E.R., The golgi Body And Vesicles
Thousands of structures with membranes crowd the eukaryotic cytoplasm, the most numerous being called the endoplasmic reticulum (ER), a dense network of membranes running through the cytoplasm of every cell and enclosing a network of interconnected tubes (cisternae), which form a connecting channel throughout the cytoplasm. 'Endoplasmic' means 'inside the cytoplasm', and 'reticulum' means 'network'. The E.R. can make up a significant percentage of the overall volume of the cell. There are two types of ER: rough ER (RER), so-called because its cytoplasmic face is dotted with ribosomes, and smooth ER (SER), which is devoid of ribosomes. The RER is more extensive than SER and acts as a protein producer and storage vessel. Amino acid chains, freshly synthesised by the ribosomes, slide through tiny holes in its membrane into the cisternae, where they remain until they are sent elsewhere in the cytoplasm, or to the cell edge where they are secreted or incorporated into the cell membrane. The membranes of the ER usually form a tightly packed and flattened sac-like structures, that form inter-connected compartments within the cytoplasm. The internal space formed by the membrane sheets is
When the protein is ready, small vesicles break off from the concave face of the Golgi apparatus and move towards the surface of the cell. They fuse with the cell surface membrane and release their contents to the outside. The membranes of the vesicles, originally part of the rough ER membrane, become incorporated in the cell surface membrane. 6) Providing a structural skeleton to maintain cellular shape. (E.g. The smooth ER of a rod cell from the retina of the eye) 4)Producing lipids and steroids. (Smooth ER) Cytologists, the biologists who make the cell their special study, have found that the Golgi apparatus sometimes determines the destination of its freight with the help of carbohydrate markers, which act as labels. For example, adding the sugar mannose-6-phosphate to a protein will ensure that it is sent to a particular organelle called a lysosome. Other sugars may direct a Golgi product elsewhere, such as the cell membrane. Most targeting is not, in fact, by sugars but by "signal sequences" in the protein chain. This form of intracellular labelling is called "protein targeting". Proteins travel from the ER through the cisternae of the Golgi apparatus and to the cell edge in a unique manner. A section of endoplasmic tube containing the protein snaps off from the rest of the ER network and closes shut immediately at each end, imprisoning the protein in a vesicle which fuses with a nearby Golgi compartment, thus transferring its contents. The proteins move from one Golgi sac to the next in this way, and eventually protein-filled vesicles are pinched off, ready for secretion. These secretary vesicles often hang around near the cell boundary, waiting to be expelled. The process of secretion, in which the vesicle fuses with the outer membrane and releases its cargo to the outside world
Some common words found in the essay are:
Camillo Golgi, ER SER, Proteins RER, Vesicles Thousands, Smooth ER, golgi apparatus, ER RER, RER Likewise, rough er, Body Golgi, cell membrane, Rough ER, smooth er, er lumen, cell surface membrane, cytoplasm cell, proteins lipids, vesicle fuses, cell surface, sacs rough er, steroid hormones,
Approximate Word count = 1219
Approximate Pages = 5 (250 words per page double spaced)
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