Cellular Respiration Process whereby cells breakdown glucose and other food molecules to release energy.

The efficiency of cellular respiration Provides a high % of energy in a controlled manner Energy released from glucose banked in ATP Energy released from glucose (as heat and light) Gasoline energy converted to movement 100% About 40% 25% Burning glucose in an experiment “Burning” glucose in cellular respiration Burning gasoline in an auto engine Figure 6.2B

BIOLOGY AND SOCIETY: FEELING THE “BURN” When you exercise Muscles need energy in order to perform work Enzymes in muscle cells help a cell use glucose and oxygen to produce ATP

Aerobic metabolism When enough oxygen reaches cells to support energy needs Anaerobic metabolism When the demand for oxygen outstrips the body’s ability to deliver it

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 Figure 6.1

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

Sunlight energy Ecosystem Photosynthesis (in chloroplasts) Glucose Carbon dioxide Oxygen Water Cellular respiration (in mitochondria) for cellular work Heat energy Figure 6.3

Energy and Food A large amount of energy is stored within the chemical bonds of food. Burning 1g glucose (C6H12O6) releases 3811 C of heat. Calorie - amount of energy needed to raise the temperature of 1g of H2O 1ºC. Cells do not burn glucose , but gradually break it down to release the energy.

CELLULAR RESPIRATION: AEROBIC HARVEST OF FOOD ENERGY The main way that chemical energy is harvested from food and converted to ATP This is an aerobic process—it requires oxygen

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 Figure 6.4

Cellular Respiration Three Steps Glycolysis Krebs Cycle Electron Transport Chain

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 Cellular respiration can produce up to 38 ATP molecules for each glucose molecule consumed Unnumbered Figure 6.1

ATP the cell’s chemical energy ATP molecules are the key to energy coupling ATP molecules store energy during the process of cellular respiration ATP power nearly all forms of cellular work

The Role of ATP Cellular money Cells “earn” ATP in exergonic reactions Cells “spend” ATP in endergonic reactions adenine P P P ribose

Adenosine triphosphate Adenosine diphosphate (ADP) Energy Coupling Hydrolysis breaks a phosphate group bond from the ATP molecules releasing energy The exergonic reaction supplies energy for cellular work Adenine Phosphate groups Hydrolysis Energy Ribose Adenosine triphosphate Adenosine diphosphate (ADP) Figure 5.4A

Potential energy of molecules Phosphorylation How ATP powers cellular work Reactants Products Potential energy of molecules Protein Work Figure 5.4B

Dehydration synthesis The ATP cycle Hydrolysis Dehydration synthesis Energy from exergonic reactions Energy for endergonic reactions Figure 5.4C

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

Why does electron transfer to oxygen release energy? When electrons move from glucose to oxygen, it is as though they were falling This “fall” of electrons releases energy during cellular respiration Release of heat energy Figure 6.5

Cell with Mitochondria (red spots)

Mitochondria Site of Krebs cycle and Electron Transport Chain

An overview of cellular respiration High-energy electrons carried by NADH GLYCOLYSIS ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS KREBS CYCLE Glucose Pyruvic acid Cytoplasmic fluid Mitochondrion Figure 6.8

Stage 1: Glycolysis A molecule of glucose is split into two molecules of pyruvic acid

Glycolysis breaks a six-carbon glucose into two three-carbon molecules These molecules then donate high energy electrons to NAD+, forming NADH

Glycolysis makes some ATP directly when enzymes transfer phosphate groups from fuel molecules to ADP Figure 6.9

Cell with Mitochondria (red spots)

Mitochondria Site of Krebs cycle and Electron Transport Chain

An overview of cellular respiration High-energy electrons carried by NADH GLYCOLYSIS ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS KREBS CYCLE Glucose Pyruvic acid Cytoplasmic fluid Mitochondrion Figure 6.8

Stage 2: The Krebs Cycle The Krebs cycle completes the breakdown of sugar

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

II. Krebs Cycle Process whereby pyruvate is broken down into CO2 in a series of energy releasing reactions. Only occurs if O2 is present (aerobic respiration). Takes place within the mitochondria of the cell. Each pyruvate that goes through the cycle produces 1 ATP, 4 NADH, 1 FADH2 and 3 CO2 (2 X that amount for each glucose molecule).

An overview of cellular respiration High-energy electrons carried by NADH GLYCOLYSIS ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS KREBS CYCLE Glucose Pyruvic acid Cytoplasmic fluid Mitochondrion Figure 6.8

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 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 ions flow through ATP synthase ATP synthase takes the energy from this flow and synthesizes ATP

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

ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS Pathways of molecular breakdown Food, such as peanuts Polysaccharides Fats Proteins Sugars Glycerol Fatty acids Amino acids Amino groups Pyruvic acid ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS Glucose G3P Acetyl CoA KREBS CYCLE GLYCOLYSIS Figure 6.16

NADH and Electron Transport Chains The path that electrons take on their way down from glucose to oxygen involves many stops 1/2 (from food via NADH) Energy for synthesis of 2 H 2 e Electron transport chain 2 e 1/2 2 H Figure 6.6

The Metabolic Pathway of Cellular Respiration Cellular respiration is an example of a metabolic pathway A series of chemical reactions in cells All of the reactions involved in cellular respiration can be grouped into three main stages Glycolysis The Krebs cycle Electron transport

FERMENTATION: ANAEROBIC HARVEST OF FOOD ENERGY Some of your cells can actually work for short periods without oxygen For example, muscle cells can produce ATP under anaerobic conditions Fermentation 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

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

The food industry uses yeast to produce various food products Figure 6.16

SUMMARY OF KEY CONCEPTS Chemical Cycling Between Photosynthesis and Cellular Respiration Heat Sunlight Cellular respiration Photosynthesis Visual Summary 6.1

The Overall Equation for Cellular Respiration Oxidation: Glucose loses electrons (and hydrogens) Glucose Carbon dioxide Electrons (and hydrogens) Energy Reduction: Oxygen gains electrons (and hydrogens) Oxygen Visual Summary 6.2

The Metabolic Pathway of Cellular Respiration Glucose Oxygen Water Energy Visual Summary 6.3

How is a Marathoner Different from a Sprinter? Long-distance runners have many slow fibers in their muscles Slow fibers break down glucose for ATP production aerobically (using oxygen) These muscle cells can sustain repeated, long contractions

Sprinters have more fast muscle fibers Fast fibers make ATP without oxygen - - anaerobically They can contract quickly and supply energy for short bursts of intense activity

The dark meat is an example of slow fiber muscle Leg muscles support sustained activity The white meat consists of fast fibers Wing muscles allow for quick bursts of flight

ATP needed to drive biosynthesis Cells, tissues, organisms Biosynthesis of macromolecules from intermediates in cellular respiration ATP needed to drive biosynthesis GLUCOSE SYNTHESIS KREBS CYCLE Acetyl CoA Pyruvic acid G3P Glucose Amino groups Amino acids Fatty acids Glycerol Sugars Proteins Fats Polyscaccharides Cells, tissues, organisms Figure 6.17