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Cytosol
the semifluid portion of the cytoplasm
Eukaryotic cell
A type of cell with a membrane-enclosed organelles. Organisms with this (protists, plants, fungi, and animals) are created with these.
Prokaryotic cell
A type of cell lacking a membrane-enclosed nucleus and membrane-enclosed organelles. Organisms with these (bacteria and archaea) are called these.
nucleotide
The building block of a nucleic acid, consisting of a five carbon sugar covalently bonded to a nitrogenous base and one or more phosphate groups.
cytoplasm
the contents of the cell enclosed by the plasma membrane; in eukaryotes, the portion exclusive of the nucleus.
plasma membrane
The membrane at the boundary of every cell that acts as a selective barrier, regulating the cell’s chemical composition.
cytoskeleton
a network of microtubules, microfilaments, and intermediate filaments the extend throughout the cytoplasm and serves a variety of mechanical, transport, and signaling functions.
mitochondrion
An organelle in eukaryotic cells that serves as the site of cellular respiration; uses oxygen to break down organic molecules and synthesize ATP.
peroxisome
An organelle containing enzymes that transfer hydrogen atoms from various substrates to oxygen (O2), producing and the degrading hydrogen peroxide (H2O2).
lysosome
A membrane-enclosed sac of hydrolytic enzymes found in the cytoplasm of animal cells and some protists.
golgi apparadtus
An organelle in eukaryotic cells consisting of stacks of flat membranous sacs that modify, store, and route products of the endoplasmic reticulum and synthesize some products, notably non cellulose carbohydrates.
ribosomes
A complex of rRNA and protein molecules that functions as a site of protein molecules that functions as a site of protein synthesis in the cytoplasm; consists of a large subunit and a small subunit. In eukaryotic cells, each subunit is assembled in the nucleus.
chromatin
the complex of DNA and proteins that makes up eukaryotic chromosomes. when the cell is not dividing, it exists in its dispersed form, as a mass of very long, thin fibers that are not visible with a light microscope.
nucleoulus
A specialized the structure in the nucleus consisting of chromosomal regions containing ribosome RNA genes along with ribosomal proteins imported from the cytoplasm; site of rRNA synthesis and ribosomal subunit assembly.
nuclear envelope
In a eukaryotic cell, the double membrane that surrounds the nucleus, perforated with pores that regulate traffic with the cytoplasm. The outer membrane is continuous with the endoplasmic reticulum.
nuclear lamina
A netlike array of protein filaments that lines the inner surface of the nuclear envelope and helps maintain the shape of the nucleus.
chromosomes
a cellular structure consisting of one DNA molecule and associated protein molecules. a eukaryotic cell typically has multiple, linear chromosomes, which are located in the nucleus. a prokaryotic cell often has a single, circular chromosome, which is found in the nucleotide, a region that is not enclosed by a membrane.
nucleus
An atom’s central core, containing protons and neutrons,
The organelle of a eukaryotic cell that contains the genetic material in the form of chromosomes, made up of chromatin
A cluster of neurons.
rough ER
That portions of the endoplasmic reticulum with ribosomes attached.
smooth ER
That portions of the endoplasmic reticulum that is free of ribosomes.
endoplasmic reticulum
An extensive membranous network in eukaryotic cells, continuous with the outer nuclear membrane and composed of ribosomes-studded (rought) and ribosome-free (smooth)
cell wall
a protective layer external to the plasma membrane in the cells of plants, prokaryotes fungi, and some protists. polysaccharides such as cellulose,
chloroplast
An organelle found in plants and photosynthetic protists that absorbs sunlight and uses it to drive the synthesis of organic compound from carbon dioxide.
central vacuole
In a mature plant cell, a large membranous sac with diverse roles in growth, storage, and sequestration.
endomembrane system
The collection of membranes inside and surrounding a eukaryotic cell, related either through direct physical contact or by the transfer of membranous vesicles; includes the plasma membrane, the nuclear envelope, the smooth and rough endoplasmic reticulum, the Golgi apparatus, lysosomes, vesicles, and vacuoles.
vesicles
A membranous sac in the cytoplasm of a eukaryotic cell.
phagocytosis
A type of endocytosis in which large particular substances or small organism are taken up by a cell. It is carried out by some protists and by certain immune cells of animals (in mammals, mainly macrophages, neutrophils, and dendritic cells).
pinocytosis
A type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes.
food vacuoles
A membranous sac formed by phagocytosis of microorganisms or particles to be used as food by the cell.
contractile vacuoles
A membranous sac the helps move excess water out of certain freshwater protists.
centrosome
A structure present in the cytoplasm of animal cells that functions as a microtubule - organizing center and is important during cell division. This has two centrioles.
centrioles
A structure in the centrosome of an animal cell composed of a cylinder of microtubule triplets arranged in a 9 + 0 pattern. A centrosome has a pair of centrioles.
endosymbiosis
A mutually beneficial relationship between two species in which one organism lives inside the cell or cells of another organism.
endosymbiont theory
The theory that mitochondria and plastids, including chloroplasts, originated as prokaryotic cells engulfed by host cells. The engulfed cell and its host cell then evolved into a single organism.
serial endosymbiosis
A hypothesis for the origin of eukaryotes consisting of a sequence of endosymbiotic events in which mitochondria, chloroplasts, and perhaps other cellular structures were derived from small prokaryotes that had been engulfed by larger cells.
Selective permeability
A property of biological membranes that allows them to regulate the passage of substances across them.
Amphipathic
Having both a hydrophilic region and a hydrophobic region.
Fluid mosaic model
The currently accepted model of cell membrane structure, which envisions the membrane as a mosaic of protein molecules drifting laterally in a fluid bilayer of phospholipids.
Integral proteins
A transmembrane protein with hydrophobic regions that extend into and often completely span the hydrophobic interior of the membrane and with hydrophilic regions in contact with the aqueous solution on one or both sides of the membrane (or lining the channel in the case of a channel protein).
Peripheral proteins
A protein loosely bound to the surface of a membrane or to part of an integral protein and not embedded in the lipid bilayer.
Transport proteins
A transmembrane protein that helps a certain substance or class of closely related substances to cross the membrane.
Aquaporin
A channel protein in the plasma membrane of a plant, animal, or microorganism cell that specifically facilitates osmosis, the diffusion of free water of across the membrane.
Diffusion
The random thermal motion of particles of liquids, gases, or solids. In the presence of a concentration or electrochemical gradient, diffusion results in the net movement of a substance from a region where it is more concentrated to a region where it is less concentrated.
Concentration gradient
A region along which the density of a chemical substance increases or decreases.
Passive Transport
The diffusion of a substance across a biological membrane with no expenditure of energy.
Osmosis
The diffusion of free water molecules across a selectively permeable membrane.
Tonicity
The ability of a solution surrounding a cell to cause that cell to gain or lose water.
Isotonic
Referring to a solution that, when surrounding a cell, causes no net movement of water into or out of the cell.
Hypertonic
Reggering to a solution that, when surrounding a cell will cause the cell to lose water.
Hypotonic
Referring to a solution that, when surrounding a cell, will cause the cell to take up water.
Osmoregulation
Regulation of solute concentrations and water balance by a cell or organism.
Turgid
Swollen or distended, as in plant cells.
Flaccid
Limp. Lacking turgor (stiffness or firmness), as in a plant cell in surroundings where there is a tendency for water to leave the cell. (A walled cell becomes this if it has a higher water potential than its surroundings, resulting in the loss of water).
Plasmolysis
A phenomenon in walled cells in which the cytoplasm shrivels and the plasma membrane pulls away from the cell wall; occurs as one stage of sexual reproduction, followed later by karyogamy.
Facilitated diffusion
The passage of molecules or ions down their electrochemical gradient across a biological membrane with the assistance of specific transmembrane transport proteins, requiring no energy expenditure.
Ion channels
A transmembrane protein channel that allows a specific ion to diffuse across the membrane down its concentration or electrochemical gradient.
Gated channels
A transmembrane protein channel that opens or closes in response to a particular stimulus.
Active transport
The movement of a substance across a cell membrane against its concentration or electrochemical gradient, mediated by specific transport proteins and requiring an expenditure of energy.
Sodium-potassium pump
A transport protein in the plasma membrane of animal cells that actively transports sodium out of the cell and potassium into the cell.
Membrane potential
The difference in electrical charge (voltage) across a cell’s plasma membrane due to the differential distribution of ions. Membrane potential affects the activity of excitable cells and the transmembrane movement of all charged substances.
Cotransport
The coupling of the “downhill” diffusion of one substance to the “uphill” transport of another against its own concentration gradient.
Exocytosis
The cellular secretion of biological molecules by the fusion of vesicles containing them with the plasma membrane.
Endocytosis
Cellular uptake of biological molecules and particulate matter via formation of vesicles from the plasm membrane.
Receptor-mediated endocytosis
The movement of specific molecules into a cell by the inward budding of vesicles containing proteins with receptor sites specific to the molecules being taken in; enables a cell to acquire bulk quantities of specific substances.
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