Enzymes, Energy, and Metabolism: Key Concepts for Biology

Energy

the capacity to do work

Kinetic energy

energy of motion

Potential energy

stored energy

Chemical bonds

a form of potential energy

Heat energy

a form of energy

Thermodynamics

study of energy and energy transfer

First Law of Thermodynamics

Total energy in the universe is constant; energy can be transferred to different forms.

Photosynthesis

light energy transferred to chemical energy

Second Law of Thermodynamics

The entropy of the universe is always increasing.

Entropy

measure of the disorder in the universe

Free energy (G)

the energy available to do work

Enthalpy (H)

energy in the bonds of a molecule

Entropy (S)

disorder in the universe

Temperature (T)

temperature

G=H-TS

formula for free energy

Chemical Reaction

A + B → C; A, B: reactants, substrates; C: product

∆G

change in free energy; ∆G=∆H-T∆S

Endergonic reactions

require energy added to the reaction; ∆G is positive

Exergonic reactions

release free energy; ∆G is negative

Activation energy

energy needed to get started for all reactions

Catalysts

substances that can lower activation energy and speed up reactions

Enzymes

molecules that catalyze reactions in living cells; most are proteins

Active site

a region of amino acids on the enzyme that binds to the substrate

Induced fit

binding where both enzyme and substrate change shape slightly to bind

Cofactors

typically metal ions present in the active site to help enzyme catalyze reactions

Coenzymes

typically small organic molecules often part of oxidation-reduction reactions

Competitive Inhibition

molecules that temporarily inhibit enzyme function by competing with substrate for active site

Noncompetitive Inhibition

molecules that temporarily inhibit enzyme function by binding to an allosteric site

Biochemical pathway

a series of linked reactions where the product of one reaction becomes the substrate for the next

Feedback inhibition

end product inhibits the first enzyme in the pathway to ensure it is not running unless needed