Chapter 9 Cellular Respiration Harvesting Chemical Energy 1

Chapter 9 Cellular Respiration: Harvesting Chemical Energy 1

Respiration Facts: All the energy in all the food you eat can be traced back to sunlight If you exercise too hard, your muscles shut down from a lack of oxygen 2

FEELING THE “BURN” When you exercise: Muscles need energy in order to perform work Your cells use oxygen to release energy from the sugar glucose Both aerobic and anaerobic burning of glucose can take place in your cells 3

Aerobic & Anaerobic Metabolism Aerobic metabolism - When enough oxygen reaches cells to support energy needs - Maximum energy production Anaerobic metabolism – When the demand for oxygen outstrips the body’s ability to deliver it – Low energy production 4

Anaerobic Metabolism Without enough oxygen, muscle cells break down glucose to produce lactic acid Lactic acid is associated with the “burn” associated with heavy exercise If too much lactic acid builds up, your muscles give out 5

Physical Conditioning Allows your body to adapt to increased activity The body can increase its ability to deliver oxygen to muscles Long-distance runners wait until the final sprint to exceed their aerobic capacity 6

Why Photosynthesis? Only producers are capable of Photosynthesis Light energy from the sun powers this chemical process that makes organic molecules (sugars) This process occurs in the mesophyll cells of leaves of producers (plants & algae) 7

ENERGY FLOW IN THE BIOSPHERE Energy stored in food can be traced back to the sun Fuel molecules in food store solar energy in chemical bonds Animals depend on plants to convert solar energy to chemical energy This chemical energy is in the form of sugars and other organic molecules 8

Autotrophs & Heterotrophs Autotrophs - Plants and other organisms that make all their own organic matter from inorganic nutrients Heterotrophs - Humans and other animals that cannot make organic molecules from inorganic ones 9

The Cycle of Energy Producers Biologists refer to plants and other autotrophs as the producers in an ecosystem Consumers Heterotrophs are consumers, because they eat plants or other animals 10

Chemical Cycling The ingredients for photosynthesis are carbon dioxide and water CO 2 is obtained from the air by a plant’s leaves H 2 O is obtained from the damp soil by a plant’s roots Chloroplasts rearrange the atoms of these ingredients to produce sugars (glucose) and other organic molecules Oxygen gas is a by-product of photosynthesis 11

Chemical Cycling Both plants and animals perform cellular respiration Cellular respiration is a chemical process that harvests energy from organic molecules and occurs in the mitochondria The waste products of cellular respiration, CO 2 and H 2 O, are used in photosynthesis 12

Sunlight supplies the energy! Sunlight energy Ecosystem Raw materials for cellular respiration Bonds of Glucose, made in chloroplasts, contain the stored energy Photosynthesis (in chloroplasts) Glucose Oxygen Carbon dioxide Water Cellular respiration (in mitochondria) Raw materials for photosynthesis Glucose broken down to release energy for cellular work Cellular energy Heat energy 13

AEROBIC HARVEST OF FOOD ENERGY Cellular respiration is the main way that chemical energy is harvested from food and converted to ATP for cellular work Cellular respiration is an aerobic process requiring oxygen 14

The Versatility of Cellular Respiration Cellular respiration can “burn” other kinds of molecules besides glucose: Diverse types of carbohydrates Fats Proteins 15

The Overall Equation for Cellular Respiration A common fuel molecule for cellular respiration is glucose This is the overall equation for what happens to glucose during cellular respiration Glucose Oxygen Carbon dioxide Water Energy 16

But Remember … Cellular Respiration is a metabolic pathway, not a single reaction Many chemical reactions, both aerobic and anaerobic, are involved in the process of cellular respiration Lots of enzymes are required for the process to occur 17

The Relationship Between Cellular Respiration and Breathing Cellular respiration and breathing are closely related Cellular respiration requires a cell to exchange gases with its surroundings Breathing exchanges these gases between the blood and outside air 18

Breathing Lungs Muscle cells Cellular Respiration 19

The Role of Oxygen in Cellular Respiration During cellular respiration, hydrogen and its bonding electrons change partners Hydrogen and its electrons go from sugar to oxygen, forming water 20

Redox Reactions Chemical reactions that transfer electrons from one substance to another are called oxidationreduction reactions REDOX short for oxidationreduction reactions 21

Redox Reactions The loss of electrons during a redox reaction is called oxidation The acceptance of electrons during a redox reaction is called reduction Reducing agent: Oxidizing agent: e- donor e- acceptor 22

REDOX in Cellular Respiration Glucose loses electrons (and hydrogens) Oxidation Glucose Oxygen Carbon dioxide Water Reduction Oxygen gains electrons (and hydrogens)] 23

Comparison Respiration Occurs in all organisms Photosynthesis Occurs in only chlorophyll containing organisms Breaks down glucose Stores light energy as chemical energy in the bonds of glucose Releases carbon Produces glucose and dioxide, water, & ATP oxygen Exergonic Reaction Endergonic reaction 24

The Metabolic Pathway of Cellular Respiration Cellular respiration is an example of a metabolic pathway A series of chemical reactions in cells either building or breaking down molecules 25

The Metabolic Pathway of Cellular Respiration All of the reactions involved in cellular respiration can be grouped into three main stages Glycolysis – occurs in cytoplasm The Krebs cycle – occurs in matrix of mitochondria Electron transport – occurs across the mitochondrial membrane 26

A Road Map for Cellular Respiration Mitochondrion Cytosol High-energy electrons carried mainly by NADH High-energy electrons carried by NADH Glycolysis Glucose 2 Pyruvic acid Krebs Cycle Electron Transport 27

Glycolysis Stage One 28

Stage 1: Glycolysis takes place in the cytoplasm Oxygen NOT required Process breaks a six-carbon glucose into two, three-carbon molecules A molecule of glucose is split into two molecules of pyruvic acid These molecules then donate high energy electrons to NAD+, forming NADH 29

Glycolysis METABOLIC PATHWAY 2 Pyruvic acid Glucose 30

Glycolysis Co. A Acetic acid Pyruvic acid CO 2 Coenzyme A Acetyl-Co. A (acetyl-coenzyme A) 31

Glycolysis Summary The Krebs cycle extracts the energy of sugar by breaking the acetic acid molecules all the way down to CO 2 The cycle uses some of this energy to make ATP The cycle also forms NADH and FADH 2 ( 2 energy carrier molecules) 32

Krebs Cycle Stage Two 33

Stage 2: The Krebs Cycle The Krebs cycle completes the breakdown of sugar It occurs inside the mitochondria In the Krebs cycle, pyruvic acid from glycolysis is first “prepped” into a usable form by combining it with enzyme Co-A to make Acetyl-Co. A 34

ACETYL Co-A Input Output 2 1 Acetic acid 2 CO 2 3 ADP Krebs Cycle 3 NAD 4 FAD 5 6

Electron Transport Stage 3

Stage 3: Electron Transport Electron transport releases the energy your cells need to make the most of their ATP The molecules of electron transport chains are built into the inner membranes of mitochondria 37

Stage 3: Electron Transport 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 38

Electron transport chain Cytochromes carry electron carrier molecules (NADH & FADH 2) down to oxygen Chemiosmosis: energy coupling mechanism ATP synthase: produces ATP by using the H+ gradient (proton-motive force) pumped into the inner membrane space from the electron transport chain; this enzyme harnesses the flow of H+ back into the matrix to phosphorylate ADP to ATP (oxidative phosphorylation) 39

Protein complex Electron carrier Inner mitochondrial membrane Electron flow Electron transport chain ATP synthase 40

Food Polysaccharides Sugars Glycerol Fats Fatty acids Proteins Amino acids Amino groups Glycolysis Acetyl. Co. A Krebs Cycle Electron Transport 41

Adding Up the ATP Cytosol Mitochondrion Glycolysis Glucose 2 Pyruvic acid 2 Acetyl. Co. A Krebs Cycle Electron Transport Maximum per glucose: by direct synthesis by ATP synthase Figure 426. 14

FERMENTATION: ANAEROBIC HARVEST OF FOOD ENERGY Some of your cells can actually work for short periods without oxygen (anaerobic respiration) For example, muscle cells can produce ATP under anaerobic conditions Called Fermentation Involves The anaerobic harvest of food energy 43

Fermentation in Human Muscle Cells Human muscle cells can make ATP with and without oxygen They have enough ATP to support activities such as quick sprinting for about 5 seconds A secondary supply of energy (creatine phosphate) can keep muscle cells going for another 10 seconds To keep running, your muscles must generate ATP by the anaerobic process of fermentation 44

Glycolysis is the metabolic pathway that provides ATP during fermentation Pyruvic acid is reduced by NADH, producing NAD+, which keeps glycolysis going In human muscle cells, lactic acid is a by-product 45

2 ADP+ 2 Glycolysis 2 NAD Glucose 2 Pyruvic acid + 2 H 2 Lactic acid fermentation 46

Fermentation in Microorganisms Various types of microorganisms perform fermentation Yeast cells carry out a slightly different type of fermentation pathway This pathway produces CO 2 and ethyl alcohol

2 ADP+ 2 2 ATP 2 CO 2 released Glycolysis 2 NAD Glucose 2 Pyruvic acid + 2 H 2 Ethyl alcohol Alcoholic fermentation 48

The food industry uses yeast to produce various food products 49

Related metabolic processes Fermentation: alcohol~ pyruvate to ethanol lactic acid~ pyruvate to lactate Facultative anaerobes (yeast/bacteria) Beta-oxidation lipid catabolism 50

Review: Cellular Respiration Glycolysis: – 2 ATP (substrate-level phosphorylation) Kreb’s Cycle: – 2 ATP (substrate-level phosphorylation) Electron transport & oxidative phosphorylation: – 2 NADH (glycolysis) = 6 ATP – 2 NADH (acetyl Co. A) = 6 ATP – 6 NADH (Kreb’s) = 18 ATP – 2 FADH 2 (Kreb’s) = 4 ATP 38 TOTAL ATP/glucose 51

52