Biology Chapter 2

The law of conservation of energy; the energy of the universe is constant, thus if the energy of a system increases, the energy of its surroundings must decrease, and vice versa.

The entropy (disorder) of the universe (or system) tends to increase.

• The energy in a system that can be used to drive chemical reactions. If the change in free energy of a reaction (Delta G, the free energy of the products minus the free energy of the reactants) is negative (exergonic), the reaction will occur spontaneously.
• (Delta G positive ='s non-spontaneous: endergonic)

The amount of energy required to produce the transition state of a chemical reaction. If the activation energy for a reaction is very high, the reaction occurs very slowly. Enzymes (and other catalysts) increase reaction rates by reducing the activation energy.

Something that increases the rate of a chemical reaction by reducing the activation energy for that reaction. The Delta G of the reaction remains unchanged.

Thermodynamically unfavorable reactions in the cell can be driven forward by reaction coupling. In reaction coupling, one very favorable reaction is used to drive an unfavorable one. This is possible because free energy changes are additive.

The reactants in an enzyme-catalyzed reaction. Substrate binds at the active site of an enzyme.

The three-dimensional site on an enzyme where substrates (reactants) bind and a chemical reaction is facilitated.

Protein-cleaving enzymes

An enzyme that transfers a phosphoryl group from ATP to other compounds. Kinases are frequently used in regulatory pathways, phosphorylating other enzymes.

An enzyme that dephosphorylates (or removes a phosphoryl group) from a compound.

An enzyme that transfers a free-floating inorganic phosphate to another molecule.

The modification of enzyme activity through interaction of molecules with specific sites on the enzyme other than the active site (called allosteric sites)

The inhibition of an early step in a series of events by the product of a later step in the series. This has the effect of stopping the series of events when the products are plentiful and the series is unnecessary. Feedback inhibition is the most common form of regulation in the body, controlling such things as enzyme reactions, hormone levels, blood pressure, body temperature etc.

An enzyme inhibitor that binds at a site other than the active site of an enzyme (i.e. binds at an allosteric site). This changes the three-dimensional shape of the enzyme such that it can no longer catalyze the reaction.

An enzyme inhibitor that competes with substrate for binding at the active site of the enzyme. When the inhibitor is bound, no product can be made.

• 1. Remove Oxygen
• 2. Add Hydrogen 
• 3. Add electrons to a molecule

• 1. Add Oxygen
• 2. Remove Hydrogen
• 3. Remove electrons from a molecule

Breaking down molecules

Building up molecules (metabolism)

A four-carbon molecule that binds with the two-carbon acetyl unit of acetyl-CoA to form citric acid in the first step of the Krebs Cycle

The oxidation of high-energy electron carriers (NADH and FADH2) couples to the phosphorylation of ADP, producing ATP. In eukaryotes, oxidative phosphorylation occurs in the mitochondria.

A group of three enzymes that decarboxylates pyruvates, creating an acetyl group and carbon dioxide. The acetyl group is then attached to coenzyme A to produce acetyl-CoA, a substrate in the Krebs cycle. In the process, NAD+ is reduced to NADH. The pyruvate dehydrogenase complex is the second stage of cellular respiration.

The product of glycolysis; 2 pyruvic acid (pyruvate) molecules are produced from a single glucose molecule. In the absence of oxygen, pyruvic acid undergoes fermentation and is reduced to either lactic acid or ethanol; in the presence of oxygen, pyruvic acid is oxidizied to produce acetyl-CoA, which can enter the Krebs cycle.

The anaerobic splitting of a glucose molecule into 2 pyruvic acid molecules, producing two net ATP molecules and two NADH molecules. This is the first step in cellular respiration.

The third stage of cellular respiration, in which acetyl-CoA is combined with oxaloacetate to form citric acid. The citric acid is then decarboxylated twice and isomerized to recreate oxaloacetate. In the process, 3 molecules of NADH, 1 molecule of FADH2, and 1 molecule of GTP are formed.

A series of enzyme complexes found along the inner mitochondrial membrane. NADH and FADH2 are oxidized by these enzymes; the electrons are shuttled down the chain and are ultimately passed to oxygen to produce water. The electron energy is use to pump H+ out of the mitochondrial matrix; resulting H+ gradient is subsequently used to drive the production of ATP.

The enzyme the catalyzes the phosphorylation of glucose to form glucose-6-phosphate in the first step of glycolysis. This is one of the main regulatory steps of this pathway. Hexokinase is feedback-inhibted by glucose-6-P.

The enzyme the catalyzes the phosphorylation of fructose-6-phosphate to form fructose-1-6-biphosphate in the third step of glycolysis. This is the main regulatory step of glycolysis. PFK is feedback-inhibited by ATP.

Presence of oxygen

Without the presence of oxygen

The reduction of pyruvate to either ethanol or lactate in order to regenerate NAD+ from NADH. Fermentation occurs in the absence of oxygen, and allows glycolysis to continue under those conditions.

A non-protein, but organic molecule (such as vitamin) that is covalently bound to an enzyme as part of the active site.

A protein complex found in the inner membrane of the mitochondria. Is is essentially a channel that allows H+ ions to flow from the intermembrane space to the matrix (down the gradient produced by the enzyme complexes of the electron transport chain); as the H+ ions flow through the channel, ATP is synthesized from ADP and Pi.

The reduced form (carried electrons) of NAD+. This is the most common electron carrier in cellular respiration.

A term from glycogen breakdown