Cell Biology

The foundational principle of biology stating that all living organisms are composed of cells, the cell is the basic structural and functional unit of life, and all cells arise from pre-existing cells through division. This theory, formulated in the 19th century, unified biology and provided a framework for understanding life at its most fundamental level.

A selectively permeable phospholipid bilayer that surrounds every cell, controlling the passage of substances into and out of the cell. It contains embedded proteins that serve as channels, receptors, and enzymes, enabling the cell to interact with its environment and maintain homeostasis.

Double-membrane-bound organelles often called the powerhouses of the cell because they generate most of the cell's supply of adenosine triphosphate (ATP) through oxidative phosphorylation. Mitochondria possess their own circular DNA and ribosomes, supporting the endosymbiotic theory of their evolutionary origin from ancient bacteria.

The biological process by which a cell copies its entire genome before cell division, ensuring each daughter cell receives a complete and accurate set of genetic instructions. The process is semiconservative, meaning each new DNA molecule consists of one original strand and one newly synthesized strand.

A type of cell division that produces two genetically identical daughter cells from a single parent cell, used for growth, repair, and asexual reproduction in eukaryotic organisms. It proceeds through defined phases: prophase, metaphase, anaphase, and telophase, followed by cytokinesis.

A specialized form of cell division that reduces the chromosome number by half, producing four genetically unique haploid gametes from a single diploid cell. It involves two successive divisions and incorporates crossing over and independent assortment to generate genetic diversity.

An extensive network of membrane-enclosed tubules and flattened sacs connected to the nuclear envelope, existing in two forms: rough ER (studded with ribosomes for protein synthesis and processing) and smooth ER (involved in lipid synthesis, detoxification, and calcium storage).

The complex system of communication that governs basic cellular activities and coordinates cell actions. Cells detect and respond to chemical signals from their environment through signal transduction pathways, which convert extracellular signals into intracellular responses such as gene expression changes or metabolic adjustments.

A highly regulated and orderly process of programmed cell death that eliminates damaged, infected, or unnecessary cells without triggering inflammation. It is essential for development, tissue homeostasis, and immune function, and its dysregulation is implicated in cancer and autoimmune diseases.

Undifferentiated cells with the unique ability to self-renew through mitotic division and to differentiate into specialized cell types. They are classified by potency: totipotent cells can become any cell type including placental tissue, pluripotent cells can form any body cell, and multipotent cells are restricted to certain lineages.