Unit 2: Cell Structure and Function

• organelles: membrane-enclosed structures within eukaryotic cells
• cytosol: a semifluid, jellylike substance in which subcelluar components are suspended
• nucleoid: a dense region of DNA in a prokaryotic cell
• nucleus: contains most of the genes in the eukaryotic cell
• nuclear envelope: encloses the nucleus, separating its contents from the cytoplasm
• chromatin: the complex of DNA and proteins making up chromosomes
• ribosomes: complexes made of ribosomal RNA and protein which are the cellular components that carry out protein synthesis
• endomembrane system: consists of the nuclear envelope, the endoplasmic reticulum, the Golgi apparatus, lysosomes, various kinds of vesicles and vacuoles, and the plasma membrane
• vesicles: membrane sacs that specialize in moving products into, out of, and within a cell
• smooth ER: The outer surface lacks ribosomes
• rough ER: studded with ribosomes on the outer surface of the membrane
• Golgi apparatus: an organelle in eukaryotic cells consisting of stacks of flat, membranous sacs that modify, store, and route products of the ER and synthesize some products, notably noncellulose carbohydrates
• lysosome: a membrane-closed sac of hydrolydic enzymes found in the cytoplasm of animal cells and some protists
• phagocytosis: a type of endocytosis in which large, particulate substances or small organisms are taken up by the cell
• vacuole: a membrane-bound vesicle whose specialized function varies in different kinds of cells
• contractile vacuole: a membranous sac that helps move excess water out of certain freshwater protists
• mitochondrion: an organelle in eukaryotic cells that serves as the site of cellular respiration; uses oxygen to break down organic molecules and synthesize ATP
• chloroplast: an organelle found in plants and photosynthetic that absorbs sunlight and uses it to drive the synthesis of organic compounds from carbon dioxide and water
• endosymbiont theory: the theory that mitochondria and chloroplasts originated as prokaryotic cells engulfed by an ancestral eukaryotic cell, which became its host cell and then evolved into a single organism
• crista: an infolding of the inner membrane of the mitochondrion; the inner membrane houses electron transport chains and molecules of the enzyme catalyzing the synthesis of ATP
• Matrix: the compartment of the mitochondrion enclosed by the inner membrane and containing enzymes and substrates for the citric acid cycle, as well as ribosomes and DNA
• stroma: the dense, fluid liquid within the chloroplast surrounding the thylakoid membrane and containing ribosomes and DNA; involved in the synthesis of organic molecules from carbon dioxide and water
• plastid: one of a family of closely related organelles that includes chloroplasts, chromoplasts, and amyloplasts
• peroxisome: an organelle containing enzymes that transfer hydrogen atoms from various substrates to oxygen, producing and then degrading hydrogen peroxide
• cytoskeleton: a network of microtubules, mircofilaments, and intermediate filaments that extend throughout the cytoplasm and serve a variety of mechanical, transport, and signal functions
• microtubule: a hollow rod composed of tubulin proteins that makes up parts of the cytoskeleton
• centriole: a structure in the centrosome composed of a cylinder of microtubule arranged in a certain pattern
• flagellum: a long cellular appendage specializing in locomotion
• cilium: a short appendage containing microtubules that is specialized for locomotion or moving fluid past the cell
• dyneins: In cilia and flagella, a large motor protein extending from one microtubule doublet to the adjacent doublet; ATP hydrolysis drives changes in dynein shape that lead to bending of cilia and flagella
• microfilament: A cable composed of actin proteins in the cytoplasm making up part of the cytoskeleton and acting alone or with myosin to cause cell contraction
• actin: A globular protein that links into chains, two of which twist helically about each other, forming microfilaments in muscle and other kinds of cells
• cortex: The outer region of cytoplasm, that has a more gel-like consistency than the inner regions due to the presence of multiple microfilaments
• myosin: a type of motor protein that associates into filaments that interact with actin filaments to cause cell contraction
• intermediate filament: A component of the cytoskeleton that includes filaments intermediate in size between microtubules and microfilaments
• primary cell wall: a relatively thin and flexible layer that surrounds the plasma membrane of a young cell
• middle lamella: a thin layer of adhesive extracellular material, primarily pectins, found between primary walls
• extracellular matrix (ECM): the meshwork surrounding animal cells, consisting of glycoproteins, polysaccharides, and proteoglycans synthesized and secreted by the cells
• collagen: a glycoprotein in the extracellular matrix of animal cells that forms strong fibers, found in connective tissue and bone; the most abundant protein in animals
• selective permeability: a property of biological membranes that allows them to regulate the passage of substances across them