Introduction to Metabolism Chapter 6

Metabolism - sum of organism’s chemical processes. Enzymes start processes. Catabolic pathways release energy (breaks down complex molecules) Anabolic pathways consume energy (builds complicated molecules)

Energy - ability to do work. Kinetic energy - energy of motion; potential energy - amount of stored energy available. Energy can be converted from one form to another.

Cellular respiration breaks down glucose - energy available to do work. Thermodynamics - study of energy transformations. 1 Closed system (i.e. liquid in a thermos) - isolated from surroundings. 2 Open system - energy (and often matter) transferred between system and surroundings.

Open system – energy transferred between system and surroundings

Earth is a closed system – ozone keeps heat from escaping

1 st law of thermodynamics - energy can be transferred and transformed, but cannot be created or destroyed. 2 nd law of thermodynamics - every energy transformation must make the universe more disordered. Measure of disorder in system - entropy.

Spontaneous reactions - reactions that occur without outside help. Nonspontaneous reactions require outside help. Spontaneous processes increase stability of system and nonspontaneous processes decrease stability.

Spontaneity of system determined by amount of free energy (energy available to do work) Free energy (G) in system is related to total energy (H) and its entropy (S) by this relationship: G = H - TS, (T is temperature in Kelvin units)

To be spontaneous, system has to give up energy (decrease in H), give up order (decrease in S), or both. System at equilibrium is at maximum stability.

Exergonic reaction gives off free energy. Endergonic reaction requires free energy.

Cells maintain disequilibrium because they are open; have constant flow of material in/out of cell.

Cells do 3 types of work. 1 Mechanical work - beating of cilia, contraction of muscle cells, and movement of chromosomes. 2 Transport work - pumping substances across membranes against direction of spontaneous movement. 3 Chemical work - driving endergonic reactions (synthesis of polymers from monomers)

ATP (adenosine triphosphate) required to do work - type of nucleotide consisting of nitrogenous base adenine, sugar ribose, chain of 3 phosphate groups. Phosphate bonds unstable - release energy when broken. Phosphate group can be transferred to another molecule (phosphorylation) becomes more reactive molecule.

ATP recycled by adding phosphate group to ADP.

Inorganic phosphate

Catalyst - chemical that changes rate of reaction. Enzyme - type of catalyst. Enzymes regulate movement of molecules through metabolic pathways. Chemical reactions involve breaking bonds and making bonds.

Adding water breaks the polymer into monomers

Activation energy (E A ) needed to start reaction. Exergonic reactions - activation energy released back to surroundings; more energy released with formation of new bonds. Activation energy - amount of energy necessary to push the reactants over energy barrier.

Activation energy

Difference between free energy of products and free energy of reactants is delta G. Enzyme speed reactions by lowering E A. Enzymes do not change delta G.

Substrate - reactant that binds to enzyme. When substrate, or substrates, binds to enzyme, enzyme catalyzes conversion of substrate to product.

Enzyme

Substrate will fit only in enzyme’s active site (area on enzyme that matches up with substrate). As substrate binds, enzyme changes shape leading to tighter induced fit, bringing chemical groups in position to catalyze reaction.

Enzymes – reusable, recycled. Most metabolic enzymes can catalyze reactions forward and reverse directions. Low substrate concentrations, increase in substrate speeds binding to available active sites. Active sites can become saturated, slowing down the reaction.

As temperature increases, rate of reaction increases. At certain temperatures enzyme denatures -stops functioning.

Enzymes have optimal pH (between pH for most enzymes)

Many enzymes require cofactors (nonprotein helpers) to start reaction. Organic cofactors, coenzymes, include vitamins or molecules derived from vitamins.

Inhibitors bind to active site on enzyme; stops reaction from starting. lf inhibitor binds to same site as substrate - competitive inhibition. If inhibitor binds somewhere other than active site - noncompetitive inhibition.

Molecules can inhibit enzyme by attaching to allosteric site on enzyme (site that is not active site) Regulators can inhibit/activate enzyme.

Feedback inhibition - increase in end product causes process to stop; decrease starts process.