Kapitel 3 Flashcards
Thermodynamic quantity that measures the degree of disorder in a system.
entropy
A small molecule that stores energy or chemical groups in a form that can be donated to many different metabolic reactions. Examples include ATP - acetyl CoA - and NADH.
activated carrier
Molecule capable of picking up an electron from a molecule with weak electron affinity and transferring it to a molecule with a higher electron affinity.
electron carrier
An enzyme-catalyzed process by which complex molecules are formed from simple substances by living cells; also called anabolism.
biosynthesis
Removal of electrons from an atom - as occurs during the addition of oxygen to a carbon atom or when a hydrogen is removed from a carbon atom. The opposite of reduction.
oxidation
A molecule on which an enzyme acts.
substrate
Activated carrier that donates the carbon atoms in its readily transferable acetyl group to many metabolic reactions - including the citric acid cycle and fatty acid biosynthesis; the acetyl group is linked to coenzyme A (CoA) by a thioester bond that releases a large amount of energy when hydrolyzed.
acetyl CoA (acetyl coenzyme A)
Activated carrier closely related to NADH and used as an electron donor in biosynthetic pathways. In the process it is oxidized to NADP+.
NADPH (nicotine adenine dinucleotide phosphate)
Substance that accelerates a chemical reaction by lowering its activation energy; enzymes perform this role in cells.
catalyst
For a reversible chemical reaction - the ratio of substrate to product when the rates of the forward and reverse reactions are equal.
equilibrium constant (K)
Nucleoside diphosphate produced by hydrolysis of the terminal phosphate of ATP.
ADP (adenosine 5′-diphosphate)
acetyl CoA (acetyl coenzyme A)
Activated carrier that donates the carbon atoms in its readily transferable acetyl group to many metabolic reactions - including the citric acid cycle and fatty acid biosynthesis; the acetyl group is linked to coenzyme A (CoA) by a thioester bond that releases a large amount of energy when hydrolyzed.
G - ΔG - ΔG°—see free energy - free-energy change.
ΔG°
Addition of electrons to an atom - as occurs during the addition of hydrogen to a carbon atom or the removal of oxygen from it. The opposite of oxidation.
reduction
Molecule that easily gives up an electron - thereby becoming oxidized.
electron donor
Process by which molecules and small particles move from one location to another by random - thermally driven motion.
diffusion
Activated carrier widely used in the energy-producing breakdown of sugar molecules.
NADH
Concentration of substrate at which an enzyme works at half its maximum velocity; serves as a measure of how tightly the substrate is bound.
Michaelis constant (KM)
The sum total of the chemical reactions that take place in the cells of a living organism.
metabolism
Set of metabolic pathways by which large molecules are made from smaller ones.
anabolism
General term for any process in a cell in which the uptake of molecular oxygen (O2) is coupled to the production of CO2.
respiration
The maximum rate of an enzymatic reaction - reached when the active sites of the enzyme molecules in a sample are fully occupied by substrate.
Vmax
Energy that can be harnessed to do work - such as driving a chemical reaction.
free energy (G)
Covalent bond whose hydrolysis releases an unusually large amount of free energy under the conditions existing in a cell. Examples include the phosphodiester bonds in ATP and the thioester linkage in acetyl CoA.
high-energy bond
Atom or molecule that readily takes up electrons - thereby becoming reduced.
electron acceptor
Chemical group derived from acetic acid.
acetyl group
State in which the forward and reverse rates of a chemical reaction are equal so that no net chemical change occurs.
equilibrium
The acceleration of a chemical reaction brought about by the action of a catalyst; virtually all reactions in a cell require such assistance to occur under conditions present in living organisms.
catalysis
“Delta G”: in a chemical reaction - the difference in free energy between reactant and product molecules. A large negative value of ΔG indicates that the reaction has a strong tendency to occur. The standard free-energy change (ΔG°) is the free-energy change measured at defined concentration - temperature - and pressure.
free-energy change (ΔG)
The concentration of substrate at which an enzyme works at half its maximum rate. Large values of KM usually indicate that the enzyme binds to its substrate with relatively low affinity.
KM
Small molecule used to carry and transfer acetyl groups needed for a variety of metabolic reactions - such as the synthesis of fatty acids.
coenzyme A
A protein that catalyzes a specific chemical reaction.
enzyme
Set of enzyme-catalyzed reactions by which complex molecules are degraded to simpler ones with release of energy; intermediates in these reactions are sometimes called catabolites.
catabolism
Nucleotide produced by the energetically favorable hydrolysis of the final two phosphate groups from ATP - a reaction that drives the synthesis of DNA and RNA.
AMP (adenosine 5′ monophosphate)
Linked pair of chemical reactions in which free energy released by one reaction serves to drive the other reaction.
coupled reaction
The number of substrate molecules an enzyme can convert into product per second.
turnover number
The energy that must be acquired by a molecule to undergo a chemical reaction.
activation energy
