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19 Cards in this Set

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define catalyst
increase the rate of a chemical reaction without being consumed
T/F catalysts alter the thermodynamics (delta G or Keq) of a reaction
False, enzymes lower the activation energy but do not change the overall thermodynamics
A reaction will occur spontaenously if delta G is...
negative (exergonic)
How do enzymes increase the rate of a reaction
they lower the activation energy
How do enzymes lower the activation energy of a reaction? What are the 5 strategies used?
they stabilize the transition state
1. orientation/ proximity/ entropic effects
2. covalent catalysis
3. acid/ base catalysis
4. metal ion catalysis
5. strain/ distortion
What catalytic stragies do serine proteases use
entropic effects, covalent catalysis, acid base catalysis
What component of the serine proteases is responsible for the acid/ base catalysis
The Asp-His group
What is the role of the serine residue in serine proteases
it acts as a nucleophile that attacks the carbonyl carbon to form an acyl enzyme intermeditae
what is delta G at equilibrium
0
What are the two models of subtrate binding
lock and key
induced fit
How do orientation/ proximity effects catalyze reactions
they orient the reactants and products and keep them physically close together
how does covalent catalysis make reactions go faster
a covalent intermediate is formed, the reaction is broken into two smaller steps with two different, smaller activation energies
How does acid/ base catalysis make reactions go faster
acid/ base reactions can acitvate nucleophiles or electrophiles (deprotonate the nucleophile, protonate a carbonyl group etc)
How does strain/ distortion catalysis make reactions go faster
straining the substrate reaises it's energy and brings it closer to the acivation energy of the reaction
Describe what happens in the serine protease mechansim after the polypeptide binds
Histidine hydrogen bonds the proton on the serine OH group making serine a strong nucleophile
What happens in the serine protease mechaism after histidine hydrogen bonds the serine's OH hydrogen
serine acts a nucleophile and attacks the carbonyl carbon of the peptide forming a tetrahedral acyl-enzyme intermediate. the negative charge on the oyxgen is stabilized by hydrogen bonding to another neraby serine
What happens in the serine protease mechaism after the acyl enzyme intermediate is formed?
the electrons from the carbonyl oxygen fall back down and amino side of the peptide is ejected. Histidine gives the proton back to the amino group
After the amino group leaves (protonated by histidine), what happens next in the serine protease mechanism?
Histidine deprotonates a water molecule making a strongly nuclephilic hydroxide ion. The hydroxide attacks the ester linkage leftover from the polypeptide.
What happens in the serine protease mechaism after the hydroxide ion attacks
A tetrahedral intermediate is formed, the oxygen is stabilized by the oxyanion hole (serine, glycine). The intermediate collapses and a carboxylate anion (the other half of the polypeptide) is ejected