2016 Ch 9: Cellular Respiration

Chapter 9: Cellular Respiration From Topic 2.1 Understanding: Anabolism is the synthesis of complex molecules from simpler molecules including the formation of macromolecules from monomers by condensation reactions. Catabolism is the breakdown of complex molecules into simpler molecules including the hydrolysis of macromolecules into monomers. From Topic 2.8 Essential idea: Cell respiration supplies energy for the functions of life. Nature of science: Assessing the ethics of scientific research—the use of invertebrates in respirometer experiments has ethical implications (4.5). Skill: Analysis of results from experiments involving measurement of respiration rates in germinating seeds or invertebrates using a respirometer. Understandings: Cell respiration is the controlled release of energy from organic compounds to produce ATP. ATP from cell respiration is immediately available as a source of energy in the cell. Anaerobic cell respiration gives a small yield of ATP from glucose. Aerobic cell respiration requires oxygen and gives a large yield of ATP from glucose. Applications and skills: Application: Use of anaerobic cell respiration in yeasts to produce ethanol and carbon dioxide in baking. Application: Lactate production in humans when anaerobic respiration is used to maximize the power of muscle contractions. Guidance: Details of the metabolic pathways of cell respiration are not needed but the substrates and final waste products should be known. There are many simple respirometers which could be used. Students are expected to know that an alkali is used to absorb CO2, so reductions in volume are due to oxygen use. Temperature should be kept constant to avoid volume changes due to temperature fluctuations. Aim 8: The ethics of the use of animals in experiments could be discussed in relation to respirometer experiments. Large-scale use of food plants for biofuels and the resulting impact on food prices has ethical implications. From Topic 8.2 Nature of science: Paradigm shift—the chemiosmotic theory led to a paradigm shift in the field of bioenergetics (2.3) Understandings: Cell respiration involves the oxidation and reduction of electron carriers. Phosphorylation of molecules makes them less stable. Energy released by oxidation reactions is carried to the cristae of the mitochondria by reduced NAD and FAD. The structure of the mitochondrion is adapted to the function it performs. In glycolysis, glucose is converted to pyruvate in the cytoplasm. Glycolysis gives a small net gain of ATP without the use of oxygen. In aerobic cell respiration pyruvate is decarboxylated and oxidized, and converted into acetyl compound and attached to coenzyme A to form acetyl coenzyme A in the link reaction. In the Krebs cycle, the oxidation of acetyl groups is coupled to the reduction of hydrogen carriers, liberating carbon dioxide. Transfer of electrons between carriers in the electron transport chain in the membrane of the cristae is coupled to proton pumping. In chemiosmosis protons diffuse through ATP synthase to generate ATP. Oxygen is needed to bind with the free protons

Chapter 9: Cellular Respiration From Topic 8.2 Guidance: The names of the intermediate compounds in gylcolysis and the Krebs cycle are not required. Applications and skills: Application: Electron tomography used to produce images of active mitochondria. Skill: Analysis of diagrams of the pathways of aerobic respiration to deduce where decarboxylation and oxidation reactions occur. Skill: Annotation of a diagram of a mitochondrion to indicate the adaptations to its function.

Introduction Catabolism: breaking of large molecules to smaller molecules, as a result it releases stored energy C 6 H 12 O 6 + 6O 2  6 CO H 2 O + energy (ATP) and heat Efficiency 40% 20%

How Energy is Transferred Energy is transferred in the form of electrons Electrons are transferred through hydrogens (it is the mechanism for electron transfer) Some energy is stored as phosphate bonds in ATP Hydrogen carriers (NAD+) shuttle electrons in oxidation- reduction reactions LEO-GER: -Loss of e- is oxidation -Gain of e- is reduction.

Electron Carriers: NADH and FADH 2 FADH 2 NADH

Generating Energy in the form of ATP There are two ways for ATP synthesis: - Oxidative Phosphorylation: uses energy from a series of redox reactions that occurs in the electron transport chain to produce ATP - Substrate Level Phosphorylation: when an enzyme transfers a phosphate group from a substrate molecule to ADP forming ATP

Fuel For Respiration Food is the source of energy (digestion) Ultimately the source of energy for cell respiration comes from photosynthesis, when plants produces glucose.

Other Sources of “Fuel” Glucose is the best fuel Polysaccharides are broken to release glucose Proteins can be broken down to be Amino acids and then converted to intermediate products that are broken down in Krebs. Lipids are broken down to glycerol (to Glycolysis) and fatty acids (to Krebs)

Stages of Cellular Respiration There are three main stages: Glycolysis Krebs Cycle (Citric Acid Cycle) Electron Transport (Chemiosmosis)

Glycolysis Glycolysis: “splitting of sugar” occurs in the cytosol -Must invest 2 ATP’s first -Produces 4 ATP’s at the end, but a net gain of 2 ATP’s -Followed by “prep” step, when acetyl CoA turns to pyruvate (pyruvic acid)

Glycolysis Glycolysis: can occur with or without O 2 ; but the process itself doesn’t require O 2

“Prep” Step “Prep” Step: this is not the official name! but we can’t find a better name for it. Hahah… -The conversion of pyruvate to acetyl CoA before entering the Citric Acid Cycle (aka Krebs/tricarboxylic acid cycle (TCA)) -Produces two NADH (since there’s two pyruvates that enter and two acetyl CoA’s that comes out

Citric Acid Cycle Citric Acid Cycle: -Occurs in the mitochondrial matrix -For each Acetyl CoA, 3 NADH, 1 FADH 2 1 ATP, 2 CO 2 are produced.

Electron Transport Chain and Chemiosmosis Occurs in the inner membrane of the mitochondria between the matrix and the intermembrane space Transport is carried out by a series of membrane proteins Some carry just electrons, while others take protons with electrons (H+ and e-) Produces water and a lot of ATP at the end

Electron Transport Chain and Chemiosmosis Chemiosmosis: when energy in the form of H+ ions gradient across a membrane is used to make ATP ml

Total Energy Yield A review of Cellular Respiration - What each stage produces and contributes to the total energy yield from cellular respiration

Fermentation Fermentation: w/o O 2 Krebs and ETC cannot occur -It is an extension of glycolysis in anaerobic conditions -Can produce ATP by substrate level phosphorylation only -needs to replenish the NAD+ as an e- carrier to keep it going There are two types: -Alcoholic Fermentation -Lactic Acid Fermentation

Fermentation Lactic Fermentation: this causes the pain you feel after you exercise too much; also used in making cheese and yogurt Alcoholic Fermentation: this is used for brewing, winemaking, and baking