Chapter 3: Energy, Catalysis, and Biosynthesis Flashcards

Vocabulary flashcards covering key concepts from Energy, Catalysis, and Biosynthesis (Chapter 3), including thermodynamics, enzymes, free energy changes, reaction coupling, and activated carriers.

Metabolism

The total amount of energy that a cell pertains, which can either be utilized or released through catabolic and anabolic pathways.

Catabolic Pathway

A metabolic pathway concerned with breaking down complex molecules into smaller subunits through hydrolysis and releasing the chemical energy housed within their bonds.

Anabolic Pathway

A metabolic pathway concerned with building larger molecules (polymers) from smaller ones (monomers), which requires an input of energy.

Entropy

A measurement of disorder or chaos in a system, which increases as heat is released during energy transfers.

Second Law of Thermodynamics

A law of thermodynamics stating that energy transfers are not $100\text{\%}$ efficient because energy is lost in the form of heat, leading to an increase in entropy.

Kinetic Energy

The energy of motion possessed by moving objects or randomly vibrating molecules.

Potential Energy

Stored energy held for later use, such as energy stored within chemical bonds or food.

First Law of Thermodynamics

A law of thermodynamics stating that energy can neither be created nor destroyed, only transferred or transformed from one form to another.

Autotroph

A self-producing organism, such as a plant, that uses light energy to synthesize its own food molecules through photosynthesis.

Heterotroph

A consumer organism that cannot produce its own food and must consume other organisms to obtain energy.

Decomposer

An organism, such as a fungus, that feeds solely on dead organisms or waste products to recycle energy back into the soil.

Light Dependent Stage

Stage one of photosynthesis occurring in the chloroplast, where electromagnetic energy from the sun and water molecules are used to activate energy carriers like $ATP$ and $NADPH$, releasing oxygen as a byproduct.

Carbon Fixation

Stage two of photosynthesis (also known as the Calvin Cycle or Light Independent Cycle) in which carbon dioxide is converted into sugar or glucose.

Aerobic Respiration

The metabolic process in which glucose is broken down in the presence of oxygen within the mitochondria to produce $ATP$, releasing carbon dioxide as a waste product.

Oxidation

A chemical reaction involving the loss or release of an electron by an atom or molecule.

Reduction

A chemical reaction involving the gain of an electron by an atom or molecule.

Free Energy ($G$)

The portion of a system's energy that can be harvested to do work or drive chemical reactions.

Free Energy Change ($\Delta G$)

The change in free energy during a reaction, which determines whether the reaction can occur spontaneously.

Activation Energy

The energy barrier or minimum kinetic energy required for a chemical reaction to initiate spontaneously.

Enzyme

A biological catalyst, usually protein-based, that increases the rate of a chemical reaction by lowering its activation energy without being consumed or altering the final product.

Active Site

The specific region on an enzyme that binds to a substrate molecule using noncovalent bonds to form an enzyme-substrate complex.

Energetically Favorable Reaction

A reaction with a negative free energy change ($\Delta G < 0$) that loses free energy, increases disorder, and can occur spontaneously.

Energetically Unfavorable Reaction

A reaction with a positive free energy change ($\Delta G > 0$) that requires an input of energy to proceed.

Reaction Coupling

The pairing of an energetically unfavorable reaction with an energetically favorable one so that the overall net free energy change ($\Delta G$) remains negative.

Equilibrium

The state of a chemical reaction where the rate of the forward reaction equals the rate of the reverse reaction, resulting in a free energy change ($\Delta G$) of zero.

Standard Free Energy Change ($\Delta G^\circ$)

A reference value for free energy change independent of molecular concentration, measured under ideal conditions where reactants and products are at $1\,mol/dm^3$.

Equilibrium Constant ($K$)

A value directly proportional to the standard free energy change ($\Delta G^\circ$) that indicates the ratio of substrates to products at chemical equilibrium and reflects noncovalent binding strength.

Chemical Siphon

A sequence of coupled reactions where an energetically favorable reaction harvests released free energy to drive a subsequent energetically unfavorable reaction step.

Activated Carrier

A small organic molecule that temporarily stores energy in high-energy chemical bonds or high-energy electrons to fuel energetically unfavorable reactions.

Adenosine Triphosphate (ATP)

The primary activated carrier in cells that stores transferable chemical energy in its terminal phosphate bond.

Phosphorylation

The chemical transfer of a phosphate group from an activated carrier like $ATP$ to another molecule.

Phosphoanhydride Bond

The high-energy bond linking terminal phosphate groups in an $ATP$ molecule, which releases free energy upon hydrolysis.

Hydride Ion ($H^-$)

A unit consisting of two high-energy electrons and one proton transferred by electron carriers such as $NADH$ and $NADPH$.

NADPH

An activated electron carrier that carries high-energy electrons and a hydrogen ion, acting primarily as a reducing agent in anabolic pathways.

NADH

An activated electron carrier generated during catabolic reactions (such as glycolysis and the Krebs cycle) that stores energy for cellular respiration.

Acetyl CoA

An activated carrier molecule that stores and transfers energy in an acetyl group during cellular metabolism.