AP Biology Unit 3 part 2

Metabolism

The sum of all chemical reactions occurring within a cell or organism.

Catabolism

The metabolic process that breaks down larger molecules (like carbohydrates, fats, and proteins) into smaller units, releasing energy usually in the form of ATP.

Anabolism

The set of metabolic pathways that construct larger, more complex molecules (like proteins or DNA) from smaller ones.

Metabolic Pathway

A series of enzyme-catalyzed chemical reactions where the product of one reaction becomes the substrate for the next.

Substrate

The specific molecule upon which an enzyme acts.

Product

The final molecule(s) formed after a chemical reaction has occurred.

Enzyme

A biological catalyst, typically a protein, that speeds up chemical reactions by lowering the activation energy needed for the reaction to occur.

Active Site

The specific region on an enzyme where the substrate binds and the reaction occurs.

Enzyme-Substrate Complex

A temporary molecular structure formed when an enzyme binds to its substrate.

Cofactor

A nonprotein chemical compound, often a metal ion like Mg²⁺ or Zn²⁺, that assists enzymes in performing catalytic activity.

Coenzyme

An organic cofactor, often derived from vitamins (such as NAD⁺ from niacin), that helps transfer chemical groups or electrons during enzymatic reactions.

Denaturation

A structural change in an enzyme (or other protein) caused by extreme heat, pH, or chemicals, resulting in the loss of its functional shape and, therefore, its activity.

Optimal Temperature

The specific temperature at which an enzyme functions most effectively.

Optimal pH

The pH level at which an enzyme's activity is at its maximum.

Competitive Inhibition

A type of enzyme inhibition where a molecule resembling the substrate binds to the enzyme's active site, preventing the actual substrate from binding.

Noncompetitive Inhibition

Inhibition in which a molecule binds to an enzyme's allosteric site (not the active site), changing its shape and reducing its ability to catalyze reactions.

Allosteric Site

A secondary binding site on an enzyme that allows regulation.

Induced Fit Model

A modern model of enzyme action stating that when the substrate binds, the enzyme slightly changes its shape to fit more snugly around it.

Energy of Activation (Ea)

The minimum amount of energy required for a chemical reaction to begin.

Energy

The capacity to do work or cause change. It exists in many forms, including light, heat, chemical, and mechanical energy, all essential for life processes.

Kinetic Energy

The energy associated with motion, such as moving molecules, flowing electrons, or muscle contractions.

Potential Energy

Stored energy based on position or structure. For example, chemical bonds store potential energy that can be released during reactions.

Chemical Energy

A type of potential energy stored in the bonds of molecules, especially in compounds like glucose and ATP.

Mechanical Energy

The energy related to the movement or position of objects, such as muscle movement or cilia beating in cells.

Heat

The energy lost as random molecular motion during energy conversions. Although it contributes to entropy, it cannot be fully used to perform work in biological systems.

First Law of Thermodynamics

Also known as the Law of Energy Conservation; states that energy cannot be created or destroyed, only transformed from one form to another.

Second Law of Thermodynamics

States that every energy transformation increases the entropy (disorder) of the universe; no energy transfer is 100% efficient because some energy is always lost as heat.

Entropy

A measure of disorder or randomness in a system. As systems move toward equilibrium, entropy increases.

Exergonic Reaction

A chemical reaction that releases free energy (ΔG < 0), such as cellular respiration. These reactions are spontaneous.

Endergonic Reaction

A reaction that absorbs free energy from its surroundings (ΔG > 0) and is nonspontaneous, such as photosynthesis.

ATP (Adenosine Triphosphate)

The cell's main energy currency, consisting of adenine, ribose, and three phosphate groups. Breaking a phosphate bond releases energy for cellular work.

ADP (Adenosine Diphosphate)

The molecule that results when ATP loses one phosphate group. It can be recharged into ATP during energy-producing processes.

Coupled Reactions

Reactions in which energy released by an exergonic process (like ATP hydrolysis) drives an endergonic process (like protein synthesis).

Functions of ATP

ATP provides energy for chemical work (biosynthesis), transport work (pumping molecules across membranes), and mechanical work (muscle contraction or chromosome movement).

Redox Reaction

A type of chemical reaction involving the transfer of electrons between molecules, essential for energy flow in biological systems.

Oxidation

The loss of electrons from a molecule, often releasing energy. (Remember: OIL = Oxidation Is Loss.)

Reduction

The gain of electrons by a molecule, often storing energy. (RIG = Reduction Is Gain.)

Cellular Respiration

A multi-step metabolic pathway that breaks down glucose (C₆H₁₂O₆) in the presence of oxygen to produce carbon dioxide, water, and ATP.

Glycolysis

The first stage of cellular respiration that occurs in the cytoplasm. It breaks one glucose molecule into two pyruvates, producing a net gain of 2 ATP and 2 NADH.

Pyruvate Oxidation

A preparatory step in which each pyruvate is converted into acetyl-CoA, producing NADH and releasing CO₂ before entering the citric acid cycle.

Citric Acid Cycle (Krebs Cycle)

A cyclic series of reactions occurring in the mitochondrial matrix that completes glucose oxidation, producing ATP, NADH, FADH₂, and CO₂.

Electron Transport Chain (ETC)

A sequence of proteins in the inner mitochondrial membrane that transfer electrons from NADH and FADH₂, using the released energy to pump protons (H⁺) and create a gradient.

Chemiosmosis

The process in which protons (H⁺) flow down their concentration gradient through ATP synthase, driving the synthesis of ATP from ADP and phosphate.

ATP Synthase

An enzyme embedded in the inner mitochondrial membrane that produces ATP as protons move through it during chemiosmosis.