SBI4U BIOCHEMISTRY Enzymes Ms. Manning

Essential Questions: What are enzymes and what is their role in normal cellular function? What are the chemical structures and mechanisms of various common enzymes? What are the factors that affect the function of enzymes in cellular processes? Why/how are enzymes used in the food and pharmaceutical industry?

What does this look like? Map of Glucose Metabolism

Homework Question: What is a metabolic (biochemical) pathway? What is the role of enzymes in metabolic pathways? http://highered.mcgraw-hill.com/classware/ala.do?isbn=0072965819&alaid=ala_1032272&showSelfStudyTree=true

How are macromolecules brought into the body converted into molecules that make up the body? The body’s metabolism consists of a large number of biochemical pathways that consist of sequences of chemical reactions. convert substrate molecules into specific products needed by the body.

Types of Biochemical Pathways There are two fundamental types of biochemical pathways. Anabolic pathways build complex products from less complex substrates Catabolic pathways break down complex molecules to make energy available for biological processes.

Which of these reactions are: a) anabolic b) catabolic? Neutralization (acid-base) reaction Hydrolysis reaction Oxidation-reduction (redox) reaction Condensation (dehydration) synthesis reaction

Enzymes Proteins (globular structure) that catalyze chemical reactions In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzymes converts them into different molecules, called the products Why is an enzyme called a catalyst?

Elephant Toothpaste Recipe - Hydrogen Peroxide - Soap 2 H2O2  O2 + 2 H2O What will happen to the new recipe when a catalyst is added?

Enzyme Characteristics What characteristic was presented in the demo? Speed up chemical reactions! Almost all cellular reactions need enzymes to occur at significant rates. Without enzymes, chemical reactions would still occur, but they would happen much to slowly to sustain life.

How do enzymes work? http://highered.mcgraw-hill.com/classware/ala.do?isbn=0072965819&alaid=ala_1032270&showSelfStudyTree=true

Enzymes in Digestion

Enzyme Characteristics What characteristic was presented in the lock and key activity? Enzymes are specific for one particular reaction or group of related reactions. Lactose (milk sugar) Triglycerides (lipid) Amylose (starch) Protein Lactase Lipase Amylase Protease

Homework Question: #3-4, pg. 115 What is the difference?

Homework Question: #1 pg. 115 Enzymes called catalysts because they speed up chemical rxns Interact with substrates to convert them to products Substrates drawn to active site through weak bonds Intra-substrate bonds weakened and substrate is split apart Weakening of intra-substrate bonds by enzyme makes rxn occur faster

Enzyme Action and the Hydrolysis of Sucrose Enzyme sucrase breaks down a molecule of sucrose into glucose and fructose http://highered.mcgraw-hill.com/classware/ala.do?isbn=0072965819&alaid=ala_1032271&showSelfStudyTree=true

Homework Question: #2, pg. 115 Catabolic – enzyme breaks substrate apart – exergonic reaction (yeilds energy) Anabolic – enzyme builds larger substrate by joining two substrates – endergonic reaction (requires energy)

Enzyme Structure Hormone-sensitive lipase HSL catalyzes the breakdown of stored fat

The active site of HSL (green) catalyzes the breakdown of TGs Adipocyte (fat cell) TG The active site of HSL (green) catalyzes the breakdown of TGs in a process called Lipolysis. Glycerol FA Triglyceride HSL + H2O (hydrolysis) FA Glycerol FA Diglyceride Composite image of the HSL model to illustrate the putative localization of the regulatory module of in the three-dimensional structure. The HSL model is displayed in spacefill representation, with the residues in the catalytic triad colored green (Ser), white (Asp), and magenta (His). Contreras J A et al. J. Biol. Chem. 1996;271:31426-31430 ©1996 by American Society for Biochemistry and Molecular Biology

Activation Energy and Enzymes

What is activation energy? a) The thermal energy associated with random movements of molecules b) The energy released through the active breaking of chemical bonds c) The difference in free energy between reactants and products d) The energy required to initiate a chemical reaction

Explain the role of activation energy in a reaction Explain the role of activation energy in a reaction. How does an enzyme affect activation energy? Activation energy  the amount of energy needed to trigger the reaction. Without reaching the activation energy, reactions can't take place. Enzymes catalyze this process by lowering the amount of energy required to activate the reaction.

Activation Energy and Enzymes The amount of activation energy that is required is considerably less when enzyme is present.

Factors that Affect Enzyme Activity (reaction rate) Q#1-4 pg. 116 on enzyme worksheet

Enzyme is said to be denatured – no longer a catalyst

Enzyme is said to be denatured – no longer a catalyst

Other Regulators of Enzyme Activity

Enzyme Cofactors (pg. 117) Q#1 - Describe the general role of cofactors in enzyme activity Non-protein, bound to enzyme May be organic or inorganic ions Enhance enzyme activity - “helper” change enzyme active site shape make active site more reactive

Examples of Inorganic Cofactors Mg in Chlorophyll Fe in heme group of hemoglobin

Organic Cofactors Active site Coenzymes e.g., NAD Prosthetic group (perm. attached) Active site Enzyme Coenzyme (detaches) Prosthetic Groups e.g., FAD

Important Organic Cofactors Nicotinamide Adenine Dinucleotide (NAD) coenzyme derived from vitamin B3 carries and transfers electrons and functions as oxidizing agent in redox reactions Active site Enzyme Coenzyme (detaches) e.g., NAD

Important Organic Cofactors Flavin Adenine Dinucleotide (FAD) prosthetic group like NAD, FAD functions as a reducing agent in cellular respiration and donates electrons to the electron transport chain Active site Enzyme Prosthetic group (perm. attached) Prosthetic Group e.g., FAD

Covalent Modulation Enzymes can be activated or inactivated by covalent modification. A common example is phosphorylation of an enzyme (addition of a phosphate group to the amino acids serine, threonine, or tyrosine) mediated by another enzyme called a kinase . The phosphorylation is reversible, and other enzymes called phosphatases typically catalyze the removal of the phosphate group from the enzyme.

Enzyme Inhibitors Types of Inhibitors Enzymes may become deactivated Temporarily or Permanently Types of Inhibitors Reversible Inhibitors Irreversible Inhibitors

Reversible Inhibitors Used to control enzyme activity Involves the substrate or the end product of the reaction For example: a build up of the end product – called feedback inhibition http://highered.mcgraw-hill.com/classware/ala.do?alaid=ala_1032273

Competitive Inhibitors Competitive Inhibitors have a similar shape as the substrate Compete with the substrate to bind to the active site, but no reaction occurs Block the active site so no substrate can fit

Competitive Inhibition

Non-Competitive Inhibitors Binds to a different site on the enzyme Does not compete with the substrate to bind to the active site Two ways to non-competitively inhibit the enzyme: 1. slow down the reaction or 2. changes the shape of the active site (allosteric inhibition) Which of the following diagrams represents allosteric inhibition?

Substrate active site enzyme Inhibitor site enzyme active site (a) Reaction Substrate active site enzyme Inhibitor site Substrate binds with the active site of enzyme Reaction occurs and product molecules are produced (b) Inhibition enzyme active site Inhibitor site Inhibitor Inhibitor binds with the inhibitor site of the enzyme Substrate may still bind with the enzyme but the reaction rate is reduced

Substrate active site enzyme Substrate active site Inhibitor (a) Reaction Substrate active site enzyme Substrate binds with the active site of enzyme Reaction occurs and product molecules are produced (b) Inhibition Substrate active site enzyme Inhibitor Inhibitor binds with the inhibitor site of the enzyme and changes the structure of the active site Inhibitor prevents binding of the substrate by changing the active site shape

Substrate active site enzyme Substrate active site Inhibitor (a) Reaction Substrate active site enzyme Substrate binds with the active site of enzyme Reaction occurs and product molecules are produced (b) Inhibition Substrate active site enzyme Inhibitor Inhibitor binds with the inhibitor site of the enzyme and changes the structure of the active site Inhibitor prevents binding of the substrate by changing the active site shape

Substrate active site enzyme Inhibitor site enzyme active site (a) Reaction Substrate active site enzyme Inhibitor site Substrate binds with the active site of enzyme Reaction occurs and product molecules are produced (b) Inhibition enzyme active site Inhibitor site Inhibitor Inhibitor binds with the inhibitor site of the enzyme Substrate may still bind with the enzyme but the reaction rate is reduced

Check for Understanding Q#2 – Distinguish between competitive and non-competitive inhibition Competitive inhibitor competes with the substrate for binding to the active site of the enzyme and prevents reaction Non-competitive inhibitor does not compete for the active site, binds to a different site, either slows down or completely prevents reaction.

Check for Understanding Q#2 – Explain how allosteric inhibitors differ from other non-competitive inhibitors:  While non-competitive inhibitors reduce enzyme activity and slow down the reaction rate, allosteric inhibitors block the active site altogether and prevent its functioning completely

Irreversible Inhibitors Also called poisons For example: certain heavy metals E.g., cadmium, lead, mercury Retained in the body and lost slowly Cyanide is a poison that prevents the activity of cytochrome C oxidase, an enzyme in the electron transport chain in the cell. It therefore inhibits ATP production and cellular respiration.

Cytochrome c oxidase

Why are enzymes so tightly regulated by co-factors and inhibitors?

Control of Metabolism Biochemical reactions are controlled in part by the specificity of substrate biding, but the human body could not function if all enzymes were present together and all operating maximally with no regulation. There would be biochemical chaos with substances being synthesized and degraded at the same time. Instead, the body tightly regulates enzymes through metabolic pathways and by controlling specific enzymes within a pathway. This approach allows an entire pathway to be turned on or off by simply regulating one or a few enzymes. Metabolic pathways can also be regulated by switching specific genes on or off.

Why is it important to know how enzymes are regulated? Enzymes play a critical role in everyday life. Many heritable genetic disorders occur because there is a deficiency or total absence of one or more enzymes. Other disease conditions (e.g., cancer) result because there is an excessive activity of one or more enzymes. Routine medical tests monitor the activity of enzymes in the blood, and many of the prescription drugs (e.g., penicillin,) exert their effects through interactions with enzymes. Enzymes and their inhibitors can be important tools in medicine, agriculture, and food science.

Test study tip: Create a concept map that summarizes the regulation of enzyme activity Include the following terms: temperature Active site Co-factors pH Enzyme inhibitors Co-enzymes Enzyme concentration Competitive inhibitor Allosteric inhibitor Substrate concentration Non-competitive inhibitor Irreversible inhibitors denature Inhibitor site Enzyme reation rates Reversible inhibitors