Chapter 6-Metabolism: Energy and Enzymes

6.1 Energy

• energy-capacity to do work
• kinetic energy-energy to do motion
• potential energy-stored energy
• chemical energy-interactions of atoms, one to the other, in a molecule
• laws of thermodynamics
• 1st: law of conservation of energy
• energy cannot be created or destroyed but can only be changed from one form to another
• 2nd:
• energy cannot be changed from one form to another without a loss of usable energy
• entropy-measure of randomness or disorder

6.1 Metabolic Reactions and Energy Transformations

• metabolism-sum of all the reactions that occur in a cell
• reactants-substances that participate in a reaction
• products-substances that form as a result of a reaction
• a reaction will occur spontaneously if it increases the entropy of the universe
• free energy-amount of energy available
• exergonic reactions-reactions where ΔG is negative and energy is released
• endergonic reactions-products have more free energy than reactants, can only occur if there is an input of energy
• coupled reactions-energy released by an exergonic reaction is used to drive an endergonic reaction
• ATP to ADP + is exergonic and energy is released
• ATP (adenosine triphosphate)-common energy currency of cells
• ADP (adenosine disphosphate)-ATP +
• use of ATP as carrier of energy
1. provides a common energy currency that can be used in many different types of reactions
2. when ATP becomes ADP + , the amount of energy released is just enough for biological purposes so little energy is wasted
3. ATP breakdown is coupled to endergonic reactions in such a way that it minimizes energy loss
• 3 uses for ATP
• chemical work
• supplies energy needed to synthesize macromolecules that make up the cell
• transport work
• supplies energy needed to pump substances across the plasma membrane
• mechanical work
• supplies energy needed to permit muscles to contract, cilia and flagella to beat, chromosomes to move, etc.
• ATP is a nucleotide composed of adenine and ribose (adenosine) and 3 phosphate groups
• "high energy" because a phosphate group is easily removed, 7.3 kcal per mole

6.3 Metabolic Pathways and Enzymes

• metabolic pathway-a series of linked reactions beginning with a particular reactant and terminate with an end product
• enzyme-protein molecules that functions as an organic catalyst to speed a chemical reaction
• substrates-reactants in an enzymatic reaction
• energy activation-energy must be added to causes molecules to react with one another
• active site-one small part of the enzyme that complexes with the substrate(s)
• enzyme forms complex with the substrate (ES-complex)
• the enzyme and substrate fit together like a key fits a lock
• induced-fit model-the enzyme is induced to undergo a slight alteration to achieve optimum fit
• some enzymes participate in the reaction
• the presence or absence of an enzyme can determine which reaction takes place
• factors affecting enzymatic speed
• substrate concentration
• more collisions between substrate molecules and the enzyme, but when the active sites are filled continuously, the rate of activity can no longer increase. Maximum rate has been reached
  
• temperature and pH
• more collisions, but if temperature is too high activity levels out and then declines because the enzyme is denatured
  
• enzyme concentration
• enzyme inhibition
• when a product is in abundance, it binds competitively with the active site, but when the product is used up, inhibition is reduced and more product can be produced
• cyanide, penicilllin, poisons
  
• enzyme cofactors
• enzymes require an inorganic ion or organic to function properly
  
• denature-enzyme's chape changes during denaturation, and it can no longer bind its substrates efficiently
• feedback inhibition-when concentration of the product is always kept within a certain range
  
• allosteric site-regulatory binding site on an enzyme that controls the activity of that enzyme
  
• cofactors-necessary ions or molecules, suhc as copper, zinc, or iron (inorganic)
• coenzymes-organic, nonprotein molecules
• vitamins-relatively small organic molcules that are required in trace amounts in our diet and in the diet of other animals for synthesis of coenzymes
• a deficiency in vitamins results in a lack of coenzyme and therefore enzymatic actions (niacin - pellagra, riboflavin - cracks at mouth corners)

6.4 Metabolic Pathways and Oxidation-Reduction

• oxidation-loss of electrons
• reduction-gain of electrons
• photosynthesis
• 6 CO₂ + 6 H₂O + Energy → C₆H₁₂O₆ + 6 O₂
• chloroplasts capture solar energy and convert it by way of an electron transport system
• NADP⁺ (nicotinaminde adenine dinucleotide phosphate)-coenzyme of oxidation-reduction active during photosynthesis
• NADP⁺ + 2e^- + H⁺ → NADPH
• cellular respiration
• C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + Energy
• NAD⁺ (nicotinamide adenine dinucleotide)-a coenzyme involved in oxidations suhc as those that occur during cellular respiration, carrying a positive charge
• NAD⁺ + 2e^- + H⁺ → NADH
• electron transport system-a series of membrane-bound carriers that pass electrons from one carrier to another
• in ETS, each carrier is reduced and then oxidized
• ATP synthase complexes-particles spanning the cell membrane containing a channel that allows hydeogen ions to flow down their electrochemical gradient
• chemiosmosis-the production of ATP due to a hydrogen ion gradient across a membrane