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Tour of the Cell

actin

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.

basal body

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.

cell fractionation

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

cell wall

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

central vacuole

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

centriole

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 involved in cell division.

centrosome

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

chloroplast

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.

chromatin

The complex of DNA and proteins that makes up a eukaryotic chromosome. When the cell is not dividing, chromatin exists as a mass of very long, thin fibers that are not visible with a light microscope.

chromosome

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

cilium

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.

collagen

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.

contractile vacuole

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

cytoplasm

The entire contents of the cell, exclusive of the nucleus, and bounded by the plasma membrane.

cytoplasmic streaming

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

cytoskeleton

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

cytosol

The semifluid portion of the cytoplasm.

desmosome

A type of intercellular junction in animal cells that functions as an anchor.

dynein

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

electron microscope (EM)

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

endomembrane system

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

endoplasmic reticulum (ER)

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

eukaryotic cell

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

extracellular matrix (ECM)

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

fibronectin

A glycoprotein that helps cells attach to the extracellular matrix.

flagellum

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

food vacuole

A membranous sac formed by phagocytosis.

gap junction

A type of intercellular junction in animal cells that allows the passage of material or current between cells; also known as a communicating junction.

glycoprotein

A protein covalently attached to a carbohydrate.

Golgi apparatus

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

granum

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

integrin

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

intermediate filament

A component of the cytoskeleton that includes all filaments sized between microtubules and microfilaments.

light microscope (LM)

An optical instrument with lenses that refract (bend) visible light to magnify images of specimens.

lysosome

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

microfilament

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.

microtubule

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

microvillus

One of many fine, fingerlike projections of the epithelial cells in the lumen of the small intestine that increase its surface area.

middle lamella

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

mitochondrial matrix

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

mitochondrion

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

motor protein

Proteins that grip the cytoskeleton to cause cell motility (cell location or parts within the cell). Bk

myosin

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

nuclear envelope

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

nuclear lamina

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

nucleoid

A dense region of DNA in a prokaryotic cell.

nucleolus

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

nucleus

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

organelle

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

peroxisome

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

phagocytosis

A type of endocytosis involving large, particulate substances.

plasma membrane

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

plasmodesma

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

plastid

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

primary cell wall

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

prokaryotic cell

A type of cell lacking a membrane-enclosed nucleus and membrane-enclosed organelles; found only in the domains Bacteria and Archaea.

proteoglycan

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

pseudopodium

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

ribosome

A cell organelle constructed in the nucleolus and functioning as the site of protein synthesis in the cytoplasm; consists of rRNA and protein molecules, which make up two subunits.

rough ER

That portion of the endoplasmic reticulum studded with ribosomes.

scanning electron microscope (SEM)

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

secondary cell wall

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

smooth ER

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

stroma

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

thylakoid

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

tight junction

A type of intercellular junction in animal cells that prevents the leakage of material between cells.

tonoplast

A membrane that encloses the central vacuole in a plant cell, separating the cytosol from the cell sap.

transmission electron microscope (TEM)

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

transport vesicle

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

ultracentrifuge

A machine that spins test tubes at the fastest speeds to separate liquids and particles of different densities.

vacuole

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.

vesicle

A sac made of membrane inside of cells.

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