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Enzymes Understanding The Concepts Biology Notes Cha6
How would you define enzymes?
“Enzymes are proteins that catalyze i.e. speed up the biochemical reactions and are not changed during the reaction”. The molecules at which enzymes act are called substrate, and the enzyme converts them into different molecules called products.
Characteristics of Enzymes Almost all enzymes are proteins i.e. they are made of amino acids.
Most enzyme reaction rates are millions of times faster than those of comparable uncatalyzed reactions. As with all catalysts, enzymes are not consumed by the reactions they catalyze.
Enzymes are usually very specific for the type of reaction and the nature of their substrates.
Only a small portion of enzyme molecules is directly involved in catalysis. This catalytic region is known as the active site. It recognizes and binds the substrate and then carries out the reaction.
Enzyme production can be enhanced or diminished by a cell according to needs. Enzyme activity can also be regulated by inhibitors and activators.
Some enzymes do not need any additional components to work. However, others require non-protein molecules or ions called cofactors. Cofactors can be either inorganic (e.g. metal ions) or organic (e.g. flavin and heme). If organic cofactors are tightly bound to enzymes, they are called prosthetic groups. If organic cofactors are loosely attached to enzymes, they are called coenzymes. Coenzymes transport chemical groups from one enzyme to another. Some important vitamins (e.g. riboflavin, thiamine, and folic acid) act as coenzymes.
Several enzymes work together in a specific order, creating metabolic pathways. In a metabolic pathway, one enzyme takes the product of another enzyme as a substrate. After the reaction, the product is passed on to the next enzyme.
What do you mean by activation energy and why it is referred to in the definition of enzymes?
Enzymes are proteins that catalyze (i.e. speed up) biochemical reactions and are not changed during the reaction. The molecules at which enzymes act are called substrates, and the enzyme converts them into different molecules, called products. All chemical reactions require activation energy. lt is defined as; “The minimum energy required to start a reaction”. The need for activation energy acts as a barrier to the beginning of the reaction. Enzymes lower such barriers by decreasing the requirement of activation energy. Thus, in the presence of enzymes, reactions proceed at a faster rate. Energy is required to climb a hill. If the hill is steeper, more energy will be needed
How does pH affect enzyme activity?
pH affect enzyme activity: All enzymes work at their maximum rate at a narrow range of pH, called optimum pH. A slight change (increase or decrease) in this pH causes retardation in enzyme activity or blocks it completely. Every enzyme has its specific optimum pH value.
Example: Pepsin (an enzyme that works in the stomach) is active in an acidic medium (low pH) while trypsin (working in the small intestine) shows its activity in an alkaline medium (high pH). Changes in pH can affect the ionization of amino acids at the active site.
In a range of 0-35°C, the rate of reaction of an enzyme is proportional to temperature. Above 35°C and below 0°C, enzyme activity slows down eventually stops explain why?
An increase in temperature will speed up the rate of enzyme-catalyzed reactions, but only to a certain limit. Above 35oC and below 0oC: When the temperature is raised well above 35oC, the enzyme activity slows down and eventually stops because the heat energy increases the vibrations of atoms of enzyme molecules and the globular structure of the enzyme is lost. This is known as the denaturation of enzymes. It results in a rapid decrease in the rate of enzyme action and it can get blocked completely as well.
If the temperature lowers below 350C, the enzyme activity lowers until the enzyme reaches a minimum temperature at which the enzyme activity is the least. The enzyme activity stops completely at 0oC. The vibrations of atoms of enzyme molecules decrease, protein changes shape and the active site is no longer complementary to the substrate molecule.
What characteristic of enzymes makes them specific for substrates?
Specificity of enzymes: There are over 2000 known enzymes, each of which is involved in one specific chemical reaction. Enzymes are also substrate-specific.
Example: The enzyme protease (which breaks peptide bonds in proteins) will not work on starch (which is broken down by an enzyme amylase). Similarly, the lipase enzyme acts only on lipids and digests them into fatty acids and glycerol.
Specificity is determined by the shape of the active site: The specificity of different enzymes is determined by the shapes of their active sites. Active sites possess specific geometric shapes that fit with specific substrates.
Briefly describe the factors that affect the activity of enzymes.
Factors affecting enzyme activity: Enzymes are very sensitive to the environment in which they work. Any factor that can change the chemistry or shape of the enzyme molecule, can affect its activity. Some of these factors that can affect the rate of enzyme action are: 1) Temperature 2) Substrate concentration 3) pH
1) Temperature: An increase in temperature speeds up the rate of enzyme-catalyzed reactions, but only to a point. Every enzyme works at its maximum rate at a specific temperature called “the optimum temperature” for that enzyme.
When the temperature rises to a certain limit, the heat adds in the activation energy and also provides kinetic energy for the reaction. So reactions are accelerated. But when the temperature is raised well above the optimum temperature, heat energy increases the vibrations of atoms of enzyme and the globular structure of the enzyme is lost.
This is known as the denaturation of the enzyme. It results in a rapid decrease in the rate of enzyme action and it may be blocked completely.
2) Substrate concentration: If enzyme molecules are available in a reaction, an increase in substrate concentration increases the rate of reaction. If enzyme concentration is kept constant and the amount of substrate is increased, a point is reached where any further increase in substrate does not increase the rate of reaction anymore. When the active sites of all enzymes are occupied (at high substrate concentration), any more substrate molecules do not find free active sites. This state is called saturation of active sites and the reaction rate does not increase.
3) pH: All enzymes work at their maximum rate at a narrow range of pH, called optimum pH. A slight change (increase or decrease) in this pH causes retardation in enzyme activity or blocks it completely. Every enzyme has its specific optimum pH value. Example: Pepsin (an enzyme that works in the stomach) is active in an acidic medium (low pH) while trypsin (working in the small intestine) shows its activity in an alkaline medium (high pH). Changes in pH can affect the ionization of amino acids at the active site.
Describe the lock and key mechanism of enzyme action.
Lock and key mechanism of enzyme action: In order to explain the mechanism of enzyme action a German chemist Emil Fischer, in 1894, proposed the lock and key model. According to this model, both the enzyme and the substrate possess specific complementary geometric shapes that fit exactly into one another. This model explains enzyme specificity.
Biology Notes for Class 9th Pdf Download
Biology SSC Par one Class 9th notes according to FBISE syllabus. Includes solved exercises, discussion questions, MCQs, great board questions, and chapter overview.
Q1: Define metabolism and its types?
The word metabolism is derived from a Greek word meaning “Change”
The concept of metabolism was first of all given by Ibn-e-Nafees.
The sum of all Chemical reactions that take place in living organisms is called Metabolism.
Types of Metabolism:
There are two types of metabolism.
I. Anabolism: It is a constructive process in which small molecules combine to form a larger molecule is called anabolism. These types of reactions are called anabolic reactions
Q2: Define activation energy? How enzymes lower the activation energy of substrate?
Ans: Activation energy: The minimum amount of energy required to convert a reactant into a product is called activation energy.
Outlines of lowering activation energy: Enzymes lower the activation energy in several ways. They do so by,
Altering the shape of the substrates and reducing the amount of energy required to complete the transition.
Disrupting the charge distribution.
Bringing substrates in the correct orientation to react.
Q3: Write the characteristics of enzymes.
Ans: Characteristics of enzymes:
Enzymes are globular proteins in nature and are secreted by cells.
The enzymes function as catalyst and increase the rate of chemical reaction. iii. They lower the activation energy of reactions.
i Enzymes are usually very specific for the type of reaction and for the nature of their substrate. v. A small amount of enzyme can bring change in a large amount of substrate.
Enzymes are sensitive to change in pH of the substrate.
Some enzymes work inside the cells called intracellular enzymes. Like mitochondrial enzymes while some enzymes like pepsin work in stomach.
Enzymes activity can also be regulated by inhibitor and activators.
Q4: Define the following terms?
Substances that enhance the activity of the enzyme are called activators.
The non-protein molecules or ions required by enzymes for activity are called Co-factors. e.g. metallic ions and organic molecules.
If the organic cofactor is loosely attached with the enzyme, they are called Co-enzymes mostly coenzymes are vitamins riboflavin, thiamine, folic acid.
It is an organic cofactor that is tightly attached with enzymes they are called prosthetic groups.
Enzyme without cofactor is called Apo enzymes.
Enzyme with cofactor is called Holoenzyme. OR Complete enzyme is called Holoenzyme.
The substances on which enzymes act are called substrates.
A region on an enzyme where the substrate binds during the reaction is called an active site.
The amount of energy required to start a biochemical reaction is called activation energy.
Q5: Why enzymes are specific in their function discuss?
Ans: Enzymes are very specific in their action because of their active site. An enzyme generally catalyzes only one kind or one type of chemical reaction. Therefore, they are specific for the certain substrates. One particular enzyme cannot speed up many different types of reactions.
No reaction can occur in a cell unless its own specific enzyme is present.
According to this model active site of the enzyme and substrate have specific geometric shapes. The substances molecule exactly fits in the active site of the enzyme just like a lock and a key. The enzyme is the lock and substrate is the key. This model suggests that the active site is a rigid and non-flexible structure.
Mechanism: According to the lock and key hypothesis the enzyme (key) combined with a specific substrate (lock) and chemically changing the substrate into a new product. No change occurs in the enzyme during or after the reaction.
inducted fit model:
History: This model was first proposed by American Biologist DanielKoshland in 1958. It is also called the Hand and Glove model. According to this model active sites of enzymes are flexible.
Mechanism: Koshland suggested that when a substrate combines with an enzyme it induces changes in the enzyme structure. This change helps the enzyme to perform its catalytic activity more effectively. So, the active sites of the enzymes are not rigid and are flexible.
Q7: What is the effect of temperature, PH and substrate concentration on enzymes activity?
Ans: I. Effect of temperature:
Enzymes are very sensitive to the change in temperature. With the increase in temperature, the activity of the enzyme also increases but there is a limit to the increase. This limit is called optimum temperature. The optimum temperature for the human enzymes is between 35 – 40 Co and the average temperature is 37Co. When the temperature is above 40Co denaturing of the enzyme quickly starts. At 0 Co the enzyme becomes inactive and cannot perform its function.
ii. Effect of pH: The activity of enzymes varies with changes in pH. The pH at which the activity of an enzyme is maximum is called optimum pH. The optimum pH value for most enzymes is between 6-8. The activity of the enzyme pepsin in the stomach works best at a pH of 2 and trypsin at a pH of 8. A change in pH can stop enzyme activity. Any change in Ph can lower the enzymatic activity. Extreme changes in the pH of solutions denture the enzymes.
iii. Effect of substrate concentration: The rate of reaction increases with the increase in substrate concentration. When enzymes become saturated. At saturation point, the reaction cannot increase further enzymes are said to be saturated when all of its active sites are occupied by the substrate.
Biology SHORT QUESTIONS Enzymes
C. Write short Answers to the following questions.
Q1: Differentiate between lock and key model and the induced-fit model?
Ans Difference between lock and key model and the induced-fit model.
In what way does an enzyme affect the chemical reactions in its catalysis?
Enzymes are biological catalysts. They speed up the chemical reaction by lowering the activation energy needed for the reaction. Enzymes lower the activation energy in several ways. Altering the shape of the substrate Disrupting the charge distribution Bringing substrates in the correct orientation to react
How are enzymes specific for the substrate?
Enzymes are very specific in their action, An enzyme catalysis is only one specific reaction. Enzyme due to its specific chemical nature and structure can react with a specific substrate. That’s why one particular enzyme cannot speed up different types of reactions. Proteases convert only protein into amino acid and lipase converts lipids into fatty acid.
What will be the effect on digestion if we take some digestive enzymes from outsides?
If we take some digestive enzymes from outside the digestion will efficiently and effectively occur. It is very important that we preserve the body’s ability to make enzymes. If supplemental plant digestive enzymes are taken with a meal, these digestive enzymes begin their work immediately. The supplemental digestive enzymes will break down the food, thus saving the body from having to release as many of its own enzymes.
What is meant by the denaturation of enzymes?
The change in the structure of enzymes resulting from the breakdown of the weak ionic and hydrogen bonding in enzymes is called the denaturation of enzymes.
What is the term used to describe the temperature and pH at which enzymes can work most effectively in a reaction?
All enzyme work at a specific temperature, increase or decrease in specific temperature effect the rate of enzymes action. The temperature at which the enzymes work best is called optimum temperature.
Example: the optimum temperature for human enzymes is between 35-40 Co. Most enzymes work best at a pH between 6-8 which is called optimum pH. So, the term used to describe the temperature and pH on which the enzymes work properly is called optimum temperature.
Federal Board Islamabad Enzymes Biology Notes Chapter 6 Free Pdf Download