11th Class Biology Chapter 3 Notes | Get Now
11th Class Biology Chapter 3 Notes cover the topic “Enzymes,” which explains how biological catalysts speed up chemical reactions in living organisms. This chapter is essential for understanding metabolism, digestion, and other life processes covered later in your biology course.
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These notes break down complex enzyme concepts into simple, easy-to-understand points to help you prepare effectively for your exams.
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What is an Enzyme?
An enzyme is defined as a protein that speeds up a biochemical reaction without being used up itself. According to the 11th Class Biology Chapter 3 Notes, enzymes are essential for proper activities of life because reactions proceed very slowly without them.
Key points about enzymes:
- The study of enzymes is called enzymology
- Enzymes act on a specific reactant called substrate
- There is a lock and key relationship between substrate and enzyme
- Enzymes never become part of the product
- Common suffixes include “-ase” (e.g., sucrase, lipase) though some end in “-in” (e.g., pepsin, trypsin)
- All enzymes are globular proteins
Cofactors and Coenzymes
This section of the 11th Class Biology Chapter 3 Notes explains the non-protein components that help enzymes function properly.
Types of Cofactors
- Activators – inorganic ions like Mg++, Fe++, Cu++, Zn++
- Coenzymes – organic molecules like vitamins (NAD, Biotin)
- Prosthetic Group – tightly bounded coenzyme situation
Important Terms
- Apoenzyme – the inactive protein portion remaining after removal of cofactor
- Holoenzyme – the active complex formed by enzyme plus cofactor
- Active Site – the site where substrate binds during catalysis
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Exoenzymes and Endoenzymes
The 11th Class Biology Chapter 3 Notes classify enzymes based on where they perform their function:
- Exoenzymes – enzymes that come out of the cell and catalyze reactions in their environment (e.g., pepsin secreted by chief cells)
- Endoenzymes – enzymes formed within a cell and act within the same cell
Enzyme vs Proenzyme
Some enzymes like pepsin are produced in inactive form called proenzyme. For example, pepsinogen (proenzyme) is converted into active pepsin by HCl in the stomach.
Characteristics of Enzymes
According to these 11th Class Biology Chapter 3 Notes, enzymes have the following key characteristics:
- Globular Proteins – all enzymes are globular proteins
- Speed Up Reactions – enhance chemical reactions without being consumed
- No Effect on End Product – do not change the nature of the final product
- Minute Amount – very small amounts are highly effective
- Specific in Action – act on specific substrates
- Sensitive to Temperature – work best at optimum temperature (37°C for humans)
- Sensitive to pH – function properly at specific pH levels
- Sensitive to Substrate Concentration – rate increases with substrate concentration up to a limit
- Requirement of Co-factors – needed for proper performance
- Lower Activation Energy – reduce the energy needed for reactions
- Enzyme Larger than Substrate – most enzymes are bigger than their substrates
Mechanism of Enzyme Action
Understanding how enzymes work is a crucial part of the 11th Class Biology Chapter 3 Notes.
Lock and Key Hypothesis
Proposed by E. Fischer in 1890, this hypothesis states that enzymes have a particular shape into which the substrate fits exactly, just like a lock and key.
Induced Fit Hypothesis
In 1959, Mr. Koshland proposed that the active site could be modified slightly as the substrate interacts with the enzyme, allowing it to perform its catalytic activity more effectively.
Active Site Components
The active site of an enzyme has two parts:
- Binding Site – holds the proper substrate and forms the ES-complex
- Catalytic Site – transforms the substrate into product or products
Factors Affecting Enzyme Activity
This is one of the most important sections in the 11th Class Biology Chapter 3 Notes for exam preparation.
1. Enzyme Concentration
The rate of reaction is proportional to enzyme concentration if temperature and pH remain constant. However, there is a limit after which increasing enzymes will not increase the reaction rate.
2. Substrate Concentration
At constant enzyme concentration, the rate of reaction increases with substrate concentration until a saturation point is reached.
3. Temperature
Every enzyme has an optimum temperature for maximum activity. Human enzymes work best at 37°C. Excess temperature causes denaturation, making the enzyme inactive.
4. Effect of pH Value
Different enzymes work best at specific pH levels:
| Enzyme | Optimum pH |
|---|---|
| Pepsin | 2.00 |
| Sucrase | 4.50 |
| Enterokinase | 5.50 |
| Salivary amylase | 6.80 |
| Catalase | 7.60 |
| Chymotrypsin | 7.00-8.00 |
| Pancreatic lipase | 9.00 |
| Arginase | 9.70 |
Enzyme Inhibitors
The 11th Class Biology Chapter 3 Notes also explain how certain substances can reduce enzyme activity.
Definition
Inhibitors are small molecules which fit into active sites or other parts of enzymes and reduce the rate of enzyme-controlled reactions.
Types of Inhibitors
1. Irreversible Inhibitors
- Check the rate of reaction by occupying active sites permanently
- Destroy the structure of protein through covalent bonds
2. Reversible Inhibitors
Divided into two types:
- Competitive Inhibitors – have similar structure to substrate and compete for the active site
- Non-competitive Inhibitors – attach to other parts of enzyme, not the active site
FAQs
Q1: What does 11th Class Biology Chapter 3 Notes cover?
11th Class Biology Chapter 3 Notes cover enzymes, their structure, cofactors, mechanism of action, factors affecting enzyme activity, and inhibitors, all essential for exam preparation and conceptual understanding.
Q2: What is the lock and key hypothesis?
The lock and key hypothesis, proposed by E. Fischer in 1890, states that enzymes have a specific shape into which the substrate fits exactly, similar to how a key fits into a lock.
Q3: What factors affect enzyme activity?
The main factors affecting enzyme activity are enzyme concentration, substrate concentration, temperature, and pH value. Each enzyme works best at its own optimum temperature and pH level.
Q4: What is the difference between competitive and non-competitive inhibitors?
Competitive inhibitors have similar structure to the substrate and compete for the active site, while non-competitive inhibitors attach to other parts of the enzyme without directly blocking the active site.
Q5: What is the difference between apoenzyme and holoenzyme?
Apoenzyme is the inactive protein portion remaining after removal of the cofactor, while holoenzyme is the complete active complex formed when the enzyme combines with its cofactor.
Q6: Where can I get 11th Class Biology Chapter 3 Notes?
You can download complete 11th Class Biology Chapter 3 Notes with diagrams, definitions, and solved MCQs for free on TaleemWorld.com to prepare thoroughly for your biology exams.