Cellular Respiration: Harvesting Chemical Energy Chapter 9 Cellular Respiration: Harvesting Chemical Energy

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

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

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

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

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

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)

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

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

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

Chemical Cycling 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 rearrange the atoms of these ingredients to produce sugars (glucose) and other organic molecules Oxygen gas is a by-product of photosynthesis

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, CO2 and H2O, are used in photosynthesis

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

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

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

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

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

Breathing Lungs Muscle cells Cellular Respiration

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

Redox Reactions Chemical reactions that transfer electrons from one substance to another are called oxidation-reduction reactions REDOX short for oxidation-reduction reactions

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: e- donor Oxidizing agent: e- acceptor

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

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

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

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

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

Glycolysis Stage One

Stage 1: Glycolysis 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

Glycolysis METABOLIC PATHWAY 2 Pyruvic acid Glucose

Glycolysis CoA Acetic acid Pyruvic Acetyl-CoA acid (acetyl-coenzyme A) 31 31

Glycolysis Summary The Krebs cycle extracts the energy of sugar by breaking the acetic acid molecules all the way down to CO2 The cycle uses some of this energy to make ATP The cycle also forms NADH and FADH2 ( 2 energy carrier molecules) 32 32

Krebs Cycle Stage Two

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-CoA

ACETYL Co-A ADP Krebs Cycle Input Output Acetic acid 2 CO2 3 NAD FAD 1 Acetic acid 2 CO2 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

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

Electron transport chain Cytochromes carry electron carrier molecules (NADH & FADH2) 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)

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

Food Polysaccharides Fats Proteins Sugars Glycerol Fatty acids Amino acids Amino groups Acetyl- CoA Krebs Cycle Glycolysis Electron Transport

Adding Up the ATP Cytosol Mitochondrion Glycolysis 2 Acetyl- CoA 2 Pyruvic acid Krebs Cycle Electron Transport Glucose Maximum per glucose: by direct synthesis by ATP synthase by direct synthesis Figure 6.14

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

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

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

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

Fermentation in Microorganisms Various types of microorganisms perform fermentation Yeast cells carry out a slightly different type of fermentation pathway This pathway produces CO2 and ethyl alcohol

Alcoholic fermentation 2 ADP+ 2 2 CO2 released 2 ATP Glycolysis 2 NAD 2 NAD Glucose 2 Ethyl alcohol 2 Pyruvic acid + 2 H Alcoholic fermentation

The food industry uses yeast to produce various food products

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

Review: Cellular Respiration Glycolysis: 2 ATP (substrate-level phosphorylation) Kreb’s Cycle: Electron transport & oxidative phosphorylation: 2 NADH (glycolysis) = 6ATP 2 NADH (acetyl CoA) = 6ATP 6 NADH (Kreb’s) = 18 ATP 2 FADH2 (Kreb’s) = 4 ATP 38 TOTAL ATP/glucose