Chapter 6: Energy Flow in the Life of a Cell What is Energy? Answer: The capacity to do work Types of Energy: 1) Potential Energy = Stored energy Positional (stored in location of object) Chemical (stored in bonds) Electrical (stored in batteries) Potential energy can be converted to kinetic energy (& vice versa) 2) Kinetic Energy = Energy by movement Light (movement of photons) Heat (movement of particles) Electricity (movement of charged particles) 1
Laws of Thermodynamics: Describe the quantity (total amount) and quality (usefulness) of energy 1st Law of Thermodynamics: (Law of Conservation of Energy) Amount of energy in universe remains constant Energy is neither created or destroyed Energy can be converted (e.g., Chemical Heat) 2nd Law of Thermodynamics: When energy converted, the amount of useful energy is decreased No process is 100% efficient Figure 6.2 Audesirk 2 & Byers Figure 6.3 / 6.4 Audesirk 2 & Byers Chemical Reaction: Process that forms or breaks the chemical bonds holding atoms together + Reactants + Products Types of Chemical Reactions: Exergonic: Reaction liberates energy Endergonic: Reaction requires energy to proceed 2
All chemical reactions require activation energy to begin: Energy required to jumpstart a chemical reaction Must overcome repulsion of atoms due to negative charged electrons Activation Energy Nucleus Repel Nucleus Activation Energy Cellular Respiration: (Exergonic) Energy in reactants > Energy in products Photosynthesis: (Endergonic) Energy in reactants < Energy in products Figure 6.5 / 6.7 Audesirk 2 & Byers 3
Exergonic Reactions: ( Downhill Reactions ) Endergonic Reactions: ( Uphill Reactions ) 4
Coupled Reaction: An exergonic reaction supplies the energy needed to drive an endergonic reaction How is Cellular Energy Carried Between Reactions? Answer: Energy-Carrier Molecules Characteristics of Energy-Carrier Molecules: Rechargeable Pick up energy (Exogonic reaction) Transport energy Drop off energy (Entergonic reaction) Unstable (Short-term energy storage) Function within a single cell Types of Energy-Carrier Molecules: 1) Adenosine Triphosphate (ATP) Most common energy-carrier molecule Synthesized from adenosine diphosphate (ADP) Coupled ATP Reactions: Figure 6.8 / 6.9 / 6.10 / 6.11 Audesirk 2 & Byers 5
Types of Energy-Carrier Molecules: 2) Electron carriers (e.g., Nicotinamide Adenine Dinucleotide NADH)) Donate high-energy electrons to other molecules Coupled Electron Carrier Reactions: Figure 6.12 Audesirk 2 & Byers Figure 6.13 Audesirk 2 & Byers Metabolism: Sum of all chemical reactions in a cell Reactions are linked in Metabolic Pathways Photosynthesis (Chloroplast) Cellular Respiration (Mitochondria) How do Cells Regulate Metabolic Reactions? 1) Couple exogonic / endergonic reactions together 2) Synthesize energy-carrier molecules 3) Regulate enzyme production / activity 6
Figure 6.14 Audesirk 2 & Byers What are Enzymes? Answer: Molecules (proteins) that catalyze chemical reactions What are Catalysts? Answer: Molecules that speed up chemical reactions Important Features: Catalysts only speed up reactions that would occur spontaneously Catalysts are not destroyed or altered in the reaction Lower activation energy Figure 6.15 Audesirk 2 & Byers Unique Properties of Enzymes (compared to other catalysts): 1) Enzymes are specific (High Specificity) Catalyze only one, or a few, chemical reactions Structure dictates specificity Enzymes = Biological Catalysts Active Site: Location where substrate(s) can bind 7
Unique Properties of Enzymes (compared to other catalysts): 2) Enzymes activity is regulated A) Regulate synthesis of enzyme Enzymes = Biological Catalysts B) Regulate active state of enzyme (inactive vs. active form) C) Feedback Inhibition: Regulate enzyme activity by [product] Figure 6.17 Audesirk 2 & Byers Unique Properties of Enzymes (compared to other catalysts): 2) Enzymes activity is regulated A) Regulate synthesis of enzyme Enzymes = Biological Catalysts B) Regulate active state of enzyme (inactive vs. active form) C) Feedback Inhibition: Regulate enzyme activity by [product] D) Allosteric Regulation: Regulate active site shape via small molecules Figure 6.16 Audesirk 2 & Byers 8
Unique Properties of Enzymes (compared to other catalysts): 2) Enzymes activity is regulated A) Regulate synthesis of enzyme Enzymes = Biological Catalysts B) Regulate active state of enzyme (inactive vs. active form) C) Feedback Inhibition: Regulate enzyme activity by [product] D) Allosteric Regulation: Regulate active site shape via small molecules E) Competitive Inhibition: Regulate active site via molecular competition Figure 6.18 Audesirk 2 & Byers Enzyme Activity can be Influenced by the Environment: A) 3 - Dimensional structure of enzymes due to hydrogen bonding Factors affecting hydrogen bonding ph (optimal = 6 8) Salt concentration Temperature B) Some enzymes require helper molecules Co-enzymes (bind with enzyme; assist in reaction) Example: B - vitamins (e.g., Vitamin B 12 ) necessary for DNA synthesis Figure 6.19 Audesirk 2 & Byers 9