Cellular Respiration: Obtaining Energy from Food Chapter 6 Cellular Respiration: Obtaining Energy from Food Laua Coronado Chap 6 Bio 10

Biology and : Marathoners versuSocietys Sprinters Sprinters do not usually compete at short and long distances. Natural differences in the muscles of these athletes favor sprinting or long-distance running. Laua Coronado Chap 6 Bio 10

Muscle Fibers The muscles that move our legs contain two main types of muscle fibers: Slow twitch fibers Generate less power Last longer Generate ATP using oxygen Fast twitch fibers Generate more power Fatigue much more quickly Can generate ATP without using oxygen All human muscles contain both types of fibers but in different ratios. Laua Coronado Chap 6 Bio 10

ENERGY FLOW AND CHEMICAL CYCLING IN THE BIOSPHERE Animals depend on plants to convert solar energy to: Chemical energy of sugars Other molecules we consume as food Photosynthesis: Uses light energy from the sun to power a chemical process that makes organic molecules. Laua Coronado Chap 6 Bio 10

Producers and Consumers Plants and other autotrophs (self-feeders): Make their own organic matter from inorganic nutrients. Heterotrophs (other-feeders): Include humans and other animals that cannot make organic molecules from inorganic ones. Autotrophs are producers because ecosystems depend upon them for food. Heterotrophs are consumers because they eat plants or other animals. Laua Coronado Chap 6 Bio 10

Figure 6.1 Figure 6.1 Producer and consumer Laua Coronado Chap 6 Bio 10 Figure 6.1

Chemical Cycling between Photosynthesis and Cellular Respiration The ingredients for photosynthesis are carbon dioxide and water. CO2 is obtained from the air by a plant’s leaves. H2O is obtained from the damp soil by a plant’s roots. Chloroplasts in the cells of leaves: Use light energy to rearrange the atoms of CO2 and H2O, which produces Sugars (such as glucose) Other organic molecules Oxygen Laua Coronado Chap 6 Bio 10

Cellular Respiration Plant and animal cells perform cellular respiration, a chemical process that: Primarily occurs in mitochondria Harvests energy stored in organic molecules Uses oxygen Generates ATP The waste products of cellular respiration are: CO2 and H2O Used in photosynthesis Laua Coronado Chap 6 Bio 10

Cellular Respiration Animals perform only cellular respiration. Plants perform: Photosynthesis and Cellular respiration Laua Coronado Chap 6 Bio 10

Figure 6.2 Sunlight energy enters ecosystem Photosynthesis C6H12O6 Glucose O2 Oxygen CO2 Carbon dioxide H2O Water Figure 6.2 Energy flow and chemical cycling in ecosystems Cellular respiration ATP drives cellular work Heat energy exits ecosystem Laua Coronado Chap 6 Bio 10 Figure 6.2

CELLULAR RESPIRATION: AEROBIC HARVEST OF FOOD ENERGY Cellular respiration is: The main way that chemical energy is harvested from food and converted to ATP An aerobic process—it requires oxygen Laua Coronado Chap 6 Bio 10

CELLULAR RESPIRATION: AEROBIC HARVEST OF FOOD ENERGY Cellular respiration and breathing are closely related. Cellular respiration requires a cell to exchange gases with its surroundings. Cells take in oxygen gas. Cells release waste carbon dioxide gas. Breathing exchanges these same gases between the blood and outside air. Laua Coronado Chap 6 Bio 10

Figure 6.3 O2 CO2 Breathing Lungs O2 CO2 Muscle cells Cellular Figure 6.3 How breathing is related to cellular respiration. Cellular respiration Laua Coronado Chap 6 Bio 10 Figure 6.3

Glucose loses electrons Oxygen gains electrons (and hydrogens) Oxidation Glucose loses electrons (and hydrogens) C6H12O6  6 O2 6 CO2  6 H2O Glucose Oxygen Carbon dioxide Water Figure 6.UN2 Redox reaction The Overall Equation for Cellular Respiration A common fuel molecule for cellular respiration is glucose. The overall equation for what happens to glucose during cellular respiration: Reduction Oxygen gains electrons (and hydrogens) Laua Coronado Chap 6 Bio 10 Figure 6.UN02

The Role of Oxygen in Cellular Respiration Cellular respiration can produce up to 38 ATP molecules for each glucose molecule consumed. During cellular respiration, hydrogen and its bonding electrons change partners. Hydrogen and its electrons go from sugar to oxygen, forming water. This hydrogen transfer is why oxygen is so vital to cellular respiration. Laua Coronado Chap 6 Bio 10

Redox Reactions Chemical reactions that transfer electrons from one substance to another are called: Oxidation-reduction reactions or Redox reactions for short The loss of electrons during a redox reaction is called oxidation. The acceptance of electrons during a redox reaction is called reduction. During cellular respiration glucose is oxidized while oxygen is reduced. Laua Coronado Chap 6 Bio 10

Citric Acid Cycle Electron Transport Glycolysis ATP ATP ATP Figure 6.UN3 Glycosis orientation diagram ATP ATP ATP Laua Coronado Chap 6 Bio 10 Figure 6.UN03

Why does electron transfer to oxygen release energy? When electrons move from glucose to oxygen, it is as though the electrons were falling. This “fall” of electrons releases energy during cellular respiration. Cellular respiration is: A controlled fall of electrons A stepwise cascade much like going down a staircase Laua Coronado Chap 6 Bio 10

1 H2 O2 2 Release of heat energy H2O Figure 6.4 A simple redox reaction H2O Laua Coronado Chap 6 Bio 10 Figure 6.4

NADH and Electron Transport Chains The path that electrons take on their way down from glucose to oxygen involves many steps. The first step is an electron acceptor called NAD+. The transfer of electrons from organic fuel to NAD+ reduces it to NADH. The rest of the path consists of an electron transport chain, which: Involves a series of redox reactions Ultimately leads to the production of large amounts of ATP Laua Coronado Chap 6 Bio 10

Electron transport chain Electrons from food e e Stepwise release of energy used to make NAD NADH ATP 2 H 2 e Electron transport chain Figure 6.5 The role of oxygen in harvesting food energy. 2 e 2 1 2 H O2 Hydrogen, electrons, and oxygen combine to produce water H2O Laua Coronado Chap 6 Bio 10 Figure 6.5

An Overview of Cellular Respiration Is an example of a metabolic pathway, which is a series of chemical reactions in cells All of the reactions involved in cellular respiration can be grouped into three main stages: Glycolysis The citric acid cycle Electron transport Laua Coronado Chap 6 Bio 10

Figure 6.6 Mitochondrion Cytoplasm Cytoplasm Animal cell Plant cell High-energy electrons carried by NADH High-energy electrons carried mainly by NADH Glycolysis Citric Acid Cycle 2 Pyruvic acid Electron Transport Glucose Figure 6.6 A road map for cellular respiration ATP ATP ATP Laua Coronado Chap 6 Bio 10 Figure 6.6

The Three Stages of Cellular Respiration Stage 1: Glycolysis A six-carbon glucose molecule is split in half to form two molecules of pyruvic acid. These two molecules then donate high energy electrons to NAD+, forming NADH. Three steps Uses two ATP molecules per glucose to split the six-carbon glucose Makes four additional ATP directly when enzymes transfer phosphate groups from fuel molecules to ADP Produces a net of two molecules of ATP per glucose molecule. Laua Coronado Chap 6 Bio 10

Energy investment phase INPUT OUTPUT 2 ATP 2 ADP Glucose Key Figure 6.7 Glycolysis (Step 1) Carbon atom Phosphate group High-energy electron Energy investment phase Laua Coronado Chap 6 Bio 10 Figure 6.7-1

Energy investment phase INPUT OUTPUT NADH NAD 2 ATP 2 ADP Glucose Key NAD Figure 6.7 Glycolysis (Step 2) Carbon atom NADH Phosphate group High-energy electron Energy investment phase Energy harvest phase Laua Coronado Chap 6 Bio 10 Figure 6.7-2

Energy investment phase INPUT OUTPUT NADH 2 ATP NAD 2 ADP 2 ATP 2 ADP 2 Pyruvic acid Glucose 2 ADP NAD 2 ATP Key Figure 6.7 Glycolysis (Step 3) Carbon atom NADH Phosphate group High-energy electron Energy investment phase Energy harvest phase Laua Coronado Chap 6 Bio 10 Figure 6.7-3

Enzyme P ADP ATP P P Figure 6.8 Figure 6.8 ATP synthesis by direct phosphate transfer P P Laua Coronado Chap 6 Bio 10 Figure 6.8

Stage 2: The Citric Acid Cycle Completes the breakdown of sugar. In the citric acid cycle, pyruvic acid from glycolysis is first “prepped.” The citric acid cycle: Extracts the energy of sugar by breaking the acetic acid molecules all the way down to CO2 Uses some of this energy to make ATP Forms NADH and FADH2 Laua Coronado Chap 6 Bio 10

Figure 6.9 INPUT OUTPUT Oxidation of the fuel generates NADH (from glycolysis) (to citric acid cycle) NAD NADH CoA Pyruvic acid loses a carbon as CO2 Acetic acid Acetic acid attaches to coenzyme A Acetyl CoA Pyruvic acid Figure 6.9 The link between glycolysis and the citric acid cycle: the conversion of pyruvic acid to acetyl coA. CO2 Coenzyme A Laua Coronado Chap 6 Bio 10 Figure 6.9

INPUT OUTPUT ATP Citric Acid Cycle Citric acid Acetic acid 2 CO2 ADP  P ATP Citric Acid Cycle 3 NAD 3 NADH Figure 6.10 The citric acid cycle FAD FADH2 Acceptor molecule Laua Coronado Chap 6 Bio 10 Figure 6.10

Stage 3: Electron Transport Releases the energy your cells need to make the most of their ATP. The molecules of the electron transport chain are built into the inner membranes of mitochondria. The chain functions as a chemical machine that uses energy released by the “fall” of electrons to pump hydrogen ions across the inner mitochondrial membrane. These ions store potential energy. Laua Coronado Chap 6 Bio 10

Stage 3: Electron Transport When the hydrogen ions flow back through the membrane, they release energy. The hydrogen ions flow through ATP synthase. ATP synthase: Takes the energy from this flow Synthesizes ATP Laua Coronado Chap 6 Bio 10

Electron transport chain Space between membranes H H H H H H H H Electron carrier H H H H H Protein complex Inner mitochondrial membrane FADH2 FAD Figure 6.11 How electron transport drives ATP synthase machines Electron flow H 1 O2  2 H H2O 2 NADH NAD ADP  P ATP H H H H H Matrix Electron transport chain ATP synthase Laua Coronado Chap 6 Bio 10 Figure 6.11

ETC Inhibitor Cyanide is a deadly poison that: Binds to one of the protein complexes in the electron transport chain Prevents the passage of electrons to oxygen Stops the production of ATP Laua Coronado Chap 6 Bio 10

The Versatility of Cellular Respiration In addition to glucose, cellular respiration can “burn”: Diverse types of carbohydrates Fats Proteins Laua Coronado Chap 6 Bio 10

Food Polysaccharides Fats Proteins Sugars Glycerol Fatty acids Amino acids Figure 6.12 Energy from food Citric Acid Cycle Acetyl CoA Glycolysis Electron Transport ATP Laua Coronado Chap 6 Bio 10 Figure 6.12

Figure 6.13 Cytoplasm Mitochondrion 6 NADH 2 NADH 2 NADH 2 FADH2 Glycolysis 2 Acetyl CoA 2 Pyruvic acid Citric Acid Cycle Electron Transport Glucose Maximum per glucose: Figure 6.13 A summary of ATP yield during cellular respiration Cellular respiration can generate up to 38 molecules of ATP per molecule of glucose. 2 ATP 2 ATP About 34 ATP About 38 ATP by direct synthesis by direct synthesis by ATP synthase Laua Coronado Chap 6 Bio 10 Figure 6.13

FERMENTATION: ANAEROBIC HARVEST OF FOOD ENERGY Some of your cells can actually work for short periods without oxygen. Fermentation is the anaerobic (without oxygen) harvest of food energy. After functioning anaerobically for about 15 seconds: Muscle cells will begin to generate ATP by the process of fermentation Fermentation relies on glycolysis to produce ATP. Laua Coronado Chap 6 Bio 10

Laua Coronado Chap 6 Bio 10

FERMENTATION: ANAEROBIC HARVEST OF FOOD ENERGY Glycolysis: Does not require oxygen Produces two ATP molecules for each glucose broken down to pyruvic acid Pyruvic acid, produced by glycolysis, is Reduced by NADH, producing NAD+, which keeps glycolysis going. In human muscle cells, lactic acid is a by-product. Laua Coronado Chap 6 Bio 10

Figure 6.14 INPUT OUTPUT 2 ADP 2 ATP  2 P Glycolysis 2 NAD 2 NAD 2 NADH 2 NADH 2 Pyruvic acid  2 H Glucose 2 Lactic acid Figure 6.14 Fermentation: Producing lactic acid Laua Coronado Chap 6 Bio 10 Figure 6.14

The Process of Science: Does Lactic Acid Buildup Cause Muscle Burn? Observation: Muscles produce lactic acid under anaerobic conditions. Question: Does the buildup of lactic acid cause muscle fatigue? Hypothesis: The buildup of lactic acid would cause muscle activity to stop. Experiment: Tested frog muscles under conditions when lactic acid could and could not diffuse away. Laua Coronado Chap 6 Bio 10

diffusion of lactic acid; diffusion of lactic acid Battery Battery Force measured Force measured Frog muscle stimulated by electric current Figure 6.15 A.V. Hill's apparatus for measuring muscle fatigue Solution allows diffusion of lactic acid; muscle can work for twice as long Solution prevents diffusion of lactic acid Laua Coronado Chap 6 Bio 10 Figure 6.15

The Process of Science: Does Lactic Acid Buildup Cause Muscle Burn? Results: When lactic acid could diffuse away, performance improved greatly. Conclusion: Lactic acid accumulation is the primary cause of failure in muscle tissue. However, recent evidence suggests that the role of lactic acid in muscle function remains unclear. Laua Coronado Chap 6 Bio 10

Fermentation in Microorganisms Fermentation alone is able to sustain many types of microorganisms. The lactic acid produced by microbes using fermentation is used to produce: Cheese, sour cream, and yogurt dairy products Soy sauce, pickles, olives Sausage meat products Laua Coronado Chap 6 Bio 10

Fermentation in Microorganisms Yeast are a type of microscopic fungus that: Use a different type of fermentation Produce CO2 and ethyl alcohol instead of lactic acid This type of fermentation, called alcoholic fermentation, is used to produce: Beer Wine Breads Laua Coronado Chap 6 Bio 10

INPUT OUTPUT 2 ADP 2 ATP  2 P 2 CO2 released Glycolysis 2 NAD 2 NAD 2 NADH 2 NADH 2 Pyruvic acid  2 H Glucose 2 Ethyl alcohol Figure 6.16a Fermentation: Producing ethyl alcohol Laua Coronado Chap 6 Bio 10 Figure 6.16a

Evolution Connection: Life before and after Oxygen Glycolysis could be used by ancient bacteria to make ATP when little oxygen was available, and before organelles evolved. Today, glycolysis: Occurs in almost all organisms Is a metabolic heirloom of the first stage in the breakdown of organic molecules Laua Coronado Chap 6 Bio 10

Figure 6.17 Earth’s atmosphere O2 present in 2.1 Earth’s atmosphere O2 present in 2.1 First eukaryotic organisms 2.2 Atmospheric oxygen reaches 10% of modern levels 2.7 Atmospheric oxygen first appears Billions of years ago 3.5 Oldest prokaryotic fossils 4.5 Origin of Earth Figure 6.17 A time line of oxygen and life on Earth Laua Coronado Chap 6 Bio 10 Figure 6.17

C6H12O6 Sunlight O2 Cellular respiration CO2 H2O Heat C6H12O6 Sunlight O2 ATP Cellular respiration Photosynthesis Figure 6.UN6 Summary: Chemical cycling CO2 H2O Laua Coronado Chap 6 Bio 10 Figure 6.UN06

C6H12O6  6 O2 6 CO2  6 H2O  Approx. 38 ATP Figure 6.UN7 Summary: Overall equation for cellular respiration Laua Coronado Chap 6 Bio 10 Figure 6.UN07

Glucose loses electrons (and hydrogens) Oxidation Glucose loses electrons (and hydrogens) C6H12O6 CO2 Electrons (and hydrogens) ATP O2 H2O Figure 6.UN8 Summary: Role of oxygen in cellular respiration Reduction Oxygen gains electrons (and hydrogens) Laua Coronado Chap 6 Bio 10 Figure 6.UN08

Figure 6.UN09 Mitochondrion O2 6 NADH 2 NADH 2 NADH 2 FADH2 Glycolysis Acetyl CoA Citric Acid Cycle 2 Pyruvic acid Electron Transport Glucose 2 CO2 4 CO2 H2O Figure 6.UN9 Summary: Metabolic pathway of cellular respiration About 34 ATP 2 ATP by direct synthesis by direct synthesis 2 ATP by ATP synthase About 38 ATP Laua Coronado Chap 6 Bio 10 Figure 6.UN09