BIOL 2160 Lecture Notes - Lecture 3: Exergonic Reaction, Allosteric Regulation, Activation Energy

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5 Feb 2017
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CHAPTER 3 BIOL 2160
REACTIONS
A+BC+D
REACTANTSPRODCUTS
This equation represents cellular respiration: C6H12O6+6O26CO2+6H2O
Reaction proceeds in both the forward and the reverse directions at the same time. It is
bidirectional.
Net movement in the forward direction.
Catabolic reaction: breakdown of larger molecules into smaller molecules. Releases
energy.
Anabolic reaction: production of larger molecules from smaller reactants. Requires
energy.
BIOENERGETICS
First Law of Thermodynamics: energy cannot be destroyed or created, only
transformed.
o Conversion of light energy into glucose by plants
Second Law of Thermodynamics: with every transfer or transformation of energy,
some useable energy is released as heat.
o 100 units potential energy (free energy) 75 units kinetic energy (thermal) + 25
units kinetic energy (motion).
ENDERGONIC VS. EXERGONIC
Endergonic reactions: chemical reactions that require an input of energy. Products
contain more free energy than the reactants. Energetically uphill.
o Example: ball at bottom of hill needs energy to get up hill.
Cell phone needs energy, battery releases energy.
o Do not proceed spontaneously, only when energy is put into them
o Energy from the environment (food) is broken down in exergonic reactions to
drive the endergonic reactions in our bodies.
Exergonic reactions: chemical reactions that release energy. Products will have less free
energy than the reactants. Energetically downhill.
o Tend to proceed spontaneously
o Example: ball at top of hill rolling down
ACTIVATION ENERGY
The energy required for the reactants to engage in a reaction.
Most molecules lack the activation energy needed for a reaction to occur.
Activation energy can take the form of heat (molecules colliding together)
Activation energy barriers can also be surmounted through catalysts
ENZYMES
A class of proteins that serve as biological catalysts. Catalysts are chemicals that:
o Increase the rate of a reaction
o Are not changed by the reaction (so can be used repeatedly)
o Have no effect on free energy of reactants or products.
o In enzymatic reactions, reactants are called substrates
Speeds up reaction but doesn’t change or make reaction happen
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o
o speed up reaction by lowering activation energy
LIGAND-RECEPTOR INTERACTIONS
Ligand B has a higher affinity for the protein than Ligand A because it can make more
bonds with the protein.
o Ligand that makes more protein bonds has a high affinity (based on charge)
Anything that binds to receptors, have to be specific to each other.
Low receptor concentration
Most enzymes specific for one, maybe two, substrates.
NAMING ENZYMES
The first enzymes discovered were given arbitrary names. An international committee
later decided to end all enzymes with the suffix ase.
They also decided to make the first part of the name apply to the function of the enzyme.
o Phosphatases remove phosphate groups.
o Synthetases catalyze dehydration synthesis.
ENZYME ACTIVITY
Measured by the rate at which substrate is converted to product
Influenced by:
o Concentration of enzyme and substrate
o Enzyme-substrate affinity
o Temperature: increase tempincrease rate of reaction
Too much heat denatures enzymes
o pH: optimum pH for where the enzyme is located in your body.
Optimum pH is due to changes in enzyme conformation
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