Enzyme Catalysis Flashcards

Question

What does a 20% decrease in ΔG+ do?

Answer 1

20% decrease in ΔG+ can increase the reaction by 10 fold *80% decrease --> 10000 fold increase in v

Answer 2

Region where binds to substrates and other cofactors Contains catalytic groups (2-3 residues) --> directly participate in making and breaking bonds Interaction of enzyme and substrate at active site promotes formation of transition state Active site most responsible for lowering ΔG+

Answer 3

Occupies a 3D cleft or crevice with special micro-environment Water usually excluded from cleft Takes up small % of total enzyme volume

Answer 4

Weak interactions - electrostatic - van Der Waals - H bonding Controls specificity of binding through precise orientation of atoms in the site

Answer 5

Contains 129 AA Only 6 important residues (5% of total sequence) Only 2 are catalytic groups (2% of total sequence) (Glutamate and Aspartate)

Answer 6

substrates found to the active site through multiple noncovalent interactions ^only become significant when numerous substrate atoms come close to numerous enzyme atoms

Answer 7

Releases free energy (binding energy) b/w substrate and the enzyme

Answer 8

Represents the lowering of the activation energy by the enzyme It is released by the formation of many weak interactions from the induced fit

Answer 9

When the enzyme facilitates the formation of the transition state

Answer 10

Unbound enzyme has a rigid active site Substrate has a shape complementary to the active site Enzyme and substrate fit exactly into each other Model explains enzyme specificity but not the stabilization of the transition state by the enzyme

Answer 11

Unbound enzyme has flexibly active site Substrate has arbitrary shape relative to active site After substrate binds, enzyme changes shape and become complementary to the substrate shape Explains both specific you and stabilization and release of binding energy *substrate and enzyme both change and modify to each other*

Answer 12

Active site contains a reactive group (usually powerful nucleophile) that makes a temporary covalent attachment to the substrate during the reaction I.e.: chymotrypsin active site peptide hydrolysis --> O in serine attacks carbonyl C on peptide bond to form a covalent bond

Answer 13

Molecule other than water becomes a proton donor or acceptor I.e.: histidine residue in the active site of chymotrypsin

Answer 14

An enzyme brings together two distinct substrates along a common binding surface I.e.: carbonic anhydrase binding CO2 and water in adjacent sites to facilitate their reaction

Answer 15

1) promote the formation of nucleophiles by direct coordination (during reaction) I.e.: Zn for carbonic anhydrase in CO2 hydration 2) act as electrophile said by stabilizing a negative charge on a reaction intermediate (after reaction) I.e.: Mg for EcoRV endonuclease in DNA hydrolysis 3) serve as a bridge between enzyme and substrate I.e.: Mg for myosin in ATP hydrolysis

Answer 16

A protease Cleaves C terminal aromatic and methionine (large hydrophobic) Use of catalytic triad- Ser195, His57, Asp102 (only 1.2% of total active site AA) Made up of 3 chains= 241 residues

Answer 17

Ln of decimal is negative As fraction becomes smaller, the ln term becomes even more negative ``` Ln0.5= -0.69 Ln0.18= -1.78 ```

Answer 18

It is thermodynamically favorable but kinetic ally unfavorable b/c of the partial double bond character on the peptide bond -->harder to cleave due to the slight + on carbon --> also not a very good electrophile so the nucleophile can't come in and attack properly

Answer 19

Acylation- formation of covalent Acyl-enzyme intermediate 1) His accepts proton from OH group of serine --> Gen base catalysis 2) Alkoxide ion (O-) formed on serine after proton transferred ' 3) O- attacks and forms a covalent bond with the peptide bond that is "hard to cleave" --> specifically attacks the carbon --> formation of tetrahedral intermediate 4) Asp is providing stabilization to the amide group in His 5) tetrahedral intermediate creates an oxyanion hole due to negative charge on the once double bonded oxygen on the substrate 6) His proton (originally from serine) bonded to the N on the once peptide bond 7) cleavage of N with proton (reformation of C=O) and free peptide formed with H bonding with N on His

Answer 20

Provides for hydrogen bonding with the extremely negative oxygen Creates binding energy in the tetrahedral intermediate

Answer 21

Deacylation- regeneration of free enzyme 1) A water H bonds with N on His, leading to a negative O in the water and a good nucleophile. This is the binding energy in the reaction 2) the O- attacks C=O bond 3) formation of Oxyanion again with the loss of the double bond becoming a C-O

Enzyme Catalysis Flashcards

(45 cards)