Exam Focus: Distinguish clearly between finite and continuous cell lines. Cell fusion, especially the chemical method using **PEG**, is a high-yield question, usually asked in the context of Hybridoma technology.
The process of transferring cells from a confluent primary culture or an existing cell line to fresh medium and a new culture vessel. This step is essential to prevent growth arrest due to contact inhibition or nutrient depletion.
These cell lines, typically derived from normal tissue, have a **limited lifespan** in vitro, undergoing a fixed number of cell divisions before they stop dividing (senescence).
These cell lines are **immortal** and can be cultured indefinitely. They are usually derived from malignant tumors or result from spontaneous or induced transformation of a finite cell line. They are genetically unstable and often used in industrial production (e.g., therapeutic proteins).
Cell growth in culture follows four phases when plotted as cell number versus time:
The process of joining two or more cells to form a single, hybrid cell (heterokaryon), often essential for creating hybridomas in antibody production.
Uses inactivated **Sendai virus** (or other enveloped viruses) whose surface glycoproteins induce the fusion of cell membranes.
Uses a brief, high-voltage electric pulse to create transient pores in adjacent cell membranes, leading to their fusion.
Uses chemical agents to destabilize the cell membranes. The most common agent is **Polyethylene Glycol (PEG)**, which facilitates fusion and is widely used in hybridoma technology.
Methods designed to culture tissue fragments or whole organs while retaining their physiological structure and function.
Tissue fragments are suspended in a drop of medium from a coverslip and inverted over a hollow slide, allowing nutrient access while promoting gaseous exchange.
Tissue explants are supported on a suitable platform (e.g., lens paper) inside a watch glass, with the medium maintained just below the tissue, often used for embryonic organs.