YIJC [H2] CI3.2 Respiration (N)(S)(vetted)

2025 JC2 BIOLOGY LECTURE NOTES 1 CORE IDEA 3: ENERGY AND EQUILIBRIUM TOPIC 3.2: CELLULAR RESPIRATION Learning Outcomes: (a) Identify components of mitochondria in drawings, photomicrographs and electronmicrographs. (f) Outline the process of glycolysis, highlighting the location, raw materials used and products formed. (Knowledge of details of the intermediate compounds and isomerization is not required.) (g) Outline the process of the link reaction and Krebs cycle, highlighting the location, raw materials used and products formed. (In terms of dehydrogenation and decarboxylation.) (h) Outline the process of oxidative phosphorylation including the role of oxygen and the electron transport chain in aerobic respiration (names of complexes in the ETC are not required). (i) Explain the production of a small yield of ATP from respiration in anaerobic conditions in yeast and in mammalian muscle tissue. (j) Explain the significance of the formation of ethanol in yeast and lactate in mammals in the regeneration of NAD. (k) Investigate the effect of factors such as substrate concentration, type of substrate and temperature on the rate of respiration. (l) Outline chemiosmosis in respiration. (Names of complexes in the ETC are not required.) References: Campbell and Reece. Biology. (11th edition). Chapter 10 : Cell Respiration, P. 2 36 – 256 (or corresponding chapter in other editions) Note: This textbook is available in our library. You may wish to borrow it to supplement your reading when necessary. 1) Introduction 1.1 Energy and ATP 1.2 The Mitochondrion 1.3 Cellular Respiration 2) Aerobic Respiration 2.1 Glycolysis 2.2 Link Reaction 2.3 Krebs Cycle 2.4 Oxidative Phosphorylation 3) Anaerobic Respiration 3.1 Alcoholic Fermentation 3.2 Lactate Fermentation 4) Respiratory Quotient 5) Factors Affecting Rate of Respitation H2

2 1 INTRODUCTION • Life processes in every cell are driven by energy. Energy flows into the ecosystem as sunlight and leaves as heat, while chemical elements essential to life are recycled. • Photosynthesis allows plants to convert energy from light into chemical ener gy stored in organic molecules, while cellular respiration occurs to break down the organic molecules to yield adenosine triphosphate (ATP), which drives many cellular processes. Fig 1.1: Energy flow and chemical recycling in ecosystems

3 1.1 ENERGY AND ATP • Respiration involves the release of chemical energy, in the form of adenosine triphosphate (ATP), from organic molecules through a series of oxidation-reduction (redox) reactions. Fig. 1.1.1: Structure of ATP, ADP and AMP The roles of ATP in cells include: (a) Energy Currency – ATP serves as the energy currency of the cell. Energy is released when ATP is hydrolysed to ADP (30.6 kJ per mole of ATP, 1 J = 0.239 cal). The energy released can be used in various cellular processes, such as enzyme reactions, protein synthesis, active transport, muscular contractions, etc. – ATP can be re synthesised from ADP by the addition of a phosphate group, catalysed by the enzyme ATP synthase. (b) Regulation of Metabolic Reactions – ATP has an allosteric effect on the regulation of metabolic reactions (e.g. ATP acts as an allosteric inhibitor of phosphofructokinase in glycolysis) . The concentration of ATP relative to ADP and AMP acts as an index of the energy status of the cell, determining the rates of reactions of regulatory enzymes involved in the metabolic pathway.

4 Fig. 1.1.2: Hydrolysis of ATP and condensation of ADP 1.2 THE MITOCHONDRION Learning Outcome (a): Identify components of mitochondria in drawings, photomicrograph and electron micrographs. [Retrieval Practice] Refer to Topic 1.1 Organelles and Cellular Structures lecture notes. • The mitochondrion is involved in aerobic respiration, which results in the formation of ATP. Fig. 1.2.1: (a) Mitochondrion in an animal cell; (b) Structure of a mitochondrion; (c) Electron micrograph of a mitochondrion

5 • It is an organelle bound by a double membrane. The outer membrane is smooth, while the inner membrane is extensively folded to form cristae. The enzyme ATP synthase , as well as the electron transport chain (ETC), are embedded on the inner membrane. • The mitochondrial matrix contains enzymes, circular DNA, RNA, and 70S ribosomes. 1.2 CELLULAR RESPIRATION • Respiration refers to a series of cellular processes by which organic compounds (glucose and other substrates) are broken down with the help of enzymes to release energy, in the form of ATP, for other cellular processes. • Cells can undergo respiration in the presence of oxygen ( aerobic respiration ) or absence of oxygen (anaerobic respiration). Fig. 1.3.1: Overview of cellular respiration Cellular Respiration Aerobic Respiration Glycolysis Anaerobic Respiration Link Reaction Krebs Cycle Oxidative Phosphorylation Glycolysis Fermentation Alcoholic Fermentation Lactate Fermentation

6 2 AEROBIC RESPIRATION • In the presence of oxygen, glucose is broken down to yield carbon dioxide, water and energy. The oxidation of one molecule of glucose yields sufficient energy to produce 32 ATP molecules. C6H12O6 + 6 O2  6 CO2 + 6 H2O + Energy • Aerobic respiration occurs in four stages: No. Stage Process Location 1 Glycolysis Breakdown of glucose (6C) to form 2 molecules of pyruvate (3C) Cytosol 2 Link Reaction Conversion of pyruvate (3C) to acetyl-CoA (2C) Mitochondrial Matrix 3 Krebs Cycle Oxidation of acetyl-CoA (2C) via a series of reactions Mitochondrial Matrix 4 Oxidative Phosphorylation Electron transfer down the electron transport chain resulting in the production of ATP Inner Mitochondrial Membrane Fig. 2.1: Overview of aerobic respiration (Simplified) Link reaction 1 2 3 4

7 Fig. 2.2: Overview of aerobic respiration Glycolysis Link Reaction Krebs Cycle Oxidative Phosphorylation

8 2.1 GLYCOLYSIS Learning Outcome (f): Outline the process of glycolysis, highlighting the location, raw materials used and products formed. • Glycolysis occurs under both aerobic and anaerobic conditions, and takes place in the cytosol. • Glycolysis involves the breakdown of one molecule of glucose (6C) to two molecules of pyruvate (3C). • Glycolysis consists of an energy investment phase and an energy payoff phase. – During the energy investment phase, 2 molecules of ATP are used per glucose molecule. – During the energy payoff phase, 4 molecules of ATP are synthesised per glucose molecule. – Therefore, the net yield of glycolysis is 2 ATP per glucose molecule. Fig. 2.1.1: Overview of glycolysis

9 Steps in Glycolysis Step 1: Phosphorylation Glucose (6C) is phosphorylated to glucose-6-phosphate (G6P) using a molecule of ATP. This step is the 1st priming reaction. It functions to: 1) Keep respiratory substrate in cell Glucose is a polar molecule that can diffuse across the cell surface membrane via glucose transporters. Phosphorylation confers a negative charge on G6P, preventing it from moving out of the cell 2) Maintain concentration gradient of glucose Rapid conversion of glucose to G6P keeps the intracellular concentration of glucose low, thus favouring the diffusion of glucose into the cell. Enzyme: hexokinase Step 2: Isomerisation Glucose-6-phosphate is isomeri sed to fructose -6- phosphate. Step 3: Phosphorylation Fructose-6-phosphate is phosphorylated to fructose-1,6- bisphosphate using a second molecule of ATP. This step is the 2nd priming reaction. Enzyme: phosphofructokinase Step 4: Lysis Fructose-1,6-bisphosphate is cleaved to form 2 molecules of glyceraldehyde-3-phosphate / triose phosphate (3C). Step 5: Oxidation and Phosphorylation Glyceraldehyde-3-