energy in cells and the use of ATP as an energy source

Free energy

the capacity to do work; the amount of energy stored in a system that is available to do work

Exergonic reaction

a spontaneous chemical reaction in which there is a net release of free energy "energy outward", - ΔG

Endergonic reaction

a non spontaneous chemical reaction in which free energy is absorbed from the surroundings "energy inward", + ΔG

Catabolism

breakdown of complex molecules, releases energy, -ΔG

Anabolism

synthesis of complex molecules, storing energy, +ΔG

energy coupling reactions

the use of energy released from an exergonic reaction to drive an endergonic reaction, When two reactions are coupled, they can be added together to give an overall reaction, and the ΔG of this reaction will be the sum of the ΔG values of the individual reactions, as long as the overall ΔG is negative, both reactions can take place.

Phosphorylated intermediate

A molecule (often a reactant) with a phosphate group covalently bound to it, making it more reactive (less stable) than the unphosphorylated molecule.

ATP (adenosine triphosphate)

an adenine-containing nucleoside triphosphate that releases free energy when its phosphate bonds are hydrolyzed. This energy is most commonly used to drive endergonic reactions in cells

describe the release of energy from ATP

The bonds between the phosphate groups of ATP can be broken down by hydrolysis. The reaction is exergonic and releases -7.3 kcal of energy per mole of ATP hydrolyzed, The release of energy during the hydrolysis of ATP comes from the chemical change of the system to a state of lower free energy, not from the phosphate bonds themselves

why is ATP used

free energy released by ATP hydrolysis is comparable to that required for many endergonic reactions in the cell, ATP is a precursor for RNA synthesis, ATP is similar to a rechargeable battery

Transition state

an unstable condition when the molecules have absorbed enough energy for the bonds to break

Activation energy

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

Catalyst

a chemical agent that selectively increases the rate of a reaction without being consumed by the reaction by decreasing the activation energy

Enzyme

a macromolecule serving as a catalyst, a chemical agent that increases the rate of a reaction many times without being consumed by the reaction by lowering activation energy. Enzymes don't change ΔG Most enzymes are proteins

Active site

region where an enzyme binds the substrate and forms the packet where catalysis occurs

Substrate

the reactant in an enzyme-catalyzed reaction

Induced fit

The change in shape of the active site of an enzyme so that it binds more snugly to the substrate, induced by entry of the substrate.

enzyme-substrate complex

A temporary complex formed when an enzyme binds to its substrate molecule(s).

What factors effect enzyme activity?

pH and temperature

Allosteric regulation

the binding of a regulatory molecule (allosteric regulator) to a protein at one site that affects the function of the protein at a different site, can activate or inhibit enzyme activity

Feedback inhibition

a method of metabolic control in which the end product of a metabolic pathway acts as an inhibitory of an enzyme within that pathway, Feedback inhibition is common because the environment is constantly changing but cells do not