Apple Experiment Come down and get an apple and a slice of lemon. When you get back to your seat: 1. Take a big bite of your delicious apple. 2. Immediately squeeze lemon juice over the apple flesh that is now exposed from the bite. 3. IMPORTANT! Don’t get lemon juice all over the apple. Make sure that it is ONLY on the area that you just bit! 4. Set the lemon aside and wipe any lemon juice off of your hands with a napkin. 5. Take another bite from the opposite side of your apple. 6. Set your apple aside.

What Are Enzymes? ( Enzymes are __________ (tertiary and quaternary structures). An enzyme is a _________ in cellular reactions. A catalyst accelerates a reaction.

Enzymes Are ________ for what they will catalyze Are _________ Usually end in -_____-Sucrase-Lactase-Maltase

How do enzymes work? Each enzyme has a unique 3-D shape, including a surface groove called an ______ _____. The enzyme works by binding a specific chemical reactant (_________) to its active site, causing the substrate to become unstable and react. The resulting __________ is then released from the active site.

How do enzymes work? Enzymes work by _______ ______ which ________ activation energy.

Enzyme-Substrate Complex enzyme The reactant an enzyme acts on is specifically called the _________. Enzyme Substrate Joins

______ _____ enzyme substrate A specific region of an enzyme molecule which binds to the substrate. Enzyme Substrate Active Site

Shape of a Protein An enzyme fits with its substrate like a ____ and ____.

EnzymeAnimation : Gary E. Kaiser View : hill.com/sites/ /student_view0/chapter2/animation__how_enzyme s_work.html

Enzymes are ____ ________ in the reactions they catalyze. Think of them as tiny machines in manufacturing. The more machines, the faster the accumulation of _________. Image: Wine Bottling : Wine Vats:

Formats for writing a chemical reaction. ( ________ ) _______ + ________ > _________ ( ________ ) __________ > ________ ________

4 levels of Protein Structure

How Do You Stop an Enzyme? How Do You Stop an Enzyme? Irreversible egg protein denaturation caused by high temperature (while cooking it). _______________ Alteration of a protein shape through some form of external stress Denatured protein can’t carry out its cellular function.

Factors Affecting Enzyme Activity Temperature pH Cofactors & Coenzymes Inhibitors

Temperature & pH Think about what kind of cell or organism an enzyme may work in… Temperatures far above the normal range _________ enzymes (This is why very high fevers are so dangerous. They can cook the body’s proteins) (This is why very high fevers are so dangerous. They can cook the body’s proteins) Most enzymes work best near __________ pH (6 to 8).

Coenzymes & Cofactors substances (zinc, iron, copper, vitamins) Non-protein substances (zinc, iron, copper, vitamins) are sometimes need for proper enzymatic activity. Coenzyme versus Cofactor: What’s the dif? _________ more general term. Includes inorganic and organic molecules. _________ type of Cofactor, But specifically organic molecules. Image: EnzymeCofactor : Public domain Wiki, Ribbon-diagram showing carbonic anhydrase II. The grey sphere is the zinc cofactor in the active site.

Coenzyme : Vitamin B12 Example : Example : Most _________ are coenzymes essential in helping move atoms between molecules in the formation of carbohydrates, fats, and proteins. Exclusively synthesized by ___________ (found primarily in meat, eggs and dairy products). Image: VitaminB12 : NIH, Public Domain

Two Types of Enzyme Inhibitors 1. ___________ ____________: resembleenzyme’s normal substrate compete active site Chemicals that resemble an enzyme’s normal substrate and compete with it for the active site. Enzyme Competitive inhibitor Substrate

1. Competitive inhibitors: esembleenzyme’s normal substrate compete active site Resemble an enzyme’s normal substrate and compete with it for the active site. Image: Competitive Inhibition : www-biol.paisley.ac.uk/.../chapter3_2.htmlwww-biol.paisley.ac.uk/.../chapter3_2.html

Two Types of Enzyme Inhibitors _______________ ______________: o not enter the active sitebind to another part enzymeenzymechange its shapealtering the active site Do not enter the active site, but bind to another part of the enzyme causing the enzyme to change its shape, altering the active site. Enzyme active site altered Noncompetitive Inhibitor Substrate

Enzyme Inhibitors B locking an enzyme's activity can kill a pathogen or correct a metabolic imbalance. Many _____ are enzyme inhibitors. Enzyme inhibitors are also used as _________ and __________. Images Dead Bug : Prescription Drugs :

Regulation of Enzyme Activity

Enzyme activity is regulated by four different mechanisms* (1) Allosteric control (2) Covalent modification *changes in enzyme levels due to regulation of protein synthesis or degradation are additional, long-term ways to regulate enzyme activity

Allosteric regulation of enzyme activity (1) Allosteric regulation = the activation or inhibition of an enzyme’s activity due to binding of an effector molecule at a regulatory site that is distinct from the active site of the enzyme (2) Allosteric regulators generally act by increasing or decreasing the enzyme’s affinity for the substrate

Covalent modification (1) Covalent modification allows an enzyme to be rapidly activated or inactivated (2) With covalent modification, regulation of a enzyme activity is achieved at low energy costs to the cell (i.e. regulation does not require synthesis of a new enzyme or inhibitory protein). (3) Phosphorylation is a good example of how enzymes are activated and inactivated by covalent post-translational modifications

Covalent modification regulates the catalytic activity of some enzymes Can either activate it or inhibit it by altering the conformation of the enzyme or by serving as a functional group in the active site.

Summary of regulatory mechanisms (1) Allosteric regulation ATP activation/CTP inhibition of ATCase sigmoidal kinetics cAMP activation of cAMP-dependent protein kinase (2) Reversible covalent modification Phosphorylation Ser/Thr protein kinases, Tyr kinases, kinase cascades

CCC Allosteric Enzyme ATCase + Active relaxed form Inactive tense form ATCase RRRR RRRR RRRR CCC COO - CH 2 HN-C-COO - H H O H 2 N-C-O-PO 3 2- = O H 2 N-C- = COO - CH 2 N-C-COO - H Catalytic subunits Regulatory subunits ATP CTP Nucleic acid metabolism Feedback inhibition AspartateCarbamoyl phosphate Carbamoyl aspartate CTP Juang RH (2004) BCbasics Quaternary structure

Sigmoidal Curve Effect Sigmoidal curve Exaggeration of sigmoidal curve yields a drastic zigzag line that shows the On/Off point clearly Positive effector (ATP) brings sigmoidal curve back to hyperbolic Negative effector (CTP) keeps Consequently, Allosteric enzyme can sense the concentration of the environment and adjust its activity Noncooperative (Hyperbolic) Cooperative (Sigmoidal) CTP ATP vovo vovo [Substrate] OffOn Juang RH (2004) BCbasics

[S] vovo Mechanism and Example of Allosteric Effect A I [S] vovo vovo (+) (-) X X X R = Relax (active) T = Tense (inactive) Allosteric site Homotropic (+) Concerted Heterotropic (+) Sequential Heterotropic (-) Concerted Allosteric site KineticsCooperationModels (-) (+) Juang RH (2004) BCbasics

Activity Regulation of Glycogen Phosphorylase P A P A P P A A Covalent modification P P GP kinase GP phosphatase 1 Non-covalent P A P A P P P A P A A A A AMP ATP Glc-6-P Glucose Caffeine Glucose Caffeine spontaneously R T R T Garrett & Grisham (1999) Biochemistry (2e) p.679