activation energy
the amount of initial energy necessary for reactions to occur
This small amount of energy input necessary for all chemical reactions to occur is called the activation energy.
active site
a specific region on the enzyme where the substrate binds
The location within the enzyme where the substrate binds is called the enzyme’s active site.
allosteric inhibition
the mechanism for inhibiting enzyme action in which a regulatory molecule binds to a second site (not the active site) and initiates a conformation change in the active site, preventing binding with the substrate
This type of inhibition is called allosteric inhibition (Figure 4.9).
anabolic
describes the pathway that requires a net energy input to synthesize complex molecules from simpler ones
Remember that anabolic cellular pathways require energy to synthesize complex molecules from simpler ones and catabolic pathways release energy when complex molecules are broken down.
bioenergetics
the concept of energy flow through living systems
Scientists use the term bioenergetics to describe the concept of energy flow (Figure 4.2) through living systems, such as cells.
catabolic
describes the pathway in which complex molecules are broken down into simpler ones, yielding energy as an additional product of the reaction
Remember that anabolic cellular pathways require energy to synthesize complex molecules from simpler ones and catabolic pathways release energy when complex molecules are broken down.
competitive inhibition
a general mechanism of enzyme activity regulation in which a molecule other than the enzyme’s substrate is able to bind the active site and prevent the substrate itself from binding, thus inhibiting the overall rate of reaction for the enzyme
When this happens, the enzyme is inhibited through competitive inhibition, because an inhibitor molecule competes with the substrate for binding to the active site.
endergonic
describes a chemical reaction that results in products that store more chemical potential energy than the reactants
These chemical reactions are called endergonic reactions and they are non-spontaneous.
enzyme
a molecule that catalyzes a biochemical reaction
Each reaction step is facilitated, or catalyzed, by a protein called an enzyme.
exergonic
describes a chemical reaction that results in products with less chemical potential energy than the reactants, plus the release of free energy
Reactions that have a negative change in free energy and consequently release free energy are called exergonic reactions.
feedback inhibition
a mechanism of enzyme activity regulation in which the product of a reaction or the final product of a series of sequential reactions inhibits an enzyme for an earlier step in the reaction series
In a most efficient and elegant way, cells have evolved to use the products of their own reactions for feedback inhibition of enzyme activity.
heat energy
the energy transferred from one system to another that is not work
For example, electrical energy, light energy, and heat energy are all different types of energy.
kinetic energy
the type of energy associated with objects in motion
Energy associated with objects in motion is called kinetic energy (Figure 4.5).
metabolism
all the chemical reactions that take place inside cells, including those that use energy and those that release energy
Together, all of the chemical reactions that take place inside cells, including those that consume or generate energy, are referred to as the cell’s metabolism.
noncompetitive inhibition
a general mechanism of enzyme activity regulation in which a regulatory molecule binds to a site other than the active site and prevents the active site from binding the substrate; thus, the inhibitor molecule does not compete with the substrate for the active site; allosteric inhibition is a form of noncompetitive inhibition
On the other hand, in noncompetitive inhibition, an inhibitor molecule binds to the enzyme in a location other than the active site, called an allosteric site, but still manages to block substrate binding to the active site.
potential energy
the type of energy that refers to the potential to do work
This type of energy is called potential energy (Figure 4.5).
substrate
a molecule on which the enzyme acts
The chemical reactants to which an enzyme binds are called the enzyme’s substrates.
thermodynamics
the science of the relationships between heat, energy, and work
Thermodynamics refers to the study of energy and energy transfer involving physical matter.
ATP
(also, adenosine triphosphate) the cell’s energy currency
During the light reactions of photosynthesis, energy is provided by a molecule called adenosine triphosphate (ATP), which is the primary energy currency of all cells.
glycolysis
the process of breaking glucose into two three-carbon molecules with the production of ATP and NADH
Glycolysis is the first step in the breakdown of glucose to extract energy for cell metabolism.
acetyl CoA
the combination of an acetyl group derived from pyruvic acid and coenzyme A which is made from pantothenic acid (a B-group vitamin)
Acetyl CoA can be used in a variety of ways by the cell, but its major function is to deliver the acetyl group derived from pyruvate to the next pathway in glucose catabolism.
ATP synthase
a membrane-embedded protein complex that regenerates ATP from ADP with energy from protons diffusing through it
Hydrogen ions diffuse through the inner membrane through an integral membrane protein called ATP synthase (Figure 4.19 b).
chemiosmosis
the movement of hydrogen ions down their electrochemical gradient across a membrane through ATP synthase to generate ATP
This flow of hydrogen ions across the membrane through ATP synthase is called chemiosmosis.
citric acid cycle
a series of enzyme-catalyzed chemical reactions of central importance in all living cells that harvests the energy in carbon-carbon bonds of sugar molecules to generate ATP; the citric acid cycle is an aerobic metabolic pathway because it requires oxygen in later reactions to proceed
Describe the relationships of glycolysis, the citric acid cycle, and oxidative phosphorylation in terms of their inputs and outputs.
electron transport chain
a series of four large, multi-protein complexes embedded in the inner mitochondrial membrane that accepts electrons from donor compounds and harvests energy from a series of chemical reactions to generate a hydrogen ion gradient across the membrane
The electron transport chain (Figure 4.19 a) is the last component of aerobic respiration and is the only part of metabolism that uses atmospheric oxygen.
oxidative phosphorylation
the production of ATP by the transfer of electrons down the electron transport chain to create a proton gradient that is used by ATP synthase to add phosphate groups to ADP molecules
Describe the relationships of glycolysis, the citric acid cycle, and oxidative phosphorylation in terms of their inputs and outputs.
anaerobic cellular respiration
the use of an electron acceptor other than oxygen to complete metabolism using electron transport-based chemiosmosis
In contrast, some living systems use an inorganic molecule as a final electron acceptor; both methods are a type of anaerobic cellular respiration.
fermentation
the steps that follow the partial oxidation of glucose via glycolysis to regenerate NAD+; occurs in the absence of oxygen and uses an organic compound as the final electron acceptor
Processes that use an organic molecule to regenerate NAD+ from NADH are collectively referred to as fermentation.
These terms were extracted from Concepts of Biology – 1st Canadian Edition by Charles Molnar and Jane Gair, eCampusOntario (originally published by BCcampus) which is licensed under a Creative Commons Attribution 4.0 International License. Chapter content adapted from Concepts of Biology by OpenStax (© Rice University), licensed under CC BY 4.0.