Chapter 6 How Cells Harvest Chemical Energy Power

Chapter 6 How Cells Harvest Chemical Energy Power. Point Lectures for Biology: Concepts and Connections, Fifth Edition – Campbell, Reece, Taylor, and Simon Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

How Is a Marathoner Different from a Sprinter? • Human muscles contain two different types of muscle fibers – That perform differently under different conditions Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• The different types of muscle fibers – Function either aerobically, with oxygen, or anaerobically, without oxygen • Cellular respiration – Is the process by which cells produce energy aerobically Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

INTRODUCTION TO CELLULAR RESPIRATION 6. 1 Photosynthesis and cellular respiration provide energy for life • Cellular respiration makes ATP and consumes O 2 – During the oxidation of glucose to CO 2 and H 2 O Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• Photosynthesis uses solar energy – To produce glucose and O 2 from CO 2 and H 2 O Sunlight energy ECOSYSTEM Photosynthesis in chloroplasts CO 2 Glucose H 2 O O 2 Cellular respiration in mitochondria ATP (for cellular work) Heat energy Figure 6. 1 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

6. 2 Breathing supplies oxygen to our cells and removes carbon dioxide • Breathing provides for the exchange of O 2 and CO 2 – Between an organism and its environment O 2 CO 2 Breathing Lungs CO 2 Bloodstream O 2 Muscle cells carrying out Cellular Respiration Glucose O 2 Figure 6. 2 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings CO 2 H 2 O ATP

6. 3 Cellular respiration banks energy in ATP molecules • Cellular respiration breaks down glucose molecules – And banks their energy in ATP C 6 H 12 O 6 Glucose + 6 O 2 Oxygen gas Figure 6. 3 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 6 CO 2 Carbon dioxide + 6 H 2 O Water + ATPs Energy

CONNECTION 6. 4 The human body uses energy from ATP for all its activities • ATP powers almost all cellular and body activities Table 6. 4 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

6. 5 Cells tap energy from electrons “falling” from organic fuels to oxygen • Electrons lose potential energy – During their transfer from organic compounds to oxygen Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• When glucose is converted to carbon dioxide – It loses hydrogen atoms, which are added to oxygen, producing water Loss of hydrogen atoms (oxidation) C 6 H 12 O 6 + 6 O 2 6 CO 2 + Glucose 6 H 2 O + Energy (ATP) Gain of hydrogen atoms (reduction) Figure 6. 5 A Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• Dehydrogenase removes electrons (in hydrogen atoms) from fuel molecules (oxidation) – And transfers them to NAD+ (reduction) H O NAD Oxidation H Reduction 2 H + 2 H O + 2 H Dehydrogenase + 2 e Figure 6. 5 B Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings NADH (carries 2 electrons) + H

• NADH passes electrons – To an electron transport chain • As electrons “fall” from carrier to carrier and finally to O 2 – Energy is released in small quantities NADH NAD �ATP 2 e H Controlled release of energy for synthesis of ATP tra El ns ect po ro rt n ch ain 2 e 2 H H 2 O Figure 6. 5 C Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 1 2 O 2

STAGES OF CELLULAR RESPIRATION AND FERMENTATION • 6. 6 Overview: Cellular respiration occurs in three main stages • Cellular respiration – Occurs in three main stages Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• Stage 1: Glycolysis – Occurs in the cytoplasm – Breaks down glucose into pyruvate, producing a small amount of ATP Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• Stage 2: The citric acid cycle – Takes place in the mitochondria – Completes the breakdown of glucose, producing a small amount of ATP – Supplies the third stage of cellular respiration with electrons Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• Stage 3: Oxidative phosphorylation – Occurs in the mitochondria – Uses the energy released by “falling” electrons to pump H+ across a membrane – Harnesses the energy of the H+ gradient through chemiosmosis, producing ATP Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• An overview of cellular respiration NADH High-energy electrons carried by NADH FADH 2 and GLYCOLYSIS Glucose Pyruvate CITRIC ACID CYCLE OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) Mitochondrion Cytoplasm ATP Substrate-level phosphorylation CO 2 ATP CO 2 Substrate-level phosphorylation Figure 6. 6 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings ATP Oxidative phosphorylation

6. 7 Glycolysis harvests chemical energy by oxidizing glucose to pyruvate • In glycolysis, ATP is used to prime a glucose molecule – Which is split into two molecules of pyruvate NAD 2 2 NADH + 2 H Glucose 2 Pyruvate 2 ADP Figure 6. 7 A Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings +2 P 2 ATP

• Glycolysis produces ATP by substrate-level phosphorylation – In which a phosphate group is transferred from an organic molecule to ADP Enzyme P P P Adenosine ADP ATP P Organic molecule (substrate) Figure 6. 7 B Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings P

• In the first phase of glycolysis – ATP is used to energize a glucose molecule, which is then split in two 1 3 Steps – A fuel molecule is energized, using ATP. Glucose ATP PREPARATORY PHASE (energy investment) Step 1 ADP P Glucose-6 -phosphate P Fructose-1, 6 -diphosphate 2 ATP 3 ADP P Step A six-carbon intermediate splits 4 into two three-carbon intermediates. Figure 6. 7 C Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 4

• In the second phase of glycolysis – ATP, NADH, and pyruvate are formed P Step A redox reaction generates 5 6 9 NADH. NAD P 5 +H P ADP P P 1, 3 -Diphosphoglycerate 6 7 6 ATP P P 7 P 8 8 H 2 O 8 2 -Phosphoglycerate 8 H 2 O P P 9 ADP Phosphoenolpyruvate (PEP) 9 ADP 9 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 7 P 3 -Phosphoglycerate 7 Figure 6. 7 C 6 ADP ATP ENERGY PAYOFF PHASE 5 P 6 NADH +H P P NADH Steps – ATP and pyruvate 6 9 are produced. NAD Glyceraldehyde-3 -phosphate (G 3 P) 9 ATP Pyruvate

6. 8 Pyruvate is chemically groomed for the citric acid cycle • Prior to the citric acid cycle – Enzymes process pyruvate, releasing CO 2 and producing NADH and acetyl Co. A NADH H 2 Co. A Pyruvate 1 3 CO 2 Figure 6. 8 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Coenzyme A Acetyl Co. A (acetyl coenzyme A)

6. 9 The citric acid cycle completes the oxidation of organic fuel, generating many NADH and FADH 2 molecules • In the citric acid cycle – The two-carbon acetyl part of acetyl Co. A is oxidized Acetyl Co. A CITRIC ACID CYCLE 2 CO 2 3 NAD FADH 2 3 NADH FAD 3 H ATP Figure 6. 9 A Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings ADP P

• The two carbons are added to a four-carbon compound, forming citrate – Which is then degraded back to the starting compound Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• For each turn of the cycle – Two CO 2 molecules are released – The energy yield is one ATP, three NADH, and one FADH 2 Co. A Acetyl Co. A 2 carbons enter cycle Oxaloacetate NADH 1 Citrate H NAD 5 CO 2 leaves cycle 2 CITRIC ACID CYCLE Malate NADH H ADP P FADH 2 4 ATP FAD Alpha-ketoglutarate 3 CO 2 leaves cycle Succinate NADH Step 1 Acetyl Co. A stokes the furnace. Figure 6. 9 B Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings H NAD Steps 2 and 3 NADH, ATP, and CO 2 are generated during redox reactions. Steps 4 and 5 Redox reactions generate FADH 2 and NADH.

6. 10 Most ATP production occurs by oxidative phosphorylation • Electrons from NADH and FADH 2 – Travel down the electron transport chain to oxygen, which picks up H+ to form water • Energy released by the redox reactions – Is used to pump H+ into the space between the mitochondrial membranes Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• In chemiosmosis, the H+ diffuses back through the inner membrane through ATP synthase complexes – Driving the synthesis of ATP H+ Intermembrane space . Protein complex H H+ FADH 2 Electron flow NADH H+ + H+ Electron carrier Inner mitochondrial membrane Mitochondrial matrix H+ H+ H H + 1 O + 2 H+ 2 2 H+ H+ H 2 O Electron Transport Chain OXIDATIVE PHOSPHORYLATION Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings ATP synthase FAD NAD+ Figure 6. 10 H+ + ADP P H+ ATP Chemiosmosis

CONNECTION 6. 11 Certain poisons interrupt critical events in cellular respiration • Various poisons – Block the movement of electrons – Block the flow of H+ through ATP synthase – Allow H+ to leak through the membrane Cyanide, carbon monoxide Rotenone H+ H+ H + Oligomycin H+ H + H+ H+ ATP Synthase DNP FADH 2 NADH NAD FAD 1 O 2 2 H+ 2 + H+ H+ Figure 6. 11 H+ Electron Transport Chain Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings H 2 O ADP P ATP Chemiosmosis

6. 12 Review: Each molecule of glucose yields many molecules of ATP • Oxidative phosphorylation, using electron transport and chemiosmosis – Produces up to 38 ATP molecules for each glucose molecule that enters cellular respiration Electron shuttle across membrane Cytoplasm Mitochondrion 2 NADH (or 2 FADH 2) 2 NADH GLYCOLYSIS 2 Glucose Pyruvate 2 Acetyl Co. A 2 ATP by substrate-level phosphorylation Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings CITRIC ACID CYCLE 2 ATP by substrate-level phosphorylation Maximum per glucose: Figure 6. 12 6 NADH About 38 ATP 2 FADH 2 OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) about 34 ATP by oxidative phosphorylation

6. 13 Fermentation is an anaerobic alternative to cellular respiration • Under anaerobic conditions, many kinds of cells – Can use glycolysis alone to produce small amounts of ATP Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• In lactic acid fermentation – NADH is oxidized to NAD+ as pyruvate is reduced to lactate 2 NAD 2 2 NADH 2 NAD GLYCOLYSIS 2 ADP 2 Glucose P 2 ATP 2 Pyruvate Figure 6. 13 A Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 2 Lactate

• In alcohol fermentation – NADH is oxidized to NAD+ while converting pyruvate to CO 2 and ethanol 2 NADH NAD 2 GLYCOLYSIS 2 ADP 2 P Glucose 2 2 ATP CO 2 released 2 ��Ethanol 2 Pyruvate Figure 6. 13 B Figure 6. 13 C Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

INTERCONNECTIONS BETWEEN MOLECULAR BREAKDOWN AND SYNTHESIS • 6. 14 Cells use many kinds of organic molecules as fuel for cellular respiration Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings

• Carbohydrates, fats, and proteins can all fuel cellular respiration – When they are converted to molecules that enter glycolysis or the citric acid cycle Food, such as peanuts Carbohydrates Fats Sugars Glycerol Proteins Fatty acids Amino groups Glucose G 3 P Pyruvate GLYCOLYSIS Acetyl Co. A ATP Figure 6. 14 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings CITRIC ACID CYCLE OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis)

6. 15 Food molecules provide raw materials for biosynthesis • Cells use some food molecules and intermediates from glycolysis and the citric acid cycle as raw materials • This process of biosynthesis ATP needed to drive biosynthesis ATP – Consumes ATP CITRIC ACID CYCLE GLUCOSE SYNTHESIS Acetyl Co. A Pyruvate G 3 P Glucose Amino groups Amino acids Proteins Fatty acids Glycerol Fats Cells, tissues, organisms Figure 6. 15 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Sugars Carbohydrates

6. 16 The fuel for respiration ultimately comes from photosynthesis • All organisms – Can harvest energy from organic molecules • Plants, but not animals – Can also make these molecules from inorganic sources by the process of photosynthesis Figure 6. 16 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings