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Chapter 4


8 Pages

Course Code
BIOL 1000
Julie Clark

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Tanya Sivamanoharan Thurs, Oct, 14/11 Biology- chap# 4 Notes ENERGY AND ENZYMES 4.1- Energy and the Laws of Thermodynamics -energy is detected through its ability to do work, move object against opposing forces -energy the capacity to do work (friction, gravity, pressure) 4.1a- Energy Exists in Different Forms and States -energy exists in diff. forms (heat, chemical, electrical, mechanical) -electromagnetic radiation (light) is also energy -energy can be transformed from one form to another -all forms of energy belong to one of the two states: kinetic or potential -kinetic energy energy possessed by an object b/c it’s in motion (waves, photons of light, flow of electrons) -potential energystored energy- energy an object has b/c of its location and chemical structure (chemical potential energy) 4.1b- The Laws of Thermodynamics Describe the Energy Flow in Natural Systems -thermodynamics the study of energy and its transformations -system the object being studied in thermodynamics (cell, earth, a molecule) -surroundings everything outside the system (universe) -there are 3 types of systems: isolated, open , and closed -closed system exchange energy but not matter with its surroundings -open system-> exchange both energy and matter with its surroundings -living organisms are open systems 4.1c- The First Law ofthhermodynamics -research from the 19 century lead to 2 fundamental laws of thermodynamics -1 law of thermodynamics energy can be transformed from one form to another, transferred from one place to another, but cannot be created or destroyed -1 law also called the principle of conservation of energy 4.1d- The Second Law of Thermodynamics -each time energy transformed to diff. form, some energy is lost in surroundings and is unavailable to do work (not always 100% efficient) -usually the energy is lost as heat -entropy the disorder or randomness in the universe (causes unusable energy) -2ndlaw of thermodynamics the total disorder (entropy) of a system and its surroundings always increases -systems will move towards arrangements of greater entropy -it takes energy to maintain low entropy 4.1e- Life and The Second Law of Thermodynamics -life is highly ordered and nonrandom -cells can make highly ordered structures from less ordered starting material -DNA, proteins, and ribosomes are ordered structures made from simple building blocks -things become more ordered in a living cell and not disordered -living things bring in energy and matter to reduce entropy and maintain low entropy (food) -the living things give off heat, and by-products of metabolism like carbon dioxide which increases entropy of surroundings 4.2- Free Energy and Spontaneous Reactions -spontaneous reactions chemical or physical reaction that occurs without outside help -spontaneous reactions can be fast or slow (lighting a match or rusting of a nail) 4.2a- Energy Content and Entropy Contribute to Making a Reaction Spontaneous -there are 2 factors that determine a spontaneous reaction 1. –reactions tend to be spontaneous if products have less potential energy than reactants -enthalpy (H)  the potential energy in a system -endothermic products have more potential energy than reactants, reactions that absorb energy -exothermic processes that release energy 2. –reactions are spontaneous when products are less ordered than reactants -reactions occur spontaneously if the entropy of the product is greater than entropy of reactants, if products are more random than reactants -phase changes (solidliquidgas) result in increase of entropy 4.2b- The Change in Free Energy Indicates Whether a Reaction is Spontaneous nd -from 2 law of thermodynamics we know transformations are not 100% efficient, and energy s lost by increase in entropy -free energy (G) portion of the system’s energy available to do work - the change in free energy is calculated by subtracting initial state from final state -free energy can be calculated by equation below: -Hchange in enthalpy -S change in entropy over course of reaction -T absolute temperature in Kelvins -for a spontaneous reaction the G must be –ve -the enthalpy and entropy of the reaction influence overall G -a –ve G means that the products have less free energy than the reactants -concentration gradient the concentration diff. that drives diffusion 4.2c- Life and Equilibrium -equilibrium maximum stability -chemical equilibrium where the reaction does not stop but the rate of the forward reaction = the rate of the backward reaction -as system reaches equilibrium, the free energy reaches its lowest point where the system reaches maximum stability (G is zero) -equilibrium pointa state of balance between opposing factors that push a reaction in either direction -many living organisms never reach equilibrium b/c they are open systems, and they reach equilibrium when they die -most frequently the free energy of organisms is –ve b/c they usually take in energy-rich molecules 4.2d- Metabolic Pathways Consist of Exergonic and Endergonic Reactions -based on free energy all reactions can be divided into 2 groups: exergonic reactions and endergonic reactions -exergonic reactions one that releases free energy, G is –ve b/c products have less free energy than reactants -endergonic reactions reactants involved in reaction need to gain free energy from the surroundings, G is +ve b/c products contain more free energy than reactants (pg# 78 fig. 4.10) -there are 2 pathways in metabolic reactions: catabolic and anabolic (pg# 78 fig 4.10) -catabolic pathway energy released by breaking down complex molecules to simpler compounds -anabolic pathways consume energy to build complex molecules from simple ones (photosynthesis) 4.3- The Energy Currency of the Cell: ATP -reactions that use energy to make simple components into complex molecules are endergonic and have a +ve G -these reactions may be catabolic or anabolic -the energy needs for these endergonic reactions is a nucleotide called adenosine triphosphate (ATP) 4.3a- ATP Hydrolysis Releases Free Energy -ATP contain large amounts of free energy b/c they have high energy phosphate bonds -ATP made of a 5-carbon sugar, ribose, linked to a nitrogenous base adenine and a chain of 3 phosphate groups -most of the potential energy in ATP is within the 3 phosphate groups -the –ve charges of the phosphates groups repel each other, making the bonds unstable -removing 1 or 2 phosphates from the chain causes a spontaneous reaction that releases large amounts of free energy -breakdown of ATP by hydrolysis makes adenosine diphosphate (ADP) and an inorganic phosphate ATP + H2O ADP+P 4.3b- ATP and Energy Coupling -when ATP dissolves in water, hydrolysis reaction releases free energy as heat that warms up the water -this energy can be saved by a coupled reaction coupling the hydrolysis reaction to an endergonic reaction -energy couplingthe process by which ATP is brought in close contact with a reactant molecule involved in an endergonic reaction, when ATP is hydrolyzed, the terminal phosphate group is transferred to the reactant molecule -ex of a coupling reaction is when glutamic acid and ammonia make glutamine and water -if G is –ve than the reaction is spontaneous and releases energy -coupling system works by joining an exergonic reaction, the hydrolysis of ATP, to the endergonic biosynthesis reaction -all endergonic reactions of living organisms (growth, reproduction, movement, and response to stimuli) are made possible by coupling reactions 4.3c- Regeneration of ATP - ATP breakdown to ADP and P is an exergonic reaction that can be couple to make endergonic reactions spontaneous -ATP is a renewable resource made by recombining ADP and P (endergonic reaction) -the energy for ATP synthesis comes from exergonic breakdown of complex molecules that contain a lot of free energy -complex molecules include food, carbohydrates, fats, and proteins -the breakdown and synthesis of ATP is called the ATP cycle 4.4- The Role of Enzymes in Biological Reactions -laws of thermodynamics are useful b/c it tells us if a process needs energy or is spontaneous -laws do not say anything about speed of reaction -a spontaneous reaction does not mean it proceeds rapidly -speed of a reaction can be altered by group of proteins called enzymes 4.4a- The Activation Energy Represents a Kinetic Barrier -chemical reactions need bonds to be broken and new bonds to be made -bonds must be strained or made less stable in order to break
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