Kapitel 2

Question 1

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)

Answer 1

Δ G

Question 2

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)

Answer 2

acetyl CoA

Question 3

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)

Answer 3

acid

Question 4

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)

Answer 4

activated carrier

Question 5

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)

Answer 5

activation energy

Question 6

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)

Answer 6

ADP (adenosine 5′-diphosphate)

Question 7

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.

Answer 7

aerobic respiration

Question 8

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)

Answer 8

ATP (adenosine 5′-triphosphate)

Question 9

(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)

Answer 9

base

Question 10

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.

Answer 10

buffer

Question 11

Substance that can lower the activation energy of a reaction (thus increasing its rate) - without itself being consumed by the reaction.

Answer 11

catalyst

Question 12

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.

Answer 12

chemical group

Question 13

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)

Answer 13

citric acid cycle [tricarboxylic acid (TCA) cycle - Krebs cycle]

Question 14

Linked pair of chemical reactions in which the free energy released by one serves to drive the other. (Figure 2–29)

Answer 14

coupled reaction

Question 15

Stable chemical link between two atoms produced by sharing one or more pairs of electrons. (Panel 2–1 - pp. 90–91)

Answer 15

covalent bond

Question 16

The net drift of molecules through space due to random thermal movements.

Answer 16

diffusion

Question 17

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.

Answer 17

electron-transport chain

Question 18

A noncovalent - ionic bond between two molecules carrying groups of opposite charge. (Panel 2–3 - pp. 94–95)

Answer 18

electrostatic attraction

Question 19

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)

Answer 19

entropy (S)

Question 20

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)

Answer 20

equilibrium

Question 21

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)

Answer 21

FAD/FADH2 (flavin adenine dinucleotide/reduced flavin adenine dinucleotide)

Question 22

Energy-storage lipid in cells. Composed of triglycerides—fatty acids esterified with glycerol.

Answer 22

fat

Question 23

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)

Answer 23

fermentation

Question 24

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)

Answer 24

free energy (G) (Gibbs free energy)

Question 25

See ΔG.

Answer 25

free-energy change (Δ ΔG.)

Question 26

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)

Answer 26

glycogen

Question 27

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)

Answer 27

glycolysis

Question 28

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)

Answer 28

GTP (guanosine 5′-triphosphate)

Question 29

Noncovalent bond in which an electropositive hydrogen atom is partially shared by two electronegative atoms. (Panel 2–3 - pp. 94–95)

Answer 29

hydrogen bond

Question 30

Water molecule associated with an additional proton. The form generally taken by protons in aqueous solution.

Answer 30

hydronium ion (H3O+)

Question 31

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)

Answer 31

hydrophobic force

Question 32

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.

Answer 32

macromolecule

Question 33

The sum total of the chemical processes that take place in living cells. All of catabolism plus anabolism. (Figure 2–14)

Answer 33

metabolism

Question 34

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)

Answer 34

NAD+/NADH (nicotinamide adenine dinucleotide/reduced nicotinamide adenine dinucleotide)

Question 35

Electron carrier system closely related to NAD+/NADH - but used almost exclusively in reductive biosynthetic - rather than catabolic - pathways. (Figure 2–36)

Answer 35

NADP+/NADPH (nicotinamide adenine dinucleotide phosphate/reduced nicotinamide adenine dinucleotide phosphate)

Question 36

Biochemical process carried out by certain bacteria that reduces atmospheric nitrogen (N2) to ammonia - leading eventually to various nitrogen-containing metabolites.

Answer 36

nitrogen fixation

Question 37

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)

Answer 37

oxidation (verb oxidize)

Question 38

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.

Answer 38

pH scale

Question 39

Positively charged subatomic particle that forms part of an atomic nucleus. Hydrogen has a nucleus composed of a single proton (H+).

Answer 39

proton (H+)

Question 40

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)

Answer 40

reduction (verb reduce)

Question 41

Polysaccharide composed exclusively of glucose units - used as an energy-storage material in plant cells. (Figure 2–51)

Answer 41

starch

Question 42

Molecule on which an enzyme acts.

Answer 42

substrate

Question 43

Type of (individually weak) noncovalent bond that is formed at close range between nonpolar atoms. (Table 2–1 - p. 45 and Panel 2–3 - pp. 94–95)

Answer 43

van der Waals attraction