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