Lecture 4

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Enzymes and reactions

Spontaneity = ___

Enzyme = Decrease G# = _________________Mechanism = “Induced fit”

Rate = ___

“Active site” ________________ stabilize TS

Decreasing DG‡: Proximity + Orientation

Active site:

Bring products togetherIn precise orientation

Not just binding!

Forces change in substrate conformation as well!

Active site interactions can stabilize the TSActive site residues can initiate reactions

Keep molecules under “strain” to facilitate reaction

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 importantHow is the shape formed?

Formation of active sites

Active site review

Small part of total enzyme

3D architecture is importantSpecific residues importantNot necessarily contiguous residues

How does an active site form?

Protein must “fold”into structureHow does protein “fold?”

First, understand protein compositionProteins made up of _____________

What is an amino acid?

Molecule with _____ group and ___________ group

Each amino acid has a different “R” groupThere are _____ different amino acids

H2

NCOOH

C

R

H

Amino acids, pH and charge

Amino acid titration curve

Asp titration curve

Amino acids in cells…

H2

NCOOH

C

R

H

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?