Unit 3: Energy and Enzymes

Vocabulary terms and definitions related to the laws of thermodynamics, cellular energy processes, and enzyme structure and regulation.

First law of thermodynamics

The law stating that energy is neither created nor destroyed, but can be transferred from one form to another.

Second law of thermodynamics

The law stating that entropy is constantly increasing; when energy is transferred, some of it is given off and there will be less energy available at the end of the process.

Entropy

A measure of chaos that increases as biological molecules are assembled and energy is given off; the entropy of two atoms decreases when a bond forms between them.

Free energy

The amount of energy stored in the bonds of a molecule that is available to do work.

Exergonic reactions

Chemical reactions that release energy.

Endergonic reactions

Chemical reactions that absorb energy; an example is the formation of a bond between two atoms.

Catabolic processes

Exergonic processes that break down complex molecules into simpler ones.

Anabolic processes

Endergonic processes that build simpler molecules into complex ones.

Coupling

The cellular practice of using exergonic reactions to provide energy for endergonic reactions, such as coupling ATP to the production of sucrose.

Enzymes

Molecules, typically identified by the suffix -ase, whose shape and active sites are essential for lowering activation energy and catalyzing reactions without being changed themselves.

Activation energy ($E_A$)

The energy required to bring on the transition state when substrate bonds break and reactions run spontaneously.

Active site

The specific location on an enzyme where substrates bind; its polarity, size, and charge are designed to hold and stress substrate bonds.

Denaturation

The loss of the tertiary or quaternary structure of a protein, resulting in a loss of function, often caused by changes in pH or temperature.

Induced fit

A phenomenon where an enzyme's shape changes slightly upon substrate entry to hold the substrate more tightly and improve catalytic function.

Cofactors

Nonprotein portions or minerals needed for an enzyme to take its functional active shape.

Coenzymes

Organic molecules, such as many vitamins, that are required for an enzyme to become a functional holoenzyme.

Competitive inhibition

When an inhibitor binds to the active site of an enzyme, physically preventing the substrate from binding and slowing down the reaction.

Allosteric site

A location on an enzyme, distinct from the active site, where regulatory molecules bind.

Non-Competitive Regulation

Also called allosteric regulation; occurs when a molecule binds to an allosteric site to either activate or inhibit enzyme activity.

Point of saturation

The level of substrate concentration where all available enzymes are in use, meaning additional substrate will not increase the reaction rate.

Feedback inhibition

A process where the end products of a metabolic pathway act as allosteric inhibitors of enzymes earlier in the same pathway to maintain homeostasis.