Chapter 3: Metabolism & Energy — Vocabulary Flashcards

Vocabulary-style flashcards covering core concepts from Chapter 3: metabolism, energy transfer, enzymes, glycolysis, Krebs cycle, ETC, ATP synthesis, lipid metabolism, and regulatory mechanisms.

Metabolism

Sum of all chemical reactions in the body; occurs in cells of all organ systems; includes energy storage and use.

Anabolism (Anabolic reactions)

Synthesis processes that require energy input to build larger molecules (e.g., storing fat).

Catabolism (Catabolic reactions)

Breakdown processes that release energy by degrading molecules.

Bioenergetics

Study of energy transfer in biological systems.

Metabolic pathway

A linked series of chemical reactions transforming substrates to end products.

Reactants (substrates) and products

Starting chemicals (A + B) that are converted to end products (C + D) in a reaction.

Bidirectional reaction

A reaction that can proceed in both forward and reverse directions.

Glycolysis

Cytosolic pathway that converts glucose to 2 pyruvate with a net gain of 2 ATP and 2 NADH.

Condensation reaction

A reaction in which water is produced as two molecules join.

Hydrolysis

A reaction in which water is used to break a bond.

Phosphorylation

Addition of a phosphate group to a molecule.

Dephosphorylation

Removal of a phosphate group from a molecule.

Oxidation

Loss of electrons (a redox process).

Reduction

Gain of electrons (a redox process).

Kinetic energy

Energy of motion (motion-related energy).

Potential energy

Stored energy; examples include chemical, mechanical, and gravitational energy.

First Law of Thermodynamics

Energy cannot be created or destroyed; it is conserved and transformed between forms.

Second Law of Thermodynamics

Entropy tends to increase; energy becomes more dispersed as reactions proceed.

Entropy

Measure of randomness or disorder in a system.

Equilibrium constant (K)

K = [products]/[reactants] at equilibrium; indicates tendency of reaction to proceed in a direction.

Law of Mass Action

Reaction rate depends on concentrations of reactants and products relative to equilibrium.

Exergonic reaction

Releases energy and proceeds spontaneously under the right conditions.

Endergonic reaction

Requires energy input and does not proceed spontaneously.

Activation energy

Energy required to start a reaction; represents the energy barrier to reaction.

Coupled reactions

Linking an exergonic reaction to an endergonic one so the overall process proceeds.

Enzymes

Proteins that catalyze chemical reactions, are not consumed, and lower activation energy.

Active site

Region of an enzyme where the substrate binds.

Substrate specificity

Enzymes act on a specific set of substrates or a substrate group.

Lock-and-key model

Model of enzyme specificity where substrate fits precisely into the active site.

Induced-fit model

Model where enzyme changes shape to better bind the substrate.

Allosteric regulation

Modulators bind to a regulatory site, altering enzyme activity (activation or inhibition).

Allosteric enzyme

Enzyme with a regulatory site; shows sigmoidal kinetics and can regulate pathways.

Allosteric activator

Molecule that increases enzyme affinity for substrate or catalytic rate.

Allosteric inhibitor

Molecule that decreases enzyme affinity for substrate or catalytic rate.

Covalent regulation

Regulation of enzyme activity via covalent modification (e.g., phosphorylation).

Protein kinase

Enzyme that adds phosphate groups (phosphorylation) to proteins.

Phosphatase

Enzyme that removes phosphate groups (dephosphorylation) from proteins.

Cofactor

Inorganic ion (e.g., Mg2+, Zn2+) required for enzyme activity.

Coenzyme

Organic molecule (e.g., NAD+, FAD) that participates in enzymatic reactions.

NAD+ / NADH

Nicotinamide adenine dinucleotide; NAD+ accepts electrons to form NADH (oxidized vs reduced).

FAD / FADH2

Flavin adenine dinucleotide; FAD accepts electrons to form FADH2.

Glycolysis (overview)

10-step cytosolic pathway converting glucose to 2 pyruvate; net 2 ATP and 2 NADH.

Hexokinase (HK)

Enzyme that phosphorylates glucose to glucose-6-phosphate (G6P), trapping glucose in the cell.

Phosphofructokinase (PFK)

Rate-limiting glycolytic enzyme; allosterically regulated by ADP/AMP (activators) and ATP/citrate (inhibitors).

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH)

Enzyme in glycolysis generating NADH and 1,3-bisphosphoglycerate.

Phosphoglycerate kinase

Enzyme in glycolysis that produces ATP via substrate-level phosphorylation.

Pyruvate kinase

Enzyme that generates ATP in glycolysis from phosphoenolpyruvate (PEP).

Pyruvate

End product of glycolysis; can enter mitochondria for aerobic metabolism or be reduced to lactate anaerobically.

Lactate dehydrogenase (LDH)

Converts pyruvate to lactate, regenerating NAD+ under anaerobic conditions.

Cori cycle

Lactate produced in muscle is transported to liver, where it is converted to glucose.

Glucose-6-phosphate (G6P)

Phosphorylated glucose; trapped in the cell and can enter glycolysis or glycogen synthesis.

Glycogenesis

Synthesis of glycogen from glucose.

Glycogenolysis

Breakdown of glycogen to glucose-6-phosphate.

G-6-phosphatase

Liver/kidney enzyme that dephosphorylates G6P to glucose for export.

Linking step

Pyruvate to acetyl-CoA in mitochondria; generates NADH and connects glycolysis to Krebs cycle.

Acetyl-CoA

Two-carbon molecule that enters the Krebs cycle.

Krebs cycle (TCA cycle / Citric acid cycle)

Mitochondrial matrix cycle producing NADH, FADH2, and ATP; two turns per glucose.

Citrate synthase

First enzyme of the Krebs cycle that combines acetyl-CoA with oxaloacetate.

Oxidative phosphorylation

Production of ATP using the electron transport chain and a proton gradient across the inner mitochondrial membrane.

Electron Transport Chain (ETC)

Series of protein complexes that transfer electrons and pump protons to generate a gradient.

ATP synthase

Enzyme that uses the proton gradient to synthesize ATP from ADP and Pi.

Substrate-level phosphorylation

Direct transfer of a phosphate from a substrate to ADP to form ATP; occurs in glycolysis and Krebs cycle.

β-oxidation

Breakdown of fatty acids in mitochondria to generate acetyl-CoA, NADH, and FADH2.

Palmitate

A 16-carbon saturated fatty acid; oxidation yields a large amount of ATP (107 ATP).

Acetyl-CoA regulation of glycolysis

High acetyl-CoA leads to citrate formation, which inhibits PFK; requires oxaloacetate to combine with acetyl-CoA for Krebs.

Oxaloacetate (OAA)

Krebs cycle intermediate required to condense with acetyl-CoA to form citrate.

Creatine kinase (CK) reaction

Fastest ATP-producing pathway in muscle; transfers phosphate from phosphocreatine to ADP.

Phosphocreatine (CrP)

Storage form of high-energy phosphate in muscle used to rapidly regenerate ATP.

ATP yield per glucose (aerobic)

Approximately 32 ATP per glucose via glycolysis, Krebs cycle, and oxidative phosphorylation.

Glycolysis location

Cytosol; does not require oxygen.

Mitochondrial compartments

Matrix, intermembrane space, inner and outer membranes involved in energy metabolism.

Oxygen as final electron acceptor

O2 accepts electrons at the end of the ETC to form water.