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Opening image. Energy and Metabolism CHAPTER 6. Energy Capacity to do work, which is any change in the state or motion of matter Measured as heat energy Unit of measure is the kilocalorie (kcal). Potential energy Capacity to do work owing to position or state

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  1. Opening image

  2. Energy and MetabolismCHAPTER 6

  3. Energy • Capacity to do work, which is any change in the state or motion of matter • Measured as heat energy • Unit of measure is the kilocalorie (kcal)

  4. Potential energy • Capacity to do work owing to position or state • Chemical energy is potential energy stored in chemical bonds • Kinetic energy • Energy of motion

  5. Closed system does not exchange energy with its surroundings • Organisms are open systems Closedandopensystems

  6. First law of Thermodynamics • Energy cannot be created or destroyed • Energy can be transferred and changed in form • Organisms cannot produce energy, but as open systems, they can capture it

  7. Second law of Thermodynamics • Entropy is continuously increasing • No energy transfer is 100% efficient • Some energy is dissipated as heat • Organisms maintain their organization only with input of energy from surroundings

  8. Figure 6-8Page 129

  9. Metabolism • Sum of all the chemical activities taking place in an organism • Anabolism • Complex molecules synthesized from simpler substances • Catabolism • Larger molecules broken down into smaller ones

  10. Enthalpy is total potential energy of a system • As entropy increases, amount of free energy decreases • H = G + TS • H is enthalpy • G is free energy • S is entropy • T is absolute temperature in degrees Kelvin

  11. Exergonic reaction • Releases energy that can perform work • In coupled reaction, supplies input of free energy to drive an endergonic reaction • Endergonic reaction increases free energy

  12. Dynamic equilibrium • In a chemical reaction, rate of change in one direction is the same as in the opposite direction • When concentration of reactant molecules increases, the reaction shifts until equilibrium is re-established

  13. Adenosine triphosphate (ATP) • Holds readily available energy for very short periods • Donates energy by means of terminal phosphate group • Common link between • Exergonic and endergonic reactions • Catabolism and anabolism

  14. ATP and ADP

  15. ATP – LIFE’S ENERGY CURRENCY ATP = Adenosine Triphosphate Energy is released when ATP is hydrolyzed (broken down by water) to ADP. ATP is restored from ADP and an input of energy. ATP’s energy is used to drive endergonic (energy-requiring) reactions.

  16. ATP linksexergonicand endergonic reactions

  17. Redox reactions • Substance that becomes oxidized gives up energy • Substance that becomes reduced receives energy • Essential part of cellular respiration, photosynthesis, and other chemical reactions

  18. NAD

  19. Model of the surface of an enzyme. • Enzymes • Biological catalysts • Cells regulate the rate of chemical reactions with enzymes • Lower activation energy (energy required to break existing bonds) • Although most enzymes are proteins, some types of RNA molecules have catalytic activity as well

  20. Enzymes Lower a Reaction’s Activation Energy

  21. Lock and Key Model of an Enzyme

  22. Active site (a) (b)

  23. Hexokinase, an enzyme (blue), binding its substrate, glucose (yellow). The Fit Between Enzyme and Substrate is Critical and Precise

  24. Enzymes • Work best at specific temperature and pH conditions • Catalyze virtually every chemical reaction that takes place in an organism • Some enzymes consist only of protein • Some enzymes have two components • Protein called apoenzyme • Cofactor • ENZYMES ARE NAMED ACCORDING TO THEIR SUBSTRATES AND KINDS OF REACTIONS THEY CATALYZE AND THEY END IN “-ASE”

  25. The Environment & Enzymes • The rate at which an enzyme can bind to substrate is called the turnover number. • The turnover number of an enzyme is maximized under the ideal conditions for that enzyme. • Each enzyme has ideal conditions that include: • Temperature • pH • Substrate concentration

  26. As nearly all enzymes are proteins, conditions such as pH and temperature are known to greatly affect proteins by denaturing them. Denaturation is, by definition, a change in the secondary, tertiary, and/or quaternary structure of the protein. These conformational changes would render the enzyme inactive.

  27. Temperature • Temperature has two effects on enzymes. • Changes the rate of molecular motion • Increasing temperature increases molecular motion. • Increases the rate of catalysis • Optimum temperature-the temperature at which the enzyme has the highest rate of catalysis. • Decreasing temperature decreases molecular movement. • Decreases the rate of catalysis • Causes changes in the shape of an enzyme • Temperature changes above optimum will denature the enzyme. • This changes its shape, and it can no longer bind substrate and catalyze the reaction. • This is why a high fever is potentially dangerous.

  28. pH • In the three dimensional shape of an enzyme • some amino acid side chains are exposed to the environment. • In a basic environment • the acidic side chains could donate protons. • In an acidic environment • the basic side chains could accept protons. • Both of these events will change the shape of the enzyme, • making it less able to bind substrate, thus less able to catalyze the reaction.

  29. Why Enzymes Need Vitamins • Some enzymes need special molecules to help them function correctly. • Cofactors are inorganic molecules such as iron or zinc that help enzymes work properly. • Coenzymes are organic molecules that bind to enzymes and make them work properly. • Vitamins are the precursors for many coenzymes. • Vitamin B2 is made into FAD. • Niacin is made into NAD. • Vitamins must be acquired from the diet, since cells cannot make them.

  30. ENZYMES IN ACTION • CAT OWNERS – HYDROLYSIS OF UREA FROM CAT’S URINE INTO CO2 AND NH3 GIVES A LITTER BOX ITS CHARACTERISTIC ODOR, WHICH SAYS IT IS IN NEED OF A CLEANING!

  31. This reaction is catalyzed by UREASE produced by BACTERIA that are always floating around in the air. Some of the bacteria settle out of the air and grow and reproduce in the litterbox. At ROOM TEMP AND pH of 8, a molecule of urease can catalyze about 30,000 molecules of urease per second. Without the catalyst, this reaction would take about 3 million years. => it happens at more than a trillion times it’s natural rate.

  32. Enzymes - Activity Temperature and pH effect enzyme action

  33. Enzymes - Activity Temperature and pH effect enzyme action

  34. Enzymes - Activity Enzyme and substrate concentrations

  35. Important classes of enzymes [insert table 6-1 when available]

  36. EXAMPLES OF ENZYME USE • Meat tenderizers are enzymes that tenderize the meat by pre-digesting it. • All enzymes are proteins, and proteins are denatured by high temperatures. • To tenderize an inexpensive cut of meat, you would sprinkle "Accent" on the meat and let it sit for a while. If you put the meat in the oven immediately, the enzyme has no time to act.

  37. In Siamese cats, an enzyme affects coat color, and only is functional in the cooler, peripheral parts of the body. Therefore, the coat of a Siamese is light in color except at the ends of the appendages, ears, and tail.

  38. In seals, the enzyme, which results in dark pigment in the hair, is also active only at lower temperatures. At birth, baby seals are born with a white coat, since the hair was formed while they were in the warm uterus of the mother. After birth, the hair grows dark in color, as the skin of the seal is relatively cool (it insulated from the core temperature by a thick layer of blubber).

  39. Inhibitors are molecules that attach to enzymes and make them unable to bind to substrate. Many drugs, pesticides and herbicides are enzyme inhibitors. Types of inhibition Competitive inhibition Non-competitive inhibition (allosteric inhibition) Negative-feedback inhibition Enzyme Inhibition

  40. Competitive inhibitors closely resemble the substrate. Therefore they bind to the active site of the enzyme. They block the substrate from binding. Example: Sulfa drugs Competitive Inhibition

  41. Competitive and noncompetitive inhibition

  42. Allosteric Inhibition • A molecule attaches to the enzyme at a site other than the active site and changes the shape of the enzyme. This inhibits it.

  43. Substrate Inhibitor Inhibitor binds to active site Enzyme (a) Substrate Active site Substrates Inhibitor Enzyme (b) Active site not suitable for receptionof substrates

  44. Reversible inhibition • Competitive inhibition • Inhibitor competes for the substrate for the active site • Noncompetitive inhibition • Inhibitor binds with enzyme at a site other than active site • Irreversible inhibition • Inhibitor combines with an enzyme and permanently inactivates it

  45. Inactive form of the enzyme Active form of the enzyme Enzyme-substrate complex Cyclic AMP Allosteric site Active Site Substrates Substrates Regulator (inhibitor) (c) (a) (b)

  46. Gene Regulation • Enzymes are proteins. • Protein production is controlled by genes. • Certain chemicals in the cell turn particular enzyme-producing genes on or off depending on the situation. • Called gene-regulator proteins • Those that decrease the amount of an enzyme made are called gene-repressor proteins. • Those that increase the amount of an enzyme made are called gene-activator proteins. • Example: Malate synthetase

  47. Feedback inhibition • Formation of an end product inhibits an earlier reaction in the metabolic pathway

  48. Signs & SymptomsNewborns affected by PKU usually do not show any signs of the disease at birth. But within the first few weeks of life they begin to show neurologic disturbances such as epilepsy. Signs also include skeletal changes such as a small head, short stature, and flat feet. PKU sufferers may also have a skin disorder called eczema.Long Term EffectsPKU-affected children who are not diagnosed and do not eliminate phenylalanine from the diet will suffer from irreversible brain damage and mental retardation. Properly treated individuals should live a normal, healthy life.TreatmentTreatment of PKU is the elimination of phenylalanine from the diet. Phenylalanine is commonly found in protein-containing foods such as meat. Babies who are diagnosed with PKU must immediately be put on a special milk/formula substitute. Later in life, the diet is mainly vegetarian. What is it?Phenylketonuria (PKU) is a hereditary disease that is caused by the lack of a liver enzyme required to digest phenylalanine. Phenylalanine is an amino acid that is most commonly found in protein-containing foods such as meat, cow's milk, over the counter infant formulas (both regular and soy) and breast milk.

  49. PKU test for newborns • A phenylketonuria (PKU) test is done to check whether a newborn baby has the enzyme needed to use phenylalanine in his or her body. Phenylalanine is an amino acid that is needed for normal growth and development. If a baby's body does not have the enzyme that changes phenylalanine into another amino acid called tyrosine, the phenylalanine level builds up in the baby's blood and can cause brain damage, seizures, and mental deficiencies.

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