Respiration H2 2015

NANYANG JUNIOR COLLEGE H2 Biology Respiration J1/2015 1 RESPIRATION Learning Outcome Core Topic 6 – Cellular Physiology and Biochemistry Candidates should be able to: (d) List and give an overview of the 4 stages of aerobic respiration and indicate where each stage takes place in an eukaryotic cell and mitochondria, and add up the energy captured (as ATP, reduced NAD and FAD) in each stage. (e) Explain the production of a small yield of ATP from anaerobic respiration and the formation of ethanol in yeast and lactate in mammals. Content Outline 1. Introduction (a) The Need for Energy in Living Organisms (b) Overview of Cellular Respiration (c) Role of Adenosine Triphosphate (ATP) (d) Role of Nicotinamide Adenine Dinucleotide (NAD) and Flavin Adenine Dinucleotide (FAD) 2. Aerobic Respiration (a) Overview (b) Glycolysis (c) Link Reaction (d) Krebs Cycle (e) Oxidative Phosphorylation 3. Anaerobic Respiration (a) Alcoholic Fermentation (b) Lactic Fermentation 4. Regulation of Respiration 5. Respiratory Quotient 6. Respirometer 7. Comparison Tables (for Photosynthesis and Respiration) References 1. Campbell, N.A. & Reece, J.B. ( 2010) Biology . Chapter 9: Cellular Respiration and Fermentation. 9th Edition. Pearson Education Inc.

NANYANG JUNIOR COLLEGE H2 Biology Respiration J1/2015 2 1. Introduction (a) The Need For Energy in Living Organisms The life processes of every cell are driven by energy. Energy flows into the ecosystem as sunlight and leaves as heat while the chemical elements essential to life are recycled. Photosynthesis allows plants to convert energy from sunlight into chemical potential energy stored in organic molecules of food. Animals then obtain this energy by co nsuming plants and other animals. Cellular respiration is then carried out to break down these energy fuels into adenosine triphosphate (ATP) which drives most cellular work. Living cells require ATP for energy -consuming activities such as assembling poly mers, pumping substances across membranes, moving and reproducing. Energy flow and chemical recycling in ecosystems (b) Overview of Cellular Respiration Cellular respiration is the process by which chemical energy in organic molecules (e.g. carbohydrates, fats and proteins) is released by oxidation. The energy released is then used to generate ATP. Cellular respiration includes two processes: aerobic respiration (requires oxygen) and anaerobic respiration (does not require oxygen). The presence of oxygen, therefore, determines the type of respiration that will take place in the living cell.

NANYANG JUNIOR COLLEGE H2 Biology Respiration J1/2015 3 (c) Role of Adenosine Triphosphate (ATP) Adenosine Triphosphate (ATP) is an instant source of energy found in all living cells and is therefore known as the universal energy carrier or energy currency in living organisms. Energy released during respiration, is thus stored in the form of ATP. (i) Structure of ATP  ATP consists of a ribose sugar, an adenine base and 3 phosphate groups. (ii) Properties of ATP  ATP is soluble and can transport chemical energy to energy-consuming processes anywhere within the cell.  Hydrolysis of ATP requires the addition of water and releases energy.  ATP is converted to ADP and inorganic phosphate (Pi).  Phosphorylation of ADP can form ATP. This reaction releases water and is known as condensation. The enzyme that catalyses the reaction is called ATP synthase.  ADP is phosphorylated with inorganic phosphate (Pi) to form ATP. Hc = -30.6 kJ mol-1

NANYANG JUNIOR COLLEGE H2 Biology Respiration J1/2015 4 (d) Role of Nicotinamide Adenine Dinucleotide (NAD) and Flavin Adenine Dinucleotide (FAD) NAD and FAD are coenzymes to dehydrogenases involved in cellular respiration. Their ability to exist in the oxidised or reduced state allows them to function as proton and electron carriers. The reduced form is more energetically valuable. (i) Nicotinamide Adenine Dinucleotide (NAD)  During aerobic respiration, glucose is oxidised by a series of dehydrogenation reactions.  At each of these reactions (in glycolysis, link reaction and Krebs cycle), protons (H+) and electrons (e-) are released and transferred to oxidised NAD (NAD+) to form reduced NAD (NADH + H+). NAD+ + 2H+ + 2e-  NADH + H+ (ii) Flavin Adenine Dinucleotide (FAD)  During aerobic respiration, glucose is oxidised by a series of dehydrogenation reactions.  At each of these reactions (in Krebs Cycle)., protons (H+) and electrons (e-) are released and transferred to oxidised FAD (FAD) to form reduced FAD (FADH2) FAD + 2H+ + 2e-  FADH2

NANYANG JUNIOR COLLEGE H2 Biology Respiration J1/2015 5 2. Aerobic Respiration (a) Overview Although carbohydrates, proteins and fats are all fuels that can act as respiratory substrates for the production of ATP, it is important to learn about the stages of aerobic respiration particularly by tracking the oxidation or breaking down of glucose molecules as it is the most common fuel utilised by living cells. The general equation below shows the oxidation of glucose in aerobic respiration. This is a simplified equation as aerobic respiration does not take place in a single reaction but the cumulative result of four major sequential stages. Each stage is compri sed of a series of reactions. Each reaction is catalysed by a specific enzyme. C6H12O6 + 6O2 → 6CO2 + 6H2O Hc = -2880 kJ mol-1 Aerobic respiration takes place through four main stages. Stage Requirements for oxygen Location Processes 1) Glycolysis Does not require the presence of oxygen Cytoplasm Oxidation of glucose (6C) to form two molecules of pyruvate (3C). 2) Link Reaction Occurs only in the presence of oxygen (Note: Oxygen is not directly involved in this stage) Mitochondrial matrix of eukaryotic cells or cytosol of prokaryotes Oxidation of pyruvate (3C) to form acetyl-CoA 3) Krebs Cycle (also known as Citric Acid / Tricarboxylic Acid (TCA) Cycle) Occurs only in the presence of oxygen (Note: Oxygen is not directly involved in this stage) Mitochondrial matrix of eukaryotic cells or cytosol of prokaryotes Further oxidation of acetyl-CoA occurs via a series of reactions. 4) Oxidative Phosphorylation Occurs only in the presence of oxygen (Note: Oxygen is directly involved in this stage) Inner mitochondrial membrane of eukaryotes or cell surface membrane of prokaryotes Electrons released via oxidation in the first three stages are passed along the electron transport chain, resulting in production of large amounts of ATP. Specific processes occurring in each of these stages will be elaborated in the later sections.

NANYANG JUNIOR COLLEGE H2 Biology Respiration J1/2015 6 Overview of the four stages of aerobic respiration Link Reaction

NANYANG JUNIOR COLLEGE H2 Biology Respiration J1/2015 7 (b) Glycolysis Glycolysis occurs in the cytoplasm (independent of oxygen) and it involves the breakdown of glucose (6C) to yield pyruvate (3C), reduced nicotinamide adenine dinucleotide (reduced NAD) / NADH + H+ and ATP. No CO2 is released in glycolysis. Glycolysis can be divided into two phases: (i) Energy Investment Phase (ii) Energy Pay-Off Phase Energy input and output of glycolysis

NANYANG JUNIOR COLLEGE H2 Biology Respiration J1/2015 8 (i) Energy Investment Phase (also known as the Preparatory Phase) Energy in the form of ATP is use d in this p hase of glycolysis (2 ATP per glucose molecule). 1) Activation of glucose occurs to make it more chemically reactive  Phosphorylation of glucose using ATP  Glucose  Glucose-6-phosphate  Catalysed by hexokinase 2) Isomerisation of glucose-6-phosphate to fructose-6-ph