AAn Introduction to Metabolismn Introduction to Metabolism

• Bioenergetics • Enzymes

ThermodynamicsThermodynamics• Energy (E)~ capacity to do work; Kinetic energy~ energy of motion;

Potential energy~ stored energy• Thermodynamics~ study of Energy transformations• 1st Law: conservation of energy; E transferred/transformed, not

created/destroyed• 2nd Law: transformations increase entropy (disorder, randomness)

A few more definitions…..

ENTROPY (S) – the degree or measure of disorder

FREE ENERGY (G) – energy which is available to do work

TOTAL ENERGY (H) – all energy (including that not available for work)

So….H = G + S

And more applicable to us is that:

G = H – T SEXERGONIC- a reaction that releases any free energy - G

ENDERGONIC- a reaction that absorbs/stores free energy + G

Metabolism/BioenergeticsMetabolism/Bioenergetics

• Metabolism: The totality of an organism’s chemical processes; managing the material and energy resources of the cell

• Catabolic pathways: degradative process such as cellular respiration; releases energy

• Anabolic pathways: building process such as protein synthesis; photosynthesis; consumes energy

Free energyFree energy

• Free energy: portion of system’s E that can perform work (at a constant T)

• Exergonic reaction: net release of free E to surroundings

• Endergonic reaction: absorbs free E from surroundings

Energy Coupling & ATPEnergy Coupling & ATP

• E coupling: use of exergonic process to drive an endergonic one (ATP)

• Adenosine triphosphate

• ATP tail: high negative charge

• ATP hydrolysis: release of free E

• Phosphorylation (phosphorylated intermediate)~ enzymes

EnzymesEnzymes

• Catalyst- any chemical agent that accelerates a reaction and is NOT consumed by that reaction. (can be reused)

• Enzyme- Biological catalysts, usually proteins that help to lower the activation energy of or facilitate a reaction.

• “-ase” endings• Substrate: enzyme reactant. It’s what a

particular enzyme acts upon

• Active site: pocket or groove on enzyme that binds to substrate

• Induced fit model: As substrate binds, it “induces” the enzyme to change shape.

Effects on Enzyme ActivityEffects on Enzyme Activity

• Temperature- the “goal” is greatest number of collisions with out denaturing.

• pH-most enzymes have an optimal pH of 6-8 (but some digestive enzymes much lower)

• Cofactors: nonprotein/inorganic helpers

– ex.: zinc, iron, copper

– May bind to enzyme, substrate, or both

• Coenzymes:organic helpers;

– ex.: vitamins

WebLink

Enzyme InhibitorsEnzyme Inhibitors• Certain chemicals which prevent enzyme

activity• Irreversible (covalent); reversible (weak bonds)

• Competitive: competes for active site; mimics the substrate

– Can usually be overcome by increasing the substrate.

• Noncompetitive: bind to another part of enzyme (allosteric site) altering its conformation.

• The binding of an ACTIVATOR stabilizes the active form

• The binding of an INHIBITOR stabilizes the inactive form

• Cooperativity: when a substrate binding to one subunit enhances the bind capabilities of the remaining subunits…. WebLink