METABOLISM

Cell Metabolism Sum of all chemical reactions Catabolic pathways: break down release energy cellular respiration Anabolic pathways: build consume energy photosynthesis

ENERGY Capacity to do work Kinetic: energy of motion Potential: stored Chemical: potential, stored in molecules Thermodynamics Energy cannot be created or destroyed Energy transformation ↑ entropy of universe

Free energy – portion that can perform work when temp Free energy – portion that can perform work when temp. uniform; available for work

Exergonic and Endergonic Reactions

Closed & Open Systems Glucose is broken down in a series of exergonic reactions that power the work of the cell. The product of each reaction becomes the reactant for the next

ATP – adenosine triphosphate

Energy coupling by phosphate transfer. ATP hydrolysis provides the energy to convert glutamic acid to glutamine

ATP CYCLE ATP + H20↔ ADP + Pi + energy

ENZYMES Organic catalysts Lower activation energy Substrate specific Active site Affected by environmental factors Not consumed in the reaction

Hydrolysis of Sucrose

REACTANTS AB: sucrose (glucose & fructose) CD: water (hydroxyl & hydrogen) PRODUCTS AC: glucose BD: fructose

Enzymes lower activation energy

Inhibition of Enzyme Activity No inhibition – substrate can bind to active site Competitive inhibition – inhibitor mimics the substrate and competes for the active site. Noncompetitive inhibition – inhibitor binds to enzyme at site other than active site and alters the shape of the active site (no longer functional)

Allosteric Interactions Two or more polypeptides subunits, both with active sites. Allosteric sites – specific receptors for enzyme regulators, may be activators or inhibitors. Changes in response to concentration of regulators AMP (activator) & ATP (inhibitor) may fit same allosteric site

Feedback Inhibition Ex. Inhibition of ATP generating pathway Switching off of a pathway by its end product Promotes cell efficiency – cell does not waste resources making more product than necessary

Cooperativity - amplifies the response to substrates -one substrate primes an enzyme to readily accept additional molecules

Localization: Cell structures bring order Multienzyme complex: assembles team of enzymes for entire metabolic pathway Fixed location within cell on membranes In solution within organelles