Metabolism can be defined as the sum total of processes occurring in a living organism. Heat is produced during all of these processes, therefore the metabolic rate is the rate of heat production. All biological processes ultimately use oxidation, so the rate of oxygen consumption can theoretically be used to estimate metabolic rate.
Transduction is the conversion of energy from one form to another. There are 3 major stages of transduction in the biosphere: photosynthesis, cell respiration (energy given up, production of ATP), and cell work. Energy involved in cell work can be mechanical, synthetic, chemical, asmotic or electrical. Contraction is the change of chemical energy to mechanical energy.
Metabolism as a rate of heat production can be measured. All cellular events result in the production of heat. A calorie is the amount of heat required to raise 1g of water 1 degree Celsius. Direct calorimetry is the direct measurement of heat, and is very difficult to determine. Indirect calorimetry involves the measurement of oxygen consumption, or the measurement of carbon and nitrogen content of excreted materials to determine metabolic rate.
During exercise, indirect calorimetry devices must measure external work. Oxygen is not used immediately for energy (since immediate energy sources and glycogen provide the initial sources of energy and are nonoxidative sources). Also, lactic acid is produced during vigorous exercise and the body buffers this buildup with bicarbonate-carbonic acid system. Therefore R does not = RQ. During and after exercise, urine production is inhibited and nitrogen is also lost in sweat, so the release of nitrogen is difficult to measure. Knowing all these factors, one can account for them and still get an estimate of metabolic rate.
EPOC is Excessive Postexercise Oxygen Consumption. This refers to the persistence of metabolic response even after exercise stops.
Efficiency is the fraction of energy liberated as external work, expressed as a percentage.
Steady-state exercise occurs when oxygen consumption (VO2) is relatively constant. This is directly proportional to the submaximal work load.
When testing on a treadmill, the grade is added to create external work (lifting the body up the incline).
Wednesday, April 2, 2008
All About Enzymes!
Enzymes are molecules that catalyze, or increase, the rates of chemical reactions by lowering the activation energy of the reaction. Enzymes are usually large molecules with 1 site for a substrate (reactant) to attach. This is known as the active site. When a substrate is attached, the two together are known as the enzyme-substrate complex. The products are released after the reaction occurs.
Modulators attach at the binding site of enzymes and affect the catalytic rate of the enzymes. Stimulators increase the rate while inhibitors decrease it. ATP, for example, is an inhibitor, while ADP and Pi are stimulators.
Alloterism describes the effect of modulators, since they can change the shape of parts on the enzyme. A multivalent enzyme is one which can be affected by several modulators.
Maximum velocity (Vmax) is a descriptive parameter of enzynmes. The Michaelis-Menten constant (Km) describes the interaction between a substrate and an enzyme. It occurs when the concentration of the substrate is 1/2 Vmax.
At rest, normally high levels of ATP and CP inhibit energy metabolism. When exercise starts, ATP breaks down and the existence of ADP and Pi stimulate energy metabolism.
Modulators attach at the binding site of enzymes and affect the catalytic rate of the enzymes. Stimulators increase the rate while inhibitors decrease it. ATP, for example, is an inhibitor, while ADP and Pi are stimulators.
Alloterism describes the effect of modulators, since they can change the shape of parts on the enzyme. A multivalent enzyme is one which can be affected by several modulators.
Maximum velocity (Vmax) is a descriptive parameter of enzynmes. The Michaelis-Menten constant (Km) describes the interaction between a substrate and an enzyme. It occurs when the concentration of the substrate is 1/2 Vmax.
At rest, normally high levels of ATP and CP inhibit energy metabolism. When exercise starts, ATP breaks down and the existence of ADP and Pi stimulate energy metabolism.
Oxidative Energy Sources
Oxidative sources provide far more available energy than nonoxidative or immediate energy sources. The potential sources of oxidative energy include sugar, carbs, fats and amino acids. Through this process, far more energy is liberated from a glucose molecule than other processes, since the process of glucose catabolism is carried much farther.
Glucose + O2 ----oxidative metabolism---->36ATP + CO2 + H2O
Fats and amino acids can only be catabolized by oxidative metabolism. Fat metabolism results in the release of far more energy:
Palmate + O2 ----OM----> 129ATP + CO2 + H20
In order to break down amino acids for energy, the nitrogen residue must first be removed- either through transamination (transfer) or oxidativer deamination in the liver (removal).
Glucose + O2 ----oxidative metabolism---->36ATP + CO2 + H2O
Fats and amino acids can only be catabolized by oxidative metabolism. Fat metabolism results in the release of far more energy:
Palmate + O2 ----OM----> 129ATP + CO2 + H20
In order to break down amino acids for energy, the nitrogen residue must first be removed- either through transamination (transfer) or oxidativer deamination in the liver (removal).
Nonoxidative (Glycolytic) Energy Sources
Glucose is a simple sugar that can be broken down for energy. Many glucose subunits can combine and be stored in the body as glycogen. Our muscles are densely packed with enzymes for this breakdown, so it can happen very rapidly.
Glucose ----glycolysis----> 2ATP + 2 Lactate
Glycogen is the main source of energy since free glucose supply is low in skeletal muscle, and is used for muscle contraction lasting more than a few seconds. Like the immediate energy sources, glucose is water-soluble and exists in the cytoplasm of the cell. There is more energy available from glucose/glycogen than from the immediate energy sources, but much less than oxidative energy sources. Even though lactate is produced as a byproduct, the formation and removal of this acid are in balance.
Glucose ----glycolysis----> 2ATP + 2 Lactate
Glycogen is the main source of energy since free glucose supply is low in skeletal muscle, and is used for muscle contraction lasting more than a few seconds. Like the immediate energy sources, glucose is water-soluble and exists in the cytoplasm of the cell. There is more energy available from glucose/glycogen than from the immediate energy sources, but much less than oxidative energy sources. Even though lactate is produced as a byproduct, the formation and removal of this acid are in balance.
Immediate Energy Sources
There are 3 components of immediate energy sources in muscle: ATP, Creatine Phosphate, and Myokinase. All three are water-soluble, so they reside in the aqueous part of the cell near the myosin and actin (contractile proteins of muscle).
ATP (adenosine triphosphate) is degraded by enzymes called ATPases, and the process usually involves combining with water; therefore, is referred to as hydrolysis. The chemical products of hydrolysis are ADP and Pi, where Pi is an inorganic phosphate. The standard free energy of ATP is 11 kcal/mol.
Creatine phosphate (CP) is 5-6x more abundant in resting muscle than ATP. It serves as a reserve of phosphate energy to regenerate ATP by rephosphorylising ADP.
CP + ADP ----creatine kinase----> ATP + C
The resulting Creatine is then rephosphorylated with mitochondrial creatine kinase which accesses mitochondrial ATP.
The enzyme adenylate kinase, also known as myokinase, can generate 1 ATP and 1 AMP from 2ADPs.
ATP and CP together are known as phosphagen. Exisiting ATP can't sustain maximal contraction for more than 2 seconds; and even with the assistance of CP and myokinase, other energy sources are needed to kick in if contraction lasts over 5-15 seconds.
ATP (adenosine triphosphate) is degraded by enzymes called ATPases, and the process usually involves combining with water; therefore, is referred to as hydrolysis. The chemical products of hydrolysis are ADP and Pi, where Pi is an inorganic phosphate. The standard free energy of ATP is 11 kcal/mol.
Creatine phosphate (CP) is 5-6x more abundant in resting muscle than ATP. It serves as a reserve of phosphate energy to regenerate ATP by rephosphorylising ADP.
CP + ADP ----creatine kinase----> ATP + C
The resulting Creatine is then rephosphorylated with mitochondrial creatine kinase which accesses mitochondrial ATP.
The enzyme adenylate kinase, also known as myokinase, can generate 1 ATP and 1 AMP from 2ADPs.
ATP and CP together are known as phosphagen. Exisiting ATP can't sustain maximal contraction for more than 2 seconds; and even with the assistance of CP and myokinase, other energy sources are needed to kick in if contraction lasts over 5-15 seconds.
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