Lecture 10 Flashcards
What is the cell’s workhorse?
proteins
What is one of the cell’s workhorses?
enzymes
What are enzymes?
proteins (or RNA)
What do enzymes do?
-CATALYSE the making and breaking of covalent bonds in the cell
-INCREASE REACTION RATES
-allow MILDER reaction conditions (i.e. near neutral pH and low temperatures)
-can DISPLAY VERY HIGH specificity (distinguish between optical isomers)
-REGULATE reactions and pathways
Who discovered enzymes, and how?
Anselme Payen
-discovered in a brewery
-discovered first enzyme diastase
-did NOT know amylase was a protein
Enzymes work by lowering what?
they lower the activation energy
What are the four catalysis mechanisms/key features to lower the activation energy?
Proximity
Orientation
Strain/ distortion
Acid-base catalysis
What is the proximity catalysis mechanism?
What is the orientation catalysis mechanism?
What is the strain/distortion catalysis mechanism?
if binding puts strain on bond making it easier for reaction to occur
enzymes encourage substrate distortion into its transition state conformation
What is the acid/base catalysis mechanism?
protons (H+) donated/accepted or hydroxyls (OH-) a great nucleophile is generated:
-enzymes overcome very low concentrations of these reactive molecules in the environment
-in the active site of enzymes concentration of OH- or H+ in vicinity of bond to be attacked can be effectively 1 M
Enzymes have remarkable specificity- what can explain this?
LOCK AND KEY: binding site has complementary shape to substrate
INDUCED FIT: contact between part of the binding site and the substrate induces a change in shape of the active site to bind to the substrate
What are enzymes?
a. They catalyze reactions
b. They increase reaction rates
c. They allow milder reaction conditions
d. They can display very high specificity
e. All of the above
e. All of the above
Explain Fischer’s Lock and Key
The substrate fits perfectly into it’s enzyme’s active site leading to an enzyme complex
-the enzyme and substrate fit together like a lock and a key
-substrate complements catalytic site geometry
Explain Induced Fit
The substrate and enzyme do not appear to be a perfect fit, but the substrate induces the enzyme to change shape of the binding site so they can fit
Enzyme active sites share what five common features?
1) The active site is a three-dimensional cleft or crevice created by amino acids from different parts of the primary structure.
2) The active site constitutes a small portion of the enzyme volume.
3) Active sites create unique MICRO ENVIRONMENTS.
4) The interaction of the enzyme and substrate at the active site involves MULTIPLE WEAK interactions.
5) Enzyme specificity depends on the molecular architecture at the active site.
What is unique about lysozyme active site residues?
they are distributed among the sequence appearing to be scattered, but when folded they all come together to form the active site
What are the four types of specificity?
1) Absolute
2) Bond
3) Group
4) Stereo
What is absolute specificity?
substrate specific
-enzyme specific to only one substrate
Urease?
What is bond specificity?
bond type specific
-enzyme specific to certain types of bonds
What is group specificity?
chemical group specific
-enzyme specific to certain types of chemical groups
What is stereo specificity?
chirality specific (i.e. D/L isomers)
-enzyme specific to stereochemistry (chirality) of substrate
The active site of an enzyme:
a) is a series of amino acids which bind the enzyme
b) is a linear sequence of amino acids that react with each other
c) binds covalently to the substrate
d) allows water to enter into the active site and thereby solvate the substrate
e) none of the above
e) none of the above
