Kapitel 2 Flashcards
Change in the free energy during a reaction: the free energy of the product molecules minus the free energy of the starting molecules. A large negative value of ΔGindicates that the reaction has a strong tendency to occur. (Panel 2–7 - pp. 102–103)
Δ G
Small water-soluble activated carrier molecule. Consists of an acetyl group linked to coenzyme A (CoA) by an easily hydrolyzable thioester bond. (Figure 2–38)
acetyl CoA
A proton donor. Substance that releases protons (H+) when dissolved in water - forming hydronium ions (H3O+) and lowering the pH. (Panel 2–2 - pp. 92–93)
acid
Small diffusible molecule that stores easily exchangeable energy in the form of one or more energy-rich covalent bonds. Examples are ATP - acetyl CoA - FADH2 - NADH - and NADPH. (Figure 2–31)
activated carrier
The extra energy that must be acquired by atoms or molecules in addition to their ground-state energy in order to reach the transition state required for them to undergo a particular chemical reaction. (Figure 2–21)
activation energy
Nucleotide produced by hydrolysis of the terminal phosphate of ATP. Regenerates ATP when phosphorylated by an energy-generating process such as oxidative phosphorylation. (Figure 2–33)
ADP (adenosine 5′-diphosphate)
Process by which a cell obtains energy from sugars or other organic molecules by allowing their carbon and hydrogen atoms to combine with the oxygen in air to produce CO2 and H2O - respectively.
aerobic respiration
Nucleoside triphosphate composed of adenine - ribose - and three phosphate groups. The principal carrier of chemical energy in cells. The terminal phosphate groups are highly reactive in the sense that their hydrolysis - or transfer to another molecule - takes place with the release of a large amount of free energy. (Figure 2–33)
ATP (adenosine 5′-triphosphate)
(1) A substance that can reduce the number of protons in solution - either by accepting H+ ions directly - or by releasing OH– ions - which then combine with H+ to form H2O. (2) The purines and pyrimidines in DNA and RNA are organic nitrogenous bases and are often referred to simply as bases. (Panel 2–2 - pp. 92–93)
base
Solution of weak acid or weak base that resists the pH change that would otherwise occur when small quantities of acid or base are added.
buffer
Substance that can lower the activation energy of a reaction (thus increasing its rate) - without itself being consumed by the reaction.
catalyst
Certain combinations of atoms—such as methyl (–CH3) - hydroxyl (–OH) - carboxyl (–COOH) - carbonyl (–C=O) - phosphate (–PO32–) - sulfhydryl (–SH) - and amino (–NH2) groups—that have distinct chemical and physical properties and influence the behavior of the molecule in which the group occurs.
chemical group
Central metabolic pathway found in aerobic organisms. Oxidizes acetyl groups derived from food molecules - generating the activated carriers NADH and FADH2 - some GTP - and waste CO2. In eukaryotic cells - it occurs in the mitochondria. (Panel 2–9 - pp. 106–107)
citric acid cycle [tricarboxylic acid (TCA) cycle - Krebs cycle]
Linked pair of chemical reactions in which the free energy released by one serves to drive the other. (Figure 2–29)
coupled reaction
Stable chemical link between two atoms produced by sharing one or more pairs of electrons. (Panel 2–1 - pp. 90–91)
covalent bond
The net drift of molecules through space due to random thermal movements.
diffusion
Series of reactions in which electron carrier molecules pass electrons “down the chain” from higher to successively lower energy levels. The energy released during such electron movement can be used to power various processes. Electron-transport chains present in the inner mitochondrial membrane (called the respiratory chain) and in the thylakoid membrane of chloroplasts generate a proton gradient across the membrane that is used to drive ATP synthesis. See especially Figures 14–18 and 14–52.
electron-transport chain
