Enzymes Essential knowledge 4.B.1: Interactions between molecules affect their structure and function.

Exergonic vs Endergonic (Spontaneous vs. Nonspontaneous) Exergonic/Spontaneous: releases energy no energy needed G = + More stable Endergonic/Nonspontaneous: absorbs (stores) energy energy needed G = - Less stable

Chemical Reaction Reactants – go into the reaction (aka substrates) Productions – comes out of a reaction Chemical reactions require bonds of reactants to break and form new bonds to create a product

Activation Energy Energy to get a reaction started Typically if a bond between two molecules exist it is because the molecule is stable  however, a molecule can form bond with new molecules to become even more stable Although this is the case we must first break the bonds in the molecule that is currently stable…we call the energy needed to break these bonds activation energy Fig Progress of the reaction Products Reactants ∆G < O Transition state Free energy EAEA DC BA D D C C B B A A

Partner Share Time Explain ways you can speed up chemical reactions. (At least TWO). Or ways to get the reactants into a transition state.

Ways to Speed Up Reactions Can be in the form of heat (thermal energy) causes the movement of molecules to increase  results in molecules colliding more often  increases rxn rate. Why can’t we use this method in living things? Denatures proteins and kills cells Speed up ALL reactions  not just desired reactions What do we use instead? ENZYMES = Biological catalyst

Class Review – What is an enzyme??????

What is an enzyme? Macromolecule that acts as a catalyst (recall a catalyst speeds up chemical reactions…if you put chocolate syrup in a cup of milk its going to take a really long time before you have chocolate milk; however, you can use a spoon to speed up the reaction-in this example the spoon acts as the catalyst) Enzyme is not consumed…it can be used over and over again…it is not part of the reaction…it just helps the reaction take place Usually a protein (which is going to be our main focus…but recall…there is also RNA that can speed up reactions called ribozymes)

How Enzyme Lower Activation Barrier lowers activation energy by enabling the reactant molecules to absorb enough energy to reach the transition state even at moderate temperatures Cannot change G  does not turn an endergonic reaction (nonspontaneous) into an exergonic reaction (spontaneous); can only speed up a chemical reaction that was already destined to happen When the substrate enters the active site of the protein, interactions between the chemical groups of the substrate and the R groups (side chains) of the amino acids interact causing the enzyme to change shape Lowers the activation energy by causing the bonds of the reactant to break…new bonds form to create more stable molecules (products)

Substrate Specificity of Enzymes Enzymes are very specific to particular reactions  because they are so specific they can control which reactions take place and don’t take place and any particular time

Pair Share Explain how enzymes are so specific to the substrates they recognize and metabolize.

How are enzymes specific to Enzymes? Most enzymes are proteins  macromolecule with unique 3D shape  DNA determines mRNA which determines codon which determines order of amino acid  R groups on amino acid will determine how the protein folds  resulting in protein shape  protein shape will have an activation site that allows the substrate to fit in a way that lowers the activation energy The active site can lower an E A barrier by Orienting substrates correctly Straining substrate bonds Providing a favorable microenvironment Covalently bonding to the substrate

Substrates Enzyme Products are released. Products Substrates are converted to products. Active site can lower E A and speed up a reaction. Substrates held in active site by weak interactions, such as hydrogen bonds and ionic bonds. Substrates enter active site; enzyme changes shape such that its active site enfolds the substrates (induced fit). Active site is available for two new substrate molecules. Enzyme-substrate complex

Pair share – What factors would influence the rate at which a particular amount of enzyme coverts substrate into products.

Pair Share - Answer Concentration of substrate – more substrate = more product UNLESS Enzyme is saturated Enzyme is said to be saturated if all enzyme molecules have their active sites engaged  you will not get products faster by adding more substrate because ALL enzymes are fully activated If we needed to produce products faster when enzymes are saturated the body would need to create more enzymes

Local Conditions (Enzymes Environments) Impact on Enzyme Activity As we have seen the shape of the protein determines its function Changing the shape of the protein would cause the enzyme to be less effective or completely ineffective pH and temperature both have an impact of the enzyme and can change its shape Each enzyme has an optimal temperature and pH value The optimal temperature of most human enzymes is degrees Celsius OR 98.6 degrees F. Increase temps cause reactions to happen faster  but at some point the thermal agitation of the enzyme disrupts the bonds between the R group in the amino acid changing the enzyme shape

Cofactors Nonprotein helpers for catalytic activity May be permanent or reversible Can be inorganic (metals such as zinc, iron, copper) OR organic (vitamins) Organic cofactors are more specifically called coenzymes

Pair Share: What does inhibition mean? What does activation mean? Describe ways you can inhibit or activate an enzyme. Why would you want to inhibit an enzyme?

Enzyme Inhibitors Inhibitors – essentially turn off or inactivate the enzyme; some inhibitors are irreversible (such as toxins or poisons), others are reversible Two main types of inhibition: Competitive: Resembles normal substrate; binds to activation site; reduces productivity of enzyme because blocks substrate from entering active site; can be overcome by increasing the concentration of substrate Noncompetitive: Hinders enzyme by binding to another part of the enzyme other than the active site; results in a change in the enzyme shape  active site changes preventing substrate from entering (a) Normal binding (c) Noncompetitive inhibition (b) Competitive inhibition Noncompetitive inhibitor Active site Competitive inhibitor Substrate Enzyme

Regulation of enzyme activity helps control metabolism Chemical chaos would result if all the cell’s metabolic pathways were operating simultaneously Cell’s regulate enzymes by switching them on or off (gene regulation – essentially making the enzyme or not – another way to say it is expressing the gene or not expressing the gene) Also control metabolism by regulating the activity of the enzyme once it is made

Allosteric Regulation Can be used to activate (turn on) or inhibit (turn off) an enzyme Allosteric regulation is the controlling of an enzyme by the binding of a regulatory (activator or inhibitor) molecule (a) Allosteric activators and inhibitors Inhibitor Non- functional active site Stabilized inactive form Inactive form Oscillation Activator Active formStabilized active form Regulatory site (one of four) Allosteric enzyme with four subunits Active site (one of four)

Feedback Inhibition End product shuts down the pathway Prevents cell from wasting chemical resource by synthesizing more products than is needed

Fig Intermediate C Feedback inhibition Isoleucine used up by cell Enzyme 1 (threonine deaminase) End product (isoleucine) Enzyme 5 Intermediate D Intermediate B Intermediate A Enzyme 4 Enzyme 2 Enzyme 3 Initial substrate (threonine) Threonine in active site Active site available Active site of enzyme 1 no longer binds threonine; pathway is switched off. Isoleucine binds to allosteric site