Enzyme that catalyzes the transfer of a phosphate group from ATP to a specific amino acid side chain on a target protein.

Membrane-enclosed organelle, about the size of a bacterium, that carries out oxidative phosphorylation and produces most of the ATP in eukaryotic cells.

Concentration of hydrogen ions in a solution, expressed as a logarithm.

A protein with an elongated, rodlike shape, such as collagen or a keratin filament.

Set of rules by which the information contained in the nucleotide sequence of a gene and its corresponding RNA molecule is translated into the amino acid sequence of a protein.

Long, threadlike structure composed of DNA and proteins that carries the genetic information of an organism; becomes visible as a distinct entity when a plant or animal cell prepares to divide.

Macromolecule built from amino acids that provides cells with their shape and structure and performs most of their activities.

Any protein in which the polypeptide chain folds into a compact, rounded shape. Includes most enzymes.

Long molecule made by covalently linking multiple identical or similar subunits (monomers).

Instrument used to visualize a specimen that has been labled with a fluorescent dye; samples are illuminated with a wavelength of light that excites the dye, causing it to fluoresce.

Technique for observing the detailed structure of a macromolecule at very low temperatures after freezing native structures in ice.

Describes two molecular surfaces that fit together closely and form noncovalent bonds with each other. Examples include complementary base pairs, such as A and T, and the two complementary strands of a DNA molecule.

The tendency of an atom to attract electrons.

Small organic molecule containing both an amino group and a carboxyl group; it serves as the building block of proteins.

In chemistry, describes a molecule or bond in which electrons are distributed unevenly.

Enzyme that catalyzes the removal of a phosphate group from a protein, often with high specificity for the phosphorylated site.

Molecule that accepts a proton when dissolved in water; also used to refer to the nitrogen containing purines or pyrimidines in DNA and RNA.

Region in a polypeptide chain that lacks a definite structure.

The basic unit from which a living organism is made; an aqueous solution of chemicals, enclosed by a membrane, that has an ability to self-replicate.

Positively charged particle found in the nucleus of every atom; also, another name for a hydrogen ion (H+).

A monomer that forms part of a larger molecule, such as an amino acid residue in a protein or a nucleotide residue in a nucleic acid. Can also refer to a complete molecule that forms part of a larger molecule.

The process by which plants, algae, and some bacteria use the energy of sunlight to drive the synthesis of organic molecules from carbon dioxide and water.

Sum of the atomic weights of the atoms in a molecule; as a ration of molecular masses, it is a number without units.

A molecule that releases a proton when dissolved in water; this dissociation generates hydronium (H3O+) ions, thereby lowering the ph.

Protein produced by B lymphocytes in response to a foreign molecule or invading organism. Binds to the foreign molecule or cell extremely tightly, thereby inactivating it or marking it for destruction.

Highly condensed region of an interphase chromosome; generally gene-poor and transcriptionally inactive.

Molecule or fragment of a molecule that is recognized by an antibody.

The mass of an atom relative to the mass of a hydrogen atom; equal to the number of protons plus the number of neutrons that the atom contains.

Intracellular signaling protein whose activity is determined by its association with either GTP or GDP. Includes both trimeric G proteins and monomeric GTPases, such as Ras.

Protein with multiple binding sites for other macromolecules, holding them in a way that speeds up their functional interactions.

Interaction formed when one atom donates electrons to another; this transfer of electrons causes both atoms to become electrically charged.

Chemical reaction in which a covalent bond is formed between two molecules as water is expelled; used to build polymers, such as proteins, polysaccharides, and nucleic acids.

A discrete structure of subcompartment of a eukaryotic cell that is specialized to carry out a particular function. Examples include mitochondria and the Golgi apparatus.

A noncovalent interaction that forces together the hydrophobic portions of dissolved molecules to minimize their disruption of the hydrogen-bonded network of water; causes membrane phospholipids to self-assemble into a bilayer and helps to fold proteins into a compact, globular shape.

Complete three-dimensional structure of a fully folded protein.

A weak noncovalent interaction between a positively charged hydrogen atom in one molecule and a negatively charged atom, such as nitrogen or oxygen, in another.

Large macromolecular complex, composed of rnas and proteins, that translates a messenger RNA into a polypeptide chain.

Negatively charged subatomic particle that occupies space around an atomic nucleus (e–).

Region on the surface of an enzyme that binds to a substrate molecule and catalyzes its chemical transformation.

Beadlike structural unit of a eukaryotic chromosome composed of a short length of DNA wrapped around an octameric core of histone proteins; includes a nucleosomal core particle (DNA plus histone protein) along with a segment of linker DNA that ties the core particles together.

Complex of DNA and proteins that makes up the chromosomes in a eukaryotic cell.

The maximum number of substrate molecules that an enzyme can convert into product per second.

A substance made of carbon, hydrogen, and oxygen with the general formula (CH2O)n. A carbohydrate or saccharide.

The protein-containing lipid bilayer that surrounds a living cell.

An ordered display of the full set of chromosomes of a cell, arranged with respect to size, shape, and number.

Complete structure formed by multiple, interacting polypeptide chains that form a larger protein molecule.

The linear order of monomers in a large molecule—for example, amino acids in a protein or nucleotides in DNA; encodes information that specifies a macromolecule’s precise biological function.

A molecule on which an enzyme acts to catalyze a chemical reaction.

The end of a polypeptide chain that carries a free α-amino Group.

An elongated structure whose subunits twist in a regular fashion around a central axis, like a spiral staircase.

Folding pattern, common in many proteins, in which a single polypeptide chain twists around itself to form a rigid cylinder stabilized by hydrogen bonds between every fourth amino acid.

Activated carrier that serves as the principal carrier of energy in cells; a nucleoside triphosphate composed of adenine, ribose, and three phosphate groups.

Microscopic organism that is a member of one of the two divisions of prokaryotes; often found in hostile environments such as hot springs or concentrated brine.

Contents of a cell that are contained within its plasma membrane but, in the case of eukaryotic cells, outside the nucleus.

Repetitive nucleotide sequence that caps the ends of linear chromosomes. Counteracts the tendency of the chromosome otherwise to shorten with each round of replication.

The form taken by a proton (H+) in aqueous solution.

Large structure within the nucleus where ribosomal RNA is transcribed and ribosomal subunits are assembled.

Regular local folding pattern of a polymeric molecule. In proteins, it refers to α helices and β sheets.

Region on the surface of a protein, typically a cavity or groove, that interacts with another molecule (a ligand) through the formation of multiple noncovalent bonds.

An organism whose cells have a distinct nucleus and cytoplasm.

Polymer built form covalently linked subunits; includes proteins, nucleic acids, and polysaccharides, with a molecular mass greater than a few thousand daltons.

Stable chemical link between two atoms produced by sharing one or more pairs of electrons.

One of a small group of abundant, highly conserved proteins around which DNA wraps to form nucleosomes, structures that represent the most fundamental level of chromatin packing.

A sharing or transfer of electrons that holds two atoms together.

Instrument that illuminates a specimen using beams of electrons to reveal and magnify the structure of very small objects, such as organelles and large molecules.

Microscopic organism that is a member of one of the two divisions of prokaryotes; some species cause disease. The term is sometimes used to refer to any prokaryotic microorganisms, although the world of prokaryotes also includes archaea, which are only distantly related to each other.

Repeating sequence of the atoms (–N–C–C–) that form the core of a protein molecule and to which the amino acid side chains are attached.

Molecule or part of a molecule that readily forms hydrogen bonds with water, allowing it to readily dissolve; literally, “water loving.”

An atom carrying an electrical charge, either positive or negative.

Nonpolar, uncharged molecule or part of a molecule that forms no hydrogen bonds with water molecules and therefore does not dissolve; literally, “water fearing.”

The total genetic information carried by all the chromosomes of a cell or organism; in humans, the total number of nucleotide pairs in the 22 autosomes plus the X and Y chromosomes.

Covalent cross-link formed between the sulfhydryl groups on two cysteine side chains; often used to reinforce a secreted protein’s structure or to join two different proteins together.

Contents of the main compartment of the cytoplasm, excluding membrane-enclosed organelles such as endoplasmic reticulum and mitochondria. The cell fraction remaining after membranes, cytoskeletal components, and other organelles have been removed.

Describes a protein that can exist in multiple conformations depending on the binding of a molecule (ligand) at a site other than the catalytic site; such changes from one conformation to another often alter the protein’s activity or ligand affinity.

Molecule that consists of a carboxylic acid attached to a long hydrocarbon chain. Used as a major source of energy during metabolism and as a starting point for the synthesis of phospholipids.

The order of the amino acid subunits in a protein chain. Sometimes called the primary structure of a protein.

Thin pair of closely juxtaposed sheets, composed mainly of phospholipid molecules, that forms the structural basis for all cell membranes.

Chemical reaction that involves cleavage of a covalent bond with the accompanying consumption of water (its –H being added to one product of the cleavage and its –OH to the other); the reverse of a condensation reaction.

A form of metabolic control in which the end product of a chain of enzymatic reactions reduces the activity of an enzyme early in the pathway.

Specialized organelle in algae and plants that contains chlorophyll and serves as the site for photosynthesis.

Describes genes, chromosomes, or any structures that are similar because of their common evolutionary origin. Can also refer to similarities between protein sequences or nucleic acid sequences.

Enzyme that catalyzes the covalent addition of a small molecule, such as a methyl or acetate group, to a specific amino acid side chain on a histone.

Technique used to separate the individual molecules in a complex mixture on the basis of their size, charge, or their ability to bind to a particular chemical group. In a common form of the technique, the mixture is run through a column filled with a material that binds the desired molecule, and it is then eluted from the column with a solvent gradient.

An organic molecule that is insoluble in water but dissolves readily in nonpolar organic solvents; typically contains long hydrocarbon chains or multiple rings. One class, the phospholipids, forms the structural basis for biological membranes.

Not composed of carbon atoms.

Instrument for viewing extremely small objects. Some use a focused beam of visible light and are used to examine cells and organelles. Others use a beam of electrons and can be used to examine objects as small as individual molecules.

Technique used for determining the three-dimensional Structure of a protein in solution.

A combination of atoms, such as a hydroxyl group (-OH) or an amino group (-NH2), with distinct chemical and physical properties that influence the behavior of the molecule in which it resides.

The end of a polypeptide chain that carries a free carboxyl group (–COOH).

Molecule produced by the transcription of DNA; usually single-stranded, it is a polynucleotide composed of covalently linked ribonucleotide subunits. Serves as variety of informational, structural, catalytic, and regulatory functions in cells.

The number of molecules in a mole, the quantity of a substance equal to its molecular weight in grams; approximately 6 x 10^23.

Double-stranded polynucleotide formed from two separate chains of covalently linked deoxyribonucleotide units. It serves as the cell’s store of genetic information that is transmitted from generation to generation.

Chemical compound that contains carbon and hydrogen.

Assembly of protein molecules that operates as a cooperative unit to perform a complex series of biological activities, such as replicating DNA.

Folding pattern found in many proteins in which neighboring regions of the polypeptide chain associate side-by-side with each other through hydrogen bonds to give a rigid, flattened structure.

Technique for separating a mixture of proteins or DNA fragments by placing them on a polymer gel and subjecting them to an electric field. The molecules migrate through the gel at different speeds depending on their size and net charge.

One of the two main states in which chromatin exists within an interphase cell. Prevalent in gene-rich areas, its less compact structure allows access for proteins involved in transcription.

A free-living, nonphotosynthetic, single-celled, motile eukaryote.

Small molecule that binds tightly to an enzyme and helps it to catalyze a reaction.