Chapter 5: The Working Cell Flashcards
active site
The part of an enzyme molecule where a substrate molecule attaches (by means of weak chemical bonds); typically, a pocket or groove on the enzyme’s surface.
active transport
The movement of a substance across a biological membrane against its concentration gradient, aided by specific transport proteins and requiring input of energy (often as ATP).
adenosine triphosphate (ATP)
Main energy source for cells.
aquaporin
A transport protein in the plasma membrane of some plant or animal cells that facilitates the diffusion of water across the membrane (osmosis).
cellular respiration
The aerobic harvesting of energy from food molecules; the energy-releasing chemical breakdown of food molecules, such as glucose, and the storage of potential energy in a form that cells can use to perform work; involves glycolysis, the citric acid cycle, and oxidative phosphorylation (the electron transport chain and chemiosmosis).
chemical energy
Energy available in molecules for release in a chemical reaction; a form of potential energy.
coenzyme
An organic molecule serving as a cofactor. Most vitamins function as coenzymes in important metabolic reactions.
cofactor
A nonprotein molecule or ion that is required for the proper functioning of an enzyme. See also coenzyme.
competitive inhibitor
A substance that reduces the activity of an enzyme by binding to the enzyme’s active site in place of the substrate. A competitive inhibitor’s structure mimics that of the enzyme’s substrate.
concentration gradient
An increase or decrease in the density of a chemical substance in an area. Cells often maintain concentration gradients of ions across their membranes. When a gradient exists, substances tend to move from where they are more concentrated to where they are less concentrated.
diffusion
The spontaneous tendency of a substance to move down its concentration gradient from where it is more concentrated to where it is less concentrated.
endergonic reaction
An energy-requiring chemical reaction, which yields products with more potential energy than the reactants. The amount of energy stored in the products equals the difference between the potential energy in the reactants and that in the products.
endocytosis
Cellular uptake of molecules or particles via formation of new vesicles from the plasma membrane.
energy
The capacity to perform work, or to rearrange matter.
energy coupling
In cellular metabolism, the use of energy released from an exergonic reaction to drive an endergonic reaction.
entropy
A measure of disorder. One form of disorder is heat, which is random molecular motion.
enzyme
A protein (or RNA molecule) that serves as a biological catalyst, changing the rate of a chemical reaction without itself being changed into a different molecule in the process.
exergonic reaction
An energy-releasing chemical reaction in which the reactants contain more potential energy than the products. The reaction releases an amount of energy equal to the difference in potential energy between the reactants and the products.
exocytosis
The movement of materials out of the cytoplasm of a cell by the fusion of vesicles with the plasma membrane.
facilitated diffusion
The passage of a substance through a specific transport protein across a biological membrane down its concentration gradient.
feedback inhibition
A method of metabolic control in which a product of a metabolic pathway acts as an inhibitor of an enzyme within that pathway.
first law of thermodynamics
The principle of conservation of energy. Energy can be transferred and transformed, but it cannot be created or destroyed.
fluid mosaic
A description of membrane structure, depicting a cellular membrane as a mosaic of diverse protein molecules embedded in a fluid bilayer made of phospholipid molecules.
heat
Thermal energy; the amount of energy associated with the movement of the atoms and molecules in a body of matter. Heat is energy in its most random form.
