CELLULAR RESPIRATION BIOLOGY IB/ SL Option C.3

BIOCHEMICAL REACTIONS All living organisms require a constant supply of energy to sustain life. Cellular respiration - the chemical energy stored in glucose is converted into a more usable form – ATP Requires the presence of oxygen and the correct enzymes Carbon dioxide, water and heat are also released as by-products of this reaction. C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy (ATP + heat) glucose + oxygen → carbon + water + energy dioxide . In cells control the release of chemical-bond energy from organic molecules (such as glucose) through enzyme controlled chemical reactions

Oxidation / Reduction Oxidation involves the loss of electrons from an element; oxidation frequently involves gaining oxygen or losing hydrogen Reduction involves a gain of electrons; and that reduction frequently involves losing oxygen or gaining hydrogen

Cellular respiration is an example of a Redox reaction as shown in the chemical equation below

NAD+ electron carrier Nicotinamide adenine dinucleotide Coenzyme, oxidizing agent, reduced form is NADH NADH carries electrons to ETC

Adenosine triphosphate /ATP Section 8-1 Adenine Ribose 3 Phosphate groups Go to Section:

PHOSPHORYLATION OXIDATIVE ATP synthesis powered by redox reactions Electron transport chain Requires oxygen (final electron acceptor) SUBSTRATE LEVEL ATP synthesis from transfer of phosphate group from substrate to ADP Glycolysis and Krebs cycle

Storing energy by substrate level phosphorylation Figure 8-3 Comparison of ADP and ATP to a Battery Storing energy by substrate level phosphorylation Section 8-1 ADP ATP Energy Energy Adenosine diphosphate (ADP) + Phosphate Adenosine triphosphate (ATP) Partially charged battery Fully charged battery Go to Section:

Substrate level Phosphorylation in glycolysis

Stages of Cellular Respiration GLYCOLYSIS First pathway in a cell getting energy out of food. Breaks glucose into pyruvic acid and ATP. Takes place in the cytoplasm Releases only a small amount of energy Will happen with or without oxygen   2. KREBS CYCLE Happens in the mitochondrial matrix Only takes place if oxygen is present 3. ELECTRON TRANSPORT CHAIN (Oxidative phosphorylation) Happens in the inner mitochondrial membrane

Respiration/ overview Biology: Life on Earth (Audesirk) Respiration/ overview FIGURE 8-1 A summary of glucose metabolism Chapter 8 Harvesting Energy

Glycolysis glucose  pyruvate; cytosol

Krebs cycle mitochondrial matrix, pyruvate acetyl CoA & CO2

GLYCOLYSIS In glycolysis a 6C glucose molecule is broken into 2 (3C) molecules of pyruvate (pyruvic acid) Glycolysis occurs in the cytoplasm of the cell – near the mitochondria Yields are: + 2 ATP (4 ATP – 2ATP - used to phosphorylate glucose when it enters cell) 2 NADH (NAD+ is reduced to NADH) This process is anaerobic (without oxygen)…can happen even if there is an insufficient O2 level to carry out the rest of cellular respiration

To the electron transport chain Glycolysis Section 9-1 Glucose 2 Pyruvic acid To the electron transport chain Go to Section:

Fermentation or aerobic respiration?

FERMENTATION Under anaerobic conditions, pyruvate is converted into lactate or ethanol, a process called fermentation Fermentation does not produce more ATP, but is necessary to regenerate/ recycle the high-energy electron carrier molecule NAD+, which must be available for glycolysis to continue

LACTIC ACID FERMENTATION

ALCOHOLIC FERMENTATION

Fermentation of Dough Explain how does the dough rise? Chapter 8

Mitochondrial structure Double membrane-bound organelle Inner membrane folded into christae a) Increase surface area for reactions b) ETC located here 3) Intermembrane space 4) Matrix - Kreb’s cycle

Structure of the mitochondria as seen under TEM

DOUBLE MEMBRANE ORGANELLES In eukaryotic cells, cellular respiration occurs within mitochondria, organelles with two membranes that have two compartments. The inner membrane encloses a central compartment containing the fluid matrix The outer membrane surrounds the organelle, producing an intermembrane space Chapter 8

LINK RECTION (Oxidation of Pyruvate) Occurs in mitochondrion, requires transport protein & coenzyme A Yields Acetyl CoA, 1 NADH & 1 H+ from each pyruvate (2 total) Waste – carbon dioxide

LINK REACTION

KREBS CYCLE

Electron transport chain (ETC) - Electrons from reduced coenzymes NADH and FADH2 are transferred through a series of redox reactions from one carrier to another located in the inner mitochondrial membrane until the electrons are accepted by oxygen to make water. - Every time the electron is passed, some of its energy is released and can be used to make ATP - The rest of the energy is released as heat High-energy electrons, such as those made when light strikes a chlorophyll molecule, are passed from one carrier molecule to another along a chain, like a hot potato. Every time the electron is passed, some of its energy is released and can be used to build an ATP. There is a stepwise passage of energy from molecule to molecule. Some of this bond energy is put into the ATP bond. The rest of this energy is released as heat.

Electron Transport Chain Section 9-2 Electron Transport Hydrogen Ion Movement Channel Intermembrane Space ATP synthase Inner Membrane Matrix ATP Production Go to Section:

CHEMIOSMOSIS Energy is released from electrons as they are passed down the electron transport chain Released energy used to pump hydrogen ions across the inner membrane Hydrogen ions accumulate in intermembrane space Hydrogen ions form a concentration gradient across the membrane, a form of stored energy Hydrogen ions flow back into the matrix through an ATP synthesizing enzyme Process is called chemiosmosis Chapter 8

CHEMIOSMOSIS Energy coupling ATP synthase Generates ATP Molecular mill Powered by proton flow Uses exergonic flow of electrons to pump H+ (protons) from matrix into intermembrane space, they flow back through ATP synthase H+ gradient couples redox reactions of ETC to ATP synthesis

ATP Synthase Enzyme along inner mitochondrial membrane Uses electrochemical potential energy to drive phosphorylation Proton-motive force

Mitochondrial Chemiosmosis (1) Chapter 8

Mitochondrial Chemiosmosis (2) Mitocondrial chemoosmosis 2 Mitochondrial Chemiosmosis (2) Chapter 8

Mitochondrial Chemiosmosis (3) Chapter 8

ETC produces: (per glucose) 2 NADH (from glycolysis) 2 NADH (from intermediate reactions) + 6 NADH (Krebs cycle)______________ 10 NADH x 3 ATP/NADH = 30 ATP 2 FADH2 x 2 ATP/ FADH2 = 4 ATP____ for a total 34 ATP/glucose from ETS

Cellular Respiration Energy Summary 34 ATP/glucose from ETS + 2 ATP (glycolysis) + 2 ATP (Krebs cycle)_______________ 38 ATP per glucose!!! Draw on board. Remark at end about NADH from glycolysis only making 2/molecule

Influence on How Organisms Function Metabolic processes in cells are heavily dependent on ATP generation (cyanide kills by preventing this) Muscle cells switch between fermentation and aerobic cell respiration depending on O2 availability Chapter 8