Cell Structure

Cells consist of a protoplasm enclosed within a membrane, which contains many biomolecules such as proteins and nucleic acids. Organisms can be classified as unicellular (consisting of a single cell; including most bacteria) or multicellular (including plants and animals). While the number of cells in plants and animals varies from species to species, humans contain about 100 trillion (1014) cells.  Most plant and animal cells are visible only under the microscope, with dimensions between 1 and 100 micrometres.

Breakdown

Cytoplasm....In cell biology, the cytoplasm is the material within a living cell, excluding the cell nucleus. It comprises cytosol (the gel-like substance enclosed within the cell membrane) and the organelles – the cell's internal sub-structures.

Centrioles...In cell biology a centriole is a cylindrical cell structure composed mainly of a protein called tubulin that is found in most eukaryotic cells. An associated pair of centrioles, surrounded by a shapeless mass of dense material, called the pericentriolar material, or PCM, makes up a compound structure called a centrosome. Centrioles are involved in the organization of the mitotic spindle and in the completion of cytokinesis.

Free Ribosome...Free ribosomes are located in the cytoplasm, and the bound ribosomes are attached to the endoplasmic reticulum. Free ribosomes produce proteins for the cell, while bound ribosomes produce proteins that are transported out of the cell.

Golgi Bodies or apparatus...The Golgi apparatus, also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic cells. It was identified in 1897 by the Italian scientist Camillo Golgi and named after him in 1898.

Part of the cellular endomembrane system, the Golgi apparatus packages proteins into membrane-bound vesicles inside the cell before the vesicles are sent to their destination. The Golgi apparatus resides at the intersection of the secretory, lysosomal, and endocytic pathways. It is of particular importance in processing proteins for secretion, containing a set of glycosylation enzymes that attach various sugar monomers to proteins as the proteins move through the apparatus.

Lysosomes...A lysosome is a membrane-bound organelle found in nearly all animal cells. They are spherical vesicles which contain hydrolytic enzymes that can break down virtually all kinds of biomolecules

Mitochondria...qv. The mitochondrion (plural mitochondria) is a double membrane-bound organelle found in all eukaryotic organisms, although some cells in some organisms may lack them (e.g. red blood cells). A number of organisms have reduced or transformed their mitochondria into other structures. To date, only one eukaryote, Monocercomonoides, is known to have completely lost its mitochondria. Mitochondria generate most of the cell's supply of adenosine triphosphate (ATP), used as a source of chemical energy.

Nucleus...In cell biology, the nucleus  is a membrane-enclosed organelle found in eukaryotic cells. Eukaryotes usually have a single nucleus, but a few cell types, such as mammalian red blood cells, have no nuclei, and a few others have many.

Cell nuclei contain most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these chromosomes are the cell's nuclear genome and are structured in such a way to promote cell function. The nucleus maintains the integrity of genes and controls the activities of the cell by regulating gene expression—the nucleus is, therefore, the control center of the cell.

Nucleolus...The nucleolus  is the largest structure in the nucleus of eukaryotic cells, where it is primarily responsible for the creation of ribosomes via a process known as ribosome biogenesis. Nucleoli also have other important functions like assembly of signal recognition particles and playing a role in the cell's response to stress. Nucleoli are made of proteins, DNA and RNA and form around specific chromosomal regions.

Peroxisomes...Oxidation of toxic molecules--They are involved in catabolism of very long chain fatty acids, branched chain fatty acids, D-amino acids, and polyamines, reduction of reactive oxygen species – specifically hydrogen peroxide. Also biosynthesis of plasmalogens, i.e. ether phospholipids critical for the normal function of mammalian brains and lungs. Peroxisomes contain oxidative enzymes, such as catalase, D-amino acid oxidase, and uric acid oxidase. However the last enzyme is absent in humans, explaining the disease known as gout, caused by the accumulation of uric acid.

Plasma Membrane...The plasma membrane is the boundary between the cell and its environment. It regulates what enters and exits the cell. Cells must maintain an appropriate amount of molecules to function inside them. They must also have a way to keep things out or to allow things to enter. This is the job of the plasma membrane. The plasma membrane is like the guard at a gated community. The guard must inspect those who enter and those who leave to make sure that only the people and things needed in the community are there. The plasma membrane is the boundary between the cell and its environment. It regulates what enters and exits the cell. Cells must maintain an appropriate amount of molecules to function inside them. They must also have a way to keep things out or to allow things to enter. This is the job of the plasma membrane. The plasma membrane is like the guard at a gated community. The guard must inspect those who enter and those who leave to make sure that only the people and things needed in the community are there.

Ribosome....qv...Ribosomes are composed of protein and ribosomal RNA. The structure of the ribosome is composed of two subunits. One of the subunits is larger than the other. There are four strands of rRNA that hold the structure together.

Ribosomes are produced in the nucleolus of the cell. The proteins that make up the ribosome are brought into the nucleolus and assembled into subunits. Afterward, the subunits are transported to the cytoplasm of the cell. The subunits of a ribosome join when it beings to build proteins.

Rough Endoplasmic Reticulum...Rough ER (RER) is involved in some protein production, protein folding, quality control and despatch. It is called ‘rough’ because it is studded with ribosomes. Protein folding unit.....function of RER.

It is in the lumen of the rough ER that proteins are folded to produce the highly important biochemical architecture which will provide ‘lock and key’ and other recognition and linking sites.

Smooth Endoplasmic Reticulum...Smooth E R (SER) is associated with the production and metabolism of fats and steroid hormones. It is ‘smooth’ because it is not studded with ribosomes and is associated with smooth slippery fats.

Vacuoles...A vacuole  is a membrane-bound organelle which is present in all plant and fungal cells and some protist, animal and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic molecules including enzymes in solution, though in certain cases they may contain solids which have been engulfed. Vacuoles are formed by the fusion of multiple membrane vesicles and are effectively just larger forms of these. The organelle has no basic shape or size; its structure varies according to the needs of the cell. Many functions are preformed by Vacuoles. Size and shape depend on function.

Cell Structure

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