The fluid living content of the cell that consists of two major divisions, the cytoplasm and the nucleoplasm (cell nucleus), and composed primarily of nucleic acids, proteins, lipids, carbohydrates, and inorganic salts
A cell is the structural, functional and biological unit of all organisms. It is a membrane-bound structure containing the protoplasm. The protoplasm is the fluid living content of the cell. In certain references, protoplasm is a synonymous of the term cytoplasm. In other sources, the protoplasm includes the nucleoplasm.
The protoplasm is the cell's living content. It is composed primarily of biomolecules such as nucleic acids, proteins, lipids, and carbohydrates. It also has inorganic salts and water molecules. The protoplasm is surrounded by the cell membrane.
Since prokaryotes do not have a distinct nucleus and other cytoplasmic organelles the protoplasm refers to the materials contained inside the cell membrane, i.e. the prokaryotic cytoplasm. In certain prokaryotes, particularly the Gram-negative bacteria, the protoplasm extends to the periplasmic region between the cytoplasmic membrane and the outer membrane. This region contains a gel-like material called periplasm, which is part of the protoplasm in Gram-negative bacteria.
In eukaryotes, the protoplasm consists of two major divisions: the cytoplasm and the nucleoplasm (cell nucleus). The cytoplasm is the jelly-like substance of the eukaryotic cell. It is made up of the cytosol, the vesicles, the cytoskeleton, the inclusions and the organelles except for the nucleus. Thus, the cytoplasm of a eukaryotic cell is that part of the cell between the cell membrane and the nuclear envelope. The material contained inside the nuclear envelope is called nucleoplasm. The nucleoplasm is the protoplasm of the nucleus.
The cytoplasm (of both eukaryotes and prokaryotes) is where the functions for cell expansion, growth and metabolic processes are carried out. In eukaryotic cells, the cytoplasm contains cellular organelles. These organelles perform special functions. The nucleus, for instance, is the organelle that contains the genetic material and therefore it controls cellular activities such as metabolism, growth, and reproduction by regulating gene expression. Chloroplasts are plastids containing green pigments essential for photosynthesis. Mitochondria are the organelles that synthesize energy for multifarious metabolic processes. The endoplasmic reticulum occurs as interconnected network of flattened sacs or tubule involved in lipid synthesis, carbohydrate metabolism, drug detoxification, and attachment of receptors on cell membrane proteins. It is also involved in intracellular transport, such as the transport of the products (of rough endoplasmic reticulum) to other cell parts like Golgi apparatus. Golgi apparatus is comprised of membrane-bound stacks. It is involved in glycosylation, packaging of molecules for secretion, transporting of lipids within the cell, and giving rise to lysosomes.
Protoplasm exists in two forms: a liquid-like sol state or a jelly-like gel state.
Common biological reactions
Growth and metabolism
Cells after dividing will undergo growth. The growth of the cell is enabled by metabolism. Metabolism may be categorized into two: catabolism and anabolism. Catabolism includes a series of degradative chemical reactions that break down complex molecules into smaller units, usually releasing energy in the process. Anabolism includes a sequence of chemical reactions that constructs or synthesizes molecules from smaller units, usually requiring input of energy (ATP) in the process. Thus, biomolecules, such as nucleic acids, proteins, carbohydrates, and lipids are produced, stored, and degraded inside the cell.
Protoplasm is the site of many biological processes. In eukaryotes, for instance, the site of DNA and mRNA biosyntheses is the nucleus. Proteins, in turn, are synthesized by the ribosomes. Lipid synthesis occurs in the endoplasmic reticulum.
Charles Darwin and his 19th century contemporaries viewed "protoplasm" as the holistic content of a cell; in other words, cells were composed of a mysterious "proto-plasm," a substance that had the ability of self-replication.
- From Greek (proto-), “‘first’” + (plasma), “‘something molded’”. The word was in Late Latin, meaning "first created thing," and may have existed in Medieval Greek in a different sense. It was used by Czech physiologist Johannes Evangelista Purkinje to denote the gelatinous fluid found in living tissue. This word prevailed, though Germanic language purists preferred urschleim (“‘original mucus’”).
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