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Transcript
Allometry The Problem of Size & Scaling Get it??? “A – LLAMA – TREE” Allometry How does body size affect physiological function? ◦ ◦ ◦ ◦ 8,000 species of birds 8,000 species of mammals 20,000 species of fish >2,000 species of reptiles/amphibians Great Differences in Size Allometry Mammals: Etruscan Shew (2.5g) Blue Whale (120 tons) Allometry Birds: Humming bird (2.0g) Ostrich (100kg) Allometry Can we study one end of the continuum and know something about the other end? Are there structural and/or functional consequences of changes in size scale in similar organisms? Metabolic Rate & Body Size Animal Body Mass (kg) Total VO2 (LO2/hr) Shrew 0.0048 0.036 Dog 11.7 3.9 Elephant 3833 268 Metabolic Rate & Body Size Semi-Log Plot ELEPHANT y = a*massb VO2 SHREW DOG Log Body Mass Metabolic Rate & Body Size y = a*massb ◦ y = physiological variable of interest ◦ a = intercept ◦ b = mass exponent Tells us something about the shape of the relationship (slope of line). Metabolic Rate & Body Size To transform everything into log-log: Log y = Log a + b(log mass) Metabolic Rate & Body Size Log-Log Plot y = a*massb Log VO2 DOG SHREW Log Body Mass ELEPHANT Metabolic Rate & Body Size Fundamental debate as to what the scaling exponent b is. Originally thought to be 2/3rds ◦ Max Rubner 1880s In 1932 Max Kliber concluded BMR scaled to the 3/4ths power (b=3/4). Exponent b y = a*massb If b is + : ◦ physiological variable with body mass If b is - : ◦ physiological variable with body mass If b is 0: ◦ physiological variable is unaffected by scale Exponent b Physiological Variable (b = 0) Log Body Mass Metabolic Rate & Body Size Kliber – Mouse to Elephant Curve Log VO2 /HR b= 3/4 Log Body Mass Mass-Specific Relationships Animal Shrew Dog Elephant Body Mass Total VO2 (kg) (LO2/hr) 0.0048 0.036 11.7 3.9 3833 268 VO2/mass (LO2/hr*kg) 7.4 0.33 0.07 What seems obvious at the whole animal level gets turned upside down at the mass specific tissue level! Mass-Specific Relationships Mass specific metabolic rate = looking at tissue level metabolism VO2/mass Mass-Specific Relationships SHREW Mass Specific MR LO2 /HR*kg DOG ELEPHANT Log Body Mass Mass-Specific Relationships SHREW Log Mass Specific MR LO2 /HR*kg DOG ELEPHANT Log Body Mass Mass-Specific Relationships Therefore, we see that increasing body size results in a decrease in mass specific metabolic rate. WHOLE ANIMAL Log VO2 MASS SPECIFIC Log Body Mass What does that mean?? Metabolic Rate Across Taxa What about differences between taxonomic groups? Metabolic Rate Across Taxa Log MR Similarly sized endotherms will always have higher BMRs than their ectotherm counterparts. Log Body Mass Metabolic Rate Across Taxa Log BMR Log Body Mass Metabolic Rate Across Taxa BMR for marine mammals is 2x that of similarly sized terrestrial mammals Marsupials have a BMR 30% lower than you would predict for a terrestrial mammal. Metabolic Pathways, Macromolecules, & High Energy Molecules Energy Storage Energy can be stored in different forms: ◦ Gradients ◦ Chemical bonds Gradients Molecules tend to disperse or diffuse randomly within available space. Diffusion 2 aspects of diffusion govern properties of many biological systems: 1. Leads to random distribution of molecules, but rates can be slow. 2. Source of energy that cells can utilize. Diffusion Gradients Biological systems can invest energy to move molecules out of random distribution, resulting in a diffusion gradient. This gradient is a form of energy storage that the cell can use for other purposes. Diffusion Gradients Chemical Gradients Electrical Gradients Electrochemical Gradients FIGURE 2.2 Chemical Bonds Most biologically available energy is stored in bonds ◦ Covalent bonds = Strong Bonds. Hold individual atoms together and form molecules by sharing electrons ◦ Non-Covalent bonds = Weak Bonds. Organize molecules into 3D structures. Energy Acquisition How are organisms able to utilize the energy stored in chemical bonds? How are they able to convert the chemical energy stored in food into utilizable energy? Metabolic Pathways Eat Food Fragment Enter Cells Oxidized thru Biochemical Pathways Energy, Heat, CO2, and H2O Metabolic Pathways Metabolic pathway: Series of consecutive enzymatic reactions that catalyze the conversion of substrates to products Metabolic flux: flow through a pathway Metabolic Pathways Metabolic pathways can be: ◦ Synthetic (Anabolic) ◦ Degradative (Catabolic) ◦ Combination (Amphibolic) Energy metabolism revolves around the production of ATP and other energy-rich molecules. Enzymes Enzymes = biological catalysts that aid in the conversion of substrate to product. ◦ Most are composed of protein Animals control the inner workings of cells through the use of enzymes, which interconvert macromolecules to create building blocks and control the flow of energy Enzymes 3 Important properties of enzymes: ◦ Active at very low concentrations within cell ◦ Speed up the rate of reaction without being altered in the process ◦ Do not change the nature of the products Enzymes Enzymes aid in the transfer energy from nutrients to molecules that function as energy stores. These energy rich molecules act as substrate and product in hundreds of different metabolic reactions. Reducing Equivalents Cells store energy in the form of reducing equivalents to drive metabolic processes: NAD+ NADP+ : : Nicotinamide adenine dinucleotide Nicotinamide adenine dinucleotide phosphate Redox Reactions REDduction-OXidation reactions ◦ Transfer of electrons Oxidation loss of electrons increase in oxidation state Reduction gain of electrons decrease in oxidation state Redox Reactions NAD+ is an oxidizing agent. It accepts electrons from other molecules and becomes reduced. NAD+ NADH NADH can then be used as a reducing agent to donate electrons. Reducing Equivalents In an enzymatic reaction, electrons are transferred to NAD+ or NADP+ Reduced NADH or NADPH can be used to drive other reactions. Redox Status Measure of how much reducing energy is stored to drive metabolic reactions Redox Status = [NADH] [NAD+] High Ratio = cell rich in reducing energy Low Ratio = call poor in reducing energy Reducing Equivalents Why are they important? Reducing equivalents are used in metabolic pathways in order to produce high energy molecules. High Energy Molecules High energy molecules are used as energy currency by cells: ◦ Adenosine Triphosphate (ATP) ◦ Phosphocreatine (PCR) ◦ Acetyl CoA High Energy Molecules Energy Currency The storage of high energy phosphates and controlled release of energy is the mechanism behind metabolism. ATP = The universal source of immediate energy in cellular metabolism. Adenosine Triphosphate (ATP) Adenosine Triphosphate (ATP) Each of the high energy bonds provided the same amount of energy. ATP ADP AMP Energy is not stored in the bond, but is released when the bond is broken. Adenosine Triphosphate (ATP) Phosphocreatine (PCR) PCR is used when ATP demand temporarily out strips the capacity to produce ATP. Hummingbirds, greyhounds, and cheetahs have high levels of PCR Phosphocreatine (PCR) Can diffuse easily into areas needing energy. When ATP is low, the energy stored in PCR is transferred to ADP or AMP. ADP – ATP Cycle Locomotion, Heart Fxn, Biosynthesis, Growth, etc. ATP ADP Oxidation of Fuel Energy Exchange ATP-ADP cycle is the fundamental mode of energy exchange in biological systems. Recycling is a cyclic process fueled by the food you eat and oxygen you consume. Diving Marine Mammals ATP ADP AMP PCR FAST AND CYCLIC PROCESS Levels Back to Normal Types of Fuel Macromolecules: ◦ Proteins ◦ Carbohydrates ◦ Lipids (fatty acids) Proteins Form exoskeletons, extracellular matrices, & enzymes Building blocks = amino acids (20) Long strands of amino acids are folded into 3D conformations. The structure of proteins are stabilized by many weak bonds. Proteins Proteins Environmental conditions such as temperature can alter weak bonds and disrupt 3D shape. When proteins begin to unfold, or denature, they are no longer capable of performing their function. Negatively impacts enzymatic function and metabolism. Carbohydrates Glucose = C6H12O6 Most common carbohydrate in animal diets. Versatile: cells can break it down for energy, store it for later consumption, or use it to build other needed carbohydrates. Carbohydrates Polysaccharides = larger polymers of carbohydrates that serve in energy storage and structure. Glycogen = polysaccharide that acts as an internal energy store. ◦ Broken down for use in glycolysis ◦ Important for endurance Glycogen Stores Lipids Hydrophobic Organic Molecules: ◦ Fatty Acids ◦ Triglycerides ◦ Phospholipids ◦ Steroids Fatty Acids The mammalian heart derives more than 70% of its energy from fatty acids. Fatty acids are long chains of carbon atoms that end in a carboxyl group. They can be 2-30 carbons long, and are either saturated or unsaturated. Fatty Acids Saturated F.A. = no double bonds. Unsaturated F.A. = 1≤ double bonds. Fatty Acids Fatty Acids are oxidized in the mitochondria. Pairs of carbons are sequentially cut off the ends of fatty acid chains in the form of Acetyl CoA. Cycle repeats itself until the entire fatty acid chain is broken down. Fatty Acids The most abundant energy source available to the muscle fiber is fat. The breakdown of fat to yield ATP is referred to as lipolysis. The rate at which lipolysis occurs is the limiting factor in obtaining ATP. Fatty Acids Lipolysis is responsible for resting muscle activity. Contribution to overall muscle energy supply decreases as contraction intensity increases. Once glycogen depletion occurs, exercise intensity will be reduced dramatically. ◦ “Hitting The Wall” Sprinter v. Marathoner % Fuel Type 60% FAT CHO 60-75% Exercise Intensity Biochemical Processes Biochemical pathways can be either: AEROBIC ANAEROBIC Aerobic and Anearobic Metabolism 2 Major Pathways: ◦ Glycolysis (anaerobic) takes place in the cytosol of a cell ◦ TCA / Krebs Cycle (aerobic) takes place in the mitochondrial matrix followed by oxidation by the electron transport system (ETS) in the inner mitochondrial membrane. Glycolysis Low efficiency high velocity pathway. It is the pathways that breaks down glucose. Vital source of ATP because it can proceed in the absence of oxygen (anoxia) and can produce ATP rapidly, though for brief periods. Glycolysis Glucose + 2ADP + 2NAD+ 2ATP + 2 Pyruvate + 2 NADH + 2 H+ Negative feedback regulation: ATP levels = ATP production Glycolysis Within the cytoplasm (no oxygen present): pyruvate + NADH + H+ lactate + NAD+ Regenerates NAD+ for glycolysis Lactate is slightly toxic. ◦ It can be tolerated for short periods by being retained in tissues or exported into extracellular fluid. ◦ Must me metabolized and removed from system. ◦ Associated with muscle fatigue in athletes. Glycolysis (anaerobic) So why bother? ◦ FAST! ◦ No Oxygen Needed! Environmental hypoxia: ◦ Environmental O2 levels fall below critical levels for prolonged periods. Functional anoxia: ◦ Tissue O2 demands outstrip O2 delivery from blood (ex. Exercise/diving animals). Glycolysis When oxygen is present, pyruvate is converted to Acetyl CoA and used in mitochondrial metabolism. Mitochondrial Metabolism Aerobic uses oxygen Main point of entry for mitochondrial energy producing pathway is Acetyl CoA. Acetyl CoA: ◦ Produced in many pathways. Mitochondrial Metabolism 2 Main Processes: TCA / Krebs Cycle ◦ Occurs in mitochondrial matrix ◦ Produces reducing equivalents used in ETS Oxidative Phosphorylation ◦ Occurs in Inner mitochondrial membrane ◦ Produces ATP Mitochondrial Metabolism TCA / Krebs Cycle Acetyl CoA is oxidized to form reducing equivalents: NADH and FADH2 Provides fuel for mitochondrial ATP production. TCA / Krebs Cycle TCA / Krebs Cycle For every Acetly CoA that enters cycle: 2 CO2 3 NADH 1 FADH2 1 GTP … are produced. Oxidative Phosphorylation Electron Transport System (ETS) Phosphorylation Electron Transport System (ETS) Mitochondria utilize reducing equivalents in ETS to aide in ATP production. ETS maintains an electrochemical gradient found in the inner mitochondrial membrane and utilizes it to drive ATP synthesis. Electron Transport System (ETS) Electron Transport System (ETS) Break down of NADH and FADH2 produces energy used to pump H+ into outer compartment of the mitochondria Oxidative Phosphorilation ATP is generated as H+ moves down its concentration gradient through a special enzyme called ATP synthase Oxidative Phosphorylation Net Final Score Oxidative Phosphorylation= 36 mol ATP / mol Glucose Efficient but slow Glycolysis = 2 mol ATP / mol Glucose Inefficient but fast Energy & Metabolism Cells must produce ATP at rates that match ATP demand. There will be different fuels and pathways utilized depending on the activity state of an individual Energy System v. Running Speed The primary energy source for sprinting distances up to 400 m is PCr. From 400 m to 1,500 m, anaerobic glycolysis is the primary energy source. Distances longer than 1,500 m, athletes rely primarily on aerobic metabolism. http://www.nismat.org/physcor/energy_supply.html Speed and Distance With increasing distances, average speeds decline. The average speed for the marathon world record is 12.1 mph, which is 55% of the world record sprinting speed. Remarkable since the marathon is more than 200 times the length of a 200 m race. http://www.nismat.org/physcor/energy_supply.html