Cellular Respiration: Obtaining Energy from Food

Chapter 6 Cellular Respiration: Obtaining Energy from Food PowerPoint Lectures for Campbell Essential Biology, Fourth Edition Eric Simon, Jane Reece, and Jean Dickey Campbell Essential Biology with Physiology, Third Edition Eric Simon, Jane Reece, and Jean Dickey Lectures by Chris C. Romero, updated by Edward J. Zalisko 0

Biology and Society: Marathoners versus 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.

Figure 6.00

The muscles that move our legs contain two main types of muscle fibers: Slow twitch Fast twitch

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.

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.

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.

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

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

Animals perform only cellular respiration. Plants perform: Photosynthesis and Cellular respiration

Sunlight energy enters ecosystem C6H12O6 Photosynthesis CO2 Glucose Carbon dioxide O2 H2O Oxygen Water Cellular respiration ATP drives cellular work Heat energy exits ecosystem 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

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.

O2 CO2 Breathing Lungs CO2 O2 Cellular respiration Muscle cells Figure 6.3

O2 CO2 Breathing Lungs CO2 O2 Cellular respiration Muscle cells Figure 6.3a

Figure 6.3b

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:

Oxidation Glucose loses electrons (and hydrogens) C6H12O6 Glucose + 6 O2 Oxygen 6 CO2 Carbon dioxide + 6 H2O Water Reduction Oxygen gains electrons (and hydrogens) 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.

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.

Glycolysis Citric Acid Cycle ATP ATP Electron Transport ATP 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.

1 2 O2 H2 Release of heat energy H2O Figure 6.4

Cellular respiration is: A controlled fall of electrons A stepwise cascade much like going down a staircase

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

e e Electrons from food e e NADH + NAD Stepwise release of energy used to make ATP 2 H+ 2 e El ec tr on tr an sp or t ch a in 2 e 1 2 2 H+ Hydrogen, electrons, and oxygen combine to produce water O2 H2O Figure 6.5

An Overview of Cellular Respiration 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

Mitochondrion Cytoplasm Cytoplasm Animal cell Plant cell Cytoplasm Mitochondrion High-energy electrons carried by NADH Glycolysis Glucose 2 Pyruvic acid ATP High-energy electrons carried mainly by NADH Citric Acid Cycle Electron Transport ATP ATP Figure 6.6

Cytoplasm Mitochondrion High-energy electrons carried by NADH Glycolysis Glucose 2 Pyruvic acid ATP High-energy electrons carried mainly by NADH Citric Acid Cycle Electron Transport ATP ATP Figure 6.6a

The Three Stages of Cellular Respiration With the big-picture view of cellular respiration in mind, let s examine the process in more detail.

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.

INPUT OUTPUT 2 ATP 2 ADP Glucose Key Carbon atom Phosphate group High-energy electron Energy investment phase Figure 6.7-1

INPUT OUTPUT NADH NAD+ 2 ATP 2 ADP Glucose Key Carbon atom Phosphate group High-energy electron NAD+ NADH Energy investment phase Energy harvest phase Figure 6.7-2

INPUT OUTPUT NADH NAD+ 2 ATP 2 ADP 2 ATP 2 ADP 2 Pyruvic acid Glucose Key Carbon atom Phosphate group High-energy electron 2 ADP + NAD 2 ATP NADH Energy investment phase Energy harvest phase Figure 6.7-3

Glycolysis: 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 Thus, glycolysis produces a net of two molecules of ATP per glucose molecule.

Enzyme P P ADP ATP P Figure 6.8

Stage 2: The Citric Acid Cycle The citric acid cycle completes the breakdown of sugar.

In the citric acid cycle, pyruvic acid from glycolysis is first prepped.

INPUT Oxidation of the fuel generates NADH (from glycolysis) Pyruvic acid CoA Acetic acid CO2 (to citric acid cycle) NADH NAD+ Pyruvic acid loses a carbon as CO2 OUTPUT Coenzyme A Acetic acid attaches to coenzyme A Acetyl CoA Figure 6.9

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 Blast Animation: Harvesting Energy: Krebs Cycle

INPUT OUTPUT Citric acid Acetic acid ADP + P 3 2 CO2 ATP Citric Acid Cycle NAD+ 3 FAD NADH FADH2 Acceptor molecule Figure 6.10

Stage 3: Electron Transport 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.

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

Space between membranes H+ H+ Electron carrier H+ Protein complex Inner mitochondrial membrane FADH2 Electron flow H+ H+ H+ + H+ H H+ FAD NAD+ H+ H+ H+ H+ 1 2 NADH H+ Matrix H+ H+ O2 + 2 H+ H2O ATP ADP + P H+ Electron transport chain H+ H+ ATP synthase Figure 6.11

Space between membranes H+ Electron carrier Protein complex Inner mitochondrial membrane Electron flow H+ H+ H+ + H H FADH2 FAD + H+ H+ H+ + H NAD+ H+ H+ H+ H+ 1 2 NADH H+ Matrix H+ O2 + 2 H+ H2O ATP ADP + P H+ Electron transport chain H+ H+ ATP synthase Figure 6.11a

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

The Versatility of Cellular Respiration In addition to glucose, cellular respiration can burn : Diverse types of carbohydrates Fats Proteins

Food Polysaccharides Sugars Fats Glycerol Fatty acids Glycolysis Acetyl CoA Proteins Amino acids Citric Acid Cycle Electron Transport ATP Figure 6.12

Adding Up the ATP from Cellular Respiration Cellular respiration can generate up to 38 molecules of ATP per molecule of glucose.

Cytoplasm Mitochondrion 2 NADH Glycolysis 2 Pyruvic acid 2 NADH 2 Acetyl CoA 6 NADH 2 FADH2 Citric Acid Cycle Electron Transport 2 ATP 2 ATP About 34 ATP by direct synthesis by direct synthesis Glucose Maximum per glucose: About 38 ATP by ATP synthase 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.

Fermentation in Human Muscle Cells 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.

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. Animation: Fermentation Overview

INPUT 2 ADP +2 P OUTPUT 2 ATP Glycolysis 2 NAD+ 2 NADH Glucose 2 NADH 2 NAD+ 2 Pyruvic + 2 H+ acid 2 Lactic acid Figure 6.14

INPUT 2 ADP +2 P OUTPUT 2 ATP Glycolysis 2 NAD+ 2 NADH Glucose 2 NADH 2 NAD+ 2 Pyruvic +2 + acid H 2 Lactic acid Figure 6.14a

Figure 6.14b

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.

Battery Battery Force measured Force measured Frog muscle stimulated by electric current Solution prevents diffusion of lactic acid Solution allows diffusion of lactic acid; muscle can work for twice as long Figure 6.15

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.

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

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

INPUT 2 ADP +2 P OUTPUT 2 ATP Glycolysis 2 NAD+ 2 NADH Glucose 2 CO2 released 2 NADH 2 NAD+ 2 Pyruvic +2 + acid H 2 Ethyl alcohol Bread with air bubbles produced by fermenting yeast Beer fermentation Figure 6.16

INPUT 2 ADP +2 P OUTPUT 2 ATP 2 CO2 released Glycolysis 2 NAD+ 2 NADH Glucose 2 NADH 2 NAD+ 2 Pyruvic + 2 H+ 2 Ethyl alcohol acid Figure 6.16a

Figure 6.16b

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

2.1 2.2 2.7 O2 present in Earth s atmosphere Billions of years ago 0 First eukaryotic organisms Atmospheric oxygen reaches 10% of modern levels Atmospheric oxygen first appears 3.5 Oldest prokaryotic fossils 4.5 Origin of Earth Figure 6.17

2.1 2.2 2.7 O2 present in Earth s atmosphere Billions of years ago 0 First eukaryotic organisms Atmospheric oxygen reaches 10% of modern levels Atmospheric oxygen first appears 3.5 Oldest prokaryotic fossils 4.5 Origin of Earth Figure 6.17a

Figure 6.17b

C6H12O6 Glucose +6 O2 Oxygen 6 CO2 Carbon dioxide +6 H2O Water + ATP Energy Figure 6.UN01

Oxidation Glucose loses electrons (and hydrogens) C6H12O6 Glucose + 6 O2 Oxygen 6 CO2 Carbon dioxide + 6 H2O Water Reduction Oxygen gains electrons (and hydrogens) Figure 6.UN02

Glycolysis Citric Acid Cycle ATP ATP Electron Transport ATP Figure 6.UN03

Glycolysis Citric Acid Cycle ATP ATP Electron Transport ATP Figure 6.UN04

Glycolysis Citric Acid Cycle ATP ATP Electron Transport ATP Figure 6.UN05

Heat C6H12O6 Sunlight O2 ATP Cellular respiration Photosynthesis CO2 H2 O Figure 6.UN06

C6H12O6 +6 O2 6 CO2 +6 H2O + Approx. 38 ATP Figure 6.UN07

Oxidation Glucose loses electrons (and hydrogens) CO2 C6H12O6 Electrons (and hydrogens) O2 Reduction Oxygen gains electrons (and hydrogens) ATP H 2O Figure 6.UN08

Mitochondrion O2 2 NADH 2 Glycolysis Glucose 2 Pyruvic acid NADH 6 NADH 2 FADH2 2 Acetyl CoA Citric Acid Cycle 4 CO2 2 CO2 2 ATP by direct synthesis Electron Transport by direct synthesis 2 ATP H2O About 34 ATP by ATP synthase About 38 ATP Figure 6.UN09