The act of writing definitions is an art. A perfect definition of a concept is one that is accurate, precise and has all the keywords related to the concept.  Cell Biology is the specialized field of biological science that deals with the study of the structural and functional units of living organisms i.e. cells. As biologists, writing definitions of certain topics under cell biology can sometimes become a tedious task, but no worries, we have curated ’10 definitions from Cell Biology’ for you all. 

10 Definitions from Cell Biology

Plasma Membrane-

The selectively permeable membrane forming the boundary of a cell can be referred to as a plasma membrane. It consists mostly of lipids and proteins and plays a crucial role in the cell’s activities. A key task of the plasma membrane is to regulate the flow of materials into and out of the cell. This selectivity of traffic is accomplished usually by membrane proteins that act as ion channels or transport proteins. Other membrane proteins are receptors for signal molecules (e.g. hormones, growth factors, cytokines) arriving at the cell surface; they relay the signal to other components inside the cell. Supported by the cell’s internal cytoskeleton, the plasma membrane is the site of junctions with neighbouring cells and forms attachments to the extracellular matrix, thus ensuring tissue integrity.

Source- https://www.researchgate.net/

Cell wall-

A rigid outer layer that surrounds the plasma membrane of plant, fungal, algal, and bacterial (but not animal) cells. It protects and/or gives shape to a cell, and in herbaceous plants provides mechanical support for the plant body. The cell walls in most plants and algae are composed of the polysaccharide cellulose and plant cell walls may be secondarily thickened by the addition of lignin. The cell walls of fungi consist mainly of chitin. Bacterial cell walls consist of complex polymers of polysaccharides and amino acids (for instance, the eubacteria cell wall is made of peptidoglycan).

Source- https://www.researchgate.net/

Cell plate-

The structure that forms in a dividing plant cell at the end of mitosis; separates the cytoplasm of the two daughter protoplasts. The cell plate is formed from vesicles made by dictyosomes (Golgi bodies) and arranged by the microtubules of the phragmoplast in the equatorial region of the spindle. These vesicles contain pectin, cellulose, and hemicellulose, which contribute to the middle lamella and the primary wall of the new cell wall. Certainly, the cell plate eventually fuses with the cell wall of the parent cell, dividing it into two daughter cells (thus cell plate grows centrifugally).

Plasmodesmata (sing. plasmodesma)-

Fine cytoplasmic strands that have the role to connect the protoplasts of adjacent plant cells by passing through their cell walls. Plasmodesmata are cylindrical in shape (about 20-40 nm in 1 diameter) and are lined by the plasma membrane of the two adjacent cells. The endoplasmic reticulum of the two adjacent cells are connected by a narrower structure, the desmotubule, which runs through the centre of a plasmodesma. Another key point is that plasmodesmata tend to occur in groups, forming distinct areas called primary pit fields in plants. They permit the passage of substances between the cells including ions, sugars, amino acids, and macromolecules.

Source- https://www.researchgate.net/

Kinetochore –

A plate-like structure by which the microtubules of the spindle attach to the centromere of a chromosome during nuclear division. In higher organisms, kinetochore consists of protein and RNA arranged in three layers. Basically, kinetochore acts as a motor, pulling the centromere along the attached microtubules towards the spindle pole. This process is thought to involve motor proteins, such as dynein, and the disassembly of the microtubule subunits.

Source- https://www.researchgate.net/

Aster-

A star-like arrangement of microtubules radiating from a centrosome. Asters become conspicuous in animal cells at the ends of the spindle when cell division starts. Additionally, they are believed to help locate the spindle in relation to the cell’s boundaries and to trigger cleavage of the cytoplasm when nuclear division is completed.

Nucleolus-

A small dense round body within the nucleus of a non-dividing eukaryotic cell that is the site of ribosome assembly. It forms around the nucleolar organizer, which encodes most of the segments of ribosomal RNA. Ribosomal proteins migrate to the nucleolus from their assembly sites in the cytoplasm and are packaged into ribonucleoproteins, which then return to the cytoplasm where they become mature ribosome particles.

Source- https://www.researchgate.net/

Chromosome-

A thread-like structure several to many of which are found in the nucleus of eukaryotic cells. Chromosomes are composed of DNA. They carry the genes in a linear sequence; these determine the individual characteristics of an organism. When the nucleus is not dividing, individual chromosomes cannot be identified with a light microscope. During the first stage of nuclear division (prophase), however, the chromosomes contract and, when stained, can be clearly seen under a microscope. However, each chromosome consists of two chromatids held together at the centromere.

The number of chromosomes in each cell is constant for and characteristic of the species concerned. In short, in the normal body cells of diploid organisms the chromosomes occur in pairs in the gamete-forming cells. However, the diploid number is halved and each cell contains only one member of each chromosome pair (haploid-n). All things considered, thus, in humans, each body cell contains 46 chromosomes (22 matched pairs and one pair of sex chromosomes). Each human germ cell contains 23.

Another key point is that bacterial cells contain only a single circular chromosome, typically tethered to the cell’s plasma membrane and highly aggregated into a nucleoid. Viral chromosomes can consist of one or several single-or double-stranded nucleic acid molecules (DNA or RNA).

Plasmogamy-

Fusion of the cytoplasm of two (or more) cells. It precedes the union of the nuclei in fertilization and it occurs in heterokaryosis. Plasmogamy is often reported in fungi.

Centromere-

The part of a chromosome that attaches to the spindle during the cell division process. The position of the centromere plays a key role. Two chromatids of a chromosome are held together at the centromere. The centromere usually appears as a constriction when chromosomes contract during cell division.

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Thank you for reading -10 Definitions from Cell Biology.

Team MBD

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Reference: https://www.oxfordreference.com/view/10.1093/acref/9780199204625.001.0001/acref-9780199204625