Human Physiology Lecture 2 PDF

ASD3003 Human Physiology │ Lecture 2 │ 1. Cellular Energetics 2. Enzymes 3. Homeostasis 1 1. Metabolism (代謝) A set of chemical reactions that happen in the cells of a living organism to sustain life Allows an organism to: Grow and reproduce Maintain their s...

ASD3003 Human Physiology │ Lecture 2 │ 1. Cellular Energetics 2. Enzymes 3. Homeostasis 1 1. Metabolism (代謝) A set of chemical reactions that happen in the cells of a living organism to sustain life Allows an organism to: Grow and reproduce Maintain their structures Respond to their environments Two Categories Catabolism (分解代謝) 2 Anabolism (合成代謝) Catabolism(分解代謝) A set of metabolic processes that break down large molecules into smaller units and release energy E.g. Glycolysis – metabolic pathway of the breakdown of glucose for energy 3 Anabolism(合成代謝) A set of constructive metabolic processes to synthesize complex molecules Energy is consumed in the process E.g. the construction of amino acids  protein E.g. Glycogenesis, glucose  glycogen 4 Glycogenesis and glycogenolysis 2. Enzymes 5 Enzymes are biological catalysts that increase the rate of chemical reactions remain unchanged at the end of the reaction does not change the nature of the reaction or its final result are proteins Their catalytic actions results from their complex structure Most enzymes have names ending with “~ase” E.g. maltase, lactase 6  Activation Energy Amount of energy needed by the reactants for the reaction to occur 1) Without an enzyme, only a small 3) Therefore, a larger proportion of the reactants amount of reactants has the can participate in the reaction activation energy to proceed with the reaction 2) Enzymes work on lowering the activation energy of a reaction 7 Mechanism of Enzyme Action Lock-and-Key model Enzyme directly binds to substrate at active site 活性部位, a region of the enzyme that specifically 特異性 binds the substrate and catalyzes the reaction 8 8 Factors Affecting the Rate of Enzymatic Reactions Temperature pH Enzyme activation Substrate concentration and reversible reactions 9  Temperature Most enzymes are inactive at low temperature Increase in temperature will increase the rate of enzyme- catalyzed reactions When maximum rate is reached, further temperature increase will decrease the rate of reaction since enzyme loses its active conformation構象and is denatured變性 10  pH Most enzymes are active only within a very narrow range of pH pH optimum最佳: the pH at which an enzyme functions optimally At extremes of pH the enzyme loses its active conformation and is denatured 11 pH The pH optimum of an enzyme usually reflects the pH of body fluid in which the enzyme is found 12  Cofactors are usually metal ions (e.g. Ca2+ ,Mg2+ , Cu2+, , Zn2+ ) required by enzymes for their active functions 13  Coenzymes are small organic molecules required by enzymes for function are usually derived from water-soluble vitamins 14 https://qph.ec.quoracdn.net/main-qimg- 96e6cd28426fc0df357078e93a6005e3-c  Enzyme Activation Some enzymes are produced as inactive form that are later activated within the cell Example: In the cells of the pancreas, many digestive enzymes are produced as zymogens (enzyme in an inactive form), which are activated after they are secreted into the intestine Activation of zymogens in the intestinal lumen protects the pancreatic cells from self-digestion 15 Substrate Concentration and Reversible Reactions The rate of enzymatic reactions increases when substrate concentration is increased, or Enzyme concentration is increased When the enzyme concentration is constant, the rate of the reaction increases along with the substrate concentration until it reaches a maximum rate最大速率 When maximum rate is reached, the enzyme is said to be saturated飽和 16 3. Homeostasis 17 Homeostasis 體內平衡 The ability of the body to maintain the constancy 恆常 of its internal environment E.g. blood glucose level, body temperature 18 Regulation of these physiological event usually occurs via a feedback mechanism Negative feedback負反饋 Positive feedback正反饋 Negative Feedback More common The response of the system is opposite to the change that set it in motion The end result of negative feedback is to bring a deviation in a physiological event back into line 19  Negative Feedback 20 http://oerpub.github.io/epubjs-demo- book/content/m45989.xhtml Positive Feedback A response which further enhances the change that set it in motion Fast forward mechanisms cause changes in a physiological variable before they are actually needed 21  Positive Feedback 22 http://www.apsubiology.org/anatomy/2010/20 10_Exam_Reviews/Exam_1_Review/Ch01_ Regulation_Terms.htm Important words Metabolism Saturated / Saturation Catabolism Positive feedback Negative feedback 23 Anabolism Enzyme Specific Denatured/ denaturation