Flashcards in Kapitel 2 Deck (43)
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)
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)
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)
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)
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)
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.
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)
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.
Substance that can lower the activation energy of a reaction (thus increasing its rate) - without itself being consumed by the reaction.
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.
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)
Stable chemical link between two atoms produced by sharing one or more pairs of electrons. (Panel 2–1 - pp. 90–91)
The net drift of molecules through space due to random thermal movements.
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.
A noncovalent - ionic bond between two molecules carrying groups of opposite charge. (Panel 2–3 - pp. 94–95)
Thermodynamic quantity that measures the degree of disorder or randomness in a system; the higher the entropy - the greater the disorder. (Panel 2–7 - pp. 102–103)
State in a chemical reaction where there is no net change in free energy to drive the reaction in either direction. The ratio of product to substrate reaches a constant value at chemical equilibrium. (Figure 2–30)
Electron carrier system that functions in the citric acid cycle and fatty acid oxidation. One molecule of FAD gains two electrons plus two protons in becoming the activated carrier FADH2. (Figure 2–39)
FAD/FADH2 (flavin adenine dinucleotide/reduced flavin adenine dinucleotide)
Energy-storage lipid in cells. Composed of triglycerides—fatty acids esterified with glycerol.
Anaerobic energy-yielding metabolic pathway involving the oxidation of organic molecules. Anaerobic glycolysis refers to the process whereby pyruvate is converted into lactate or ethanol - with the conversion of NADH to NAD+. (Figure 2–47)
The energy that can be extracted from a system to drive reactions. Takes into account changes in both energy and entropy. (Panel 2–7 - pp. 102–103)
free energy (G) (Gibbs free energy)
free-energy change (Δ ΔG.)
Polysaccharide composed exclusively of glucose units. Used to store energy in animal cells. Large granules of glycogen are especially abundant in liver and muscle cells. (Figure 2–51 and Panel 2–4 - pp. 96–97)
Ubiquitous metabolic pathway in the cytosol in which sugars are incompletely degraded with production of ATP. Literally - “sugar splitting.” (Figure 2–46 and Panel 2–8 - pp. 104–105)
Nucleoside triphosphate produced by the phosphorylation of GDP (guanosine diphosphate). Like ATP - it releases a large amount of free energy on hydrolysis of its terminal phosphate group. Has a special role in microtubule assembly - protein synthesis - and cell signaling. (Figure 2–58)
GTP (guanosine 5′-triphosphate)
Noncovalent bond in which an electropositive hydrogen atom is partially shared by two electronegative atoms. (Panel 2–3 - pp. 94–95)
Water molecule associated with an additional proton. The form generally taken by protons in aqueous solution.
hydronium ion (H3O+)
Force exerted by the hydrogen-bonded network of water molecules that brings two nonpolar surfaces together by excluding water between them. (Panel 2–3 - pp. 94–95)
Polymers constructed of long chains of covalently linked - small organic (carbon-containing) molecules. The principal building blocks from which a cell is constructed and the components that confer the most distinctive properties of living things.
The sum total of the chemical processes that take place in living cells. All of catabolism plus anabolism. (Figure 2–14)
Electron carrier system that participates in oxidation–reduction reactions - such as the oxidation of food molecules. NAD+ accepts the equivalent of a hydride ion (H– - a proton plus two electrons) to become the activated carrier NADH. The NADH formed donates its high-energy electrons to the ATP-generating process of oxidative phosphorylation. (Figure 2–36)
NAD+/NADH (nicotinamide adenine dinucleotide/reduced nicotinamide adenine dinucleotide)
Electron carrier system closely related to NAD+/NADH - but used almost exclusively in reductive biosynthetic - rather than catabolic - pathways. (Figure 2–36)
NADP+/NADPH (nicotinamide adenine dinucleotide phosphate/reduced nicotinamide adenine dinucleotide phosphate)
Biochemical process carried out by certain bacteria that reduces atmospheric nitrogen (N2) to ammonia - leading eventually to various nitrogen-containing metabolites.
Loss of electrons from an atom - as occurs during the addition of oxygen to a molecule or when a hydrogen is removed. Opposite of reduction. (Figure 2–20)
oxidation (verb oxidize)
Common measure of the acidity of a solution: “p” refers to power of 10 - “H” to hydrogen. Defined as the negative logarithm of the hydrogen ion concentration in moles per liter (M). pH = –log [H+]. Thus a solution of pH 3 will contain 10–3 M hydrogen ions. pH less than 7 is acidic and pH greater than 7 is alkaline.
Positively charged subatomic particle that forms part of an atomic nucleus. Hydrogen has a nucleus composed of a single proton (H+).
Addition of electrons to an atom - as occurs during the addition of hydrogen to a biological molecule or the removal of oxygen from it. Opposite of oxidation. (Figure 2–20)
reduction (verb reduce)
Polysaccharide composed exclusively of glucose units - used as an energy-storage material in plant cells. (Figure 2–51)
Molecule on which an enzyme acts.