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Bio-112 Ch 6 An Introduction to metabolism

by: mscrowell

Bio-112 Ch 6 An Introduction to metabolism Bio 112

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Ch 6 Intro to metabolism notes and images from textbook
principles of biology
Dr. Hannah Henson
Class Notes
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This 11 page Class Notes was uploaded by mscrowell on Thursday September 29, 2016. The Class Notes belongs to Bio 112 at Union University taught by Dr. Hannah Henson in Fall 2016. Since its upload, it has received 5 views. For similar materials see principles of biology in Biology at Union University.


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Date Created: 09/29/16
Bio­112 Ch 6 An Introduction to metabolism Tuesday, September 27, 2016 12:53 PM The living cell is a miniature chemical factory where thousands of  reactions occurThe cell extracts energy and applies energy to  perform workSome organisms even convert energy to light, as in  bioluminescence Metabolism: all of an organism’s chemical reactionsMetabolic  Pathway: a molecule is ALTERED in a series of steps to become  the PRODUCT Each step is catalyzed by a specific enzyme    Types of Metabolic PathwaysCatabolic pathways release energy  by breaking down complex molecules into simpler compounds Ex.: cellular respiration Anabolic pathways consume energy to build complex molecules  from simpler ones Ex.: protein synthesis from amino acids Bioenergetics: study of how energy flows through living  organisms  Forms of Energy Energy is the capacity to cause change Exists in various forms, some of which can perform work Kinetic energy energy associated with motion Thermal energy kinetic energy associated with random movement  of     atoms or molecules (overall movement) Heat is thermal energy in transfer from one object to another Light is another type of energy used to perform work Potential energy: energy that matter possesses because of its  location or structure (not kinetic energy) Not presently moving Chemical energy   potential energy available for release in a  chemical reaction Energy can be converted from one form to another   The Laws of Energy Transformation Thermodynamics is the study of energy transformations In an open system, energy and matter can be transferred between  the system and its surroundings Example? In an isolated system, no exchange of energy with the surroundings The First Law of Thermodynamics Principle of conservation of energy The energy of the universe is constant Energy can be transferred and or transformed, but it cannot be created or destroyed The Second Law of Thermodynamics Every energy transfer or transformation increases the entropy of  the universe­a measure of disorder, or randomness During every energy transfer or transformation, some energy is lost  as heat  Spontaneous processes:Occurs without energy input; they can  happen quickly or slowly For a process to occur spontaneously, it must increase entropy of the universe  Biological Order and DisorderCells create ordered structures from  less ordered materialsOrganisms also replace ordered forms of  matter and energy with less ordered forms 6.2: The free­energy change of a reaction tells us whether or not the  reaction occurs spontaneously  A living system’s free energy is energy that can do work when  temperature and pressure are uniform, as in a living cell aka Gibbs free energy The change in Gibb’s free energy (∆G) is the difference between  the free energy of final state and free energy of initial state ∆G =  G – G   final statinitial state Energy TransferDG = DH – DS*T  total energy in a reaction = H (total release of heat from fire)energy  free to do work = G (heat absorbed by pot and water)randomness in  the molecules = S (entropy)   Changes in Gibb’s free energy Only processes with a negative ∆G are spontaneousSpontaneous  processes can be harnessed to perform work Ex. Ball rolling down a mountain into a valley  If  G is positive products of the reaction contain MORE free  energy than the reactants Bond energy (H) is higher or the disorder (S) is lower If G is negative products of the reaction contain LESS free  energy than the reactants (spontaneous) Bond energy (H) is lower or the disorder (S) is higher A system in its final state is less likely to change à more stable  because it has less free energy  Equilibrium: forward and reverse reactions occur at the same rate; it is a state of maximum stability  A process is spontaneous and can perform work only when it is  moving toward equilibrium       Exergonic and Endergonic Reactions in Metabolism An exergonic reaction proceeds with a net release of free energy  and is spontaneous; ∆G is negative The magnitude of ∆G represents the maximum amount of work  the reaction can perform An endergonic reaction absorbs free energy from its surroundings  and is nonspontaneous; ∆G is positive The magnitude of ∆G is the quantity of energy required to  drive the reaction  Reactions in an isolated system eventually reach equilibrium and  can then do no work  Cells are not in equilibrium; they are open systems experiencing a  constant flow of materials   A catabolic pathway in a cell releases free energy in a series of  reactions The product of each reaction is the reactant for the next,  preventing the system from reaching equilibrium        6.3: ATP powers cellular work by coupling exergonic reactions to  endergonic reactions   A cell does three main kinds of work Chemical: pushing endergonic reactions (making polymers) Transport: pumping substances across membranes Mechanical: beating of cilia To do work, cells manage energy resources by energy coupling, the  use of an exergonic process to drive an endergonic oneMost energy  coupling in cells is mediated by ATP               The bonds between the phosphate groups of ATP can be broken by  hydrolysis Energy is released from ATP when the terminal phosphate bond is  broken  This release of energy comes from the chemical change to a state of  lower free energy, not from the phosphate bonds themselves ATP hydrolysis releases a lot of energy due to the repulsive force of  the three negatively charged phosphate group The triphosphate tail of ATP is the chemical equivalent of a  compressed spring How the Hydrolysis of ATP Performs Work  The three types of cellular work (mechanical, transport, and  chemical) are powered by the hydrolysis of ATP  (ex. Motor proteins, pumps, ATP production) In the cell, the energy from the exergonic reaction of ATP  hydrolysis can be used to drive endergonic reactions    The three types of cellular work (mechanical, transport, and  chemical) are powered by the hydrolysis of ATP  (ex. Motor proteins, pumps, ATP production) In the cell, the energy from the exergonic reaction of ATP  hydrolysis can be used to drive endergonic reactions     6.4:  Enzymes speed up metabolic reactions by lowering energy barriers Catalyst: chemical agent that speeds up a reaction without being  consumed by the reactionAn enzyme is a catalytic protein The Activation Energy BarrierEvery chemical reaction between  molecules involves bond breaking and bond formingThe initial  energy needed to start a chemical reaction is called the free energy  of activation, or activation energy (E )AActivation energy often  occurs in the form of heat that reactant molecules absorb from the  surroundings How do enzymes speed up reactions?Instead of  relying on heat, organisms carry out catalysis to speed up reactions A catalyst (ex. Enzyme) lowers the E  bArrier without being  consumed Enzymes do not affect the change in free energy (∆G); but  accelerate reactions that would occur eventually Substrate Specificity of EnzymesEnzymes are very specific for the  reactions they catalyze Substrate   the reactant that an enzyme acts on  Enzyme­substrate complex: when the enzyme binds to its substrate Active site: where the substrate binds to the enzyme, formed by only a few of the enzyme’s amino acids This induced fit of the enzyme to the substrate brings chemical groups of the active site together Catalysis in the Enzyme’s Active SiteThe  active site can lower an E Abarrier by: Orienting substrates correctly Straining substrate bonds Providing a favorable microenvironment Covalent bonding between substrate and enzyme  Effects of Local Conditions on Enzyme Activity  An enzyme’s activity can be affected by General environmental factors temperature and pH Chemicals that specifically influence the enzyme Each enzyme has an optimal temperature and pH at which its  reaction rate is the greatest  Cofactors Cofactors are nonprotein enzyme helpers Cofactors may be inorganic (such as a metal in ionic form) or  organic An organic cofactor is called a coenzyme Most vitamins act as coenzymes or as the raw materials from  which coenzymes are made  The Evolution of Enzymes Most enzymes are proteins encoded by genesChanges (mutations) in genes lead to changes in amino acid composition of an enzyme Altered amino acids in enzymes may alter activity or substrate  specificity 6.5: Regulation of enzyme activity helps control  metabolism Chemical chaos would result if a cell’s metabolic pathways  were not tightly regulated A cell does this by switching on or off the genes that  encode specific enzymes or by regulating the activity of  enzymes  Allosteric Regulation of Enzymes Allosteric regulation may either inhibit or stimulate an  enzyme’s activity When a regulatory molecule binds to a protein at one site  and affects the protein’s function at another site The binding of an activator stabilizes the active form of the  enzyme The binding of an inhibitor stabilizes the inactive form of the  enzyme  Feedback Inhibition In feedback inhibition, the end product of a metabolic  pathway shuts down the pathway prevents a cell from wasting chemical resources by synthesizing  more product than is needed


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