Enzymes Review of Reaction Terms G = (Free Energy of Products) - (Free Energy of Reactants)
-
Upload
baldric-bridges -
Category
Documents
-
view
215 -
download
1
Transcript of Enzymes Review of Reaction Terms G = (Free Energy of Products) - (Free Energy of Reactants)
![Page 1: Enzymes Review of Reaction Terms G = (Free Energy of Products) - (Free Energy of Reactants)](https://reader036.fdocuments.in/reader036/viewer/2022062519/5697bfc51a28abf838ca6e8e/html5/thumbnails/1.jpg)
EnzymesEnzymes
![Page 2: Enzymes Review of Reaction Terms G = (Free Energy of Products) - (Free Energy of Reactants)](https://reader036.fdocuments.in/reader036/viewer/2022062519/5697bfc51a28abf838ca6e8e/html5/thumbnails/2.jpg)
Review of Reaction Terms
• G = (Free Energy of Products) - (Free Energy of Reactants)
![Page 3: Enzymes Review of Reaction Terms G = (Free Energy of Products) - (Free Energy of Reactants)](https://reader036.fdocuments.in/reader036/viewer/2022062519/5697bfc51a28abf838ca6e8e/html5/thumbnails/3.jpg)
Types of Reactions
• Exergonic– Energy is released– G is negative (more
energy in reactants than products)
– Spontaneous reaction
![Page 4: Enzymes Review of Reaction Terms G = (Free Energy of Products) - (Free Energy of Reactants)](https://reader036.fdocuments.in/reader036/viewer/2022062519/5697bfc51a28abf838ca6e8e/html5/thumbnails/4.jpg)
Types of Reactions
• Endergonic– Absorbs energy (energy
must be put into the reaction)
– G is positive (more energy in the products than the reactants)
– Nonspontaneous reaction
![Page 5: Enzymes Review of Reaction Terms G = (Free Energy of Products) - (Free Energy of Reactants)](https://reader036.fdocuments.in/reader036/viewer/2022062519/5697bfc51a28abf838ca6e8e/html5/thumbnails/5.jpg)
Enzyme Function
• Enzymes are proteins that speed up reactions– Typically end in “ase” (ex. lactase)
• Highly specific – Substrate = the molecules an enzyme acts on
• Can be regulated
• Return to original structure/shape after reaction– reusable
![Page 6: Enzymes Review of Reaction Terms G = (Free Energy of Products) - (Free Energy of Reactants)](https://reader036.fdocuments.in/reader036/viewer/2022062519/5697bfc51a28abf838ca6e8e/html5/thumbnails/6.jpg)
Enzyme Function
• Immense catalytic power• Enzymes speed up a
reaction by lowering the activation energy (EA)
• Enzymes do NOT change the energy in the reactants or the products.
![Page 7: Enzymes Review of Reaction Terms G = (Free Energy of Products) - (Free Energy of Reactants)](https://reader036.fdocuments.in/reader036/viewer/2022062519/5697bfc51a28abf838ca6e8e/html5/thumbnails/7.jpg)
Enzymes & Substrates• Enzymes bring substrates
together in favorable ways in an Enzyme-Substrate Complex– Proximity and Orientation– Altered Environment (esp. a
hydrophobic pocket)– Hydrogen Transfer
• Move H from one molecule to another (to increase reactivity)
• Enzyme binds the substrate in the active site
substrates
Enzyme-Substrate Complex
products
![Page 8: Enzymes Review of Reaction Terms G = (Free Energy of Products) - (Free Energy of Reactants)](https://reader036.fdocuments.in/reader036/viewer/2022062519/5697bfc51a28abf838ca6e8e/html5/thumbnails/8.jpg)
Active Sites
• Takes up relatively small part of enzyme
• 3-D region that is put together by different parts of the linear structure
• Clefts or crevices
Active site
![Page 9: Enzymes Review of Reaction Terms G = (Free Energy of Products) - (Free Energy of Reactants)](https://reader036.fdocuments.in/reader036/viewer/2022062519/5697bfc51a28abf838ca6e8e/html5/thumbnails/9.jpg)
Active Sites
• Substrate bound to active site by:– Ionic attractions– Van der waals forces– Hydrophobic interactions– Hydrogen bonds
![Page 10: Enzymes Review of Reaction Terms G = (Free Energy of Products) - (Free Energy of Reactants)](https://reader036.fdocuments.in/reader036/viewer/2022062519/5697bfc51a28abf838ca6e8e/html5/thumbnails/10.jpg)
Induced Fit
• Enzymes and substrates do not fit together like a lock and key
• Active site is more flexible– molds around the substrate(s)– Like a glove around a
hand
![Page 11: Enzymes Review of Reaction Terms G = (Free Energy of Products) - (Free Energy of Reactants)](https://reader036.fdocuments.in/reader036/viewer/2022062519/5697bfc51a28abf838ca6e8e/html5/thumbnails/11.jpg)
Coenzymes & Cofactors• Non-protein molecules that are needed for
an enzyme to function
• When a coenzyme or cofactor binds allows it to function properly (activates it)
• Ex. Metal ions, certain vitamins
Image taken without permission from http://www2.raritanval.edu/departments/Science/full-time/Weber/Microbiology%20Majors/Chpater5/chapter5sub/chapter5sub_print.html
![Page 12: Enzymes Review of Reaction Terms G = (Free Energy of Products) - (Free Energy of Reactants)](https://reader036.fdocuments.in/reader036/viewer/2022062519/5697bfc51a28abf838ca6e8e/html5/thumbnails/12.jpg)
Inhibition
• Competitive Inhibitor– Binds to the active site– Competes with the substrate– Can be overcome by adding
more substrate
• Noncompetitive Inhibitor– Binds to enzyme in an area
other than the active site– Changes the shape of the
active site to prevent substrate binding
![Page 13: Enzymes Review of Reaction Terms G = (Free Energy of Products) - (Free Energy of Reactants)](https://reader036.fdocuments.in/reader036/viewer/2022062519/5697bfc51a28abf838ca6e8e/html5/thumbnails/13.jpg)
Phosphorylation
• Addition of a phosphate group to an enzyme
• This changes its structure– Can either activate or
inactivate the enzyme+ ATP + ADP
Phosphate group
![Page 14: Enzymes Review of Reaction Terms G = (Free Energy of Products) - (Free Energy of Reactants)](https://reader036.fdocuments.in/reader036/viewer/2022062519/5697bfc51a28abf838ca6e8e/html5/thumbnails/14.jpg)
Feedback Inhibition
• Molecules can bind to enzymes at a “regulatory” site to inhibit its activity (like a noncompetitive inhibitor)– Molecule is usually end-
product of chain of reactions– Stops entire chain of
reactions
![Page 15: Enzymes Review of Reaction Terms G = (Free Energy of Products) - (Free Energy of Reactants)](https://reader036.fdocuments.in/reader036/viewer/2022062519/5697bfc51a28abf838ca6e8e/html5/thumbnails/15.jpg)
Allosteric Inhibition
• When a protein’s function is affected by the binding of a molecule at a location other than the active site
• Both allosteric inhibition and activation is possible.
![Page 16: Enzymes Review of Reaction Terms G = (Free Energy of Products) - (Free Energy of Reactants)](https://reader036.fdocuments.in/reader036/viewer/2022062519/5697bfc51a28abf838ca6e8e/html5/thumbnails/16.jpg)
Cooperativity
• Occurs in enzymes with multiple subunits (chains)
• Binding a substrate to one subunit makes it easier for all of the rest of the subunits to bind substrates
![Page 17: Enzymes Review of Reaction Terms G = (Free Energy of Products) - (Free Energy of Reactants)](https://reader036.fdocuments.in/reader036/viewer/2022062519/5697bfc51a28abf838ca6e8e/html5/thumbnails/17.jpg)
Other methods of Regulation
• Some enzymes are synthesized in an inactive form and activated later by cleavage
• Why would removing part of the enzyme changes its function?– Removing amino acids changes its structure which
then changes its function
Cleavage by Enterokinase
Inactive trypsinogen Active trypsin
![Page 18: Enzymes Review of Reaction Terms G = (Free Energy of Products) - (Free Energy of Reactants)](https://reader036.fdocuments.in/reader036/viewer/2022062519/5697bfc51a28abf838ca6e8e/html5/thumbnails/18.jpg)
Effects of Temperature on Enzymes
• Each enzyme has a particular temperature that it functions best at
• At non-ideal temperatures:– Too high: Extra energy
causes molecules to move around too much bonds can’t be maintained
– Too low: Active site becomes less flexible can’t catalyze reactions as well.
![Page 19: Enzymes Review of Reaction Terms G = (Free Energy of Products) - (Free Energy of Reactants)](https://reader036.fdocuments.in/reader036/viewer/2022062519/5697bfc51a28abf838ca6e8e/html5/thumbnails/19.jpg)
Effect of pH on Enzymes
• Each enzyme also has a pH that it functions best at
• At non-ideal pHs excess H+ and OH- ions interfere with ionic attractions between + and – charged amino acids.