Inquiry into Life Eleventh Edition Sylvia S. Mader Chapter 7 Lecture Outline Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

7.1 Overview of cellular respiration Overall process Oxidation of glucose to carbon dioxide, water, and energy. This is an Exergonic reaction used to drive ATP synthesis which is endergonic 4 phases of respiration are required for complete oxidation of glucose Oxidation involves the removal of hydrogen atoms from substrates by redox coenzymes NAD+ and FAD

Cellular respiration

Overview of cellular respiration cont’d. NAD+ and FAD Redox coenzymes active in respiration NAD+ is reduced to NADH FAD is reduced to FADH2 FADH2 and NADH carry electrons to the electron transport chain

The NAD+ cycle

Overview of cellular respiration cont’d. Phases of cellular respiration Glycolysis (Takes place in the Cytoplasm) Use Energy from 2 ATP’s to activate glucose Breakdown of glucose to 2 molecules of pyruvate Oxidation by removal of hydrogens releases enough energy to make 2 ATP’s from each pyruvate results in a Net Gain of 2 ATP’s in this Phase per Glucose Molecule.

Phases of cellular respiration, cont’d. Preparatory reaction (Takes place in Matrix of Mitochondria) Pyruvate oxidized to acetyl CoA and carbon dioxide is removed Prep reaction occurs twice per Glucose molecule because glycolysis produces 2 pyruvates No ATP’s produced in this phase

Phases of cellular respiration, cont’d. Citric acid cycle (Takes place in Matrix of Mitochondria) Each Pyruvate was oxidized to acetyl CoA in Preparatory Reaction. Now Acetyl CoA is converted to citric acid and enters the cycle Cyclical series of oxidation reactions that produces 1 ATP and carbon dioxide per cycle turn Citric acid cycle turns twice per Glucose Molecule because 2 acetyl CoA’s are produced per glucose 2 ATP’s produced per Glucose Molecule in this phase

Overview of cellular respiration cont’d. Phases of cellular respiration, cont’d. Electron transport chain (Takes place in Cristae of Mitochondria) Series of electron carrier molecules which pass Electrons from one carrier to another releasing energy to make ATP As the electrons move from a higher energy state to a lower one, energy is released to make ATP Under aerobic conditions 32-34 ATP per glucose molecule can be produced

Phases of cellular respiration, cont’d. In Anaerobic Conditions (No Oxygen Present) Glycolysis produces Pyruvate Pivotal metabolite in cellular respiration If no oxygen is available, pyruvate is reduced to lactate (in animals) or ethanol and carbon dioxide (in plants) in a process called fermentation

Cellular respiration

7.2 Outside the mitochondria: Glycolysis Energy-investment steps Energy from 2 ATP is used to activate glucose Glucose is split into 2 3-carbon G3P molecules Energy-harvesting steps Oxidation of G3P by removal of hydrogens Hydrogens are picked up by NAD+ to form NADH Oxidation of G3P and further substrates yields enough energy to produce 4 ATP by direct substrate phosphorylation, so there’s a net gain of 2 ATP’s.

Outside the mitochondria: glycolysis cont’d. Glycolysis yields: 4 ATP by direct substrate phosphorylation 2 ATP were consumed in the investments steps Net gain of ATP from glycolysis is therefore 2 ATP 2 NADH which will carry electrons to the electron transport chain No Oxygen is required for Glycolysis to produce pyruvate. When oxygen is available pyruvate will enter the mitochondria for further oxidation If no oxygen is available, pyruvate will enter the fermentation pathway

Glycolysis

7.3 Inside the mitochondria Breathing, eating, and cellular respiration Oxygen is taken in by breathing Digested food contains glucose Oxygen and glucose are carried to cells by the bloodstream Glucose and oxygen enter cells where respiration occurs Carbon dioxide is taken by the bloodstream to the lungs

Relationship between breathing, eating, and cell respiration

Inside the mitochondria cont’d. Preparatory reaction Produces the molecule that will enter the citric acid cycle 3C pyruvate is converted to 2C acetyl CoA Carbon dioxide is produced Hydrogen atoms are removed from pyruvate and picked up to form NADH This reaction occurs twice per glucose

Inside the mitochondria cont’d. Citric acid cycle 2C acetyl group from prep reaction combines with a 4C molecule to produce 6C citrate Oxidation of citrate by removal of hydrogens Produces 3 NADH and 1 FADH2 Produces 1 ATP per cycle by direct substrate phosphorylation Cycle turns twice per glucose Total yield: 6 NADH, 2 FADH2, 2 ATP, 4 CO2

Citric acid cycle

Inside the mitochondria cont’d. Electron transport chain (ETC) 2 electrons per NADH and FADH2 enter ETC Electrons are passed to series of electron carriers called cytochromes Energy is captured and stored as a hydrogen ion concentration gradient. This process is called chemiosmosis For each NADH enough energy is released to form 3 ATP For each FADH2 there are 2 ATP produced

Overview of the electron transport chain

Inside the mitochondria cont’d. Electron transport chain cont’d. the final electron acceptor is oxygen After receiving electrons oxygen combines with hydrogen ions to form water as an end product ½ O2+ 2 e- + 2H+  H2O NAD+ and FAD recycle back to pick up more electrons from glycolysis, prep reaction, and citric acid cycle

Inside the mitochondria cont’d. Organization of cristae Electron carriers are arranged along the cristae As electrons are passed, energy is used to pump H+ into the intermembrane space of mitochondrion This builds an electro-chemical gradient that stores energy As H+ moves back into matrix energy is released and captured to form ATP by ATP synthase complexes Process is called chemiosmosis

Organization of cristae in the mitochondria

Inside the mitochondria cont’d. Energy yield from cellular respiration is 36 – 38 ATP’s per Glucose Molecule From direct phosphorylation Net of 2 ATP from glycolysis 2 ATP from citric acid cycle From chemiosmosis Electron transport chain produces 32 – 34 ATP per Glucose Molecule

Accounting of energy yield per glucose molecule breakdown

Inside the mitochondria cont’d. Efficiency of cellular respiration The difference in energy content of reactants (glucose and oxygen) and products (carbon dioxide and water) is 686 kcal ATP phosphate bond has 7.3 kcal of energy 36 ATP are produced in respiration 36 X 7.3 = 263 kcal 263/686 = 39% efficiency of energy capture The rest of the energy is lost as heat

7.4 Fermentation Fermentation Produces only a net of 2 ATP per glucose Occurs when O2 is not available Animal cells convert pyruvate to lactate Plant cells, yeasts convert pyruvate to ethanol and CO2 Fermentation regenerates NAD+ which keeps glycolysis going Produces only a net of 2 ATP per glucose

Fermentation Fig 7.10

Fermentation cont’d. Advantages and Disadvantages of fermentation Provides a low but continuous supply of ATP when oxygen is limited and only glycolysis can function Can provide a rapid burst of ATP in muscle cells, even when oxygen is in limited supply. Lactate is potentially toxic to muscles, lowering pH and causing fatigue Transported to liver where it is converted to pyruvate This process requires oxygen During exercise an oxygen debt is built up Oxygen debt is the amount of oxygen “owed” to the liver to convert accumulated lactic acid to pyruvate

Fermentation , cont’d. Energy yield of fermentation Produces only a net of 2 ATP per glucose through direct substrate phosphorylation by allowing glycolysis to continue. MUCH LESS efficient than Aerobic Cellular Respiration. Following fermentation most of the potential energy from glucose is still waiting to be released Fermentation is a way to continue an ATP supply to cells when oxygen is in short supply

7.5 Metabolism Catabolism-break down reactions Carbohydrates-digested to glucose for cell respiration Fats-digested to glycerol and fatty acids Glycerol can enter glycolytic pathway Fatty acids metabolized to acetyl CoA which enters citric acid cycle Proteins- deamination Amino acids can enter pathway at different points

Metabolism

Metabolism cont’d. Anabolism- synthesis reactions Substrates of glycolysis and citric acid cycle can be substrates for synthesis of macromolecules G3P can be converted to glycerol Acetyl groups can be converted to fatty acids Some citric acid intermediates can be converted to amino acids Anabolic reactions require the input of energy in the form of ATP generated in catabolic reactions