Chapter 6 Cellular Respiration: Obtaining Energy from Food Biology and Society: Marathoners versus Sprinters It is unusual to find a runner who complete equally well in both 100m and 1000m races. Natural differences in the muscles of these athletes favor sprinting or long-distance running. The muscles that move our legs contain two main types of muscle fibers: Slow-twitch fibers & Fast-twitch fibers Jong B. Lee, Ph.D. Slow-twitch fibers ( 지근 ): function best in marathons Generate less power Last longer Generate ATP using oxygen Fast-twitch fibers ( 속근 ): function best in sprints Generate more power Fatigue much more quickly Can generate ATP without using oxygen All human muscles contain both types of fibers but in different ratios. ENERGY FLOW AND CHEMICAL CYCLING IN THE BIOSPHERE Fuel molecules in food represent solar energy Animals depend on plants to convert solar energy to chemical energy :This chemical energy is in the form of sugars and other organic molecules. 그외 clothing, lumber, paper Autotrophs ( 자가영양생물 ): called producers ( 생산자 ) Self-feeders : organisms that make all their own organic matter from inorganic nutrients RPTSE Biology Fall 2015, Dr. Jong B. Lee 1
Heterotrophs ( 종속영양생물 ) Other-feeders Humans and other animals that cannot make organic molecules from inorganic ones Depend on autotrophs for their organic fuel and material for growth and repair Called consumers ( 소비자 ) Chemical Cycling Between Photosynthesis and Cellular Respiration The ingredients for photosynthesis are carbon dioxide and water CO 2 is obtained from the air by a plant s leaves H 2 O is obtained from the damp soil by a plant s roots Chloroplasts rearrange the atoms of these ingredients to produce sugars (glucose) and other organic molecules Oxygen gas is a by-product of photosynthesis Both plants and animals perform cellular respiration Cellular respiration is a chemical process that harvests energy from organic molecules Cellular respiration occurs in mitochondria Cellular respiration uses to convert energy extracted from organic fuel to another form of chemical energy called ATP, an energy currency in the cell The waste products of cellular respiration, CO 2 and H 2 O, are used in photosynthesis RPTSE Biology Fall 2015, Dr. Jong B. Lee 2
CELLULAR RESPIRATION: AEROBIC HARVEST OF FOOD ENERGY Cellular respiration A living version of internal combustion The main way that chemical energy is harvested from food and converted to ATP This is an aerobic process it requires oxygen 유기연료에서추출한에너지 화학에너지인 ATP 에너지로전환하기위해, O2 를필요로한다. The Relationship Between Cellular Respiration and Breathing Cellular respiration and breathing are closely related Cellular respiration requires a cell to exchange gases with its surroundings Breathing exchanges these gases between the blood and outside air The Overall Equation for Cellular Respiration A common fuel molecule for cellular respiration is glucose This is the overall equation for what happens to glucose during cellular respiration The Role of Oxygen in Cellular Respiration During cellular respiration, hydrogen and its bonding electrons change partners H + + e - The series of arrows indicates that cellular respiration consists of many chemical steps The process can produce up to 38 ATP molecules for each glucose consumed Glucose Oxygen Carbon dioxide Water Hydrogen and its electrons go from sugar to oxygen, forming water (That hydrogen transfer turns out to be the key to why oxygen is so vital to the harvest of energy during cellular respiration) Energy RPTSE Biology Fall 2015, Dr. Jong B. Lee 3
Redox Reactions Chemical reactions that transfer electrons from one substance to another are called oxidation-reduction reactions ( 산화환원반응 ) : Redox reactions for short The loss of electrons (and hydrogens) during a redox reaction is called oxidation The acceptance of electrons (and hydrogens) during a redox reaction is called reduction Energy is released when hydrogen and its bonding electrons change partners, from sugar to oxygen. Why does electron transfer to oxygen release energy? In redox reactions, oxygen is an electron grabber. When electrons move from glucose to oxygen, it is as though they were falling. Instead of gravity, it is the attraction of electrons to oxygen that causes the fall and energy release during cellular respiration This fall of electrons releases energy during cellular respiration A very rapid electron fall A very rapid electron fall generates an explosive release of energy in the form of heat and light. ex) A reaction between hydrogen gas and oxygen gas The flame represents energy released as heat and light RPTSE Biology Fall 2015, Dr. Jong B. Lee 4
NADH and Electron Transport Chains Cellular respiration is a more controlled fall of electrons: Instead of liberating food energy in a burst of flame, cellular respiration unlocks chemical energy in smaller amounts that cells can put to productive use The path that electrons take on their way down from glucose to oxygen involves many steps. The first stop is an electron acceptor called NAD + The transfer of electrons from organic fuel to NAD + (nicotinamide adenine dinucleotide) reduces it to NADH The rest of the path consists of an electron transport chain : This chain involves a series of Redox reactions This electron transport chain lead ultimately to the production of large amounts of ATP The Metabolic Pathway of Cellular Respiration A Road Map for Cellular Respiration Cellular respiration is an example of a metabolic pathway: a series of chemical reactions in cells A specific enzyme catalyzes each reaction in a metabolic pathway All of the reactions involved in cellular respiration can be grouped into three main stages 1. Glycolysis ( 해당과정 ) in cytoplasm 2. The Krebs cycle in mitochondria matrix 3. Electron transport in mitochondria inner membrane Cytosol High-energy electrons carried by NADH Glycolysis 2 Glucose Pyruvic acid Krebs Cycle Mitochondrion High-energy electrons carried mainly by NADH Electron Transport RPTSE Biology Fall 2015, Dr. Jong B. Lee 5
Stage 1: Glycolysis ( 해당과정 ) A molecule of glucose is split into two molecules of pyruvic acid in cytosol (but not mitochondria) cf) pyruvic acid ( 피브루산 ) formula: CH3-C-COOH Meanings of this metabolism ( 생화학적인의미 ) - These molecules then donate high energy electrons to NAD +, forming NADH (Generate two NADH molecules per glucose) - Generate two ATP molecules: by substrate-level of phosphorylation ( 기질수준의인산화과정에의해서 ) Substrate level of phosphorylation Glycolysis makes some ATP directly when enzymes transfer phosphate groups from fuel molecules to ADP (substrate level of phosphorylation, 기질수준의인산화 ) Enzyme Stage 2: The Krebs Cycle (= The citric acid cycle) The Krebs cycle completes the breakdown of sugar This cycle completes the breakdown of sugar produce CO 2 Generate three NADH and one FADH 2 (function as electron donor for electron transfer system) Generate two ATP molecules (by substrate level of phosphorylation) 이과정에참여하는효소들은 mitochondria 내부의액체에존재한다. 즉, mitochondria matrix 에서수행됨. RPTSE Biology Fall 2015, Dr. Jong B. Lee 6
In the citric acid cycle, pyruvic acid from glycolysis is first prepped into a usable form, Acetyl CoA. Krebs cycle Stage 3: Electron Transport Electron transport ( 전자전달 ) releases the energy your cells need to make the most of their ATP The molecules of electron transport chains are built into the inner membranes of mitochondria (electron transport chain 을구성하는단백질과그밖에분자들은 mitochondria 의내막에존재 ) RPTSE Biology Fall 2015, Dr. Jong B. Lee 7
The entire electron transport chain functions as a chemical machine that uses energy released by the fall of electrons to pump hydrogen ions across the inner mitochondrial membrane By pumping H + ions, electron transport chains store potential energy by making the ions more concentrated on one side of the membrane than on the other (these H + ions store potential energy) The energy stored by electron transport behaves something like the electron reservoir of water behind a dam The membrane, analogous to the dam, temporarily restrains the H + ions. There is a tendency for the H + ions to gush back to where they are less concentrated, just as there is a tendency for water to flow downhill. When the hydrogen ions flow back through the membrane, they release energy Space between membranes Electron carrier Protein complex H The ions flow through ATP synthase. This action spin a component of the ATP synthase and activate catalytic action. ATP synthase takes the energy from this flow and synthesizes ATP Inner mitochondrial membrane Electron flow NADH FADH 2 NAD FAD ADP Matrix Electron transport chain ATP synthase 1 2 O 2 2 H 2 O P ATP ATP synthase 는 ADP 분자에 Phosphate-group 을부착시켜 ATP 를재발생시킨다. Some of deadliest poisons (CO and HCN) do their damage by disrupting electron transport (blocking the transfer of electrons to oxygen RPTSE Biology Fall 2015, Dr. Jong B. Lee 8
The Versatility of Cellular Respiration Cellular respiration (versatile metabolic furnace) can burn other kinds of molecules besides glucose Diverse types of carbohydrates Fats Proteins Adding Up the ATP from Cellular Respiration A summary of ATP yield during cellular respiration ATP 생성상황 Glucose 2 pyruvic acid + 2 ATP + 2 NADH 2 pyruvic acid 6 CO 2 + 6 H 2 O + 2 ATP + 8 NADH + 2 FADH 2 10 NADH x 3 ATP/NADH = 30 ATP 2 FADH 2 x 2 ATP/FADH 2 = 4 ATP 4 ATP + 30 ATP + 4 ATP = 38 ATP RPTSE Biology Fall 2015, Dr. Jong B. Lee 9
FERMENTATION: ANAEROBIC HARVEST OF FOOD ENERGY Some of your cells can actually work for short periods without oxygen For example, muscle cells can produce ATP under anaerobic conditions Fermentation ( 발효 ): The anaerobic harvest of food energy Fermentation in Human Muscle Cells Human muscle cells can make ATP with and without oxygen If you start to run because you re late for class your muscle forced to work under anaerobic conditions. They have enough ATP to support activities such as quick sprinting for about 5 seconds A secondary supply of energy (creatine phosphate) can keep muscle cells going for another 10 seconds To keep running, your muscles must generate ATP by the anaerobic process of fermentation Glycolysis is the metabolic pathway that provides ATP during fermentation To harvest food energy during glycolysis, NAD+ (not NADH) must be present as an electron acceptor This is no problem under aerobic condition, because the cell regenerates its NAD+ when NADH drops its electron cargo down electron transport chains to O 2 However, this productive recycling of NAD+ cannot occur under anaerobic conditions because there is no O 2 to accept the electron Instead, NADH disposes of ( 처분하다 ) electrons by adding them to pyruvic acid produced by glycolysis 즉, 해결책 : Pyruvic acid is reduced by NADH, producing NAD+, which keeps glycolysis going Glycolysis produces just two ATPs Is not efficient compared with 38 ATPs under the aerobic condition Your cells have to consume more glucose fuel RPTSE Biology Fall 2015, Dr. Jong B. Lee 10
Lactic acid ( 젖산 ) as a by-product after fermentation in muscle cells A temporary accumulation of lactic acid in muscle cells contributes to the soreness or burning you feel after exhausting run The lactic acid eventually transported in the blood from muscles to the liver, where liver cells convert it back to pyruvic acid Oxygen debt: O 2 that metabolic pathway requires after you ve stopped vigorous activity (you breathe hard even after stopping exercise). The extra oxygen is used to generate glucose from lactic acid (gluconeogenesis) Fermentation in Microorganisms Fermentation in Microorganisms Various types of microorganisms perform fermentation Fermentation products: cheese, sour cream, yogurt ( 주로젖산때문에이러한맛이발생 ) 그밖에 soy source (soybean), pickle cucumbers, pepperoni, salami 등이있다. Yeast ( 효모 ), a microscopic fungus Yeast cells are capable of both cellular respiration and fermentation but a slightly different type of fermentation This pathway (=alcohol fermentation) produces CO 2 and ethyl alcohol RPTSE Biology Fall 2015, Dr. Jong B. Lee 11
The food industry uses yeast to produce various food products EVOLUTION CONNECTION: LIFE ON AN ANAEROBIC EARTH 산소의사용능력에따라생물체의분류 - Facultative anaerobe: an organism that harvest food energy by either cellular respiration or fermentation - Obligate anaerobe: 산소접촉시사망, 깊은토양속미생물, 캔속의미생물, 늪지대에사는미생물 - Obligate aerobe: 산소를절대적으로필요로하는생명체 Ancient bacteria probably used glycolysis to make ATP long before oxygen was present in Earth s atmosphere Glycolysis is a metabolic heirloom from the earliest cells that continues to function today in the harvest of food energy Krebs cycle & electron transport chain 은산소가존재하는 aerobic condition 에서만작동하지만 glycolysis 는 aerobic 과 anaerobic condition 에서모두작동할수있다. 그러므로아마도고대의 bacteria 들은지구의대기에산소가없을때 glycolysis 를사용하여 ATP 를만들었을것으로추정한다. RPTSE Biology Fall 2015, Dr. Jong B. Lee 12