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

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings How Is a Marathoner Different from a Sprinter? Muscles in human legs contain two different types of muscle fibers –Marathoners have more slow-twitch fibers, which perform better in endurance exercises –Sprinters have more fast-twitch fibers, which perform best in short bursts of intense activity

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings The different types of muscle fibers use different processes for making ATP –Slow-twitch fibers undergo aerobic (in the presence of O 2 ) respiration –Fast-twitch fibers undergo anaerobic (in the absence of O 2 ) respiration 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 All living organisms require energy to maintain homeostasis, to move, and to reproduce Photosynthesis converts energy from the sun to glucose and O 2 Cellular respiration breaks down glucose and releases energy in ATP Energy flows through an ecosystem; chemicals are recycled

LE 6-1 Sunlight energy ECOSYSTEM Photosynthesis in chloroplasts Glucose CO 2 O2O2 H2OH2O Cellular respiration in mitochondria (for cellular work) Heat energy ATP

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 6.2 Breathing supplies oxygen to our cells and removes carbon dioxide Breathing and cellular respiration are closely related –Breathing brings O 2 into the body from the environment –O 2 is distributed to cells in the bloodstream –In cellular respiration, mitochondria use O 2 to harvest energy and generate ATP –Breathing disposes of the CO 2 produced as a waste product of cellular respiration

LE 6-2 Breathing Lungs Muscle cells carrying out Cellular Respiration Bloodstream Glucose  O 2 CO 2  H 2 O  ATP O2O2 CO 2 O2O2

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 6.3 Cellular respiration banks energy in ATP molecules The reactants O 2 and glucose regroup to form the products CO 2 and H 2 O Energy from glucose is released and stored in ATP

LE 6-3 EnergyWaterCarbon dioxide Oxygen gasGlucose

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings CONNECTION 6.4 The human body uses energy from ATP for all its activities The body needs a continual supply of energy to maintain basic functioning In addition, ATP supplies energy (kilocalories) for voluntary activities An average adult human needs about 2,200 kcal of energy each day

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 6.5 Cells tap energy from electrons “falling” from organic fuels to oxygen The energy available to a cell is contained in the arrangement of electrons in chemical bonds Electrons lose potential energy when they “fall” from organic compounds to oxygen during cellular respiration Each step of the “fall” involves paired oxidation–reduction (redox) reactions –Oxidation: loss of electrons (in atoms) –Reduction: addition of electrons

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings The redox reactions of cellular respiration –Glucose loses electrons (in H atoms) and becomes oxidized –O 2 gains electrons (in H atoms) and becomes reduced –Along the way, the electrons lose potential energy, and energy is released

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings The redox reactions that break down glucose involve an enzyme and a coenzyme –The enzyme dehydrogenase removes electrons (in H atoms) from fuel molecules (oxidation) –The electrons are transferred to the coenzyme NAD +, which is converted to NADH (reduction)

Oxidation Dehydrogenase Reduction (carries 2 electrons) NAD  NADH HH 2H2H 2H  2 e  

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings –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 The energy released is used by the cell to make ATP

LE 6-5c NADH NAD  Electron transport chain 2e  Controlled release of energy for synthesis of ATP ATP HH 2 HH 2e  H2OH2O O2O2 2 1

STAGES OF CELLULAR RESPIRATION AND FERMENTATION 6.6 Overview: Cellular respiration occurs in three main stages 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 CO 2 and 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 electrons “falling” down the electron transport chain to pump H + across a membrane –Harnesses the energy of the H + gradient through chemiosmosis, producing ATP Animation: Cellular Respiration Overview Animation: Cellular Respiration Overview

LE 6-6 NADH High-energy electrons carried by NADH GLYCOLYSIS GlucosePyruvate Cytoplasm ATP Substrate-level phosphorylation Substrate-level phosphorylation CITRIC ACID CYCLE CO 2 ATP NADH FADH 2 and ATP Mitochondrion Oxidative phosphorylation OXIDATIVE PHOSPHORYLATION ( Electron Transport and Chemiosmosis)

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 6.7 Glycolysis harvests chemical energy by oxidizing glucose to pyruvate Glycolysis splits sugar molecules in the cytoplasm –Starts with a single 6-carbon molecule of glucose –Ends with two 3-carbon molecules of pyruvate –Produces two molecules of ATP in the process Animation: Glycolysis Animation: Glycolysis

LE 6-7a Glucose NAD  NADH HH ADP ATP P 2 2 Pyruvate

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Glycolysis produces ATP by substrate-level phosphorylation –An enzyme transfers a phosphate group from an organic molecule to ADP –A small amount of ATP is produced

LE 6-7b Enzyme Organic molecule (substrate) PP P ADP P ATP P Adenosine

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Details of glycolysis –Preparatory phase A fuel molecule (glucose) is energized, using ATP A 6-carbon intermediate splits into two 3-carbon intermediates –Energy payoff phase A redox reaction generates NADH ATP and pyruvate are produced

LE 6-7c ATP P Pyruvate ADP P P P 1,3-Diphosphoglycerate P P P P ATP ADP P P 3-Phosphoglycerate 2-Phosphoglycerate Phosphoenolpyruvate (PEP) H2OH2OH2OH2O

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 6.8 Pyruvate is chemically groomed for the citric acid cycle A large, multienzyme complex catalyzes three reactions in the mitochondrial matrix –A carbon atom is removed from pyruvate and released in CO 2 –The remaining two-carbon compound is oxidized, and a molecule of NAD + is reduced to NADH –Coenzyme A joins with the 2-carbon group to produce acetyl CoA

LE 6-8 Acetyl CoA (acetyl coenzyme A) Coenzyme A Pyruvate CO 2 NAD  NADH HH CoA 

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 6.9 The citric acid cycle completes the oxidation of organic fuel, generating many NADH and FADH 2 molecules For each turn of the citric acid cycle –Two CO 2 molecules are released –The energy yield is one ATP, three NADH, and one FADH 2 Animation: Citric Acid Cycle Animation: Citric Acid Cycle

LE 6-9a Acetyl CoA CoA CO 2 2 C ITRIC A CID C YCLE ATP NADH NAD  ADP P   3 H  FAD FADH 2 3 3

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Details of the citric acid cycle –The 2-carbon acetyl part of acetyl CoA is oxidized –The two carbons are added to a 4-compound, forming citrate –Through a series of redox reactions, two carbons are removed from citrate as CO 2 and the 4-carbon compound is regenerated –The energy-rich molecules ATP, NADH, and FADH 2 are produced

LE 6-9b Acetyl CoA CoA Oxaloacetate C ITRIC A CID C YCLE Citrate 2 carbons enter cycle leaves cycle Alpha-ketoglutarate leaves cycle CO 2 NAD  NADH  H  ADP ATP P  CO 2 NADH  H  NAD  NADH NAD   H  Malate FADH 2 FAD Succinate

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 6.10 Most ATP production occurs by oxidative phosphorylation An electron transport chain in the mitochondrial membrane creates a H + gradient –Electrons from NADH and FADH 2 travel down the chain to O 2, which picks up H + –H 2 O is formed as a product –Energy released by redox reactions actively transports H + across the membrane from the mitochondrial matrix to the intermembrane space

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings In chemiosmosis, ATP synthases drive the synthesis of ATP –Exergonic reactions of the electron transport chain produce an H + gradient that stores potential energy –ATP synthases harness the energy by acting like turbines Help the H + diffuse back against the gradient through the inner membrane Attach phosphate groups to ADP, producing ATP Animation: Electron Transport Animation: Electron Transport

LE 6-10 Intermembrane space Inner mitochondrial membrane Mitochondrial matrix Protein complex Electron carrier Electron flow NADH NAD  FADFADH 2 HH HH HH HH H2OH2O HH HH ATP synthase 2  O2O HH P  ADPATP Electron Transport Chain Chemiosmosis O XIDATIVE P HOSPHORYLATION HH HH HH HH HH HH HH

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings CONNECTION 6.11 Certain poisons interrupt critical events in cellular respiration Rotenone, cyanide, and carbon monoxide block parts of the electron transport chain Oligomycin blocks the passage of H + through ATP synthase Uncouplers such as DNP destroy the H + gradient by making the membrane leaky to H +

LE 6-11 NADH FAD FADH 2 NAD + Electron Transport Chain Chemiosmosis ATP ADP P + H2OH2O O2O H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Cyanide, carbon monoxide Rotenone Oligomycin DNP ATP synthase 2

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 6.12 Review: Each molecule of glucose yields many molecules of ATP Glycolysis and the citric acid cycle together yield four ATP per glucose molecule Oxidative phosphorylation, using electron transport and chemiosmosis, yields 34 ATP per glucose These numbers are maximums –Some cells may lose a few ATP to NAD + or FAD shuttles

LE 6-12 Cytoplasm Electron shuttle across membrane 2 G LYCOLYSIS NADH (or 2 FADH 2 ) 2 Acetyl CoA Maximum per glucose: 2 Pyruvate C ITRIC A CID C YCLE Mitochondrion FADH 2 2 O XIDATIVE P HOSPHORYLATION (Electron Transport and Chemiosmosis)  about 34 ATP  2 ATP by oxidative phosphorylation by substrate-level phosphorylation About 38 ATP  2 ATP by substrate-level phosphorylation Glucose

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 6.13 Fermentation is an anaerobic alternative to cellular respiration Fermentation –Generates two ATP molecules from glycolysis in the absence of oxygen –Recycles NADH to NAD + anaerobically Muscle cells use lactic acid fermentation –NADH is oxidized to NAD + as pyruvate is reduced to lactate

LE 6-13a GLYCOLYSIS Glucose NAD  NADH ATP P 2 ADP  2 Pyruvate NADH NAD  Lactate

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Alcohol fermentation occurs in brewing, wine making, and baking –NADH is oxidized to NAD + while converting pyruvate to CO 2 and ethanol Animation: Fermentation Overview Animation: Fermentation Overview

LE 6-13b GLYCOLYSIS Glucose NAD  NADH 2 ADP  PATP 2 2 NADH NAD  2 Pyruvate 2 CO 2 released 2 Ethanol 2

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Strict anaerobes –Require anaerobic conditions to generate ATP by fermentation –Are poisoned by oxygen Facultative anaerobes –Can make ATP by fermentation or oxidative phosphorylation depending on whether O 2 is available

INTERCONNECTIONS BETWEEN MOLECULAR BREAKDOWN AND SYNTHESIS 6.14 Cells use many kinds of organic molecules as fuel for cellular respiration Cells use three main kinds of food molecules to make ATP Carbohydrates –Hydrolyzed by enzymes to glucose, which enters glycolysis

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Proteins –Digested to constituent amino acids, which are transformed into various compounds –Become intermediates in glycolysis or the citric acid cycle

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Fats –Digested to glycerol and free fatty acids Glycerol becomes an intermediate in glycolysis Fatty acids are broken into 2-carbon fragments that enter the citric acid cycle as acetyl CoA

LE 6-14 Food, such as peanuts Sugars Glycerol Fatty acids Amino acids Amino groups Proteins Fats Carbohydrates Glucose Pyruvate G3P GLYCOLYSIS Acetyl CoA CITRIC ACID CYCLE OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis ) ATP

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 6.15 Food molecules provide raw materials for biosynthesis Some raw materials from food can be incorporated directly into an organism’s molecules Cells can also make molecules not found in food –Intermediate compounds of glycolysis and the citric acid cycle act as raw materials –Biosynthetic pathways consume ATP rather than generate it –Biosynthesis is not always the direct reverse of breakdown pathways

LE 6-15 ATP needed to drive biosynthesis ATP CITRIC ACID CYCLE Acetyl CoA Amino groups Proteins Amino acidsFatty acidsGlycerol Fats Cells, tissues, organisms Carbohydrates Sugars GLUCOSE SYNTHESIS PyruvateG3PGlucose

Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 6.16 The fuel for respiration ultimately comes from photosynthesis All organisms can harvest energy from organic molecules Plants can also make molecules from inorganic sources by photosynthesis