How is a Marathoner Different from a Sprinter? Long-distance runners have many slow fibers in their muscles Slow fibers break down glucose aerobically (using oxygen) for ATP production These muscle cells can sustain repeated, long contractions and provide endurance The physique of long-distance runners is generally much more scrawny than that of sprinters Sprinters have more fast muscle fibers Fast fibers make ATP anaerobically, without oxygen They can contract quickly and supply energy for short bursts of intense activity
The dark meat of a cooked turkey 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 What would you expect the muscle color of Canada geese to be? Why? INTRODUCTION TO CELLULAR RESPIRATION Nearly all the cells in our body break down sugars to produce ATP Most cells of most organisms harvest energy aerobically, like slow muscle fibers (endurance) The aerobic harvesting of energy from sugar is called cellular respiration Cellular respiration yields CO 2, H 2 O, and a large amount of ATP
6.1 Breathing supplies oxygen to our cells and removes carbon dioxide Breathing and cellular respiration are closely related O 2 CO 2 Lungs BREATHING O 2 in, CO 2 out CO 2 Bloodstream O 2 Muscle cells carrying out CELLULAR RESPIRATION Sugar + O 2! ATP + CO 2 + H 2 O Figure 6.1 6.2 Cellular respiration banks energy in ATP molecules Cellular respiration breaks down glucose molecules and banks their energy as ATP The process uses O 2 and releases CO 2 and H 2 O Glucose Oxygen gas Carbon dioxide Water Energy Figure 6.2A
BASIC MECHANISMS OF ENERGY RELEASE AND STORAGE 6.4 Cells tap energy from electrons transferred from organic fuels to oxygen Glucose gives up the energy stored in its covalent bonds as it is oxidized Loss of hydrogen atoms Glucose Gain of hydrogen atoms Energy Figure 6.4 6.5 Hydrogen carriers, such as NAD +, shuttle electrons during redox reactions Enzymes remove electrons from glucose molecules and transfer them to a coenzyme - a RedOx reaction OXIDATION Dehydrogenase and NAD + REDUCTION Figure 6.5
6.6 Redox reactions release energy when electrons fall from a hydrogen carrier to oxygen NADH delivers electrons to a series of electron carriers in an electron transport chain As electrons move from carrier to carrier, their energy is released in small quantities Energy released and now available for making ATP ELECTRON CARRIERS of the electron transport chain Electron flow Figure 6.6 6.7 Two mechanisms generate ATP Cells use the energy released by falling electrons to pump H + ions across a membrane The energy of the gradient is harnessed to make ATP by the process of chemiosmosis Membrane Energy from Electron transport chain ATP synthase ATP synthase uses gradient energy to make ATP High H+ concentration Low H+ concentration Figure 6.7A
ATP can also be made by transferring phosphate groups from organic molecules to ADP Enzyme This process is called substrate-level phosphorylation Organic molecule (substrate) Adenosine Adenosine New organic molecule (product) Figure 6.7B In an imperfect analogy, the electron transport chain and chemiosmosis operate much like a bicycle going downhill The bicycle is analogous to an electron traveling down its energy hill Some energy from the tires is transferred to stones and leaves (the bits of energy driving the H + ion pump) - At the bottom of the hill, the bicycle pushes through a turnstile (ATP synthase)
STAGES OF CELLULAR RESPIRATION AND FERMENTATION 6.8 Overview: Respiration occurs in three main stages Cellular respiration oxidizes sugar and produces ATP in three main stages Glycolysis occurs in the cytoplasm The Krebs cycle and the electron transport chain occur in the mitochondria An overview of cellular respiration High-energy electrons carried by NADH GLYCOLYSIS Glucose Pyruvic KREBS CYCLE ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS Cytoplasmic fluid Mitochondrion Figure 6.8
6.9 Glycolysis harvests chemical energy by changing glucose to pyruvic Glucose Pyruvic Figure 6.9A Glycolysis is an anaerobic process no O 2 is needed This process occurs in the cytoplasm 6.10 Pyruvic can be chemically groomed to enter the Krebs cycle Each pyruvic molecule is broken down to form CO 2 and a two-carbon acetyl group, which can enter the Krebs cycle with the help of a coenzyme Pyruvic Acetyl CoA (acetyl coenzyme A) Figure 6.10 CO 2
6.11 The Krebs cycle completes the oxidation of organic fuel, generating many NADH and FADH 2 molecules Acetyl CoA The Krebs cycle is a series of reactions in which enzymes strip away electrons and H + ions from each acetyl group KREBS CYCLE 2 CO 2 Figure 6.11A 6.12 Chemiosmosis powers ATP production The electrons from NADH and FADH 2 travel down the electron transport chain to oxygen Energy released by the electrons is used to pump H + ions into the space between the mitochondrial membranes In chemiosmosis, the H + ions diffuse back through the inner membrane through ATP synthase complexes, which capture the energy to make ATP
Chemiosmosis in the mitochondrion Protein complex Intermembrane space Electron carrier Inner mitochondrial membrane Electron flow Mitochondrial matrix ELECTRON TRANSPORT CHAIN ATP SYNTHASE Figure 6.12 6.14 Review: Each molecule of glucose yields many molecules of ATP For each glucose molecule that enters cellular respiration, chemiosmosis produces up to 38 ATP molecules Cytoplasmic fluid Electron shuttle across membranes Mitochondrion GLYCOLYSIS 2 Glucose Pyruvic 2 Acetyl CoA KREBS CYCLE KREBS CYCLE ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS by substrate-level phosphorylation used for shuttling electrons from NADH made in glycolysis by substrate-level phosphorylation by chemiosmotic phosphorylation Maximum per glucose: Figure 6.14
6.15 Fermentation is an anaerobic alternative to aerobic respiration Under anaerobic conditions, many kinds of cells can use glycolysis alone to produce small amounts of ATP But a cell must have a way of replenishing NAD + In alcoholic fermentation, pyruvic is converted to CO 2 and ethanol This recycles NAD + to keep glycolysis working This process occurs in some microbes and is used industrially (e.g., beer and wine making) released GLYCOLYSIS Glucose 2 Pyruvic 2 Ethanol Figure 6.15A Figure 6.15C
In lactic fermentation, pyruvic is converted to lactic As in alcoholic fermentation, NAD + is recycled Lactic fermentation is used to make cheese and yogurt Lactic is what causes your muscle aches GLYCOLYSIS Figure 6.15B Glucose 2 Pyruvic 2 Lactic INTERCONNECTIONS BETWEEN MOLECULAR BREAKDOWN AND SYNTHESIS 6.16 Cells use many kinds of organic molecules as fuel for cellular respiration Polysaccharides can be hydrolyzed to monosaccharides and then converted to glucose for glycolysis Proteins can be digested to amino s, which are chemically altered and then used in the Krebs cycle Fats are broken up and fed into glycolysis and the Krebs cycle
Pathways of molecular breakdown Food, such as peanuts Polyscaccharides Fats Proteins Sugars Glycerol Fatty s Amino s Amino groups Glucose G3P GLYCOLYSIS Pyruvic Acetyl CoA KREBS CYCLE ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS Figure 6.16 6.17 Food molecules provide raw materials for biosynthesis In addition to energy, cells need raw materials for growth and repair Some are obtained directly from food Others are made from intermediates in glycolysis and the Krebs cycle Biosynthesis consumes ATP
Biosynthesis of macromolecules from intermediates in cellular respiration ATP needed to drive biosynthesis KREBS CYCLE Acetyl CoA GLUCOSE SYNTHESIS Pyruvic G3P Glucose Amino groups Amino s Fatty s Glycerol Sugars Proteins Fats Polyscaccharides Cells, tissues, organisms Figure 6.17 6.18 The fuel for respiration ultimately comes from photosynthesis All organisms have the ability to harvest energy from organic molecules Plants, but not animals, can also make these molecules from inorganic sources by the process of photosynthesis Figure 6.18