BISC 101 Lecture Notes - Lecture 6: Peptide, Competitive Inhibition, Reaction Rate

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BISC 101 – Lecture 6 – Metabolism and Enzymes
Metabolism And Enzymes
An organism’s metabolism transforms matter and energy, subject to eh laws of
thermodynamics
Metabolism: The totality of an organism’s chemical reactions
Metabolism is a property of life that arises from interactions between molecules
within the cell
Metabolic Pathway: Begins with a specific molecule and ends with a product
Each step is catalyzed by a specific enzyme
Catabolic and Anabolic Pathways
Catabolic Pathways: Exergonic reactions that release energy by breaking down
complex molecules into simpler compounds
oHydrolysis reactions occur
oEx: Cellular Respiration: The breakdown of glucose in presence of
oxygen
oExergonic: Net release of free energy that are spontaneous
oMore energy in the reactants then products
Anabolic Pathways or Biosynthetic Reactions: Endergonic reactions that absorb
or consume energy to build complex molecules from simpler ones
oDehydration synthesis occurs
oEx: Synthesis of protein from amino acids
oEndergonic: Absorbs free energy from its surroundings and are non –
spontaneous
oMore energy in the products rather than reactants
Anabolic reactions require energy from catabolic reactions to synthesize more
complex organic molecules
Spontaneity
The free – energy change of a reaction tells us whether or not the reaction
occurs spontaneously
Reactions that occur spontaneously require no input of energy
oSpontaneous processes aren’t always necessarily fast
oEx: Explosions occur fast but rusting of an old car is slow
Other reactions that do not occur spontaneously require energy
Free Energy: Energy that can do work when temperature and pressure are
uniform in a living cell
ΔG: Overall change in free energy; Energy of products – Energy of reactants
oΔG = ΔH – TΔS
Enthalpy (ΔH): Energy required to break chemical bonds
Entropy (ΔS): Measure of disorder or randomness
Negative Change in free energy
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oReaction is spontaneous
oExergonic: Net release of free energy
Reactants hold more energy than products
oFavorable since no input of energy is needed
Positive Change in free energy
oNon – spontaneous
oEndergonic: Absorbs free energy from its surrounds
Products hold more energy than reactants
oNon – favorable since reactions require input of energy
Free energy at zero = Equilibrium
Entropy and free energy are inversely related
ATP
Most energy coupling in cells is mediated by ATP
ATP: Adenosine Triphosphate is the cell’s energy shuttle
ATP has the following components:
1. Ribose Sugar
2. Adenine Base
3. Three phosphate groups
The bonds between phosphate groups of ATP’s tail can be broken by hydrolysis
Energy is released from ATP when the terminal phosphate bond is broken
oThis reaction is referred to as ATP hydrolysis
oThis energy is used in various ways like active transport or muscle
contractions
Energy from the exergonic reaction (ATP hydrolysis) can be used to drive an
endergonic reaction
oThis leads to an overall reaction that is exergonic
Enzymes: An Introduction to Catalysis
Most chemical reactions in cell do not occur fast enough to support life unless a
catalyst is present
Reactions take place when reactants:
oCollide in a precise orientation
oHave enough kinetic energy to overcome repulsion between electrons
that come into contact as a bond forms
Substrates: Reactant molecules
oEnzymes are effective catalysts because they bring reactant molecules
together in a specific orientation so that the electrons involved in the
reaction can interact
Enzymes can also affect the amount of kinetic energy reactants must have for a
reaction to proceed
A collision between reactants create a combination of old and new bonds
Most proteins are enzymes
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