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Chapter 4

BIOL 1000 - Chapter 4 TEXTBOOK NOTES

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BIOL 1000
Nicole Nivillac

Chapter 4 NOTES – textbook Energy and Enzymes - Enzymes speed up rates of reactions without the need for an increase in temperature - In the cell, a group of enzymes called phosphatases catalyze the removal of phosphate groups from a range of molecules including proteins - The dephosphorylation reaction occurs using a phosphatase enzyme 4.1 – Energy and the Laws of Thermodynamics - Energy is the capacity to do work - Energy can be converted from one form to another - Example: in photosynthesis, energy of light is converted into chemical energy in the form of complex sugars and other organic molecules Kinetic Energy – is the energy possessed by an object because it is in motion - Examples: waves, falling rock, flow of electrons and heat - It can perform work by making other objects move Potential Energy – is stored energy - It is the energy an object has because of its location or chemical structure - The arrangement of atoms in a molecule of glucose or gasoline has potential energy stored in the specific arrangement of atoms - ^ also called chemical potential energy The First Law of Thermodynamics - Energy can be transformed from one form into another but it cannot be created or destroyed - Also called: the principle of the conservation of energy - Water at the top of Niagara Falls has potential energy which is converted to kinetic energy when it falls. From the bottom, the kinetic energy turns into various forms of potential and kinetic energy like heat, sound, etc. The Second Law of Thermodynamics - The total entropy of a system and its surroundings always increases - Each time energy is transformed from one form into another, some of the energy is lost and unavailable to do work - ^ Reason why most machines are not 100% efficient - ^ Remaining energy is being lost to the surroundings as heat which is the energy associated with random molecular motion - In cellular respiration, cells are able to convert only about 40% of potential energy in glucose into a form usable for metabolism, the remainder is lost as heat - The unusable energy that is produced during energy transformations is called entropy - ^Example of entropy: a hot coffee gets cold 4.2 – Free Energy and Reactions The change in Free Energy Free energy – The portion of a system’s energy that is available to do work - ^ abbreviated by the letter G - In living organisms, free energy accomplishes the chemical and physical work involved in activities such as the synthesis of molecules, movements, and reproduction - The change in free energy: - ^ H = change in enthalpy, S = change in entropy, T = temperature in kelvin - ^ Equation says that the free energy change as a system goes from initial to final states is the sum of the changes in energy content and entropy - For a reaction to be spontaneous, reaction must be negative - In some processes, such as combustion of methane, the large loss of potential energy, negative enthalpy, dominates in making a spontaneous reaction whereas a decrease in order (delta S increases) dominates in processes such as melting of ice at 25 degrees - (-) G indicates that the products have less free energy than the reactants - Systems that have high free energy are less stable than systems that have less free energy - A molecule of glucose can be considered as unstable and will spontaneously break down into molecules, including CO2, that have less free energy but that also are more stable. - ^ Likewise, a concentration gradient that exists across a membrane is less stable and contains more free energy than after diffusion. Metabolic Pathways - Exergonic Reaction: is one that releases free energy – the delta G is negative because the products contain less free energy than the reactants - Endergonic Reaction: the products contain more free energy than the reactants, therefore delta G is positive - The reactants involved in endergonic reactions need to gain free energy from the surroundings to form the products of the reaction - Metabolic pathway: is a series of sequential reactions in which the products of one reaction are used immediately as the reactants for the next reaction - ^ example – Catabolic Pathway: where energy is released by breakdown of complex molecules to simpler compounds Ex. Cellular respiration – whereby energy is extracted from the breakdown of food such as glucose nd - ^ 2 example – Anabolic Pathway: where energy is consumed to build complicated molecules from simpler ones (often called biosynthetic pathways) Ex. Photosynthesis - Delta G of an anabolic pathway is (+) whereas of a catabolic is (-) - Cellular respiration is a metabolic pathway made up of many individual reactions, some of which release energy (- G) whereas other require energy (+G). However when you sum the G of all reactions, the overall free energy is (-) and the pathway of cellular respiration is catabolic 4.3 – The Energy Currency of the Cell: ATP ATP Hydrolysis Releases Free Energy - ATP contain large amounts of free energy because they possess what are called high-energy phosphate bonds - ATP consists of 5-carbon sugar, ribose, linked to nitrogenous base adenine and a chain of 3 phosphate groups - ^ Each phosphate groups is closely associated with each other making the bonding arrangements unstable - ^ Removal of one or two of the 3 phosphate groups is spontaneous reaction that relieves the repulsion and releases large amounts of free energy - The breakdown of ATP is hydrolysis reaction and results in the formation of ADP (adenosine diphosphate) and a molecule of inorganic phosphate and inorganic phosphate (P) i ATP and Energy Coupling - When ATP is dissolved in water in a test tube, the hydrolysis reaction releases free energy that simply warms up the surrounding water - Within cells, hydrolysis of ATP does occur during shivering in muscle tissue to maintain body heat - Energy Coupling: ATP is brought in close contact with a reactant molecule involved in an endergonic reaction and when the ATP is hydrolyzed, the terminal phosphate group is transferred to the reaction molecule - ^ the transfer of the phosphate results in the reactant becoming phosphorylated which makes the molecule less stable - Energy coupling requires the action of an enzyme to bring the ATP and reactant molecules into close association - ^ The enzyme has a specific site on it that binds both the ATP and the reactant molecule allowing for transfer of the phosphate group Ex. AMMONIA (NH ) is 3dded to glutamic acid, an amino acid with one amino group to produce glutamine, an amino acid with 2 amino groups ^ Produced positive G value therefore reaction cannot proceed spontaneously - ^ The reaction proceeds by harnessing the energy released by ATP hydrolysis - ^ First step: the phosphate group removed from ATP is transferred to glutamic acid, forming glutamyl phosphate. The G for this reaction is (-) making the reaction spontaneous - ^ In the second step, glutamyl phosphate reacts with NH 3 Glutamic acid + NH + A3P  glutamine + ADP + P i delta G = -3.9 kcal/mol - ^ Because G is (-), the coupled reaction is spontaneous and releases energy - ^ -7.3 kcal/mol represents the potential chemical energy transferred to the glutamine molecules Regeneration of ATP - If ATP hydrolysis is an exergonic process, then ATP synthesis from ADP and Pi, is an energy- requiring endergonic process - The energy for ATP synthesis comes from the exergonic breakdown of complex molecules that contain an abundance of free energy (ex. Carbs, fats, proteins)
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