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Biology Review http://users.rcn.com Cellular Respiration and Cellular Work Note Much of the text material is from, “Essential Biology with Physiology” by Neil A. Campbell, Jane B. Reece, and Eric J. Simon (2004 and 2008). I don’t claim authorship. Other sources are noted when they are used. 2 Outline • • • • • • Harvesting of chemical energy Chemical cycle ATP and ADP Cellular respiration processes Enzymes and enzyme inhibitors Cell membrane transport 3 http://www.nick-lane.net Harvesting of Chemical Energy 4 Chemical Energy Food, gasoline, and other fuels are forms are sources of chemical energy. • Carbohydrates and fats have carbon backbones that make them rich in chemical energy. http://www.bubblews.com • 5 Harvesting of Chemical Energy • Cells and internal combustion engines use similar physical processes to perform work. • A gasoline engine mixes oxygen with octane in an explosive chemical reaction that breaks-down the covalent bonds in the carbon backbone for rapid liberation of energy. • The reaction moves the pistons in the cylinders, which ultimately drives the wheels. 6 Harvesting of Chemical Energy (continued) • Cells use oxygen to harvest chemical energy from food molecules in a more controlled process known as cellular respiration. • Aerobic cellular respiration, which requires oxygen, occurs in the mitochondria of eukaryotic cells. • Anaerobic respiration, which does not use oxygen, occurs in the cytosol of prokaryotic and eukaryotic cells. • The molecule ATP (adenosine triphosphate) is generated as a chemical energy source for cellular work in both types of respiration. 7 ATP Molecule http://biology.clc.uc.edu Adenosine triphosphate (ATP) 8 Efficiencies Automobile engines extract about 25 percent of the chemical energy to produce kinetic energy to drive the wheels—the rest is converted to heat. • Cells extract about 40 percent of the chemical energy from food molecules to perform cellular work. • The waste, or byproducts, of internal combustion engines and cellular respiration are mostly CO2 and water. • 9 Cellular Work The other 60 percent chemical energy generates body heat to maintain the body at a constant temperature—about 98.6oF or 37oC. • Sweating and other cooling mechanisms enable the body to lose excess heat including in hot environments and physical exercise. http://www.fitnessacademyhull.co.uk • 10 http://bioweb.uwlax.edu Coco as a kitten (my cat) http://www.isb.cnr.it Life Requires Chemical Energy http://www.americansingercanary.com 11 Calories • Calorie is a unit of chemical energy used in the physical and biological sciences. • A calorie (c) is the amount of energy required to raise the temperature of one gram of water by one degree Celsius (oC). 12 Calories (continued) • The caloric content of food is measured by burning it completely to ash under a container of water, and measuring the increase in the water temperature. • A handful of peanuts has enough chemical energy to boil more than a quart of water if the peanuts could be completely converted to heat. • A calorimeter is used by food scientists to measure the caloric content of foods. 13 Bomb Calorimeter http://chemistry.umeche.maine.edu 14 Kilocalories • The use of calories (c) to express the energy content of food is not practical since a calorie is a very small unit of measurement. • The daily recommended diet for adults would be about 2.0 x 106, or two million calories. • Instead, kilocalories (kcal or C) are used in which one kilocalorie is equals to 1,000 calories (c). Kilo- = 1,000. 15 Kilocalories (continued) • The daily recommended diet for adults is about 2,000 kilocalories (C). • Gender, age, basal metabolic rate, physical activity, and other factors determine recommended caloric intake. • The calories listed on food labels are always expressed in kilocalories. • A way to minimize confusion between c and C is to refer to kilocalories as food calories. 16 http://labelchoices.com Food Label 17 Have you compared food labels to determine nutritional value and calories? 18 Caloric Densities Although certain foods may have about equal food caloric content, they can differ substantially in caloric densities. http://www.asymptotia.com Each plate contains about 200 food calories. http://www.wisegeek.com 19 Caloric Accounting Caloric accounting is based on a person’s food intake, basal metabolic rate, and physical activity. • Caloric imbalances between food intake, and basal metabolic rate and physical activity can lead to weight gain or weight loss. http://i.lv3.hbo.com • 20 http://www.thelastgreenvalley.org http://www.dancinglondon.com Calorie Expenditures 535 kcal (2 mph) 160 kcal (3 mph) 510 kcal (fast)• 170 kcal (slow) http://briandesousa.com http://www.morrisville.edu 600 kcal (fast), 200 kcal (slow) 21 What are your favorite physical activities? 22 http://www.gosunstove.com Chemical Cycle 23 Solar Energy and Food Food molecules represent the storage of solar energy in indirect form, involving photosynthesis in plants. • Animals rely on plants to convert energy from sunlight to the potential energy of sugars and other organic molecules. • Humans also depend on plant life for cotton, lumber, paper, and many other products. http://solar-center.stanford.edu • 24 Autotrophs and Heterotrophs • Plants are autotrophs, or self-feeders, that synthesize organic matter from inorganic molecules such as carbon dioxide, water, and minerals from the soil. • Animals are heterotrophs, or other-feeders, that are unable to synthesize organic matter from inorganic molecules—they must obtain nutrients from food. • Heterotrophs depend on autotrophs for organic materials needed for tissue growth and repair. Autotrophs = also known as producers. Heterotrophs = consumers. 25 Food Web and Its Dependencies Autotrophs http://www.biologycorner.com Heterotrophs 26 Could you assemble a food web for human consumption patterns? 27 Chemical Cycle in Ecosystems Sunlight http://img.dailymail.co.uk Photosynthesis Chloroplasts in plants http://pws.byu.edu C6H12O6 (glucose) + O2 (oxygen) CO2 (carbon dioxide) + H2O (water) Cellular respiration Mitochondria in animals and plants http://www.soquel.org ATP Cellular work 28 http://3.bp.blogspot.com ATP and ADP 29 Cellular Respiration • The chemical equation for aerobic cellular respiration is shown on the next slide. • A key product of cellular respiration is adenosine triphosphate (ATP). • The left- and right-hand sides of the equation are shown in a previous slide, “chemical cycle in ecosystems.” • The chemical equation represents what is known as a redox reaction. Aerobic = requires oxygen. 30 Chemical Equation + (glucose) 6O2 6CO2 Cellular Respiration + 6H2O + ATP (chemical energy) ATP molecule Glucose molecule Up to 38 ATP molecules are produced for each glucose molecule. http://biology.clc.uc.edu C6H12O6 http://eurekalert.org 31 Redox Reaction • The transfer of electrons from one molecule to another molecule is an oxidation-reduction reaction. • It is also called, more simply, a redox reaction. • The loss of electrons is known as oxidation—glucose is oxidized, losing electrons to oxygen. • Oxygen is reduced by accepting electrons and hydrogen atoms from glucose. • Energy is released when electrons and hydrogen atoms change partners from sugar to oxygen. 32 Adenosine Triphosphate The tail of adenosine triphosphate (ATP) contains potential energy for cellular work. • The three phosphate groups tend to repel each other because each has a negative charge—they are held together by covalent bonds. http://biology.clc.uc.edu • 33 ATP and ADP The crowding of negative charges in the molecular tail of ATP is similar to the storing of energy in a compressed spring. • When released, a spring can perform useful work. • The release of the third phosphate group from its molecular tail makes the energy available for cellular work. • The molecule, which now has two remaining phosphate groups, is called ADP (adenosine diphosphate). http://img.weiku.com • 34 Phosphate Transfer • The third phosphate group released from ATP is transferred to other molecules. • The transfer enables cells to perform work—mechanical, chemical, or transport. 35 Examples of Cellular Work • Mechanical—phosphate groups from ATP molecules are transferred to motor proteins to enable muscle fibers to contract. • Chemical—ATP provides energy for dehydration synthesis of macromolecules such as starches and proteins. • Transport—ATP enables certain ions to be pumped across the plasma membranes of neurons and other cells. 36 ATP Cycle • ATP is restored by adding a phosphate group to ADP using the chemical energy cellular respiration harvests from food molecules (such as fats and carbohydrates). • The process is called the ATP cycle. 37 ATP Cycle (continued) ATP Potential energy from food molecules The circle turns clockwise ADP + Chemical energy for cellular work P 38 http://www2.estrellamountain.edu Cellular Respiration Processes 39 Cellular Respiration • Cellular respiration is a part of metabolism, the sum of all chemical processes in cells of the body. • Much, but not all, of cellular respiration occurs in the mitochondria. • The potential energy in food is converted to chemical energy for use by cells. • More than two dozen chemical reactions are involved in cellular respiration. • A specific enzyme catalyzes the chemical reaction in each metabolic pathway. 40 Components Glycolysis Electron micrograph of a human lymphocyte cell—a number of mitochondria are visible. Krebs Cycle Electron Transport Chain The three processes involved in cellular respiration. http://www.sinauer.com 41 Glycolysis • The enzymes for glycolysis are in the cytosol of eukaryotic and prokaryotic cells. • Glycolysis is anaerobic—it does not consume oxygen. • The process breaks glucose molecules consisting of six carbons into two, three-carbon molecules of pyruvic acid. • For each molecule of glucose, four molecules of ATP are produced. • Two electrons are also transferred to the molecule, NAD+ to produce NADH for the electron transport chain. NAD+ = an electron acceptor known as nicotine adenine dinucleotide. NADH = nicotine adenine dinucleotide, reduced. 42 http://staff.jccc.net Biochemistry of Glycolysis 43 Glycolysis (continued) • Pyruvic acid retains much of the energy of glucose that will be harvested in the Krebs cycle. • Pyruvic acid is converted to a two-carbon compound called acetic acid. • Acetic acid enters the Krebs cycle attached to a carrier molecule known as coenzyme A (CoA) to form acetyl-CoA. 44 ATP Output • Glycolysis is not an especially efficient process since only four ATP molecules are produced for every glucose molecule, along with two electrons. • In comparison, 36 ATP molecules (and many more electrons) are produced by the Krebs cycle. • To sustain energy output in glycolysis, cells compensate by consuming more glucose molecules if an adequate supply of carbohydrates is available. 45 Anaerobic Effort Cells can function for brief periods of time without oxygen through the anaerobic conversion of glucose to pyruvic acid and ATP. • Skeletal muscle fibers have sufficient amount of ATP molecules to support anaerobic activity for about 5 seconds. • These muscle fibers also have a secondary supply of the molecule creatine phosphate to provide an additional 10 seconds of energy reserve. http://blog.beyou.tv • 46 Lactic Acid • Lactic acid is a metabolic byproduct of pyruvic acid from the process of glycolysis. • During strenuous exercise, lactic acid accumulates in skeletal muscles, which can produce muscle burning sensations and soreness. • Skeletal muscles may temporarily shut down if lactic acid accumulates in high concentrations. • This is sometimes called, “hitting the wall.” 47 http://www.abbagav.com Hitting the Wall Endurance runners must learn to stay within their physiological limits until the final dash to the finish line. 48 Lactic Acid (continued) • Lactic acid is transported to the liver in the blood, where it is inactivated. • The inactivation requires oxygen, which is one reason why a person continues to breathe fast and heavy after vigorous exercise. 49 Have you ever hit the wall, so to speak? 50 Krebs Cycle • The Krebs cycle occurs in mitochondria of eukaryotic (plant, animal, and fungus) cells. • It is also known by other names, and especially the citric acid cycle. • The process is not found in prokaryotic cells because they lack mitochondria. 51 http:/biology.unm.edu Mitochondria An electron micrograph of a mitochondrion. 52 Krebs Cycle (continued) • The Krebs cycle extracts chemical energy until CO2 is formed as a byproduct of aerobic cellular respiration. • Each turn of the cycle produces two ATP molecules. • Six electrons are donated to NAD+ molecules to produce NADH for the electron transport chain. • Two electrons are also donated to the molecule FADH2, for the electron transport chain. 53 Biochemistry of the Krebs Cycle http://upload.wikimedia.org 54 Electron Transport Chain • The molecules of the electron transport chain are found in the inner membrane of the mitochondria. • Hydrogen ions (H+) “fall” toward oxygen molecules that entered the mitochondria by passive diffusion along their concentration gradient. • The process is aerobic—it requires a constant supply of oxygen molecules. • The electron transport chain uses the electrons in NADH and FADH2 to pump hydrogen ions against their concentration gradient across the mitochondrial membrane. 55 Electron Transport Chain (continued) • The hydrogen ions diffuse along their concentration gradient back into the mitochondria. • H+ inflow turns turbines of protein molecules, known as ATP synthases, in the mitochondrial membrane. ATP synthase http://www.sparknotes.com 56 Hoover Dam Hoover Dam, Nevada and Arizona http://www.mcnarybergeron.com Turbines connected to generators produce electrical energy from the downhill flow of water. Powerhouse turbines http://www.bossanova.com 57 ATP Regeneration • Energy from the spinning of an ATP synthase attaches a phosphate group to an ADP molecule to regenerate an ATP molecule. • Up to 34 ATP molecules are produced by a ATP synthase—compare this number with the much smaller ATP output from glycolysis. 58 Versatility of Cellular Respiration • So far, we have focused on glucose as a fuel source for cellular respiration. • Cellular respiration also uses other carbohydrates, fats, and proteins. • The digestive process hydrolyzes large food molecules into monomers that can be absorbed by the small intestine for glycolysis and the Krebs cycle. http://www.borderfoodsinc.com 59 http://safety.more4kids.com Carbon Monoxide and Cyanide • Carbon monoxide (CO) and cyanide block the transfer of electrons to oxygen in the electron transport chain. • The mitochondria cannot harvest food energy to convert ADP to ATP. • The cells stop working and the organism can die, usually very rapidly. 60 Enzymes and Enzyme Inhibitors http://www.unc.edu 61 Enzymes • The sum of all chemical reactions in an organism is its metabolism. • Enzymes are specialized proteins that lower activation thresholds and speed-up many types of chemical reactions. • The covalent bonds in molecules must be broken to initiate a chemical reaction. • Covalent bond breakage occurs, for example, when a disaccharide (a double sugar) is hydrolyzed into two monosaccharides (single sugars). 62 Enzymes (continued) • Energy, usually in the form of heat, is needed for a chemical reaction to occur—the threshold amount of heat is called its activation energy. • Adding substantial amounts of heat is often not possible or desirable with living cells. • Enzymes enable metabolism to occur at lower temperatures by reducing the amount of activation energy required to break molecular bonds. • Enzymes are catalysts that lower the barriers for chemical reactions to occur. 63 Induced Fit An enzyme is specific in the chemical reaction it catalyzes although thousands of different chemical reactions occur in the human body. • The active site of an enzyme has a shape that fits a portion of the substrate molecule, much like the correct key readily opens a door lock. • As an enzyme attaches to the substrate, it changes its shape slightly to enable a physical embrace between the molecules in what is called induced fit. http:/www.carefreeenzyme.com • 64 Induced Fit (continued) • The enzyme places the substrate under physical or chemical stress, making it easier to break the covalent bonds and initiate the chemical reaction. • Once the covalent bonds are broken, the enzyme molecule can bind with another substrate molecule to begin the process again. 65 Enzyme Inhibitors • Certain types of molecules can inhibit metabolic reactions by binding to enzymes and disrupting their functions. • Enzyme inhibitors are specific to the enzymes they target. • Some inhibitors are imposters of substrates that bind to enzymes. • Other inhibitors bind to a different part of the enzyme and change the shape of the active site so that it can no longer bind to the substrate. • Organisms produce enzyme inhibitors to control the overproduction of enzymes. 66 Enzyme Inhibitors (continued) Enzymes inhibitors are manufactured for many medical and biological purposes. • Malathion, an insecticide, inhibits an enzyme for the functioning of insect nervous systems. • Aerial spraying of malathion has been used to control Mediterranean fruit fly infestations in southern California—it turned-out to be a controversial program. http://www.cpaphils.org • 67 American Civil War http://nmhm.washingtondc.museum http://www.a2zcds.com During the American Civil War, many soldiers died from bacterial infections in the treatment of their wounds—possibly as many as died in battle. 68 Antibiotics Antibiotics are derived from microorganisms that disable or kill bacteria. • In the 1920s, Alexander Fleming discovered penicillin when he found a mold prevented the growth of bacteria that he was trying to cultivate in bread. • Penicillin, the first antibiotic to be developed, inhibits an enzyme needed to form the cell walls in bacteria. • • The death rates from diseases such as bacterial pneumonia and surgical infections dropped substantially once antibiotics were widely available.• 69 Antibiotics (continued) Ampicillin and bacitracin—bacterial cell walls. • Erythromycin, streptomycin, and tetracycline—bacterial ribosomes. • Ciprofloxacin—bacterial chromosomal structure. http://textbookofbacteriology.net • 70 What types of conditions can be treated with antibiotics? 71 Cell Membrane Transport 72 Cell Membrane Transport • Cells can control the flow of materials across their plasma membranes. • A major function of the plasma membrane, in addition to providing the cell boundary, is regulating the movement of molecules into and out of the cell. • Three forms of transport are: diffusion, osmosis, and active transport— the first two are passive processes that do not require chemical energy. http://upload.wikimedia.org 73 Diffusion • The heat energy of molecules causes them vibrate and this move randomly in what is called Brownian motion. • A result of the motion is diffusion, the tendency of molecules to spread into the available space. • Although each molecule moves randomly, the overall movement is in one direction, from high- to low-concentration, along its concentration gradient. 74 Diffusion and Directional Movement • The directional movement can be shown with movement of dye across a semi-permeable membrane in a container of water • The membrane has pores large enough to pass the dye molecules but not the water. • An equilibrium exists once the dye is evenly diffused—the number of molecules moving across the membrane is now about the same in both directions. • Two different dyes will diffuse along their own concentration gradients as if the other molecule did not exist. 75 Concentration Gradients Passage of time Concentration gradient Passage of time Red Green Individual concentration gradients 76 Passive Transport • Diffusion across a semi-permeable membrane is a form of passive transport since it does not require expenditure of chemical energy. • A cell’s plasma membrane is selectively permeable to some molecules. • The membrane allows certain small ions to pass (such as Na+ and K+), but not large molecules such as proteins and phosphate groups. 77 Passive Transport (continued) • Passive transport is an important process for maintaining all living cells. • For example, O2 enters the hemoglobin of red blood cells through passive diffusion to be transported in blood to meet the metabolic needs of the body’s tissues. 78 Osmosis • The passive transport of water across a semi-permeable membrane is called osmosis. • Consider a membrane separating two compartments that is permeable to H2O but not to C6H12O6 (glucose), a larger molecule. 79 Osmosis (continued) • The solution with a higher concentration of solute (in this case, glucose) is hypertonic and the solution with a lower solute concentration is hypotonic. • H2O will diffuse across the membrane from the hypotonic solution to the hypertonic solution until equilibrium is established. • The solutions are isotonic once they reach equal concentrations of glucose. 80 http://schools.moe.edu.sg Water Movement H2O molecules are small enough to pass through the semipermeable membrane, but the glucose molecules cannot pass because they are much larger. 81 Water Regulation The survival of cells depends on the body’s ability to regulate water uptake and loss. • When red blood cells are immersed in an isotonic solution, the volume of the cells remains constant. • Hypotonic and hypertonic environments can cause a cell to expand and burst or shrivel and die. http://www.mce.k12th.net • 82 Red Blood Cells http://www.ccs.k12.in.us Distilled water = hypotonic solution. Salt water = hypertonic solution. 83 Active Transport • Active transport requires the expenditure of chemical energy to move molecules across a cell’s plasma membrane. • A transport protein in the plasma membrane, using ATP as its energy source, pumps the solute across the membrane against its concentration gradient. • Active transport enables cells to maintain intracellular concentrations of molecules that differ from the extracellular environment. 84 Active Transport (continued) • A cell generally has a higher concentration of potassium (K+) ions and lower concentration of sodium (Na+) ions in the intracellular space. • The concentration differences are regulated by the sodium-potassium pump of transport proteins. • This pump is vital in enabling neurons to generate nerve impulses—or action potentials—as we will discuss in an upcoming lecture. 85 Exocytosis Large molecules, including many proteins, are too large to fit through the plasma membrane. • Transport vesicles carry proteins manufactured by the ribosomes, and fuse with the plasma membrane to empty their contents outside of the cell. • The process is known as exocytosis. http://www.linkpublishing.com • 86 Endocytosis The opposite process is endocytosis—cells take in materials such as food molecules and water in vesicles that bud inward from the plasma membrane. • Endocytosis and exocytosis both require chemical energy, and thus are active processes. http://www.pigur.co.il • 87 Can you describe the various methods of cell membrane transport? 88 Receptor-Mediated Endocytosis • Another type of endocytosis is when certain external molecules bind with receptor proteins in the plasma membrane to be transported into the cell. • This process is called receptor-mediated endocytosis. • In a genetic disorder, plasma membranes of cells cannot take-up sufficient amounts of cholesterol bound to low density lipoproteins (LDL). • High LDL levels result, which can lead to cardiovascular problems if left untreated or inadequately treated. 89 Cell Signaling • Many types of cells can communicate with each other across their plasma membranes. • A signal from outside of the cell—such as a water-soluble hormone—is received by receptor proteins in the plasma membrane or cytoplasm. • The signal triggers a chemical chain reaction inside the cell, in what is known as a signal transduction pathway. • The signal can lead to responses such as metabolic changes in the cell or rearrangement of the cytoskeleton. • Cell signaling is a key mechanism for many hormones of the endocrine system. 90