AP Biology Chapter 6: Key Terms in Metabolism

Metabolism

The entirety of an organism's chemical reactions that manages the material and energy resources of the organism.

Metabolic Pathways

Series of chemical reactions that either builds complex molecules or breaks down complex molecules to simpler ones.

Catabolic Pathways

Metabolic pathways that release energy by breaking down complex molecules to simpler molecules. One example is cellular respiration.

Anabolic Pathways

Metabolic pathways that consume energy to synthesize complex molecules from simpler molecules. Examples include the synthesis of amino acids from simpler molecules and the synthesis of proteins from amino acids.

Energy

The capacity to cause change, especially to do work.

Kinetic Energy

The energy associated with the relative motion of objects.

Thermal Energy

Kinetic energy due to the random motion of atoms and molecules.

Light

Type of energy that can be harnessed to perform work, such as powering photosynthesis in green plants.

Potential Energy

The energy that matter possesses as a result of its location or spatial arrangement (structure).

Chemical Energy

The potential energy available in molecules for release in a chemical reaction.

1st Law Of Themodynamics

The 1st law of thermodynamics states that energy can be transferred and transformed, but it cannot be created or destroyed.

2nd Law Of Thermodynamics

The principle stating that every energy transfer or transformation increases the entropy of the universe. Usable forms of energy are at least partly converted to heat.

Entropy

A measure of disorder/randomness.

Increasing Entropy

In many cases, increasing entropy is evident in physical disintegration of a system's organized structure. Much of the increasing entropy of the universe is less obvious because it takes the form of increasing amounts of heat and less ordered forms of matter.

Spontaneous Processes

Processes that occur without an overall input of energy (energetically favorable process).

Biological Order

The entropy of a particular system (such as an organism) may actually decrease as long as the total entropy of the universe (system + surroundings) increases.

Free Energy

The portion of a biological system's energy that can perform work when temperature and pressure are uniform throughout the system (as in a living cell).

Gibbs Free Energy

Energy that focuses only on the free energy of the system, rather than the free energy of the surroundings.

Negative ΔG

Spontaneous (thermodynamically favorable) reaction.

Positive ΔG

Non-spontaneous (thermodynamically unfavorable) reaction.

Chemical Equilibrium

Forward and reverse reactions occur at the same rate. Changes from the equilibrium position will have positive ΔG Values and will not be spontaneous.

Breaking Bonds

Requires energy.

Forming Bonds

Releases energy.

Exergonic Reactions

Spontaneous chemical reactions that have a net release of free energy. The magnitude of ΔG represents the maximum amount of work the reaction can perform.

Endergonic Reactions

Non-spontaneous chemical reactions in which free energy is absorbed from the surroundings. The magnitude of ΔG is the quantity of energy required to drive the reaction.

Equilibrium & Metabolism

Since systems at equilibrium are at a minimum of G and can do no work, a cell that has reached metabolic equilibrium is dead. The consistent flow of materials in and out of the cell keeps the metabolic pathways from ever reaching equilibrium.

Chemical Work

The pushing of endergonic reactions that would not occur spontaneously, such as the synthesis of polymers from monomers.

Transport Work

The pumping of substances across membranes against the direction of spontaneous movement.

Mechanical Work

The contraction of muscle cells, the beating of cilia, and the movement of chromosomes during cellular reproduction.

Energy Coupling

The use of energy released from an exergonic reaction to drive an endergonic reaction.

ATP Structure

Contains the sugar ribose, adenine (a nitrogenous base), and a chain of three phosphate groups bonded to it.

ATP Hydrolysis

Releases free energy when its phosphate groups are hydrolyzed, which is therefore used to drive endergonic reactions in cells. Also used to make RNA.

Activation Energy

The amount of energy that reactants must absorb before a chemical reaction will start.

Transition State

A state in which the reactants have low enough stability to where the bonds of the reactants can start to break and the bonds of the products can start to form.

Catalysis

A process by which a chemical agent (catalyst) selectively increases the rate of a reaction without being consumed by the reaction.

Substrate

The reactant on which an enzyme works.

Enzyme-Substrate Complex

Formed when enzymes bind to their substrate molecules.

Active Site

The specific region that allows the enzyme to bind to the substrate and form the pocket in which catalysis occurs.

Induced Fit

The change in shape of the active site of an enzyme so that it binds more tightly to the substrate.

Saturated Enzyme Population

A point in which the concentration of the substrate is too high and all enzyme molecules have all their active sites engaged. The only way to increase the rate of product formation is to add more enzymes.

Cofactors

Any non-protein molecules or ions that are required for the proper functioning (catalytic activity) of an enzyme. These can be permanently bound to the active site, or they can bind loosely and reversible (along with the substrate) during catalysis.

Coenzymes

Organic molecules serving as cofactors.

Competitive Inhibitors

Substances that reduce the activity of an enzyme by entering the active site in place of the substrate (whose structure it mimics), therefore blocking the substrate.

Non-competitive Inhibitors

Substances that reduce the activity of an enzyme by binding to a location remote from the active site, changing the enzyme's shape so that the active site no longer effectively catalyzes the conversion of substrate to product.

Allosteric Regulation

The binding of a regulatory molecule to a protein at one site that affects the function of the protein at a different site. This can either inhibit or stimulate an enzyme's activity.

Allosteric Activator

Binds to a regulatory site to stabilize the shape of the multi-subunit enzyme that has functional active sites (stabilizes the active form).

Allosteric Inhibitor

The binding stabilizes the inactive form of the multi-subunit enzyme.

Cooperativity

A type of allosteric regulation whereby a shape change in one subunit of a protein caused by substrate binding is transmitted to all the other subunits, facilitating binding of additional substrate molecules to those subunits. Binding of the substrate to one active site affects catalysis in another active site.

Feedback Inhibition

A method of metabolic control in which the end product of a metabolic pathway acts as an inhibitor of an enzyme within that pathway.