Biology in Focus Chapter 6

Metabolism

The sum total of an organism's chemical activities.

Catabolic pathways

Metabolic pathways in which molecules are broken down and energy is released.

Anabolic pathways

Metabolic pathways in which energy is used to build more complex molecules from simpler ones.

First Law of Thermodynamics

A law stating that the energy of the universe can be transferred or transformed, but the amount of it will always be constant.

Second Law of Thermodynamics

A law stating that during a transfer or transformation of energy, some energy will become thermal energy incapable of doing work within the system, which increases the random motion and entropy within the system.

Exergonic reaction

Any reaction in which free energy is released, and the products store less chemical energy than the reactants. As a result, the free energy change is negative. This energy is released as bonds form the lower-energy products.

Endergonic reaction

Any reaction in which free energy is absorbed, creating higher energy products and a positive free energy change.

ATP

Molecules responsible for powering cellular work by coupling its exergonic hydrolysis with endergonic processes.

Energy coupling

The process of using exergonic processes in tandem with endergonic processes to drive the endergonic processes.

Phosphorylation

The process by which ATP hydrolysis couples to endergonic reactions, in which a phosphate from ATP hydrolysis attaches to reactants, forming unstable intermediates. The bonding of unstable intermediates to the desired product would increase stability and is therefore favorable.

Enzymes

Macromolecules that act as catalysts, which speed reactions without being consumed by them.

Activation Energy

The energy required to destabilize the reactants of a reaction to a transition state so the reaction can occur, or the energy input needed to start a reaction.

Enzyme specificity

The ability of an enzyme to only attach to certain substrates and control what reactions happen at what time. This is caused by the substrate molecule reacting with and binding with the specific R-groups on the active site.

Substrate

The reactant that an enzyme acts upon.

Active site

The site on the enzyme where the substrate binds, formed by a few amino acids.

Cofactors

Non-protein helpers of enzymes which bind tightly to enzymes or reversibly to substrates.

Coenzymes

Cofactors that are organic molecules.

Competitive Inhibitors

An inhibitor that binds noncovalently to the active site by mimicking the substrate and blocking substrates. They can be overcome by increasing substrate concentration.

Noncompetitive Inhibitors

Inhibitors that impede enzymes by binding to a different part of the enzyme, changing its shape.

Allosteric Activation

The stabilization of an active state by binding of a regulator in enzymes which oscillate between active and inactive states. Binding to one subunit enacts a change in all of them.

Allosteric Inhibition

The stabilization of an inactive state by binding of a regulator in enzymes which oscillate between active and inactive states. Binding to one subunit enacts a change in all of them.

Feedback inhibition

Inhibition of a metabolic pathway by binding of the end product to the metabolic pathway.

Enzyme Saturation

A point of substrate concentration at which all enzymes are engaged, and adding more substrate will not increase reaction rate.