Biology Notes for Class 9 on Long and Comprehensive Questions on Enzymes

Biology Made Easy: Your Complete Guide to Understanding Enzymes at the Grade IX Level for BISE and Federal Board Examinations 

    Welcome to the world of Biology! Understanding Enzymes can seem like a daunting task for Grade IX students preparing for BISE, Federal Board Examinations, or any other competitive exams. But, what if we told you that it could be made easy and self-explanatory? That's right! Our Biology Made Easy guide is here to help you grasp the fundamentals of enzymes in a way that will not only help you ace your exams but also leave you with a better understanding of this important biological concept.

    In this comprehensive guide, we will be covering the most important topics related to enzymes, including their characteristics, factors affecting the rate of enzymes, and an in-depth explanation of enzyme specificity through the Lock and Key Model and the Induced Fit Model. These notes are designed to help students of all levels understand the basics and achieve higher marks on their exams. So, buckle up, and let's dive into the fascinating world of enzymes!

Long and Comprehensive Answers on Enzymes
From Notes Library of H.E.S (Health, Education, and Skills)

Write down the characteristics of enzymes.

Characteristics of enzymes

  The following are the characteristics of enzymes.

a. Enzymes are proteins: All enzymes are proteins that are produced in living cells. These enzymes then speed up the chemical reactions by lowering the energy of activation and then the reaction takes place in less time at normal body temperature.

b. Enzymes are specific in action: Each enzyme catalyzes only one kind of chemical reaction. For this reason, enzymes have an “active site” in which the “substrate” fits.

c. Active site: The surface region of enzymes is called the active site. Substrate: The molecules that fit in the active site are called substrates.

d. Enzymes are needed in a very small amount: Only a small amount of enzymes is needed to catalyze a relatively large quantity of substrate.

e. Enzymes activity can be initiated or stopped: 

• Activators: The substances that initiate (start) enzyme activity. 
• Inhibitors: The substances that stop enzyme activity. So the activators start while the inhibitors can stop the enzyme’s activity.

f. Enzymes become functional in presence of cofactors 

Atoms, groups of atoms and molecules that join, alter the shape, and make enzymes functional are called cofactors.

• Cofactors can be considered as the “ON-OFF” switch for activating enzymes. 
• The cofactor will be a “Prosthetic group” if it is inorganic like a metallic ion (Zinc, Copper, Iron, etc).

g. Enzymes need coenzymes to become active

 

Small organic molecules that join the enzyme molecule and make it active are called coenzymes.

• Many of these enzymes are derived from the vitamins and minerals that are essential for our life, so in the absence of coenzymes diseases related to vitamin and minerals deficiency occur. For example lack of Vitamin B1 produces beriberi. 
• Examples of coenzymes are NAD+, FAD+, etc.

h. Enzymes may be intracellular or extracellular

The enzymes that are found inside the living cells are called intracellular enzymes.

• For example mitochondrial enzymes.

The enzymes that are found outside the living cells are called extracellular enzymes.

•  For example digestive enzymes like lipase, amylase, trypsin, etc.

Write down the factors that affect the enzyme's reaction rate.

Factors affecting/influencing enzymes reaction rates

    Following are some of the factors which affect the enzyme’s rate of reaction.

i. Temperature 

• The activity of enzymes has a direct relation with temperature i.e. increase in temperature can increase an enzyme’s activity. But there is a limit for this temperature called “Optimum temperature”. 
• At very high temperatures sharp decrease in the rate of reaction occurs. This happens because of a change in the protein’s structure due to the breakdown of weak ionic bonds and hydrogen bonding. 
• The optimum temperature for human enzymes is 35 centigrade to 40 centigrade, above this temperature range cell death can occur.

ii. Effect of PH

• Like the optimum temperature for enzymes, there is also an optimal PH range for the enzyme’s activity. 
• The optimal PH range in which enzymes work properly is 6 – 8 (however pepsin works best at a PH of 2 and trypsin at a PH of 8). 
• Any change in optimal PH range results in stopping the enzyme’s activity. This happens due to the breakdown of weak ionic bonds and hydrogen bonding present in the protein from which the enzyme is made of.

iii. Concentration of substrate

• Like temperature, the concentration of substrate also has direct relation. 
• With more concentration, the enzyme’s activity increases. 
• However, enzyme-substrate limits reaction rates. An enzyme is saturated when the active site of all the molecules is occupied most of the time. At the saturation point, the reaction will not speed up, no matter how much additional substrate is added.

What do you mean by enzyme specificity? Explain it by Lock and Key Model and Induced Fit Model.

Enzyme specificity

• Enzyme specificity means each enzyme is specific for its substrate. 
• In simple words, we can say that each enzyme recognizes and react with its own substrate. Therefore one particular enzyme can’t speed up different types of chemical reactions. 
• No reaction will occur until its specific enzyme is not present.

The specificity of the enzyme can be explained with the help following two models.

i. Lock and Key model

• According to the lock and key model, the enzyme should be considered as a key that combines with a substrate which acts as a lock for its key. 
• As for every lock, there is its own key, similarly, every substrate (lock) has its specific enzymes (key) to act upon. 
• When the substrate fits into the shape of the enzyme, chemical changes occur inside the substrate and thus the new product is formed which acts as a reactant for the next step of the metabolic pathway.
• Although lock and key is the best explanation for the mechanism of enzyme activity, however, recent studies do not support this idea. Therefore induced fit model is acceptable nowadays.

ii. Induce fit model

• On the basis of new pieces of evidence Koshland in 1959 proposed an induced fit model to explain the mechanism of enzyme activity and its specificity.
• He suggested that when a substrate combines with an enzyme, it stimulates or induces changes in the enzyme structure, especially at its active site. 
• This change helps the enzyme to perform its catalytic activity more effectively.

Examples of enzymes specificity

1. Catalase: This enzyme catalyzes only the decomposition of Hydrogen-per-Oxide.
2. Protease: This enzyme is specific for the conversion of proteins into their units called amino acids.
3. Lipase: This enzyme is specific for the conversion of lipids into their units called fatty acids.