enzymes and energy. thermodynamics and biology metabolism: the totality of an organism’s chemical...
TRANSCRIPT
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Enzymes and Energy
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Thermodynamics and Biology
Metabolism: The totality of an organism’s chemical processes; managing the material and energy resources of the cell
Catabolic pathways: degradative process such as cellular respiration; releases energy
Anabolic pathways: building process such as protein synthesis; photosynthesis; consumes energy
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Energy and Enzymes
Almost all energy for life is derived from the sun.
Life requires energy.Life requires energy
The sun is the ultimate source of all energyEnergy ~ Capacity to do work Kinetic energy~ energy of motion; Potential energy~ stored energyChemical energy~ potential energy
stored within the bonds of a molecule
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Thermodynamics~ study of energy flow through living and non-living systems i.e. energy transformations
System ~ a process under study in relations to the rest of the universe
Closed System~ a system isolated from its environment
Open System ~ a system that has relationship with its environment
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Energy can neither be created, nor destroyed, but can be transformed from one form to another
First Law of thermodynamics
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Free Energy: portion of system’s energy that can perform work e.g. building the molecules in a cell
Total Energy = Free Energy + Lost Energy Free Energy < Total Energy
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Free energy
Exergonic reaction: net release of free energy to surroundings
Endergonic reaction: absorbs free energy from surroundings
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Second Laws of Thermodynamics
Energy cannot be transformed from one form to another without a loss of useful energy
i.e. every energy transformations increases the entropy (disorder, randomness) of the universe
A measure of the tendency of a system to become organized is called entropy.
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The Direction of Spontaneous Reactions (and what it takes to go the other way)
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Activation energy ~ the initial input of energy to start a chemical reaction
Energy and Chemical Reactions
Activation Energy
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Classification of chemical reaction based on whether it releases or uses energy
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Exothermic Reaction ~Is accompanied by release of energy
Reactants Products + Energy 10 energy = 8 energy + 2 energy
Reactants
Products
-DH
Ene
rgy
Energy of reactants
Energy of products
Reaction Progress
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C6H12O6 +6O2→6CO2 + 6H2O + Energy (Useful and waste)
An example of exothermic reaction is cellular respiration
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Endothermic Reaction~ involves an input of energy
Energy + Reactants Products
+DH Endothermic
Reaction progress
Ene
rgy
Reactants
ProductsActivation Energy
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6CO2 + 6H2O + Sun Energy → C6H12O6 + 6O2
An example of endothermic reaction is photosynthesis
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Enzymes as Catalysts
Enzymes ~Catalysts for biological reactions Increase the rate of reactions without being
consumed or permanently altered in the process
They are mostly proteins and certain class of RNA (ribozymes)
Increase the rate of chemical reaction by lowering the activation energy
2.2
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Enzymes Lower a Reaction’s Activation Energy
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Effect of Catalyst on Reaction Rate
reactants
products
Ene
rgy
activation energy for catalyzed reaction
Reaction Progress
No catalyst
Catalyst lowers the activation energy for the reaction.
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Name of Enzymes
Ends in –ase Identifies a reacting substance
sucrase- reacts with sucrose
lipase reacts with lipid Describes functions of enzyme
oxidase -catalyzes oxidation
hydrolase - catalyzes hydrolysis
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Classification of Enzymes
Class Reactions catalyzed Oxidoreducatase oxidation-reduction Transferases transfers group of atoms Hydrolases hydrolysis Lyases add/remove atoms to
form a double bonds Isomerases rearrange atoms Ligases combine molecules
using ATP
Table 2.2
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Mode of Action of Enzymes
Substrate: enzyme reactant An enzyme binds a substrate in a region
called the active site Active site is a hollow depression (pocket or
groove on enzyme)
Two main Models Induced fit Model
Lock and Key Model
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Induced Fit Model
Enzymes structure flexible, not rigid Enzyme and active site adjust shape to bind
substrate Increase range of substrate specificity Shape change also improve catalysis during
reaction
See Figure 2.5 and 2.6 on page 43 of your textbook
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Lock and Key Model
• An enzyme binds a substrate in the active site
• Only certain substances can fit the active site
• Amino acid R-groups in the active site help substrate bind
• Enzyme-substrate complex forms
• Substrate reacts to form product
• Product is released
• The enzyme is available to repeat the cycle
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Enzymes speed biochemical reactions
Figure 4-8: Two models of enzyme binding sites
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The active site of an enzyme is where substrate is bound.
Many Enzymes Work by Altering
the Shape of Their Substrates
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Enzyme Activity-Temperature
Low activity at low temp Rate increases with temp Activity lost with
denaturation at extreme temperatures
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Enzyme Activity- pH
Maximum activity at optimum pH R group of amino acid have proper charge to interact
with the substrate Tertiary structure of enzyme is correct Narrow range of activity Most lose activity in low or high pH
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Enzyme Activity- Concentration of Substrate
Increasing substrate concentration increases the rate of reaction (enzyme concentration is constant)
Max activity reached when all of enzyme combines with substrate
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Enzyme Inhibitors
Irreversible (covalent); reversible (weak bonds)
Competitive: competes for active site (reversible); mimics the substrate
Noncompetitive: bind to another part of enzyme (allosteric site) altering its conformation (shape); poisons, antibiotics
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Enzyme Inhibitors and Allosteric Regulation
A competitive inhibitors• Has a structure similar to substrate• Occupies the active site• Competes with substrate for active site• Has effects reversed by increasing substrate
concentration
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A Noncompetitive Inhibitor Does not have a structure like substrate Binds to the enzyme but not active site Change the shape of enzyme and active site Substrate cannot fit altered active site No reaction occurs Effect is not reversed by adding substrate
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Feedback inhibition
Control of Metabolic Pathways
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ATP and Coupled Reactions
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Adenosine Triphoshate (ATP) is the energy currency of the cell
Cellular respiration converts energy stored in the chemical bonds of food substances into chemical energy stored in ATP
ATP is made up of Adenine (nitrogenous base), a ribose sugar (Carbohydrate) and 3 phosphates groups
Ribose sugar+ Adenine → Adenosine
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Adenosine + PO4 → Adennosine Monophosphate (AMP)
AMP is a component of electron carrier and coenzyme NAD+
Adenosine +2 PO4 → Adenosine Diphosphate (ADP)
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Energy Coupling & ATP
Energy coupling: use of exothermic reaction to drive an endothermic reaction
Adenosine triphosphate ATP tail: high negative charge ATP hydrolysis: release of free E Phosphorylation (phosphorylated
intermediate)~ enzymes
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ATP - Life’s Energy Currency
Energy is released when ATP is hydrolyzed (broken down) to ADP.
ATP is restored from ADP and an input of energy.
ATP’s energy is used to drive endergonic (energy-requiring) reactions.
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ATP
Chemical work-ATP supplies the energy needed to the macromolecules that comprise the cell
Mechanical work- ATP supplies the energy needed to permit muscles to contract, cilia and flagella to beat
Transport work- ATP supplies the energy the cells need to pump substances e.g. active transport
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Enzymes
Catalytic proteins: change the rate of reactions w/o being consumed
Free E of activation (activation E): the E required to break bonds
Substrate: enzyme reactant Active site: pocket or groove on
enzyme that binds to substrate Induced fit model