Bio111 Lecture Notes Energy and Metabolism PDF

Energy and Metabolism Chapter 10 Lecture 33 Life Needs Energy 1  Energy All life depends on the continuous input of energy. Energy is essential for maintenance of ecosystems. Living things carry out physical and chemical proces...

Energy and Metabolism Chapter 10 Lecture 33 Life Needs Energy 1  Energy All life depends on the continuous input of energy. Energy is essential for maintenance of ecosystems. Living things carry out physical and chemical processes (metabolic activities) to sustain themselves e.g. move, grow, reproduce, secrete. 2  The first law of thermodynamics  “energy can neither be created nor destroyed, instead it can be transformed from one form to the other.”  Energy that maintains ecosystems is transformed from sunlight energy Chemical energy by photosynthesizing organisms (photoautotrophs), the primary producers.  Light energy is transformed to For example, the chemical (potential) energy chemical energy (energy of bonding). in food will be converted to the kinetic energy of the cheetah’s movement 3  Energy transfer Energy moves from one organism to another through feeding Photoautotrophs (primary producers) ↓ Primary consumers ↓ Secondary consumers ↓ Tertiary consumers ↓ Quaternary consumers 4  Metabolism This is the sum of all chemical reactions occurring in a biological system. There are two types: - Anabolism - Catabolism 5 c a anabolism t a b o li s m 6 7  Energy in metabolism Energy is used to form bonds between molecules. This is called bond energy. This energy is stored as potential energy which can be released during catabolism. 8  Catabolism The breaking down of complex molecules into simple ones e.g. the digestion process: starch is broken down to glucose lipids are broken down into fatty acids and glycerol proteins are broken down to amino acids Glucose is broken down to release CO2 and H2O and energy C6H12O6 + 6O2 ----> 6CO2 + 6H2O + ATP 9  Anabolism Chemical reactions in which simpler substances are combined to form more complex molecules Carbon Dioxide and Water react in the presence of light to produce glucose and oxygen: a process called photosynthesis 6CO2 + 6H2O ---> C6H12O6 + 6O2 Synthesis of proteins from amino acids Synthesis of di- and polysaccharides 10  Energy and Metabolism Chapter 10 Lecture 34 Photosynthesis 11  Photosynthesis An anabolic process by which photoautotrophs utilise energy from sunlight to produce carbohydrates (CH2O)n and O2 from CO2 and H2O. Autotrophs include green plants, algae and some bacteria. They synthesise organic from inorganic molecules. Energy from the sun is required to make organic compounds. Photosynthesis is the source of energy and free O2 is necessary to maintain ecosystems. This process is a source of the carbon found in all 12 organic molecules  Photosynthesis (cont’d)  In green plants and algae, photosynthesis takes place within the membrane-bound chloroplasts.  In bacteria, it takes place on the plasma membrane and in the cytosol. 13  Photosynthesis (cont’d) A typical leaf cell in a green plant contains about up to100 double membrane-bound chloroplasts.  Each chloroplast contains stacks/grana of vesicles called thylakoids packed within the stroma. 14 15 16  Photosynthesis (cont’d) Photosynthesis consists of a series of steps: Light reactions (light-dependent) within the thylakoid membrane of the chloroplasts Convert light energy into chemical energy (ATP), and an electron carrier NADPH is formed. This is photophosphorylation. Dark reactions (light-independent) in the stroma of the chloroplasts. NADPH and ATP used to convert CO2 into organic compounds. This is called carbon fixation or carbon assimilation 17 18  Photosynthesis (cont’d) Products of the C-assimilation are carbohydrates For every six molecules of CO2, one molecule of glucose is produced. The dark reactions rely on the products of the light reactions. Depriving green plants of light over a prolonged period of time, will affect both the light and dark reactions. 19  Respiration Takes place in all living things, all the time C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP Chemical energy of bonding is released as free energy (ATP) Cellular respiration takes place in mitochondria 20  Metabolism and Energy Acquisition Lecture 35: Respiration (Oxidation of glucose) 21  Respiration (energy harvesting) Metabolic processes whereby certain organisms obtain energy from organic molecules Processes that take place in the cells and tissues during which energy is released, and carbon dioxide is produced and absorbed by the blood to be transported to the lungs Process in which a cell breaks down sugar or other organic compounds to release energy used for cellular work 22  Respiration (energy harvesting) Process of oxidizing food molecules, like glucose, to carbon dioxide and water accompanied by the release of energy in the form of ATP May be anaerobic (no oxygen) or aerobic (with oxygen) 23  Energy harvesting (cont’d) The enzymes needed for cellular respiration are attached to the plasma membrane in prokaryotes located within the mitochondria in eukaryotes Respiration takes place in two stages: 1. Glycolysis – glucose broken down to pyruvic acid 2. Citric Acid Cycle or Tricarboxylic Acid Cycle (TCA) or Krebs Cycle - complete oxidation of pyruvic acid to carbon dioxide and water 24  Glycolysis The breakdown or splitting of glucose (6 carbons) into two 3-carbon molecules called pyruvic acid. First step in both aerobic and anaerobic glucose energy-harvesting reactions. Does not require oxygen as part of any of its chemical reactions. Takes place in the cytoplasm of cells, not in some specialized organelle. 2 pyruvic acid molecules The one metabolic pathway found in all living organisms (both prokaryotes and 25 eukaryotes)  Energy output: glycolysis Every glucose molecule produces two ATP net, two NADH and two molecules of pyruvic acid (pyruvate) 26  Fermentation Takes place in the cytosol/cytoplasm Pyruvic Acid + 2 H+ In the absence of O2, pyruvate from glycolysis is reduced by coenzymes or to lactate or ethyl alcohol. In lactic acid fermentation, lactic acid is an electron acceptor. Lactic Acid Alcoholic fermentation takes place in Ethanol and some yeasts and some plant cells. Carbon Dioxide 27  Fermentation (cont’d) It is useful in brewing alcoholic Pyruvic Acid + 2 H+ beverages from sorghum, grapes, barley, etc. or Fermentation yields lactic acid (lactate) or alcohol, and 2ATP. Lactic Acid Ethanol and Carbon Dioxide 28 29  In the presence of oxygen Three things occur Pyruvate oxidation Citric Acid Cycle (Tricarboxyclic Acid Cycle or Krebs Cycle) Oxidative phosphorylation (Electron Transport Chain) 30 Complete or incomplete breakdown of monosaccharides 31 32