AP Biology Chapters 6 and 7: Cellular Energy, Enzymes, and Cellular Respiration

Comprehensive vocabulary review flashcards for AP Biology covering bioenergetics, enzyme kinetics, thermodynamics, and cellular respiration mechanisms from Chapters 6 and 7.

Activation energy

The energy barrier that must be overcome for a chemical reaction to occur; enzymes lower this barrier and speed up the rate of reaction.

Active site

The specific region of an enzyme that binds the substrate and forms the pocket in which catalysis occurs.

Adenosine triphosphate (ATP)

The primary chemical energy currency of all living cells, providing the power needed to drive basic life processes; it is a product of cellular respiration.

Allosteric regulation

Occurs when a regulatory molecule (an effector) binds to a protein or enzyme at a site distinct from its active site, causing a reversible shape (conformational) change that either increases or decreases its activity.

Anabolic pathway

A metabolic pathway that consumes energy to build complicated molecules from simpler ones; also called biosynthetic.

Bioenergetics

The study of energy and its usage in biology, involving the movement of ATP and its usage in the body.

Catabolic pathway

A metabolic pathway involving organic compounds that have potential energy (or fuel if exergonic) that releases energy by breaking complex compounds into simpler molecules.

Catalysis

The process of increasing the rate of a chemical reaction by adding a substance called a catalyst.

Catalyst

A substance that speeds up a chemical reaction without being consumed or permanently altered in the process.

Chemical energy

The potential energy stored in the chemical bonds of molecules that living systems release, transfer, and transform to power cellular work.

Coenzyme

An organic molecule (contains carbon-hydrogen bonds) serving as a cofactor.

Cofactor

Any nonprotein molecule or ion that assists with enzyme function; can be permanently bound to the active site or bound loosely/reversibly.

Competitive inhibitor

A molecule that mimics the substrate and directly competes with the substrate for the active site on the enzyme.

Endergonic reaction

A reaction that absorbs free energy from its surroundings; the molecules store free energy, $\Delta G$ is positive ($\Delta G > 0$), and the reaction is nonspontaneous.

Energy

The capacity or ability to do work or cause change—such as growing, moving, repairing cells, and reproducing; all living things require a continuous input of energy to survive and maintain order.

Energy coupling

A process where an exergonic process gets coupled to an endergonic reaction in order to power it.

Entropy

A measure of molecular disorder, or randomness.

Enzyme

A catalyst that speeds up reactions; enzymes have active sites that bind to the substrate in order to speed up reactions by lowering activation energy.

Enzyme-substrate complex

A temporary complex formed when an enzyme binds to its substrate molecule.

Exergonic reaction

A chemical reaction in which free energy is released into the environment or surroundings; $\Delta G$ is negative ($\Delta G < 0$) because reactants have more energy than products.

Feedback inhibition

A mechanism in which the end product of a chemical pathway inhibits an earlier enzyme from the same pathway to prevent overproduction.

First law of thermodynamics

The law stating that the total content of energy is always consistent.

Free energy

The measure of usable energy in a system that can do work at constant temperature and pressure; determines whether chemical reactions happen spontaneously, and how cells extract energy from absorbed nutrients.

Heat

Thermal energy in transfer from one body of matter to another.

Induced fit

The change in shape of the active site of an enzyme caused by entry of the substrate so that it binds more snugly to the substrate.

Kinetic energy

The energy of relative motion of objects, meaning that an object needs to be moving in order for it to have kinetic energy.

Metabolic pathway

A sequence of enzyme-catalyzed chemical reactions in the cell that can break down or build molecules.

Metabolism

The sum of all chemical reactions in the body that convert food to energy.

Noncompetitive inhibitor

An inhibitor that does not directly compete with the substrate to bind to the active site; instead, it impedes enzymatic reactions by binding to another part of the enzyme.

Phosphorylated intermediate

A series of chemical reactions during cell signaling mediated by enzymes (kinases), in which each kinase in turn phosphorylates and activates another, ultimately leading to phosphorylation of many proteins.

Potential energy

Stored energy an organism holds that can be released to do cellular work; energy stored within chemical bonds.

Second law of thermodynamics

The law stating that every energy transfer or transformation increases the entropy of the universe.

Spontaneous process

A physical or chemical change that occurs naturally on its own under a given set of conditions without needing continuous external intervention or input of energy; spontaneous reactions require $\Delta G < 0$ at constant temperature and pressure, whereas if $\Delta G > 0$, the reverse reaction is spontaneous.

Thermal energy

Kinetic energy due to the random motion of particles.

Thermodynamics

The study of heat, work, temperature, and energy and how they transfer from one environment/body to another.

Acetyl CoA

A highly reactive two-carbon compound formed when pyruvate enters the mitochondria and is oxidized, releasing $\text{CO}_2$ and producing NADH.

Anaerobic respiration

Defined in the notes as a cellular process that produces ATP without the usage of $\text{O}_2$, yielding $2$ ATP per glucose and operating faster compared to aerobic respiration while producing less ATP.

ATP synthase

A large enzyme and molecular motor that synthesizes ATP from ADP and inorganic phosphate by rotating.

Beta oxidation

A metabolic sequence that breaks fatty acids down to two-carbon fragments that enter the citric acid cycle as acetyl CoA.

Cellular respiration

A metabolic process where cells break down nutrients to generate ATP.

Chemiosmosis

The movement of ions across a semipermeable membrane down their electrochemical gradient.

Citric acid cycle

The pathway where most of the $\text{NAD}^+$ and FAD gets reduced to NADH and $\text{FADH}_2$ (extracting the most electron energy from pyruvate/acetyl CoA), yielding a net output of $6$ NADH, $2$ $\text{FADH}_2$, and $2$ ATP per glucose (half of these outputs per pyruvate).

Cytochrome

Protein electron carriers operating between ubiquinone and oxygen whose prosthetic heme group contains an iron atom that accepts and donates electrons.

Fermentation

A metabolic process where carbohydrates are broken down, typically occurring in the absence of oxygen.

$$\text{NAD}^+$$

An electron carrier during cellular respiration that cycles through oxidized and reduced states.

NADH

The electron-carrying, reduced form of $\text{NAD}^+$.

Obligate anaerobe

A microorganism that can only survive, grow, and reproduce in environments completely devoid of molecular oxygen.

Oxidation

The process wherein a reducing agent (usually less electronegative) loses electrons to an oxidizing agent (usually more electronegative); observed in chemical processes like rusting and biological electron transfer from NADH through the ETC.

Oxidative phosphorylation

The final stage of aerobic respiration where cells use enzymes to oxidize nutrients to produce the majority of the cell's ATP; occurs in the inner mitochondrial membrane of eukaryotes (plasma membrane in prokaryotes) and relies on the ETC and chemiosmosis.

Proton-motive force (PMF)

The energy stored in the electrochemical gradient of protons across a membrane, created by proton pumps powered by high-energy electrons from NADH and $\text{FADH}_2$.

Redox reaction

Chemical processes that involve the transfer of electrons between two or more substances.

Reducing agent

A substance that donates electrons to another reactant in a redox reaction.

Reduction

The addition or gain of electrons to a substance in a redox reaction.

Substrate-level phosphorylation

The enzyme-catalyzed formation of ATP by direct transfer of a phosphate group to ADP from an intermediate substrate in catabolism.