Bio Chapter 6 Definitions

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Actin

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A globular protein that links into chains, two of which twist helically about each other, forming microfilaments in muscle and other contractile elements in cells.

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actin

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A globular protein that links into chains, two of which twist helically about each other, forming microfilaments in muscle and other contractile elements in cells.

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basal body

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A eukaryotic cell organelle consisting of a 9 + 0 arrangement of microtubule triplets; may organize the microtubule assembly of a cilium or flagellum; structurally identical to a centriole.

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cell fractionation

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The disruption of a cell and separation of its organelles by centrifugation.

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cell wall

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A protective layer external to the plasma membrane in plant cells, bacteria, fungi, and some protists. In plant cells, the wall is formed of cellulose fibers embedded in a polysaccharide-protein matrix. The primary cell wall is thin and flexible, whereas the secondary cell wall is stronger and more rigid and is the primary constituent of wood.

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central vacuole

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A membranous sac in a mature plant cell with diverse roles in reproduction, growth, and development

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centrosome

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Material present in the cytoplasm of all eukaryotic cells, important during cell division; the microtubule-organizing center

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centriole

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A structure in an animal cell composed of cylinders of microtubule triplets arranged in a 9 + 0 pattern. An animal cell usually has a pair of centrioles involved in cell division.

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centrosome

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Material present in the cytoplasm of all eukaryotic cells, important during cell division; the microtubule-organizing center.

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chloroplast

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An organelle found only in plants and photosynthetic protists that absorbs sunlight and uses it to drive the synthesis of organic compounds from carbon dioxide and water.

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chromosome

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A threadlike, gene-carrying structure found in the nucleus. Each chromosome consists of one very long DNA molecule and associated proteins. See chromatin.

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cilium

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A short cellular appendage specialized for locomotion, formed from a core of nine outer doublet microtubules and two inner single microtubules ensheathed in an extension of plasma membrane.

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collagen

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A glycoprotein in the extracellular matrix of animal cells that forms strong fibers, found extensively in connective tissue and bone; the most abundant protein in the animal kingdom.

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contractile vacuole

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A membranous sac that helps move excess water out of the cell.

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cortex

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The region of the root between the stele and epidermis filled with ground tissue.

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crista

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An infolding of the inner membrane of a mitochondrion that houses the electron transport chain and the enzyme catalyzing the synthesis of ATP.

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cytoplasmic streaming

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A circular flow of cytoplasm, involving myosin and actin filaments, that speeds the distribution of materials within cells.

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cytoskeleton

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A network of microtubules, microfilaments, and intermediate filaments that branch throughout the cytoplasm and serve a variety of mechanical and transport functions.

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cytosol

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The semifluid portion of the cytoplasm.

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dynein

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A large contractile protein forming the side-arms of microtubule doublets in cilia and flagell

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electron microscope

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A microscope that focuses an electron beam through a specimen, resulting in resolving power a thousandfold greater than that of a light microscope. A transmission electron microscope (TEM) is used to study the internal structure of thin sections of cells. A scanning electron microscope (SEM) is used to study the fine details of cell surfaces.

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endomembrane system

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The collection of membranes inside and around a eukaryotic cell, related either through direct physical contact or by the transfer of membranous vesicles.

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endoplasmic reticulum

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An extensive membranous network in eukaryotic cells, continuous with the outer nuclear membrane and composed of ribosome-studded (rough) and ribosome-free (smooth) regions

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endosymbiotic theory

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A hypothesis about the origin of the eukaryotic cell, maintaining that the forerunners of eukaryotic cells were symbiotic associations of prokaryotic cells living inside larger prokaryotes.

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eukaryotic cell

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A type of cell with a membrane-enclosed nucleus and membrane-enclosed organelles, present in protists, plants, fungi, and animals; also called eukaryote.

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extracellular matrix

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The substance in which animal tissue cells are embedded consisting of protein and polysaccharides.

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fibronectin

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A glycoprotein that helps cells attach to the extracellular matrix.

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flagellum

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 A long cellular appendage specialized for locomotion, formed from a core of nine outer doublet microtubules and two inner single microtubules, ensheathed in an extension of plasma membrane.

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food vacuole

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A membranous sac formed by phagocytosis.

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golgi apparatus

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An organelle in eukaryotic cells consisting of stacks of flat membranous sacs that modify, store, and route products of the endoplasmic reticulum.

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granum

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A stacked portion of the thylakoid membrane in the chloroplast. Grana function in the light reactions of photosynthesis.

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integrin

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Receptor proteins built into the plasma membrane that interconnect the extracellular matrix and the cytoskeleton.

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intermediate filament

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A component of the cytoskeleton that includes all filaments intermediate in size between microtubules and microfilaments.

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lysosome

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A membrane-enclosed bag of hydrolytic enzymes found in the cytoplasm of eukaryotic cells.

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microfilament

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A solid rod of actin protein in the cytoplasm of almost all eukaryotic cells, making up part of the cytoskeleton and acting alone or with myosin to cause cell contraction.

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microtubule

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A hollow rod of tubulin protein in the cytoplasm of all eukaryotic cells and in cilia, flagella, and the cytoskeleton.

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middle lamella

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A thin layer of adhesive extracellular material, primarily pectins, found between the primary walls of adjacent young plant cells.

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mitochondrial matrix

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The compartment of the mitochondrion enclosed by the inner membrane and containing enzymes and substrates for the Krebs cycle.

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mitochondrion

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An organelle in eukaryotic cells that serves as the site of cellular respiration.

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myosin

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A type of protein filament that interacts with actin filaments to cause cell contraction.

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nuclear envelopes

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The membrane in eukaryotes that encloses the nucleus, separating it from the cytoplasm.

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nuclear lamina

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A netlike array of protein filaments that maintains the shape of the nucleus.

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nucleoid

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A dense region of DNA in a prokaryotic cell.

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nucleolus

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A specialized structure in the nucleus, formed from various chromosomes and active in the synthesis of ribosomes.

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nucleus

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(1) An atom's central core, containing protons and neutrons. (2) The chromosome-containing organelle of a eukaryotic cell. (3) A cluster of neurons.

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organelle

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One of several formed bodies with specialized functions, suspended in the cytoplasm of eukaryotic cells.

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peroxisome

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A microbody containing enzymes that transfer hydrogen from various substrates to oxygen, producing and then degrading hydrogen peroxide.

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phagocytosis

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A type of endocytosis involving large, particulate substances.

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plasma membrane

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The membrane at the boundary of every cell that acts as a selective barrier, thereby regulating the cell's chemical composition.

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plasmodesmat

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An open channel in the cell wall of plants through which strands of cytosol connect from adjacent cells.

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plastid

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One of a family of closely related plant organelles, including chloroplasts, chromoplasts, and amyloplasts (leucoplasts).

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primary cell wall

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A relatively thin and flexible layer first secreted by a young plant cell.

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proteglycan

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A glycoprotein in the extracellular matrix of animal cells, rich in carbohydrate.

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Pseudopium

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A cellular extension of amoeboid cells used in moving and feeding.

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Ribosome

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A cell organelle constructed in the nucleolus and functioning as the site of protein synthesis in the cytoplasm

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rough ER

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That portion of the endoplasmic reticulum studded with ribosomes.

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scanning electron microscope

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A microscope that uses an electron beam to scan the surface of a sample to study details of its topography.

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secondary cell wall

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A strong and durable matrix often deposited in several laminated layers for plant cell protection and support.

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smooth ER

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That portion of the endoplasmic reticulum that is free of ribosomes.

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stroma

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The fluid of the chloroplast surrounding the thylakoid membrane; involved in the synthesis of organic molecules from carbon dioxide and water.

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thylakoid

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A flattened membrane sac inside the chloroplast, used to convert light energy to chemical energy.

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transmission electron microscope

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A microscope that passes an electron beam through very thin sections, primarily used to study the internal ultrastructure of cells.

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Transport vesicle

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A tiny membranous sac in a cell's cytoplasm carrying molecules produced by the cell.

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vacule

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A membrane-enclosed sac taking up most of the interior of a mature plant cell and containing a variety of substances important in plant reproduction, growth, and development.

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vesicle

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A sac made of membrane inside of cells.