Problem 10 - Campbell Biology Concepts & Connections

Question

Which of the following statements is not true? a. An antibody has more than one antigen-binding site. b. An antigen can have different epitopes. c. A lymphocyte has receptors for multiple and different antigens. d. A bacterium has more than one antigen.

Step-by-Step Solution

Answer

Statement 'c' is not true.

Step 1: Understand the Terminology

Familiarize yourself with the terms: antibody, antigen, epitope, and lymphocyte. An antibody is a protein produced by the immune system that recognizes and binds to antigens. An antigen is a molecule capable of inducing an immune response. An epitope is the specific part of the antigen that an antibody binds to. A lymphocyte is a type of white blood cell involved in the immune response.

Step 2: Analyze Statement a

Check if 'An antibody has more than one antigen-binding site' is true. Each antibody has two identical antigen-binding sites, which is true.

Step 3: Analyze Statement b

Check if 'An antigen can have different epitopes' is true. An antigen can indeed have multiple epitopes, each capable of being recognized by different antibodies, which is true.

Step 4: Analyze Statement c

Check if 'A lymphocyte has receptors for multiple and different antigens' is true. Each lymphocyte is specific to a single antigen epitope due to unique receptors. This makes the statement false.

Step 5: Analyze Statement d

Check if 'A bacterium has more than one antigen' is true. A single bacterium can express multiple antigens on its surface, which is true.

Key Concepts

antibody

Antibodies are crucial proteins in our immune system. They are produced by B lymphocytes (a type of white blood cell) in response to antigens. Each antibody molecule has two identical arms, each with an antigen-binding site. These sites are designed to recognize and bind to specific antigens, much like a lock and key.
The main functions of antibodies are:

• Neutralizing pathogens like viruses and bacteria.
• Marking pathogens for destruction by other immune cells.
• Activating the complement system, which helps destroy pathogens.

Antibodies can be found in blood, tissue fluids, and many secretions, playing a vital role in protecting the body from infections.

antigen

Antigens are molecules or parts of molecules that the immune system recognizes as foreign. These can include proteins from viruses, bacteria, fungi, and even pollen or food. When an antigen enters the body, it triggers an immune response. The immune system then works to destroy or neutralize the antigen.
Key points about antigens:

• They can have multiple epitopes, meaning different regions that can be recognized by different antibodies.
• Each epitope on an antigen stimulates a specific immune response.
• Common sources of antigens include pathogens and allergens.

Understanding antigens is fundamental to studying how vaccines work, as vaccines often contain antigens that train the immune system to recognize and combat specific pathogens.

lymphocyte

Lymphocytes are a type of white blood cell essential to the immune system. There are two main types of lymphocytes: B cells and T cells. Each type has unique functions in the immune response.
B cells produce antibodies, which bind to antigens. T cells, on the other hand, directly attack infected cells and help regulate the immune response.
Important characteristics of lymphocytes:

• Each lymphocyte has a unique receptor that binds to a specific antigen epitope.
• Upon binding to their specific antigen, lymphocytes can proliferate and mount a strong immune response.
• They are central to the body's ability to remember previous infections through 'memory' cells, leading to quicker responses upon re-exposure.

Lymphocytes are vital for both immediate defenses and long-term immunity.

epitope

Epitopes, also known as antigenic determinants, are the specific parts of an antigen that antibodies or lymphocyte receptors bind to. An antigen can contain multiple different epitopes, each capable of being recognized by different antibodies.
Key facts about epitopes:

• They are typically small sequences of amino acids or sugars on the surface of an antigen.
• The ability of an antigen to stimulate multiple types of immune responses is due to its multiple epitopes.
• Understanding epitopes is crucial in vaccine design, as scientists aim to target the best epitopes for a strong immune response.

In summary, epitopes are the precise targets within antigens that the immune system identifies and acts upon.