Cellular Respiration: Harvesting Chemical Energy

Bacteria are used to produce yogurt, sour cream, pepperoni, and cheese Both carbon monoxide and cyanide kill by disrupting cellular respiration

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

BIOLOGY AND SOCIETY: 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

Aerobic metabolism Anaerobic 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

Producers and Consumers Photosynthesis Light energy from the sun powers a chemical process that makes organic molecules This process occurs in the leaves of terrestrial plants

Autotrophs Heterotrophs “Self-feeders” Plants and other organisms that make all their own organic matter from inorganic nutrients Heterotrophs “Other-feeders” Humans and other animals that cannot make organic molecules from inorganic ones

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 Figure 6.2

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

Both plants and animals perform cellular respiration Cellular respiration is a chemical process that harvests energy from organic molecules Cellular respiration occurs in mitochondria The waste products of cellular respiration, CO2 and H2O, are used in photosynthesis

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

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

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 Unnumbered Figure 6.1

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 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

[Glucose loses electrons (and hydrogens)] Oxidation [Glucose loses electrons (and hydrogens)] Glucose Oxygen Carbon dioxide Water Reduction [Oxygen gains electrons (and hydrogens)] Unnumbered Figure 6.2

RS IS NECESSARY IN ALL LIVING CELLS. PLANTS ARE WELL KNOWN FOR PS, BUT THEY MUST ALSO REPIRE IN ORDER TO SURVIVE. PS - OCCURS ONLY IN PLANT CELLS CONTAINING CHLOROPHYLL DURING THE DAYLIGHT HOURS. RS - OCCURS IN ALL OF A PLANT’S LIVING CELLS 24 -7.

PLANTS NEED ENERGY TO PERFORM MANY ESSENTIAL FUNCTIONS OF LIFE: WHY IS RS NECESSARY? PLANTS NEED ENERGY TO PERFORM MANY ESSENTIAL FUNCTIONS OF LIFE: GROWTH, REPAIR, NUTRIENT MOVEMENT, REPRODUCTION, & NUTRIENT TRANSPORT.

The *Metabolic Pathway of Cellular Respiration Cellular respiration is an example of a metabolic pathway A series of chemical reactions in cells –building or degradation process All of the reactions involved in cellular respiration can be grouped into three main stages Glycolysis The Krebs cycle Electron transport * WHAT IS METABOLISM?

A Road Map for Cellular Respiration Cytosol Mitochondrion High-energy electrons carried by NADH High-energy electrons carried mainly by NADH Glycolysis 2 Pyruvic acid Krebs Cycle Electron Transport Glucose Figure 6.7

Glycolysis

Evolutionarily more advanced Cellular Respiration Evolutionarily more advanced Requires oxygen provided from photosynthesis Occurs as a second step AFTER glycolysis Much more efficient - more ATPs produced per molecule of glucose GLYCOLYSIS occurs alone or can be followed by CELLULAR REPIRATION, but cellular respiration cannot occur unless glycolysis happens first!

Glycolysis Occurs in the cytoplasm Anaerobic, not really a part of respiration Glucose molecule  2 pyruvic acid molecules 2 ATP used up, 4 ATP formed (net gain 2 ATP) 2 NADH formed Pyruvic acid and NADH enter mitochondria

In animal cells this byproduct is LACTIC ACID. What happens next??? If glycolysis ONLY occurs (no oxygen available), then pyruvate rapidly breaks down into byproducts: In animal cells this byproduct is LACTIC ACID. This is known as lactic acid fermentation. In plant cells this byproduct is ETHANOL and CO2 This is known as alcoholic fermentation. If oxygen IS available, then cellular respiration can occur.

Preparation for cellular respiration NADH and pyruvic acid enter the mitochondria (Coenzyme A) pyruvic acid (3 carbons)  acetyl CoA (2 carbons) + CO2 ©©©  ©© + © Coenzyme A is required for this step! And you have to have oxygen in this step too! 1 NADH is formed for every pyruvate conversion.

Krebs Cycle

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

In the Krebs cycle, pyruvic acid from glycolysis is first “prepped” into a usable form, Acetyl-CoA 2 1 Acetic acid 3 Pyruvic acid Acetyl-CoA (acetyl-coenzyme A) CO2 Coenzyme A Figure 6.10

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

Krebs Cycle Input Output Acetic acid 2 CO2 ADP 3 NAD FAD 2 1 3 4 5 6 Figure 6.11

Electron Transport

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

Electron transport chain Protein complex Electron carrier Inner mitochondrial membrane Electron flow Electron transport chain ATP synthase Figure 6.12

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

Food Polysaccharides Fats Proteins Sugars Glycerol Fatty acids Amino acids Amino groups Acetyl- CoA Krebs Cycle Glycolysis Electron Transport Figure 6.13

Adding Up the ATP from Cellular Respiration 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 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

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

(a) Lactic acid fermentation 2 ADP+ 2 Glycolysis 2 NAD 2 NAD Glucose 2 Pyruvic acid + 2 H 2 Lactic acid (a) Lactic acid fermentation Figure 6.15a

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

(b) Alcoholic fermentation 2 ADP+ 2 2 CO2 released 2 ATP Glycolysis 2 NAD 2 NAD Glucose 2 Ethyl alcohol 2 Pyruvic acid + 2 H (b) Alcoholic fermentation Figure 6.15b

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

EVOLUTION CONNECTION: LIFE ON AN ANAEROBIC EARTH Ancient bacteria probably used glycolysis to make ATP long before oxygen was present in Earth’s atmosphere Glycolysis is a metabolic heirloom from the earliest cells that continues to function today in the harvest of food energy

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