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They make things, they break things
What are some of the subjects that were covered in lecture this semester?
Which of these topics involve enzymes? What are some of the enzymes that you
discussed?
Some enzymes you’ve learned about: G3P dehydrogenase ATP synthase RNA polymerase (primase) Ligase DNA polymerase Kinase (aka phosphotransferase) Topoisomerase (a gyrase) Aminoacyl-tRNA synthetase And more…
Most enzymes are globular proteins Catalytic activity
Not used up in a reaction
What have you noticed about their names? Often have “-ase” suffix Often have function in name
An RNase
Ribozymes? Some enzymes are made of RNA
Example?
Enzymes lower the required Energy of Activation This allows for faster reactions This facilitates reactions that otherwise could
not occur Some enzymes can make reactions go trillions of
times faster Carbonic anhydrase (stomach) can catalyze over
1,000,000 reactions per second Temperature versus selectivity
Progress of the reaction
Products
Reactants
∆G < O
Transition state
Fre
e en
erg
y EA
DC
BA
D
D
C
C
B
B
A
A
Progress of the reaction
Products
Reactants
∆G is unaffectedby enzyme
Course ofreactionwithoutenzyme
Fre
e en
erg
y
EA
withoutenzyme EA with
enzymeis lower
Course ofreactionwith enzyme
Lock and Key Older theory Stabilization of
transition state? Enzyme flexibility?
Induced Fit Preferred method
of explanation
Substrate
Active site
Enzyme Enzyme-substratecomplex
(b)(a)
Enzyme
Products arereleased.
Products
Substrates areconverted toproducts.
Active site can lower EA
and speed up a reaction.
Substrates held in active site by weakinteractions, such as hydrogen bonds andionic bonds.
Substrates enter active site; enzyme changes shape such that its active siteenfolds the substrates (induced fit).
Activesite is
availablefor two new
substratemolecules.
Enzyme-substratecomplex
5
3
21
6
4
Substrate
Enzymes often catalyze only a single reaction
Enzymes are typically very specific
Enzymes can be inhibited by compounds Inhibitor often similar in structure to substrate
Enzymes can be inhibited at active site or a different part of the molecule Allosteric inhibition
Enzymes can be activated at allosteric sites
(a) Normal binding (c) Noncompetitive inhibition(b) Competitive inhibition
Noncompetitive inhibitor
Active siteCompetitive inhibitor
Substrate
Enzyme
NSAIDs Non-steroidal anti-inflammatory drugs Examples include: Ibuprofen, Rofecoxib,
Acetylsalicylic acid Inhibit COX-2 enzyme (cyclooxygenase-II)
COX-2 involved in synthesis of prostaglandins, which are involved in inflammation and pain
Non-protein chemical required for activity of protein
Many vitamins are cofactors E.g., Iron, Manganese, Zinc
Cofactor functions Assist with chemical reaction
Mg2+ and Taq Allow protein to fold
E.g., zinc fingers
First (often) enzyme in a biosynthesis pathway is an allosteric enzyme Multiple binding sites Binding to effector changes conformation
Enzyme 1
Enzyme 2 Enzyme 3
Inter-mediate
Inter-mediate Product
Start ofpathway
Presence of product inhibits enzyme 1
X
Also known as feed-back inhibition
Enzyme that oxidizes a substrate to form light luciferin + O2 → oxyluciferin + light
Utilized by multiple organisms Fishes, fungi, copepoda, shrimps, algæ, and
more
Reporter genes Various assays Forensics
http://www.youtube.com/watch?v=UXl8F-eIoiM Short
http://www.youtube.com/watch?v=9frgs8lUNac Long