Transcript File
Chapter 6 Cellular Respiration • Cellular metabolism involves the breaking down & building up of molecules. – Catabolism= breaking down molecules • Ex. Breaking down the foods we eat (digestion) – Anabolism= the building up of molecules • Ex. Glucose making glycogen, amino acids bonding together to form protein • Cellular respiration is the breaking down of glucose in the presence of oxygen to make ATP (energy). Chapter 6 Metabolism: Energy & Enzymes • Energy is the ability to do work – – – – – Carry out metabolic activities Growth Development Locomotion Reproduction • Most organisms get their energy from photosynthesizers – Algae – Plants – Some bacteria Forms of Energy • 2 forms of energy: 1. Kinetic: energy of motion 2. Potential: stored energy • The food we eat contains chemical energy in chemical bonds of organic molecules. Solar energy-> chemical energy-> mechanical energy-> heat Two Laws of Thermodynamics • 1st Law of Thermodynamics (Law of Conservation of energy): Energy cannot be created or destroyed, but it can be changed from one form to another. • 2nd Law of Thermodynamics: Energy cannot be changed from one form to another without a loss of usable energy. • Heat is NOT a form of usable energy (it is waste energy)! • Energy transformations make the universe less organized & more disorganized (chaos). Metabolism: sum of all the chemical reactions occurring in the cell Reactants: substances that participate in reaction Products: substances that form as a result of reaction Can you name the products & reactants in the chemical equation for cellular respiration? C6H12O6 + 6O2 6CO2 + H2O + ATP Glucose + oxygen carbon dioxide + water + energy ATP: Energy for Cells • ATP is an energy molecule made up of 3 parts: 1. 2. 3. • ATP supplies the energy need to do: 1. 2. 3. • Base adenine Sugar Three phosphate groups Chemical work: making macromolecules that make up cell Transport work: moving substances across cell membrane Mechanical work: allowing muscles to contract, cilia & flagella to beat, chromosomes to move, etc. When a phosphate group is removed from ATP, energy is released. ATP ADP + P + energy • Enzymes: proteins that speed up the rate of chemical reactions without being used up in the reaction • Energy of activation: – the energy that must be added to molecules to cause them to react H • Enzymes lower activation energy required for reactants to react by bringing the reactants in close physical proximity to each other. How Enzymes Function • Enzymes work by forming enzyme-substrate complexes S + E ES E + P • Enzymes have active sites where the substrates fit • Induced-fit model: enzymes slightly changes shape to help reaction take place Factors Affecting Enzymatic Speed • Substrate concentration – Enzyme activity increases as substrate concentration increases – Due to more collisions between substrate & enzyme • Temperature – As temperature increases, enzymatic activity increases – High temperatures can denature enzymes & make them useless (changes shape) • pH – Extreme pH denatures enzyme Enzyme Cofactors • Inorganic or organic (non-protein) helpers that aid enzymes in functioning properly • Cofactors are inorganic ions (metals) like copper, zinc, or iron • Coenzymes are organic non-protein molecules – Vitamins required to make coenzymes in our body Oxidation-Reduction Reactions • Oxidation is the loss of electrons • Reduction is the gain of electrons Na + Cl NaCl • Can apply to covalent reactions in cell – Oxidation is loss of hydrogen atom (e- + H+) – Reduction is the gain of hydrogen atoms Cellular respiration • Cellular respiration: breaking down food (primarily glucose) to release usable energy (ATP) • 4 step process 1. Glycolysis: takes place in the cytoplasm, anaerobic, releases a two ATP by breaking down glucose into two molecules of pyruvate (a C3 molecule). 2. Pyruvate to acetyl-CoA: takes place in outer compartment of mitochondria; pyruvate is converted to a C2 acetyl group attached to coenzyme A (CoA) and CO2 is given off. 3. TCA (Citric Acid, Krebs) cycle: takes place in the matrix of the mitochondria, aerobic, releases two ATP molecules per glucose molecule. 4. Electron transport and chemiosmosis: takes place in the cristae of the mitochondria, aerobic, releases A LOT of ATP (36-38 ATP molecules). NAD+ and FAD • Two coenzymes involved in oxidation-reduction reactions • They each can hold only two electrons and two hydrogen nuclei • Carry electrons to the electron transport chain in the cristae of the mitochondria, where they drop them off. Summary of Glycolysis 1. 2. 3. 4. 5. Anaerobic process that breaks down one 6 carbon molecule of glucose into two 3 carbon pyruvates. As glucose is broken down, some of its hydrogen atoms are transferred to electron acceptor NAD+ forming 2 NADH molecules. Glycolysis takes 2 ATP molecules to break apart the bonds of glucose and makes 4 ATP molecules. The net gain of ATP is two. Pyruvate and NADH will be transported to mitochondria for more reactions. Pyruvate to Acetyl CoA • • • • Each pyruvate reacts with a Coenzyme-A molecule, releasing one molecule of CO2, and producing one NADH + H+ and one acetyl-CoA molecule (two for each glucose molecule we started with). The acetyl-CoA will enter the TCA cycle in matrix. The CO2 is released as a waste product. No ATP is produced in this step, but the NADH + H+ will enter electron transport chain to release ATP later. The Citric Acid Cycle TCA (Tricarboxylic acid, citric acid, Krebs) cycle • Through a complex series of biochemical reactions, the 2-C acetyl group from the acetyl-CoA first binds to another molecule, then is broken down. The CoA is released to go back to the outer compartment. • This entire process consumes water (to get oxygen, making the process aerobic), and releases 6 NADH + H+ & 2 FADH2 molecules, 4 CO2 molecules per glucose molecule that we started with, and produces 2 ATP per glucose molecule that we started with. The Electron Transport Chain & Chemiosmosis • The electron transport chain is a series of cytochrome molecules located in the cristae • NADH & FADH2 give up their electrons & the H+ (hydrogen ions) are released into the matrix • The energy released by the electrons as they move down the chain is used to pump the hydrogen ions into the intermembrane space • Hydrogen ions build up there forming a concentration gradient The Electron Transport Chain & Chemiosmosis • Hydrogen ions then pass through ATP synthase (an enzyme) back into the matrix by simple diffusion • Hydrogen ions flowing through ATP synthase cause synthesis of ATP from ADP + P by chemiosmosis • The final electron acceptor at end of electron chain is oxygen • Water is formed when oxygen and the electrons from the electron transport chain rejoin its hydrogen protons forming water Fermentation • Anaerobic process of glucose breakdown forming lactic acid or ethanol • Inefficient source of energy • One molecule of glucose only forms 2 ATP molecules • Unicellular organisms use alcoholic fermentation to gain energy • Muscle cells can switch to lactic acid fermentation when not enough oxygen is available