell; its growth enhances cell surface area.

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CENTRIOLE

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Structure that gives rise to microtubules of cilia and flagella.

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CHLOROPLAST

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The organelle of photosynthesis in plants and many protistans.

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CHROMATID

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Of a duplicated eukaryotic chromosome, one of two DNA molecules (with associated proteins) attached to each other at the centromere.

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CHROMATIN

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A cell's collection of DNA and all of the proteins associated with it.

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CHROMOSOME

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[Gk. chroma, color, + soma, body] Of eukaryotic cells, a DNA molecule, duplicated or unduplicated, with many associated proteins. Of prokaryotic cells, a circular DNA molecule.

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CILIUM

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plural cilia. Short motile or sensory structure of certain eukaryotic cells; its core is a 9 + 2 array of microtubules.

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CYTOMEMBRANE SYSTEM

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Organelles (ER & Golgi bodies) that modify, package, and distribute new protein and lipids; also various vesicles (e.g., lysosomes) that have diverse functions.

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CYTOPLASM

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All cell parts, particles, and semifluid substances between the plasma membrane and nucleus or nucleoid.

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CYTOSKELETON

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Dynamic internal framework that structurally supports eukaryotic cells and organizes and moves a cell and its structures.

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ENDOPLASMIC RETICULUM (OR ER)

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Organelle that starts at nucleus and curves through cytoplasm. New polypeptides get side chains in rough ER (has ribosomes on its cytoplasmic side); smooth ER (has no ribosomes) is a site of lipid synthesis.

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EUKARYOTIC CELL

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[Gk. eu, good, + karyon, kernel] Cell having a nucleus and other membrane-bound organelles.

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FLAGELLUM

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plural flagella. A motile structure of many free-living eukaryotic cells. Its core has a 9 + 2 array of microtubules. Typically longer than cilia.

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FLUID MOSAIC MODEL

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A cell membrane consists of a lipid bilayer and proteins. Its lipids are mainly structural; they make it impermeable to water-soluble molecules, yet (by packing variations and movements), impart fluidity. Its diverse proteins perform most membrane functions (e.g., transport, signal reception).

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GOLGI BODY

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Organelle of lipid assembly, polypeptide chain modification, and packaging of both in vesicles for export or transport to locations in cytoplasm.

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INTERMEDIATE FILAMENT

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Cytoskeletal element; mechanically strengthens some animal cells.

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LYSOSOME

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Important organelle of intracellular digestion.

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MICROFILAMENT

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[Gk. mikros, small, + L. filum, thread] Two thin, twisted polypeptide chains; cytoskeletal element that helps cell move, and helps produce and maintain cell shapes.

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MICROGRAPH

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Photograph of an image that came into view with the aid of a microscope.

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MICROTUBULAR SPINDLE

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Bipolar array of many microtubules; forms during nuclear division and moves chromosomes apart in controlled ways.

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MICROTUBULE

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Cylinder of tubulin subunits; cytoskeletal element with roles in cell shape, growth, and motion (e.g., part of cilia, flagella, and spindle apparatus).

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MITOCHONDRION

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Double-membrane organelle of ATP formation. Only site of aerobic respiration's second and third stages. May have endosymbiotic origins.

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NUCLEAR ENVELOPE

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Outermost portion of a cell nucleus; composed of a double membrane (two lipid bilayers and associated proteins).

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NUCLEOLUS

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[L. nucleolus, tiny kernel] In a nondividing cell nucleus, a site for assembling protein and RNA subunits that will later join up as ribosomes in the cytoplasm.

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NUCLEUS

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[L. nucleus, a kernel] Of atoms, a central core of one or more protons and (in all but hydrogen atoms) neutrons. In a eukaryotic cell, the organelle that physically separates DNA from cytoplasmic machinery.

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ORGANELLE

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Membrane-bound sac or compartment in the cytoplasm having one or more specialized metabolic functions. Most eukaryotic cells have a profusion of them.

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PEROXISOME

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Vesicle in which fatty acids and amino acids are first digested to hydrogen peroxide and then converted to harmless products.

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PHOSPHOLIPID

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Organic compound that has a glycerol backbone, two fatty acid tails, and a hydrophilic head of two polar groups (one being phosphate). Phospholipids are the main structural component of cell membranes.

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PLASMA MEMBRANE

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Outermost cell membrane; structural and functional boundary between cytoplasm and the fluid outside the cell.

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PLASMODESMA

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plural plasmodesmata. Plant cell junction; a channel that connects the cytoplasm of adjoining cells.

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PROKARYOTIC CELL

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[L. pro, before, + Gk. karyon, kernel] Archaebacterium or eubacterium; single-celled organism, most often walled; lacks the profusion of membrane-bound organelles observed in eukaryotic cells.

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PSEUDOPOD

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A dynamically extending lobe of cytoplasm used for motility or engulfment.

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RIBOSOME

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Two subunits of rRNA and proteins briefly joined together as a structure on which mRNA is translated into polypeptide chains.

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SURFACE-TO-VOLUME RATIO

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Mathematical relation in which volume increases with the cube of the diameter, but surface area increases only with the square. The volume of a cell expanding in diameter only would increase faster than the surface area of the plasma membrane servicing it; a major constraint on cell size and shape.

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VESICLE

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[L. vesicula, little bladder] One of various small, membrane-bound sacs in cytoplasm that function in the transport, storage, or digestion of substances.

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WAVELENGTH

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A wavelike form of energy in motion. The horizontal distance between the crests of every two successive waves.