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Lecture 4
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Enzymes and reactions
Spontaneity = ___
Rate = ___
Enzyme = Decrease G# = _________________
Mechanism = “Induced fit”
“Active site” ________________ stabilize TS
Decreasing DG‡: Proximity + Orientation
Active site:
Bring products together
In precise orientation
Not just binding!
Forces change in substrate conformation as well!
Keep molecules under “strain” to facilitate reaction
Active site interactions can stabilize the TS
Active site residues can initiate reactions
Different enzymes = Different mechanisms
Glc  Glc-6-P: Enzyme = Hexokinase
http://web.chem.ucsb.edu/~molvisual/ABLE/induced_fit/index.html
Specificity of enzymes - Isomers
Specificity of enzymes - Stereoisomers
Effects of specificity – Tastes!
Effects of specificity – Calories!
http://commons.wikimedia.org/wiki/File:D_et_l_glucose.png
Effects of specificity – Treatment!
3D shape is important!
OK. Fine. So the shape of the active site is important
How is the shape formed?
Formation of active sites
Active site review
Small part of total enzyme
3D architecture is important
Specific residues important
Not necessarily contiguous residues
How does an active site form?
Protein must “fold”into structure
How does protein “fold?”
First, understand protein composition
Proteins made up of _____________
What is an amino acid?
Molecule with _____ group and ___________ group
H
H2N
C
COOH
R
Each amino acid has a different “R” group
There are _____ different amino acids
Amino acids, pH and charge
Amino acid titration curve
Asp titration curve
Amino acids in cells…
H
H2N
C
R
COOH
The Peptide bond: Joining amino acids
Nomenclature: Nt -> Ct
Charge on peptides is cumulative
OK. What does this all have to do with enzymes?
What is needed for proteins to fold correctly?
Can we design experiment to test?