An Introduction to Metabolism Chapter 8 Unit 3

Metabolism the totality of an organism’s chemical reactions Metabolic Pathway: begins with a molecule, goes through a series of steps, results in a product Each step catalyzed by an enzyme

Bioenergetics Catabolic Pathways: release energy by breaking down molecules EX: Cellular Respiration Anabolic Pathways: Absorb energy by building molecules EX: Photosynthesis

Energy: capacity to do work Kinetic energy (KE): energy associated with motion Heat (thermal energy) Potential energy (PE): stored energy as a result of its position or structure Chemical energy (potential available for release in a chemical reaction)

Laws of Thermodynamics Subject to two laws of thermodynamics: First Law : energy can be transferred and transformed, but cannot be created or destroyed Second Law: energy transfer or transformation makes the universe more disordered Entropy: measurement of disorder

Free energy and metabolism Exergonic Endergonic Products have less free energy than reactant molecules Energetically downhill spontaneous Products have more free energy than reactants Energetically uphill Requires energy input

ATP Powers Cells A cell does three main kinds of work: Mechanical: beating of cillia, contracting of muscles, and movement of chromosomes Transport: pumping of substances across memebranes Chemical: synthesis of polymers from monomers

ATP Consist of: Nitrogenous base adenine, sugar ribose, three phosphates Formation of ATP from ADP is endergonic When the bonds between the phosphate groups are broken energy is released

Activation Energy EA Initial investment of energy for a reaction to start Often supplied as heat that is absorbed by reactants Accelerates reactants so they collide and break bonds Transition state: reactants are in unstable condition

Enzymes Catalyze reactions by lowering activation energy Specific to reactions they catalyze

Substrate Specificity of Enzymes The reactant that an enzyme acts on is called the enzyme’s substrate The enzyme binds to its substrate, forming an enzyme-substrate complex The active site is the region on the enzyme where the substrate binds

Effects of Local Conditions on Enzymes Temperature and pH Cofactors Enzyme Inhibitiors

Temp and pH Optimal Conditions: conditions required for best enzymatic acitivity Enzymes work increases with temp increase until it goes above optimal temp Disrupts weak interactions that change the 3D structure of the enzyme

Cofactors Nonprotein helpers for catalytic activities Inorganic molecules: metals Zinc, iron, and copper Coenzymes: organic molecules vitamins

Enzyme inhibitors Competitive Inhibitors Noncompetitive Inhibitors Inhibitor and substrate compete for active site ex: penicillin blocks enzyme that bacteria use to build cell walls Noncompetitive Inhibitors inhibitor binds to site other than active site causes enzyme to change shape

Inhibition of Enzyme Activity

Regulation of Enzyme Activity Allosteric regulation: protein’s function at one site is affected by binding of a regulatory molecule to allosteric site Activator – stabilizes active form Inhibitor – stabilizes inactive form Cooperativity – one substrate triggers shape change in other active sites  increases catalytic activity

Feedback Inhibition Regulation of a metabolic pathway by its end product final product is inhibitor of earlier step no unnecessary accumulation of product