Biochem Lecture 7

Front 1

define catalyst

Back 1

increase the rate of a chemical reaction without being consumed

Front 2

T/F catalysts alter the thermodynamics (delta G or Keq) of a reaction

Back 2

False, enzymes lower the activation energy but do not change the overall thermodynamics

Front 3

A reaction will occur spontaenously if delta G is...

Back 3

negative (exergonic)

Front 4

How do enzymes increase the rate of a reaction

Back 4

they lower the activation energy

Front 5

How do enzymes lower the activation energy of a reaction? What are the 5 strategies used?

Back 5

they stabilize the transition state
1. orientation/ proximity/ entropic effects
2. covalent catalysis
3. acid/ base catalysis
4. metal ion catalysis
5. strain/ distortion

Front 6

What catalytic stragies do serine proteases use

Back 6

entropic effects, covalent catalysis, acid base catalysis

Front 7

What component of the serine proteases is responsible for the acid/ base catalysis

Back 7

The Asp-His group

Front 8

What is the role of the serine residue in serine proteases

Back 8

it acts as a nucleophile that attacks the carbonyl carbon to form an acyl enzyme intermeditae

Front 9

what is delta G at equilibrium

Back 9

0

Front 10

What are the two models of subtrate binding

Back 10

lock and key
induced fit

Front 11

How do orientation/ proximity effects catalyze reactions

Back 11

they orient the reactants and products and keep them physically close together

Front 12

how does covalent catalysis make reactions go faster

Back 12

a covalent intermediate is formed, the reaction is broken into two smaller steps with two different, smaller activation energies

Front 13

How does acid/ base catalysis make reactions go faster

Back 13

acid/ base reactions can acitvate nucleophiles or electrophiles (deprotonate the nucleophile, protonate a carbonyl group etc)

Front 14

How does strain/ distortion catalysis make reactions go faster

Back 14

straining the substrate reaises it's energy and brings it closer to the acivation energy of the reaction

Front 15

Describe what happens in the serine protease mechansim after the polypeptide binds

Back 15

Histidine hydrogen bonds the proton on the serine OH group making serine a strong nucleophile

Front 16

What happens in the serine protease mechaism after histidine hydrogen bonds the serine's OH hydrogen

Back 16

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

Front 17

What happens in the serine protease mechaism after the acyl enzyme intermediate is formed?

Back 17

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

Front 18

After the amino group leaves (protonated by histidine), what happens next in the serine protease mechanism?

Back 18

Histidine deprotonates a water molecule making a strongly nuclephilic hydroxide ion. The hydroxide attacks the ester linkage leftover from the polypeptide.

Front 19

What happens in the serine protease mechaism after the hydroxide ion attacks

Back 19

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