Cellular Respiration: Harvesting Chemical Energy Chapter 8 Cellular Respiration: Harvesting Chemical Energy

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

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 4 4

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

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

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 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) 15 15

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)

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

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 36 36