Cellular Respiration Chapter 7 pgs Food to energy

Autotrophs –“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

Harvesting Chemical Energy From photosynthesis we get carbohydrates (glucose) Cellular respiration: Breaking down the carbohydrates (glucose) to make ATP and NADH –NADH is an electron carrier Starts with glycolysis –Glyco = sugar –Lysis = breaking –Breaking down sugars

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

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

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 Relationship Between Cellular Respiration and Breathing

A common fuel molecule for cellular respiration is glucose –This is the overall equation for what happens to glucose during cellular respiration The Overall Equation for Cellular Respiration Unnumbered Figure 6.1 GlucoseOxygenCarbon dioxide WaterEnergy

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

Chemical reactions that transfer electrons from one substance to another are called oxidation-reduction reactions Redox 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 –G.E.R. L.E.O. –O.I.L. R.I.G.

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

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

What Carries the Electrons? NAD + (nicotinadenine dinucleotide) acts as the energy carrier NAD + (nicotinadenine dinucleotide) acts as the energy carrier NAD + is a coenzyme NAD + is a coenzyme It’s Reduced to NADH when it picks up two electrons and one hydrogen ion It’s Reduced to NADH when it picks up two electrons and one hydrogen ion

Glycolysis 1 six carbon glucose broken down into 2 three carbon pyruvic acid molecules Happens out in the cytoplasm

Figure 6.8 Glucose 2 Pyruvic acid

What happens next depends on whether there is oxygen present or not.

What happens after Glycolysis? Chemicals can take one of two pathways –Anaerobic (no oxygen present) fermentation Makes no ATP, but keeps the cycles going –Aerobic respiration Makes a lot of ATP

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

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 Human Muscle Cells

Fermentation If there is no oxygen some cells can convert pyruvic acid into other compounds and get some more NAD + No ATP is made, but the NAD + can keep Glycolysis going to make a little ATP 2 kinds of fermentation: Lactic acid fermentation and Alcoholic Fermentation

Lactic Acid Fermentation Converting pyruvic acid to Lactic acid –A.K.A. milk acid Bacteria are used to do this to get cheese, yogurt, and sour cream Under heavy exercise you use up Oxygen faster than you can replace it –Lactic Acid builds up and the acidity causes fatigue, pain and cramps.

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

Alcoholic Fermentation Yeast convert pyruvic acid into ethyl alcohol They break a CO 2 off of pyruvic acid The 2 carbon sugar left behind forms ethyl alcohol Basis of wine and beer industry, and bread making

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

Efficiency of Glycolysis Compare the kilocalories of Glucose with the kilocalories in the ATP that is made. The 2 ATP molecules made during glycolysis receive only 2% of the energy in glucose –Where does the rest go? It’s still in pyruvic acid This small amount of energy is enough for bacteria, but more complex organisms need more of glucoses energy.

Objectives Define Cellular respiration Describe the major events in glycolysis Compare and contrast lactic acid fermentation and alcoholic fermentation Calculate the efficiency of glycolysis

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

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

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

Figure 6.11 Input Acetic acid ADP 3 NAD  FAD Krebs Cycle Output 2 CO

Electron Transport 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

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

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

Figure 6.13 Food Polysaccharides FatsProteins SugarsGlycerolFatty acidsAmino acids Amino groups Glycolysis Acetyl- CoA Krebs Cycle Electron Transport

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