JWSS Biology Chapter 4 Enzymes

Sec3 G3 Sci Biology Enzymes- Notes 1 Name:_______________________ ( ) Class: _________ Date: __________________ JURONG WEST SECONDARY SCHOOL SCIENCE DEPARTMENT SECONDARY THREE BIOLOGY 4. Enzymes Learning Outcomes: e) explain the mode of action of enzymes in terms of an active site, enzyme-substrate complex and enzyme specificity using the ‘lock and key’ hypothesis f) investigate and explain the effects of temperature and pH on the rate of enzyme catalysed reactions What are Enzymes? Definition: Enzymes are proteins that function as a biological catalyst*. They can alter or speed up chemical reactions. They remain chemically unchanged at the end of the reaction. What are catalysts*? Catalysts are substances which alter (speed up) the rate of chemical reaction without itself being chemically changed at the end of the reaction. What reactions do Enzymes catalyse? • Enzymes either build up (anabolic reactions) or break down (catabolic reactions) complex substances • Enzymes can catalyse BOTH anabolic and catabolic reactions. Anabolic reaction (Build-up) Catabolic reaction (Break down)

Sec3 G3 Sci Biology Enzymes- Notes 2 How are enzymes named and classified? • Enzymes are named according to a scientific system. • The name of each enzyme: • Shows the substance on which the enzyme acts; and • Ends in ‘ase’. • For example, Lipase is an enzyme that acts on lipids Enzymes are protein molecules • They are made up of amino acids bonded with peptide bonds to form polypeptides. • A protein molecule is made up of one or more such polypeptide chain folded into a 3- dimensional shape. Amino acids Polypeptides Proteins The basic units of proteins. There are 20 different kinds of amino acids. Amino acids joined together by peptide bonds form a long chain known as a polypeptide. Proteins are formed when two or more polypeptide chains fold together to form a complex, three-dimensional molecule.

Sec3 G3 Sci Biology Enzymes- Notes 3 Characteristics of enzymes 1. Enzymes alter or speed up chemical reaction 2. Enzymes are required in minute (small) amounts • Enzymes remained unchanged in the reactions they catalyse • Can be used repeatedly • Small amounts of enzyme can catalyse a large number of chemical reactions 3. Enzymes are specific in their actions • Each type of enzyme can only catalyse a unique chemical reaction. • E.g. protease can only break down proteins into polypeptides. E.g. Lipases can act only on lipids and not proteins or carbohydrates • This enzyme specificity means that each chemical reaction is catalysed by a unique enzyme determined by its unique 3-dimensional structure e) explain the mode of action of enzymes in terms of an active site, enzyme-substrate complex, lowering of activation energy and enzyme specificity using the ‘lock and key’ hypothesis ‘Lock and Key’ Hypothesis 1) The enzyme is the “lock” 2) The substrate is the “key” 3) The enzyme-substrate complex forms when the substrate can fit into the active site of the enzyme. The substrate is said to be complementary to the active site. 4) When the substrate binds to the active site, a chemical reaction occurs. The substrate is converted into products. 5) Products leave the enzyme. Enzyme remains chemically unchanged, and is free to take part in the next reaction.

Sec3 G3 Sci Biology Enzymes- Notes 4 Explain using the ‘lock-and-key’ hypothesis the activity of pepsin. Pepsin is an enzyme found in the stomach. In the presence of proteins, it converts proteins into polypeptides. Explain using the ‘lock-and-key’ hypothesis the activity of pepsin in the stomach. What is Denaturation? Denaturation is the irreversible change in the 3D structure of an enzyme or any soluble protein, caused by heat or chemical such as acids or alkalis. • After denaturation, the active site of an enzyme is destroyed. • Substrate molecules would be unable to bind to the active site as the substrate is no longer complementary to the active site. • No enzyme-substrate complexes are formed, and no products are formed.

Sec3 G3 Sci Biology Enzymes- Notes 5 f) investigate and explain the effects of temperature and pH on the rate of enzyme catalysed reactions 1. Enzymes are affected by temperature • At A: Enzymes are inactive at low temperature. • At B: o As temperature increases, the amount of kinetic energy increases. o Enzyme and substrate molecules have a higher rate of effective collision. o That means, the chances of substrate fitting into the active site of the enzyme to form enzyme substrate complex increases. o More enzyme-substrate complexes are formed. o More products are formed. Therefore rate of reaction increases. o For every 10oC rise in temperature, the rate of enzyme reaction is doubled, until the optimum temperature is reached. • At C: Optimum temperature is the temperature where the enzyme activity is the fastest. • At D: o Beyond the optimum temperature, the rate of enzyme activity rapidly decreases. o Enzymes become denatured. Active site loses its shape o Substrate molecule could no longer fit into the active site of the enzyme. o Rate of reaction decreases. What happens when the temperature is too low? What happens when the temperature is too high? A B C D Scan to watch a video! Scan to try an enzyme simulation! Commented [PLX1]: https://www.youtube.com/watch?v=IoDE jeRZ0xE Commented [PLX2]: https://biomanbio.com/HTML5Gamesand Labs/LifeChemgames/enzymatichtml5page.html

Sec3 G3 Sci Biology Enzymes- Notes 6 Pitstop 3: Explain the rate of activity of the enzyme with increasing temperature. FCSS/3E PURE BIO/EOY/2019 Two enzyme experiments were carried out. The first experiment X was carried out at a constant temperature of 37°C. During the second experiment Y, the temperature was increased from 37°C to 80°C. The optimum temperature is 40°C. Which of the following graphs shows the results? Pitstop 4: No new product formed

Sec3 G3 Sci Biology Enzymes- Notes 7 2. Enzymes are affected by pH - Every enzyme has a particular pH range over which it works best. I f this pH changes, the shape of the active site of the enzyme is changed, thus the substrate will not be able to fit into the active site, and the enzyme is said to be denatured. - Extreme changes in acidity or alkalinity of the solutions denature enzymes. [explanation for pH that is NOT at optimum pH] o the rate of enzyme activity rapidly decreases. o Enzymes become denatured. Active site loses its shape o Substrate molecule could no longer fit into the active site of the enzyme. o Rate of reaction decreases. - Some enzymes work best in acidic medium while others function best in alkaline medium. Example, pepsin (protease found in stomach) has its optimum pH at 2.2 while trypsin (protease found in the small intestine) has its optimum pH of around 8. Who is correct? Why? Emery is right. Enzymes only Denature at extreme pH. Adam Bentley Emery Enzymes denature at high pH only Enzymes denature at low pH only I think it depends on the optimal pH of the enzyme. It denatures at extreme pH

Sec3 G3 Sci Biology Enzymes- Notes 8 Using named example, describe the relationship between pH and rate of enzyme activity. Pepsin works best at pH 2 OR the optimum pH of pepsin is 2. At this pH, the rate of enzyme activity is the highest. At pH below 2 or above 2, the rate of enzyme activity will decrease, because Pepsin will denature at extreme pH, active site is lost. Protein cannot fit into the active site of pepsin, no products are formed.

Sec3 G3 Sci Biology Enzymes- Notes 9 The graph below shows the rate of an enzymatic activity against temperature of enzyme R. 1 Describe the shape of the graph