Kapitel 3 Flashcards
Region of an enzyme surface to which a substrate molecule binds in order to undergo a catalyzed reaction. (Figure 1–7)
active site
Protein in which allosteric changes in conformation alter the activity of the protein and enable it to serve as a general switch allowing one molecule in a cell to affect the fate of another.
allosteric protein
Change in a protein’s conformation brought about by the binding of a regulatory ligand (at a site other than the protein’s catalytic site) - or by covalent modification. The change in conformation alters the activity of the protein and can form the basis of directed movement. (Figures 3–57 and 16–29)
allostery (adjective allosteric)
Common folding pattern in proteins - in which a linear sequence of amino acids folds into a right-handed helix stabilized by internal hydrogen-bonding between backbone atoms. (Figure 3–7)
alpha helix (α helix)
Self-propagating - stable β-sheet aggregates built from hundreds of identical polypeptide chains that become layered one over the other to create a continuous stack of β sheets. The unbranched fibrous structure can contribute to human diseases when not controlled.
amyloid fibrils
Protein secreted by activated B cells in response to a pathogen or foreign molecule. Binds tightly to the pathogen or foreign molecule - inactivating it or marking it for destruction by phagocytosis or complement-induced lysis. (Figure 24–23)
antibody
Protein produced by B cells in response to a foreign molecule or invading microorganism. Binds tightly to the foreign molecule or cell - inactivating it or marking it for destruction by phagocytosis or complement-induced lysis.
antibody (immunoglobulin - Ig)
Any molecule that can induce an adaptive immune response or that can bind to an antibody or T cell receptor.
antigen
Common structural motif in proteins in which different sections of the polypeptide chain run alongside each other - joined together by hydrogen-bonding between atoms of the polypeptide backbone. Also known as a β pleated sheet. (Figure 3–7)
beta sheet (β sheet)
Region on the surface of one molecule (usually a protein or nucleic acid) that can interact with another molecule through noncovalent bonding.
binding site
Small molecule tightly associated with an enzyme that participates in the reaction that the enzyme catalyzes - often by forming a covalent bond to the substrate. Examples include biotin - NAD+ - and coenzyme A.
coenzyme
Especially stable rodlike protein structure formed by two or more α helices coiled around each other. (Figure 3–9)
coiled-coil
The folded - three-dimensional structure of a polypeptide chain.
conformation
Portion of a protein that has a tertiary structure of its own. Larger proteins are generally composed of several domains - each connected to the next by short flexible regions of polypeptide chain. Homologous domains are recognized in many different proteins.
domain (protein domain)
Ratio of forward and reverse rate constants for a reaction. Equal to the association or affinity constant (Ka) for a simple binding reaction (A + B ⇌ AB). (Figure 3–44)
equilibrium constant (K)
The process in which a product of a reaction feeds back to inhibit a previous reaction in the same pathway. (Figures 3–55 and 3–56)
feedback inhibition
Also called GTPase; an enzyme that converts GTP to GDP.
GTP-binding protein
An enzyme that converts GTP to GDP. GTPases fall into two large families. Large trimeric Gproteins are composed of three different subunits and mainly couple GPCRs to enzymes or ion channels in the plasma membrane. Small monomeric GTP-binding proteins (also called monomeric GTPases) consist of a single subunit and help relay signals from many types of cell-surface receptors and have roles in intracellular signaling pathways - regulating intracellular vesicle trafficking - and signaling to the cytoskeleton. Both trimeric G proteins and monomeric GTPases cycle between an active GTP-bound form and an inactive GDP-bound form and frequently act as molecular switches in intracellular signaling pathways. See page 820.
GTPase
Any molecule that binds to a specific site on a protein or other molecule. From Latin ligare - to bind.
ligand
In ligand binding - the conformational coupling between two separate ligand-binding sites on a protein - such that a conformational change in the protein induced by binding of one ligand affects the binding of a second ligand.
linkage
Enzyme that catalyzes the cutting of polysaccharide chains in the cell walls of bacteria.
lysozyme
Repeating sequence of atoms along the core of the polypeptide chain.
polypeptide backbone
Linear sequence of monomer units in a polymer - such as the amino acid sequence of a protein.
primary structure
Transmissible spongiform encephalopathy—such as Kuru and Creutzfeldt–Jakob disease (CJD) in humans - scrapie in sheep - and bovine spongiform encephalopathy (BSE - or “mad cow disease”) in cows—that is caused and transmitted by an infectious - abnormally folded protein (prion). (Figure 3–33)
prion disease
