BCHM-3050 Lecture Notes - Lecture 9: Myoglobin, Hydrogen Bond, Stoichiometry
26 Jun 2018
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Chapter 8: Biological Catalysis
Enzymes and Enzyme Classes
Enzyme: biological, protein-based catalyst utilized by living organisms to accelerate biological
reactions via lowering the activation energy of the reaction in question.
Enzyme activities can be categorized by class:
oOxidoreductases
oTransferases
oHydrolases
oLyases
oIsomerases
oLigases
Oxidoreducatases: enzymes that promote the transfer of oxygens from one compound to the next
(alcohol dehydrogenases). Gain H+ = reduced. Lose H+ = oxidized
Transferases (hexokinase): phosphorylation of a compound. Take one part of one compound and
putting it on the next. CAN TRANSFER ANY GROUP
Hydrolases: uses water to help cleave any bond (carboxypeptidase A). Includes ATP cleavage
Lyases: cleave a single compound in 2 parts. CAN REMOVE ANY GROUP
Isomerases: compound A goes in and isomerized to compound B.
Ligases: opposite of a lyase. Use ATP to add something together. CAN ADD ANY GROUP.
Free Energy Diagram
**KNOW PARTS OF THE GRAPH
X axis = time
Activation Energy: the energy required by a starting species to undergo a reaction. Sometimes written
as Ea.
If ΔGprod < ΔGreact, then ΔGrxn = NEGATIVE
If ΔGprod > ΔGreact, then ΔGrxn = POSITIVE
Enzymes Stabilize Transition States
Enzymes stabilize the transition state to achieve rate enhancement (catalysis)
The size of the curve has decreased (activation energy for a catalyzed energy is LOWER than a on
catalzyed energy). ΔGrxn and the ΔG of A & B ALL REMAIN THE SAME because of Hess’ Law and
state functions.
oΔH, ΔS, etc. stay the same
Raising the temperature (T) INCREASES the rate constant (k) via increasing the AVERAGE kinetic
energy of the substrate.
oTemperature is an average of kinetic energy
oΔG of transition state (activation energy) – lowering the ΔG of the transition state by stabilizing
the transition state also INCREASES the rate constant (k).
oR = 8.314 J/molK
oA = frequency of collisions
Calculating Changes in k
Changes in the rate constant (k) and the dependence on TEMPERATURE =
ln = k2/k1 = Ea/R (1/T1 – 1/T2)
** To use the equation, the activation energy must be KNOWN)
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Enzyme: biological, protein-based catalyst utilized by living organisms to accelerate biological reactions via lowering the activation energy of the reaction in question. Enzyme activities can be categorized by class: oxidoreductases, transferases, hydrolases, lyases, isomerases, ligases. Oxidoreducatases: enzymes that promote the transfer of oxygens from one compound to the next (alcohol dehydrogenases). Take one part of one compound and putting it on the next. Hydrolases: uses water to help cleave any bond (carboxypeptidase a). Lyases: cleave a single compound in 2 parts. Isomerases: compound a goes in and isomerized to compound b. Activation energy: the energy required by a starting species to undergo a reaction. If gprod < greact, then grxn = negative. If gprod > greact, then grxn = positive. Enzymes stabilize the transition state to achieve rate enhancement (catalysis) The size of the curve has decreased (activation energy for a catalyzed energy is lower than a on catalzyed energy).
