Cell Biology Glossary

The primary energy carrier molecule in cells, consisting of adenine, ribose, and three phosphate groups. Energy is released when the terminal phosphate bond is hydrolyzed, converting ATP to ADP and inorganic phosphate.

A cellular degradation process in which the cell digests its own damaged or unnecessary components by enclosing them in double-membrane vesicles (autophagosomes) and delivering them to lysosomes for recycling.

The fundamental structural and functional unit of all living organisms, bounded by a membrane and containing genetic material and the molecular machinery needed for metabolism, growth, and reproduction.

The complex of DNA and histone proteins found in the nucleus of eukaryotic cells. Chromatin can exist in a loosely packed form (euchromatin, transcriptionally active) or a densely packed form (heterochromatin, largely inactive).

A structure of tightly coiled DNA wrapped around histone proteins that carries genetic information. Humans have 46 chromosomes (23 pairs), with one set inherited from each parent.

The final stage of cell division in which the cytoplasm of a single cell is divided into two daughter cells. In animal cells it occurs by cleavage furrow formation, while in plant cells a cell plate forms at the center.

A dynamic network of protein filaments (microfilaments, intermediate filaments, and microtubules) that gives the cell shape, enables movement, and facilitates intracellular transport and cell division.

The process by which an unspecialized cell becomes a specialized cell type with a distinct structure and function, such as a neuron, muscle cell, or red blood cell. It is driven by differential gene expression rather than changes in DNA sequence.

The passive movement of molecules from a region of higher concentration to a region of lower concentration, driven by kinetic energy. No cellular energy is required, and the process continues until equilibrium is reached.

The process by which cells internalize substances from the external environment by engulfing them in vesicles formed from the plasma membrane. Types include phagocytosis, pinocytosis, and receptor-mediated endocytosis.

A biological catalyst, typically a protein, that accelerates chemical reactions in the cell by lowering the activation energy. Enzymes are highly specific and are regulated by factors such as temperature, pH, and inhibitors.

The process by which intracellular vesicles fuse with the plasma membrane and release their contents into the extracellular space. It is used for secretion of hormones, neurotransmitters, and waste products.

The process by which the information encoded in a gene is used to synthesize a functional gene product, typically a protein. It involves transcription (DNA to mRNA) and translation (mRNA to protein), and is tightly regulated at multiple levels.

A stack of flattened membrane-bound sacs (cisternae) that modifies, sorts, and packages proteins and lipids received from the endoplasmic reticulum for transport to their final intracellular or extracellular destinations.

The ability of a cell or organism to maintain stable internal conditions despite changes in the external environment. Cells achieve homeostasis through feedback mechanisms, selective membrane permeability, and regulated metabolic pathways.

A membrane-bound organelle containing hydrolytic enzymes that digest macromolecules, old cell parts, and microorganisms at an acidic pH. Dysfunction of lysosomes can lead to lysosomal storage diseases.

The large, membrane-enclosed organelle that contains the cell's chromosomal DNA and controls gene expression, DNA replication, and cell division. It is surrounded by a double-membrane nuclear envelope with nuclear pores.

A mutated or overexpressed gene that has the potential to cause cancer. Oncogenes are typically derived from proto-oncogenes, which are normal genes involved in cell growth and division that become dysregulated through mutation.

A specialized membrane-bound or non-membrane-bound structure within a eukaryotic cell that performs a specific function, such as the nucleus, mitochondria, endoplasmic reticulum, or Golgi apparatus.

A small, membrane-bound organelle that contains enzymes for oxidative reactions, including the breakdown of fatty acids through beta-oxidation and the detoxification of harmful substances such as hydrogen peroxide.

The fundamental structural component of cell membranes, consisting of two layers of phospholipid molecules with hydrophilic heads facing outward and hydrophobic tails facing inward, creating a selectively permeable barrier.

A protein molecule, usually embedded in or on the surface of a cell membrane, that binds to specific signaling molecules (ligands) and initiates a cellular response through signal transduction pathways.

A molecular machine composed of ribosomal RNA and proteins that translates messenger RNA into polypeptide chains (proteins). Ribosomes can be free in the cytoplasm or bound to the rough endoplasmic reticulum.

Repetitive nucleotide sequences at the ends of chromosomes that protect them from deterioration and fusion with neighboring chromosomes. Telomeres shorten with each cell division and are linked to aging and cellular senescence.

A membrane-bound sac within the cell used for storage, waste disposal, and maintaining turgor pressure. Plant cells typically have a large central vacuole that stores water, ions, and metabolites, while animal cell vacuoles are smaller and more numerous.