Chapter 6 How Cells Harvest Chemical Energy 0

Chapter 6 How Cells Harvest Chemical Energy 0

0 How Is a Marathoner Different from a Sprinter? • Human muscles contain two different types of muscle fibers that perform differently under different conditions • The ratio of types of fibers is determined genetically and cannot be converted from one type to another.

0 • The different types of muscle fibers function either aerobically, with oxygen, or anaerobically, without oxygen. • The slow muscle fibers are muscle cells that can sustain repeated, long contractions but don’t generate a lot of quick power for the body. • Fast fibers are better able to produce ATP anaerobically • Cellular respiration o Is the process by which cells produce energy aerobically

INTRODUCTION TO CELLULAR RESPIRATION 0 6. 1 Photosynthesis and cellular respiration provide energy for life • In photosynthesis, which occurs in the chloroplast, the energy of sunlight is used to rearrange the atoms of CO 2 and H 2 O to produce glucose and O 2. • In cellular respiration, which occurs in the mitochondria, O 2 is consumed as glucose is broken down to CO 2 and H 2 O. • The CO 2 and H 2 O released by cellular respiration are converted through photosynthesis to glucose and O 2, which are then used in respiration.

0 • The processes of photosynthesis and cellular respiration are complementary. During these energy conversions, some energy is lost in the form of heat. • Photosynthesis uses solar energy to produce glucose and O 2 from CO 2 and H 2 O Sunlight energy ECOSYSTEM Photosynthesis in chloroplasts Glucose CO 2 H 2 O O 2 Cellular respiration in mitochondria ATP (for cellular work) Heat energy Figure 6. 1

0 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 • Respiration is gas exchange, and cellular respiration produces ATP. O 2 CO 2 Breathing Lungs CO 2 Bloodstream O 2 Muscle cells carrying out Cellular Respiration Glucose O 2 Figure 6. 2 CO 2 H 2 O ATP

0 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 + O 2 6 CO 2 Oxygen gas Carbon dioxide 6 Figure 6. 3 + 6 H 2 O Water + ATPs Energy

• Cellular respiration: o Consumes glucose. o Produces water. o Produces carbon dioxide. o Releases heat. o Is accomplished by many steps.

CONNECTION 0 6. 4 The human body uses energy from ATP for all its activities • ATP powers almost all cellular and body activities Table 6. 4

• Humans use the calories they obtain from food as their source of energy. • Humans use about 75% of their daily calories for involuntary life-sustaining activities such as digestion, circulation, and breathing.

0 6. 5 Cells tap energy from electrons “falling” from organic fuels to oxygen • During cellular respiration, the energy in glucose is carried by electrons. • Electrons lose potential energy during their transfer from organic compounds to oxygen • Oxidation is the loss of electrons, and reduction is the gain of electrons.

0 • 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 O 2 6 Glucose 6 CO 2 + 6 H 2 O + Energy (ATP) Gain of hydrogen atoms (reduction) Figure 6. 5 A

0 • In biological systems, dehydrogenase is an important enzyme involved in the regulation of redox reactions. • Dehydrogenase removes electrons (in hydrogen atoms) from fuel molecules (oxidation) and transfers them to NAD+ (reduction) H O NAD+ _ + 2 H 2 H+ Figure 6. 5 B Oxidation Dehydrogenase H + 2 e Reduction O + 2 H NADH (carries 2 electrons) + H

0 • 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 ATP NAD 2 e Controlled release of energy for synthesis of ATP H Electron transport chain 2 e 2 H Figure 6. 5 C H 2 O 1 2 O 2

STAGES OF CELLULAR RESPIRATION AND FERMENTATION • 6. 6 Overview: Cellular respiration occurs in three main stages • Cellular respiration o Occurs in three main stages 0

Do Now • What are three stages of cellular respiration?

0 • Stage 1: Glycolysis o Occurs in the cytoplasm o Breaks down glucose into pyruvate, producing a small amount of ATP

0 • Stage 2: The citric acid cycle o Takes place in the mitochondrial matrix o Completes the breakdown of glucose, producing a small amount of ATP o Supplies the third stage of cellular respiration with electrons

0 • Stage 3: Oxidative phosphorylation o Occurs in the mitochondria o Uses the energy released by “falling” electrons to pump H+ across a membrane o Harnesses the energy of the H+ gradient through chemiosmosis, producing ATP

0 • http: //www. youtube. com/watch? v=Adt. Au 5 Jg. OV 0&feature=related NADH High-energy electrons carried by NADH FADH 2 and GLYCOLYSIS Glucose Pyruvate OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis) CITRIC ACID CYCLE Mitochondrion Cytoplasm ATP Figure 6. 6 Substrate-level phosphorylation CO 2 ATP CO 2 Substrate-level phosphorylation ATP Oxidative phosphorylation

6. 7 Glycolysis harvests chemical energy by oxidizing glucose to pyruvate • “Splitting of sugar” • Glycolysis is the universal energy-harvesting process of life.

0 • In glycolysis, ATP is used to prime a glucose molecule which is split into two molecules of pyruvate 2 2 NAD+ NADH + 2 H Glucose 2 Pyruvate 2 ADP Figure 6. 7 A +2 P 2 ATP

0 • 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 P

• In the first phase of glycolysis, ATP is used to energize a glucose molecule, which is then split in two small sugars that are now primed to release energy. Steps – 1 A 3 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 4 six-carbon intermediate splits into two three-carbon intermediates. Figure 6. 7 C 4

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

Glycolysis Overview • The result of glycolysis is a conversion of glucose to two three-carbon compounds, that we call pyruvate. • The end products of glycolysis are ATP, NADH, and pyruvate. • Glycolysis Overview

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 NAD 2 Co. A Pyruvate 1 3 CO 2 Figure 6. 8 Coenzyme A Acetyl Co. A (acetyl coenzyme A)

Transition • Between glycolysis and the citric acid cycle, pyruvate is oxidized (loses electrons) while a molecule of NAD+ is reduced (gains electrons) to NADH.

0 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 Figure 6. 9 A ATP ADP P

0 • The two carbons are added to a four-carbon compound, forming citrate o Which is then degraded back to the starting compound

• For each turn of the cycle o Two CO 2 molecules are released o 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 NAD Malate NADH ADP FADH 2 4 P ATP FAD H Alpha-ketoglutarate 3 CO 2 leaves cycle Succinate NADH Step 1 Acetyl Co. A stokes the furnace. Figure 6. 9 B Steps 2 and NAD H 3 NADH, ATP, and CO 2 are generated during redox reactions. Steps 4 and 5 Redox reactions generate FADH 2 and NADH.

Citric Acid Cycle • The enzymes of the citric acid cycle are located in the mitochondrial matrix. • At the end of the citric acid cycle, most of the energy remaining from the original glucose is stored in NADH. • Citric Acid Cycle

0 6. 10 Most ATP production occurs by oxidative phosphorylation • Electrons from NADH and FADH 2 o Travel down the electron transport chain to oxygen, which picks up H+ to form water • Energy released by the redox reactions o Is used to pump H+ into the space between the mitochondrial membranes o Overview o http: //www. youtube. com/watch? v=KXsx. JNXa. T 7 w&feature=related

0 • In chemiosmosis, the H+ diffuses back through the inner membrane through ATP synthase complexes driving the synthesis of ATP. • In the electron transport chain, the final electron acceptor is an oxygen atom. • Electron Transport Chain H+ Intermembrane space . Protein complex H+ H+ FADH 2 Electron flow FAD 1 O 2 + 2 H+ H+ H+ H 2 O Electron Transport Chain OXIDATIVE PHOSPHORYLATION Figure 6. 10 ATP H+ synthase H+ NADH H+ H+ Electron carrier Inner mitochondrial membrane Mitochondrial matrix H+ H+ ADP P ATP H+ Chemiosmosis

CONNECTION 6. 11 Certain poisons interrupt critical events in cellular respiration • Various poisons o Block the movement of electrons o o Block the flow of H+ through ATP synthase Allow H+ to leak through the membrane • Rotenone is a poison commonly added to insecticides. Insects exposed to rotenone will die because of inadequate ATP production. Figure 6. 11 0

Cyanide, carbon monoxide Rotenone H+ H+ H+ Oligomycin H+ ATP Synthase H+ H+ H+ DNP FADH 2 1 NADH NAD+ O 2 2 H+ H+ H 2 O ADP P H+ Electron Transport Chain Chemiosmosis ATP

0 6. 12 Review: Each molecule of glucose yields many molecules of ATP • Oxidative phosphorylation, using electron transport and chemiosmosis o 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 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

Review • Glycolysis and the citric acid cycle must occur two times per glucose molecule. • The energy yield from the complete aerobic breakdown of a single molecule of glucose can vary with the mechanism used to shuttle NADH electrons into the mitochondrion. • http: //www. youtube. com/watch? v=Adt. Au 5 Jg. OV 0&feature=related • http: //www. youtube. com/watch? v=k. N 5 Mtq. AB_Yc

0 6. 13 Fermentation is an anaerobic alternative to cellular respiration • Cellular respiration produces the most ATP per molecule of glucose oxidized. • Under anaerobic conditions, many kinds of cells o Can use glycolysis alone to produce small amounts of ATP

0 • In lactic acid fermentation NADH is oxidized to NAD+ as pyruvate is reduced to lactate • Found in muscle cells and food products. 2 NADH 2 NAD GLYCOLYSIS Glucose 2 ADP 2 Figure 6. 13 A P 2 ATP 2 Pyruvate 2 Lactate

0 • In alcohol fermentation, NADH is oxidized to NAD+ while converting pyruvate to CO 2 and ethanol • Used in brewing, baking, and winemaking. 2 NAD 2 2 NADH 2 NAD GLYCOLYSIS 2 ADP 2 Glucose P 2 2 ATP CO 2 released 2 Ethanol 2 Pyruvate Figure 6. 13 B Figure 6. 13 C

• Strict Anaerobes-require anaerobic conditions and are poisoned by oxygen. • Facultative Anaerobe-can make ATP either by fermentation or oxidative phosphorylation, depending on whether O 2 is available. • http: //www. youtube. com/watch? v=y_k 8 x. Lr. B Ufg • http: //www. youtube. com/watch? v=t. Nqf. Ps. VAd. Yk &feature=fvw

INTERCONNECTIONS BETWEEN MOLECULAR BREAKDOWN AND SYNTHESIS 0 • 6. 14 Cells use many kinds of organic molecules as fuel for cellular respiration

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

0 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 • Biosynthesis consumes ATP needed to drive biosynthesis 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 Sugars Carbohydrates

0 6. 16 The fuel for respiration ultimately comes from photosynthesis • All organisms o Can harvest energy from organic molecules • Plants, but not animals o Can also make these molecules from inorganic sources by the process of photosynthesis Figure 6. 16