Chemical Reactions & Enzymes By the end of today you should be able to: …describe, in terms of energy, the difference between exothermic and endothermic reactions Homework Test Friday –Atomic Chem –Macromolecules –Enzymes and Chemical Reations. ?

Chemical Reactions and Enzymes

Chemical Reactions A chemical reaction is a process that changes one set of chemicals into another set of chemicals. The elements or compounds that enter into a chemical reaction are known as the reactants. The elements or compounds produced by a chemical reaction are known as products.

Energy in Reactions Chemical reactions can either release energy or absorb energy. An exergonic reaction releases energy and will often occur spontaneously. An endogonic reaction absorbs energy and will not occur spontaneously.

Burning glucose (sugar): an exergonic reaction high low Photosynthesis: an endergonic reaction high low energy content of molecules progress of reaction energy content of molecules activation energy needed to ignite glucose energy released by burning glucose glucose + O 2 CO 2 + H 2 O glucose activation energy from light captured by photosynthesis CO 2 + H 2 O net energy captured by synthesizing glucose Activation energy is the energy required to get a chemical reaction started.

Chemical Reactions & Enzymes By the end of today you should be able to: …discuss similarities between solutions and suspensions …describe and model how an enzyme speeds up chemical reactions. Homework –Chapter 3 review pg # 1-20 –Test Friday Atoms, Macromolecules, enzymes Do Now!!! –What do catalysts do?

low high energy content of molecules progress of reaction reactants products activation energy without catalyst activation energy with catalyst Enzymes - proteins that act as biological catalysts A Catalyst is a substance that speeds up the rate of a chemical reaction

Substrate Specificity of Enzymes substrate - The reactant that an enzyme acts on enzyme-substrate complex - The enzyme binds to its substrate, forming an enzyme- substrate complex active site - is the region on the enzyme where the substrate binds Induced fit of a substrate brings chemical groups of the active site into positions that enhance their ability to catalyze the reaction Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig Substrate Active site Enzyme Enzyme-substrate complex (b)(a)

Catalysis in the Enzyme’s Active Site How do Enzymes Work? In an enzymatic reaction, the substrate binds to the active site of the enzyme 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig 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

Competitive inhibition allosteric regulator molecule Allosteric inhibition Enzyme structure active site substrate enzyme allosteric regulatory site Competitive- key Fits lock, but wont Open door pH Temperature “on” or “off” keys (binding proteins) Up: Enzyme “off” Down: Enzyme “on” Regulation of Enzyme Activity Up: Enzyme “off”

An enzyme’s activity can be affected by –General environmental factors, such as temperature and pH –Chemicals that specifically influence the enzyme (cofactor) Fe, Zn, Mg, K Coenzyme –NAD –CoA Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Rate of reaction Optimal temperature for enzyme of thermophilic (heat-tolerant) bacteria Optimal temperature for typical human enzyme (a) Optimal temperature for two enzymes (b) Optimal pH for two enzymes Rate of reaction Optimal pH for pepsin (stomach enzyme) Optimal pH for trypsin (intestinal enzyme) Temperature (ºC) pH

Enzyme Inhibitors Competitive inhibitors bind to the active site of an enzyme, competing with the substrate Noncompetitive inhibitors (Allosteric inhibitors)bind to another part of an enzyme, causing the enzyme to change shape and making the active site less effective Examples of inhibitors include toxins, poisons, pesticides, and antibiotics Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig (a) Normal binding (c) Noncompetitive inhibition (b) Competitive inhibition Noncompetitive inhibitor Active site Competitive inhibitor Substrate Enzyme

Allosteric Regulation of Enzymes Allosteric regulation may either inhibit or stimulate an enzyme’s activity Allosteric regulation occurs when a regulatory molecule binds to a protein at one site and affects the protein’s function at another site Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings (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)

Identification of Allosteric Regulators (Your Drugs!!!) Allosteric regulators are attractive drug candidates for enzyme regulation Inhibition of proteolytic enzymes called caspases may help management of inappropriate inflammatory responses Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig RESULTS EXPERIMENT Caspase 1 Active site SH Known active form Substrate SH Active form can bind substrate SH Allosteric binding site Known inactive form Allosteric inhibitor Hypothesis: allosteric inhibitor locks enzyme in inactive form S–S Caspase 1 Active formAllosterically inhibited form Inhibitor Inactive form

Fig. 8-21b Caspase 1 RESULTS Active form Inhibitor Allosterically inhibited form Inactive form

Feedback Inhibition In feedback inhibition, the end product of a metabolic pathway shuts down the pathway Feedback inhibition prevents a cell from wasting chemical resources by synthesizing more product than is needed Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 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

substrates enzyme active site of enzyme Induced Fit

11. Explain the relationship among atoms, elements, and compounds. 12. What is a radioactive isotope? Describe two scientific uses of radioactive isotopes. 13. How are atoms in a compound held together? 14. Distinguish among single, double, and triple covalent bonds. 15. Explain the properties of cohesion and adhesion. Give an example of each property. 16. What is the relationship among solutions, solutes, and solvents? 17. How are acids and bases different? How do their pH values differ? 18. Explain the relationship between monomers and polymers using polysaccharides as an example. 19. Identify three major roles of proteins. 20. Describe the parts of a nucleotide. 21. Name the two basic kinds of nucleic acids. What sugar does each contain?

#2 - Water is the “UNIVERSAL SOLVENT” Water has the ability to dissolve a vast amount of different substances. Mixture – material composes of 2 or more elements (or compounds) which can be physically separated. –Two types of mixtures are Solutions – mixture where all components are evenly distributed (salt water) Suspensions – mixture of water that contains nondissolved materials (pond water)

Solutions Solute – the substance that is dissolved. Solvent – the substance that dissolves the solute.