This site is under serious rennovation. Please excuse the appearance while we update. Come back soon!
Interactive Glossary
Curious about the characters you've seen on our website? Most are based on actual proteins that are made and function within your cells. To learn about their technical and physical characteristics, browse through our glossary. We've searched long and hard for the best video footage of these nanomolecular machines, for your entertainment and learning pleasures.
the energy-requiring process in which a substance binds to a specific transmembrane protein, changing its conformation to allow the passage of the substance through the membrane against the electrochemical gradient for that substance
ATP:
nucleotide consisting of adenosine bound to three phosphate groups; it is the principal immediate energy source for prokaryotic and eukaryotic cells
Amino acids:
the monomeric units of proteins; each is composed of three functional groups attached to a central alpha-carbon; an amino group, a defining side chain, a carboxyl group
Anticodon:
a three-nucleotide sequence in each tRNA that functions in the recognition of the ocomplementary mRNA codon
Apoptosis:
a type of orderly, or programmed, cell death in which the cell responds to certain signals by initiating a normal response that leads to the death of the cell. Death by apoptosis is characterized by the overall compaction of the cell and its nucleus, the orderly dissection of the chromatin into pieces at the hands of a special DNA-splitting endonuclease, and the rapid engulfment of the dying cell by phagocytosis
Cell theory:
all organisms are composed of one or more cells. The cell is the structural unit of life
Centrioles:
cylindrical structures, about 0.2 micrometers across and typically about twice as long, that contain nine evenly spaced fibrils, each of which appears in cross sections as a band of three microtubules. Centrioles are nearly always found in pairs, with each of the members situated at right angles to one another.
Cristae:
the many deep folds that are characteristic of the inner mitochondrial membrane, which contains the molecular machinery of oxidative phosphorylation
Cytoplasm:
the part of a cell that is enclosed within the plasma membrane, containing organelles such as mitochondria which are filled with a liquid that is kept separate from the rest of the cytoplasm by biological membranes; the site where most cellular activities occur. (src: Wikipedia)
Cytoskeleton:
An elaborate interactive network composed of three well-defined filamentous structures: microtubules, microfilaments, and intermediate filaments. These elements function to provide structure support; an internal framework responsible for positioning the various organelles within the interior of the cell; as part of the machinery required for movement of materials and organelles within cells; as force-generating elements responsible for the movement of cells from one place to another; as sites for anchoring mRNAs and facilitating their translation into polypeptides; and as a signal transducer, transmitting information from the cell membrane to the cell interior
Cytosol:
the region of fluid content of the cytoplamsm outside of the membranous organelles of a eukaryotic cell.
DNA:
a double stranded nucleic acid composed of two polymeric chains of deoxyribose-containing nucleotides. The genetic material of all cellular organisms.
Dynein:
an exceptionally large, cargo-carrying, multisubunit motor protein that moves along microtubules toward their minus end.
Electron-transport or respiratory chain:
membrane-embedded electron carriers that accept high-energy electrons and sequentially lower the energy state of the electrons as they pass through the chain, with the net results of capturing energy for use in synthesizing ATP or other energy-storage molecules
Endocytosis:
mechanism for the uptake of fluids and solutes into a cell.
Endomembrane system:
functionally and structurally interrelated group of membranous cytoplasmic organelles including the endoplasmic reticulum, Golgi complex, endosomes, lysosomes, and vacuoles
Endoplasmic reticulum (ER):
a system of tubules, cisternae, and vesicles that divides the fluid content of the cytoplasm into a luminal space within the ER membrane and a cytosolic space outside the membrane
Enzymes:
vitally important protein catalyst s of cellular reactions
Facilitated diffusion:
process by which the normal diffusion rate of a substance is increased through interaction with a substance-specific membrane protein
Golgi complex:
network of smooth membranes organized into a characteristic morphology, consisting of a flattened, disk-like cisternae with dilated rims and associated vesicles and tubules. The Golgi complex functions primarily as a processing plant where proteins newly synthesized in the endoplasmic reticulum are modified in specific ways
Hydrophilic:
the tendency of polar molecules to interact with surrounding water molecules, which are also polar; “water loving”
Hydrophobic interaction:
the tendency of nonpolar molecules to aggregate so as to minimize their collective interaction with surrounding polar water molecules: “water fearing”
Integral protein:
a membrane-associated protein that penetrates or spans the lipid bilatyer
Intermembrane space:
the space between the inner and outer mitochondrial membranes
Ion channel:
a transmembrane structure permeable to a specific ion or ions.
Kinesin:
a plus end-directed motor protein that moves membranous vesicles and other organelles along microtubules through the cytoplasm.
Luminal (cisternal) space:
the region of the fluid content of the cytoplasm enclsosed by the membranes of the endoplasmic reticulum or golgi complex
Lysosome:
organelles containing digestive enzymes called acid hydrolyses; found in animal cells, fuses to vacuoles, dispense enzymes into vacuoles, and digest their contents. (src: Wikipedia)
Matrix:
one of two aqueous compartments of the mitochondrion; the matrix is located within the interior of hthe organelle; the second compartment is the intermembrane space which is located between the outer and inner mitochondrial membrane
mRNA:
the intermediate molecule with between a gene and the polypeptide for which it codes.
Metabolic pathway:
A series of chemical reactions that results in the synthesis of an end product important to cellular function
Mitosis:
process of nuclear division in which duplicated chromosomes are faithfully separated from one another, producing two nuclei, each with a complete copy of all the chromosomes present in the original cell
Mismatch repair:
DNA repair system that removes mismatche dbases that ar eincorporated by the DNA polymerase and escape the enzyme’s proofreading exonuclease
Molecular chaparones:
various familes of proteins whose role is to assit the assembly of proteins by preventing undesirable interactions
Motor proteins:
proteins that utilize the energy of ATP hydrolysis to generate mechanical forces that propel the protein, as well as attached cargo, along wone of the components of the cytosketon. Three families of motor proteins are known: kinesins and dyneins move along microtubules nad myosins move along microfilaments
Myosins:
a large family of motor proteins that moves along actincontaining microfilaments. Most myosins are plus end directed motors.
Nuclear envelope:
complex, double-membrane structure that divides the eukaryotic nucleus from its cytoplasm
Nuclear pore complex:
complex, basketlike apparatus that fills the nuclear pore like a stopper, projecting outward into both the cytoplasm and the nucleoplasm
Nucleoli:
irregular-shaped nuclear structures that function as ribosome-producing organelles
Nucleotide:
the monomer of nucleic acids, each consists of three parts: a sugar, a phosphate group, and a nitrogenous base, with the phosphate linked to the sugar a thte 5; carbon and the base at the 1; carbon
Nucleus:
the organelle that contains a eukaryotic cell’s genetic material
Okazaki fragments:
small segments of DNA that are rapidly linked to longer pieces that have been synthesized previously, to form the lagging strand
Oncogenes:
genes that encode proteins that promote the loss of growth control and the conversion of the cell to a malignant state. These genes have the ability to transform cells
Organelles:
the organizationally and functionally diverse, membranous or membrane-bounded, intracellular structures that are the defining feature of eukaryotic cells.
Peroxisomes:
simple, membrane-bound, multifunctional organelles of the cytoplasm that carry out a diverse array of metabolic reactions, including substrate oxidation leading to tformation of hydrogen peroxide.
Phagocytosis:
process by which particulate materials are taken into cells. Materials are enclosed within a fold of the plasma membrane which buds into the cytoplasm to form a vesicles called a phagosome
Plasma membrane:
the membrane serving as the boundary between the interior of the cell and its extracellular environment
Proteins:
structurally and functionally diverse group of polymers built of amino acid monomers
Receptor:
any substance that can bind to a specific molecule, often leading o uptake or signal transuction
Replication:
duplication of genetic material
RNA:
single-stranded nucleic acid composed of a polymeric chain f ribose-containing nucleotides
Ribosome:
complexes of RNA and protein that are found in all cells. Functions in the expression of the genetic code from nucleic acid into protein in a process called translation. Catalyzes the assembly of individual amino acids into polypeptide chains which involves binding mRNA and using it as a template to join together the correct sequence of amino acids. The reaction uses adapters called tRNA molecules which read the sequence of the mRNA and are attached to the amino acids. (src: Wikipedia)
Ribozyme:
an RNA molecule that functions as a catalyst in cellular reactions
RER:
Rough endoplasmic reticulum: that part of the endoplasmic reticulum that has ribosomes attached. Thee RER appears as an extensive membranous organelle composed primarily of flattened sacs (cisternae) separated by a cytosolic space. RER functions include synthesis of secretory proteins, lysosomal proteins integral membrane proteins, and membrane lipids.
Second messenger:
a substance that is formed in the cell as a result of the binding of a first messenger to a receptor at the outer surface of the cell
Signal transduction:
the overall process in which information carried by extracellular messenger molecules is translated into changes that occur inside a cell.
Signaling pathways:
the information superhighways of the cell. Each consists of a series of distinct proteins that operate in sequences. Each protein in the pathway acts by altering the conformation of the downstream protein in the series
Smooth endoplasmic reticulum (SER):
the part of the endoplasmic reticulum that is without attached ribosomes. The membranous elements of the SER are typically tubular and form an interconnecting system of pipelines curving through the cytoplasm in which they occur. The SER functions vary from cell to cell and include the synthesis of steroid hormones, detoxification of wide variety of organic compounds, mobilization of glucose from glucose 6-phosphate and sequestration of calcium ions
tRNA:
transport RNA
Template:
a single strand of DNA or RNA that contains the information (encoded as a nucleotide sequence) for construction of a complementary strand
Transcription:
the formation of an RNA from a DNA template
Transduction:
the incorporation of a gene into a cellular genome by means of a virus
Translation:
synthesis of proteins in the cytoplasm using the information encoded by an mRNA
Tricarboxylic acid cycle (TCA cycle):
the circular metabolic pathway that oxidizes acetyl CoA, converting its energy; the cycle is also known as the Krebs cycle or citric acid cycle
Vacuole:
a single membrane-bound, fluid filled structure that comprises as much as 90% of the volume of many plant cells
Vesicle:
small, intercellular, membrane-enclosed sac that stores or transports substances within a cell (src: Wikipedia)