Chapter 8: An Introduction to Metabolism

Metabolism Metabolism = Catabolism + Anabolism Catabolic reactions are energy yielding involved in the break down of more complex molecules into simpler ones Anabolic reactions are energy requiring involved in the building up of simpler molecules into more-complex ones Bioenergetics-study of how organisms use their energy resources

1st & 2nd Laws of Thermodynamics “Energy can be transferred or transformed but neither created nor destroyed.” “Every energy transfer or transformation increases the disorder (entropy) of the universe.” Note especially the waste heat

Organisms as Transformers transform energy to new forms (1st law) are less than 100% efficient (2nd law) Organisms tend to use energy in a more organized fashion therefore requiring energy ( always fighting entropy)

Free energy change- ΔG G-Free energy-energy that is available to perform work H- total energy (enthalpy) S – entropy ΔG = ΔH - T ΔS If ΔG = negative, reaction is spontaneous If ΔG = positive, reaction needs energy

Metabolic Reactions Exergonic reaction- releases energy so G decreases and ΔG is negative Endergonic reaction- absorbs free energy so G increases and ΔG is positive

Exergonic Reactions KNOW THIS CHART! “Food” Energy released

Endergonic Reactions KNOW THIS CHART! “Work” Energy required

Cells do different kinds of work Mechanical- muscles Transport- cell membrane Chemical- endergonic reactions

Summary of Metabolic Coupling Exergonic processes drive Endergonic processes ATP is an agent of energy coupling It is created by one process and is used in another!

Adenosine Triphosphate (ATP) http://www.bozemanscience.com/atp-adenosine-triphosphate

Cellular work is always powered by ATP Hydrolysis releases 7.3 kcal of energy per mole ATP Can heat the environment (keep us warm) ATP is renewable

Enzymes Catalysts speed up a reaction without being consumed An enzyme is a catalytic protein Catalysts reduce activation energy- energy needed to get a reaction going

Enzymes lower activation energy KNOW THIS CHART !!!! Enzymes lower activation energy

Catalysis as Viewed in 3D Substrate is reactant that the enzyme works on Active site is site of catalysis

Induced Fit- used to be Called “lock and key” Enzymes and substrate brought into position for optimum interaction

Environmental Factors and Enzymes Temperature- increases enzyme action until it denatures pH 6-8 depending on environment or organ Cofactors- non-protein helpers (minerals) Coenzymes- vitamins

Each Enzyme has Opt. Temp and pH Denatured? Optimal pH of most enzymes fall in 6-8 range

Competitive Enzyme Inhibitors resembles the substrate and bonds to active site, blocking it Is reversible by increasing substrate concentration

Noncompetitive Enzyme Inhibitors Binds to another site (allosteric site) not the active site Changes shape of protein so it can no longer function Toxins and Poisons- sarin, DDT

Negative Effects of Inhibition Sarin (nerve gas ) attaches to acetylcholine- important nervous system enzyme DDT Antibiotics blocks active sites of bacterial enzymes

Allosteric Regulation of Enzymes Not all inhibitors are bad. Some are used to regulate enzyme activity Can activate or inhibit enzyme Example-speeding up or slowing down of ATP production

Feedback Inhibition Pathway is switched off by the binding of the product to the allosteric site

ATP Feedback Inhibition