Transcript document
Energy in the Cell Ch. #9 Sect. 1 -To maintain homeostasis -To transmit nerve impulses -To build and repair -To power cell movement A. Cell Energy --All biological work demands energy --Energy is the ability to do work --Our cells get energy from foods --Food is broken down into energy and used to make ATP B. Exergonic Reactions --Chemical reactions that release free energy --In biological systems, the breakdown of food provides free energy --Biological systems store the free energy in the form of ---ATP C. Endergonic reactions -Biological activity or work requires Free Energy -Uses Free Energy stored in ATP to do the activity -Examples: -build structures or compounds -transport materials across the cell membrane -cell or body movement -transmit nerve signals 1. ATP ATP = Adenosine Triphosphate – Composed of 1. a nitrogen base called Adenine 2. the sugar Ribose 3. three phosphate groups attached to the Ribose – Potential Energy is stored in the phosphate bonds When free energy is needed to do work, ATP is broken down to release it’s stored energy ATP + H20 ADP + Pi + Free energy (hydrolysis) Free energy is used for endergonic reactions. 1. Maintain body temperature 2. Active transport 3. All enzyme activity 4. other processes that build biological structure 2. ADP ADP= Adenosine Diphosphate --Contains adenine, ribose and two phosphate groups --Has less potential energy than ATP because it has one less phosphate bond ADP + Pi + energy ATP + H2O (condensation) From food Energy from exergonic reactions are stored as potential energy in the phosphate bonds of ATP 3. Exergonic/Endergonic Coupled Reactions Exergonic breakdown of ATP provides free energy to drive endergonic reactions that require energy ATP + H2O ADP + Pi (exergonic) Free Energy Glucose + Fructose Sucrose (endergonic) In living systems, most processes use this coupling of reactions to function Sect. 3 D. Cell Respiration Replenishes ATP During cell respiration: 1. energy is released by breaking the bonds of food molecules (glucose) 2. the released energy (free energy) is used to make ATP. Two parts of Cell Respiration I. Anaerobic: --respiration not requiring oxygen --occurs in the cytoplasm --produces 2 net ATP (from one glucose) II. Aerobic: --respiration requiring oxygen --occurs in the mitochondria --produces 34 net ATP (from one glucose) E. Cellular Respiration I. Anaerobic (no oxygen) 1. First step : Glycolysis --Occurs in cytoplasm --Glucose is split into two 3-carbon molecules (PGAL) --2 ATP and enzymes are used to split the glucose --the two PGAL molecules are converted into two Pyruvic Acids producing 4 ATP +4 ATPs are produced from glycolysis -2 ATPs used to start glycolysis 2 net ATPs are produced by glycolysis II. Aerobic (with oxygen) --The two Pyruvic Acids are then transported into a near by mitochondria 2. Pyruvic Acid Conversion: --Two Pyruvic Acids are converted into two Acetyl CoA molecules II. Aerobic (with oxygen) 3. Citric Acid Cycle --Occurs in the Mitochondria --Each acetyl CoA combines with a 4-carbon Oxaloacetic acid molecule to make a 6-carbon molecule (Citric Acid) --The 6-carbon molecule is broken down to produce a 4-carbon molecule and releases CO2 --The electron carriers NADH and FADH2 are made --only 2 ATP are made in Citric Acid Cycle (from one Glucose!!!) one 2-carbon Acetyl CoA --Only one Acetyl CoA can enter the Citric Acid Cycle at a time 6-carbon Citric Acid 4-carbon Oxaloacetic acid Citric Acid Cycle -CO2 -NADH -NADH -FADH2 -ATP -NADH -CO2 4. Electron Transport Chain (ETC): --FADH2 and NADH are energy carriers --They deliver electrons to the top of the ETC staircase. --As electrons move down the staircase, they release energy. --The released energy is used to make ATP --Hydrogen combines with oxygen to make water at the bottom of the staircase to complete the process --32 ATP are made in ETC 1. in cytoplasm (anaerobic) Glycolysis net gain of 2 ATPs 2. in mitochondria (aerobic) Citric Acid Cycle gain of 2 ATPs 3. Final step in mitochondria (aerobic) ETC net gain of 32 ATPs TOTAL : 36 net ATPs from one Glucose Cellular Respiration produces 36 net ATPs 1. H+ ions combine with O2 to form waste H2O in ETC. Without the oxygen to accept the H+ ions, the ETC will shut down and we will die!! Quickly!!! 2. Waste CO2 is formed during the Citric Acid Cycle 3. Electron carriers for the ETC are produced in the Citric Acid Cycle Special types of Anaerobic Respiration 1. Lactic acid Fermentation (muscle cells and bacteria) --Converts glucose into lactic acid --Other products are CO2 and 2 ATP’s -- Too much Lactic Acid causes muscle fatigue during physical activity --Occurs in production of sour cream, sauerkraut and cheese Oxygen Debt --The oxygen that is owed to the body, after exercise produces excess lactic acid, so it can be converted back to pyruvic acid. --This is why you keep breathing very deep even after you have stopped running or exercising. The extra oxygen that you are breathing is used to convert the stored lactic acid in muscles back into pyruvic acid which can then be converted to acetyl CoA and then sent to the mitochondria for Aerobic breakdown. 2. Alcohol Fermentation (in bacteria and yeast) --Converts glucose to Ethyl Alcohol --other products include CO2 and 2 ATPs --Occurs in the production of wine, beer and breads In the production of breads, yeast, sugar and water are added to the dough mix. The mixture is allowed to rise for a period of time. The yeast breaks down the sugar producing CO2 which causes the dough to “rise”. The dough is then cooked in this inflated form. This is how you get ‘holes’ in your bread. Comparision of Photosynthesis and Cell Respiration Photosynthesis Endergonic reactions Occurs in plants (chloroplast) Uses CO2 and H2O Produces Glucose and Oxygen Cell Respiration Exergonic reactions eukaryote cytoplasm and mitochondria Uses glucose and O2 Produces CO2 and H2O