Health, disease and the development of medicines revision notes

Chemical Defences Against Pests

Plants produce chemicals to deter or harm pests. Examples include nicotine, which is toxic to many insects, and tannins, which make plant tissues unpalatable. Some chemicals disrupt insect nervous systems or inhibit their growth and development. These compounds can act as direct toxins or antifeedants.

Chemical Defences Against Pathogens

Plants also produce chemicals with antimicrobial properties to combat pathogens like bacteria, fungi, and viruses. These chemicals can inhibit pathogen growth or kill them directly. Some plant compounds are involved in strengthening cell walls to prevent pathogen entry or spread after infection.

Human Applications of Plant Chemicals

Numerous plant-derived chemicals have medicinal value for humans. For instance, quinine from cinchona trees treats malaria. Salicylic acid from willow bark is a precursor to aspirin, used for pain. Other plant chemicals can have analgesic, anti-inflammatory, or antimicrobial effects, demonstrating their pharmaceutical potential.

Leaf Cuticle as a Barrier

The leaf cuticle is a protective, waxy layer covering the epidermis of leaves and stems. Its primary functions include reducing water loss through transpiration and forming a physical barrier. This barrier deters pests from feeding directly on the leaf tissue and prevents the penetration of pathogens, such as bacteria and fungi, into the plant's internal cells.

Cell Wall as a Barrier

Every plant cell is surrounded by a rigid cell wall, located external to the cell membrane. Composed mainly of cellulose, the cell wall provides structural support and maintains cell turgor. Crucially, it acts as a strong physical barrier, making it difficult for pathogens to enter the cell and infect the plant. Some pathogens produce enzymes to break down cell walls, but the cell wall's robustness is an initial line of defense.

Layers of Protection

The combination of the waxy cuticle on the outer surface and the cell wall around individual cells provides a multi-layered defense system. The cuticle is the outermost defense, while the cell wall is the ultimate physical barrier that pathogens must breach to reach the cytoplasm. This double-barrier system significantly contributes to plant survival against environmental threats.

Initial Steps in Monoclonal Antibody Production

Production begins by immunising a mammal, often a mouse, with a specific antigen. This stimulates the animal's B lymphocytes to produce corresponding antibodies. These specific lymphocytes are then isolated. A key challenge is that these antibody-producing lymphocytes have a limited lifespan and cannot divide indefinitely in laboratory cultures.

Formation of Hybridoma Cells

To enable continuous production, the antibody-producing lymphocytes are fused with myeloma cells. Myeloma cells are a type of cancer cell that can divide indefinitely. The fusion of a lymphocyte and a myeloma cell creates a 'hybridoma' cell. These hybridoma cells inherit the ability to produce the desired antibody from the lymphocyte and the ability to rapidly divide and multiply from the myeloma cell.

Culturing and Antibody Production

After fusion, the hybridoma cells are cultured to grow and multiply. It is crucial to select only those hybridoma cells that are producing the desired specific antibodies. Once identified, these specific hybridoma cells can be grown in large quantities, continuously producing and secreting large amounts of the monoclonal antibodies. This continuous production is vital for their use in diagnostics and therapeutics.

Initial Exposure and Primary Response

Upon first exposure to a pathogen, the specific immune system identifies its unique antigens. This triggers a primary immune response where the body starts producing antibodies tailored to that specific antigen. This process also creates memory lymphocytes (B and T cells) that 'remember' the pathogen.

Antigen Recognition and Antibody Production

Antigens are unique molecules on the surface of pathogens. They act as signals for the immune system. Once recognised, B lymphocytes mature into plasma cells which then produce specific antibodies. These antibodies bind to the antigens, marking the pathogen for destruction by other immune cells or directly neutralising it.

Role of Memory Lymphocytes

Memory lymphocytes are crucial for long-term immunity. They are produced during the initial exposure and remain in the body. If the same pathogen is encountered again, these memory cells enable a much quicker, stronger, and more sustained secondary immune response. This rapid action often prevents the development of disease symptoms.

Secondary Immune Response

The secondary immune response is faster and more powerful than the primary response due to the presence of memory lymphocytes. These cells quickly multiply and produce large quantities of antibodies, eliminating the pathogen before it can cause illness. This is the basis of how vaccinations work.