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Cellular Respiration H.B.3A.4 Develop models of the major inputs and outputs of cellular respiration (aerobic and anaerobic) to exemplify the chemical process in which the bonds of food molecules are broken, the bonds of new compounds are formed and a net transfer of energy results. Use the models to explain common exercise phenomena (such as lactic acid buildup, changes in breathing during and after exercise, and cool down after exercise). Why Do We Need to Breathe? • Why you need oxygen? You need oxygen in order for your body to USE the food that you eat! © 2013 Vanessa Jason “Biology Roots”) Harvesting Chemical Energy • The food you eat cannot be used by cells directly. • Cells have only one usable energy form, ATP (adenosine triphosphate). • Cellular Respiration is the complex process in which cells make ATP by breaking down organic compounds. • Any food (organic) molecule, or nutrient, including carbohydrates, fats/lipids, and proteins can be processed and broken down as a source of energy to produce ATP molecules. What is the ATP produced during cellular respiration used for? • ATP can then release the energy for cellular metabolic processes: – Active Transport – Protein synthesis – Muscle contraction. What type of organism carry out cellular respiration? • Autotrophs – Use the glucose created during photosynthesis • Heterotrophs – Use organic compounds that are harvested from digestion Cellular Respiration Occurs in Two Stages • Step 1:Glycolysis – Glyco= Sugar If Oxygen is Available -Lysis- To Break Apart • Step 2: Aerobic Respiration • Aerobic = Requires Oxygen – The two steps of aerobic respiration are: 1. Citric acid cycle or Krebs cycle 2. Electron Transport Chain Where Does Cellular Respiration Occur? • Occurs in two different locations • Glycolysis occurs in the cytoplasm. • The Krebs cycle occurs in the Mitochondria Review of Mitochondria Structure • Smooth outer Membrane • Folded inner membrane • Folds called Cristae • Space inside cristae called the Matrix Many Reactions in Cellular Respiration are REDOX reaction • A chemical reaction in which there is the transfer of one or more electrons from one reactant to another. • Oxidation is the loss of electrons • Reduction is the gain of electrons. • Because the electron transfer requires a donor and an acceptor, oxidation and reduction always go together Glycolysis • Breaks down glucose into 2 pyruvate molecules (aka pyruvic acid), a 3 carbon compound. • Anaerobic = Does not require Oxygen • Carbon Dioxide is released. • As the bonds in C6H12O6 are broken, energy is released. • Net of 2 ATP molecules are made • Occurs in a series of reactions that are catalyzed by specific enzymes Chemical Reactions in Glycolysis - Glycolysis is often referred to as the “energy investment” phase because it requires 2 ATP to begin. -Four Electrons are removed from glucose and are now in a high energy state and passed on to the electron carrier NAD+ (nicotinamide adenine dinucleotide) which will carry 1 pair (two total) of electrons Which is transformed into NADH - 2 molecules of pyruvic acid are formed Summary and Advantages of Glycolysis • Although the energy created from glycolysis is minimal ( 2 ATP required + 4 ATP made = 2 ATP net gain) the process occurs very rapidly. • Another advantages is that the process does not require oxygen, which means glycolysis can quickly supply the cell with energy even when oxygen is not available to the cell. Location ATP USED ATP created Net ATP Product Cytoplasm 2 4 2 2 Pyruvates The Kreb’s Cycle: A Little History • Discovered by Hans Krebs in 1937 • He received the Nobel Prize in physiology or medicine in 1953 for his discovery • Forced to leave Germany prior to WWII because he was Jewish The Krebs Cycle • Sometimes called the Citric Acid Cycle • Requires oxygen = Aerobic • Takes place in the mitochondria • Has a seconds step: Electron Transport Chain Step 1: Pyruvic Acid passes through the two membranes of the mitochondrion into the matrix. Step 2: 1 carbon from Pyruvic Acid is removed to make CO2 Step 3: The remaining two carbons rearrange to make Acetyl-CoA which is made of 2 carbons, 1 Oxygen and 3 Hydrogen Atoms Step 4:Acetyl-CoA adds the 2-carbon acetyl group to a 4-carbon molecule already present, producing a 6-carbon molecule called citric acid. The Krebs Cycle: Energy Extraction Step 5:Citric acid is broken down into a 4carbon molecule, more carbon dioxide is released, and electrons are transferred to energy carriers. For each turn of the cycle, a molecule of ADP is converted to a molecule of ATP. At five places in the cycle, electron carriers accept a pair of high-energy electrons, and NAD+ and FAD are converted to NADH and FADH2. Summary Krebs Cycle Location Reactants Products Mitochondrial Matrix Pyruvic acid 4 CO2 molecules 6 NADH 2 FADH2 2 ATP Electron Transport • Electron transport uses the high-energy electrons from glycolysis & the Krebs cycle to synthesize ATP from ADP. • Where most of the ATP is made • Series of chemical reactions that combine hydrogen + oxygen to make water • Electron transport chain is composed of a series of electron carriers located in the inner membrane of the mitochondrion. • NADH and FADH2 pass electrons through these electron carriers and at the end an enzyme combines these electrons with Hydrogen ions and oxygen to make water Electron Transport: ATP Production • The mitochondria membrane contains proteins called ATP Synthases • ATP is made through chemiosmosis: the movement of ions across a semipermeable membrane, down their electrochemical gradient • The charge differences across the membrane forces H+ ions through channels in these enzymes, which causes the synthase to spin • With each rotation the enzyme Grabs and ADP and attaches a phosphate Making an ATP molecule Total ATP from Cellular Respiration Glycolysis, the Krebs cycle, and the electron transport chain release about 36 molecules of ATP per molecule of glucose. 2 2 CO2 32 Total ATP? 34-36 Cellular Respiration Equation • Does not represent all of the steps that occur during the process of aerobic respiration. • C6H12O6 + 6O2 6CO2 + 6H2O + energy • One glucose molecule and six oxygen molecules are needed to produce six carbon dioxide molecules and six water molecules. • Each of the reactants (glucose and oxygen) is used during different stages of aerobic respiration. – Glucose used during glycolysis – Oxygen used during Krebs Cycle and ETC • Each of the products (carbon dioxide and water) is formed during different stages of the process • The energy that is released is primarily used to produce approximately 34 to 36 molecules of ATP per glucose molecule. What Do Cells Do When Oxygen is not available? • • • • Cells can obtain energy through anaerobic respiration An =Not, Without If there is no O2 available fermentation takes place Fermentation is not as efficient as aerobic respiration – ATP is produced in minimal amounts (2 ATP) • There are two types of fermentation depending on the organism: – alcoholic fermentation & lactic acid fermentation Why am I Sore? : Lactic Acid Fermentation • Occurs in Animal cells • Ex. Muscle Tissue during vigorous exercise • The pyruvic acid formed during glycolysis is broken down to lactic acid and energy is released • Glucose Pyruvic Acid Lactic Acid Energy • Occurs so that the cell can have a continual source of energy Alcoholic Fermentation • Occurs in plant cells, yeast and some bacteria • Glucose Pyruvic acid Alcohol + Co2 + Energy • Sugars are converted into cellular energy and produce ethanol (alcohol)and carbon dioxide as metabolic wastes. • This reaction occurs in the production of ethanol fuels, in the rising of bread dough, production of yogurt, pickles and cheese.