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Biology Enzymes Enzymes B11 – analyse the roles of enzymes in biochemical reactions Textbook Chapter ___ pages _____. Cues All organisms depend on their metabolism for survival. Metabolism: particular biochemical reactions and pathways that occur in their cells. Enzymes catalyze (speed up) metabolism and increase the efficiency of these reactions. e.g. Thyroxin is a hormone that partially governs overall rate of metabolism; it is a protein hormone released by thyroid cells into the blood. Thyroxin attaches to receptor sites on surfaces of body cells where it increases rate cells consume oxygen. This promotes ATP production by cellular respiration making it available to increase rate of cell metabolism. Re: thyroid gland accumulates iodine by ___ACTIVE TRANSPORT___ in order to produce thyroxin. Enzymatic activity of all of metabolism is dependent on efficient formation of a complex between enzymes and their substrates. Shape of molecules involved permits their combination into the complexes. Anything that affects shape of molecules (___DENATURES___ molecules) will affect potential for a reaction. (re: temperature, pH, ions, etc.) Enzymatic Activity Re: Enzymes are ___PROTEINS_______ with __3o or __4o___ structure. these 3D structures are a characteristic of the unique sequence of amino acids Substrates: molecules that react with enzymes e.g. maltose is the substrate for the enzyme maltase. Unique structure of maltase allows it to bind with maltose (substrate) and form a complex that proceeds in the reaction forming two glucose molecules. Biology Cues Enzymes e.g. Sucrose (___SUBSTRATE_) reacts with sucrase (___ENZYME_____) to produce glucose and fructose. IN BOOK Catabolism: enzymatic reactions that involve the cleaving of a single substrate into two products. The above hydrolysis reactions of maltose and sucrose are good examples. (note: cata = down e.g. catastrophe) Anabolism: enzymatic reactions where substrates are bonded together to from a single product. e.g. maltase also catalyzes this reverse reaction between glucose molecules to form maltose. (note: ana = up, back, again e.g. anabolic) Many enzymatic reactions are reversible. However, conditions surrounding reaction, whether environmental or relative concentrations of substrates compared to products, determine which way a reaction will proceed. This is an example of homeostasis. Lock and Key Analogy clarifies the relationship bwtween substrates and enzymes. According to this analogy, substrates and enzymes fit together like keys in locks. This is a useful analogy because each component in reaction must have correct shape and fit together for a reaction to occur. Activated enzyme-substrate (E-S) complex: Combination of the substrate and enzyme (“key” and “lock”). Induced fit hypothesis: as E-S complex forms, it forces substrate into a slightly different shape, bending the molecule, perhaps, which leads to reaction. Reaction proceeds when required energy exists. after reaction, enzymes are available to be used again. Active site: portion or surface of enzyme that attaches to substrate and is involved in reaction. Shape of active site must fit shape of substrate for E-S complex to form. If an activated E-S complex can’t form, then no reaction can occur. Summary Biology Cues Enzymes Lock and Key analogy can be extended. Wrong key can sometimes be fit into a lock, yet does not do anything. In “enzyme language”, it is possible for a substance other than the substrate to fit into an active sit, but because configuration of this combination is not exact, no reaction will proceed and reaction that could have occurred would be blocked (inhibited). Adenosine triphosphate (ATP) provides the energy for these reactions. Activation energy: Amount of energy (ATP) required for a reaction to occur. Enzymes lower the activation energy – allows for reaction to occur with a lowered energy requirement. From book Both substrates and products of a reaction exist at own energy level. Reaction is transition between these two energy levels. Endothermic reaction: overall reaction requires net input of energy. (note: endo = inside e.g. endocytosis) Exothermic reaction: release of energy. Energy can be captured in form of ATP for further use, or is given off as heat energy. (note: exo = outside e.g. exterior) Regardless of type of reaction the energy of enzyme-controlled reactions occur at such small amounts that other cell functions are not affected. Summary Biology Cues Enzymes Summary Many enzymatic reactions exist as part of larger metabolic pathway, where one product of one step becomes substrate for a subsequent reaction and so on. Some metabolic pathways have several of these steps, each requiring a different specific enzyme. Sequential nature of a metabolic pathway means that energy and electron shifts occur in smaller amounts. Also, they allow cell to have greater regulatory control over reactions by negative feedback mechanism. This occurs when concentration of a product of one step increases high enough to begin to inhibit initial dedicated step that leads to its production. e.g. To present enzymatic activity as purely a protein function is an oversimplification. The physical structure that speeds up a reaction is a protein, but this molecule doesn’t function in isolation. e.g. The hydrolysis of maltose involves breaking of bond holding two monosaccharides together, the addition of water and the formation of new bonds attaching parts of a water molecule to each of the monosaccharide products. Without maltase present, no such hydrolysis occurs. As well, there is an energy consideration that is not reflected in the net equation. Furthermore, there are other aspects like the impact in electron distribution in maltose as the bond is being broken and again in the glucose molecules while new bonds are being formed. Regulating these additional features of an enzymatic reaction are roles of coenzymes and co-factors. Enzymatic reactions that require addition or release of small particles like H+ use organic complexes called co-enzymes. e.g. co-enzyme nicotinamide adenine dinucleotide (NAD+) which is derived from vitamin B (niacin). NAD+ (and other molecules that function similarly) transports hydrogen to or from a reaction. They are known simply as hydrogen carriers (and sometimes are called reducing agents). e.g. K1+ and Zn2+ help regulate other aspects of enzymatic reactions, such as adding stability while electron distribution shifts.