Then there's the smooth endoplasmic reticulum, which doesn't have those ribosomes on it. And that smooth endoplasmic reticulum produces other substances needed by the cell. So the endoplasmic reticulum is an organelle that's really a workhorse in producing proteins and substances needed by the rest of the cell. Endoplasmic Reticulum Rough. William Gahl, M. Featured Content. Introduction to Genomics. Rough ER is found throughout the cell but the density is higher near the nucleus and the Golgi apparatus.
This process is called translation. Certain cells of the pancreas and digestive tract produce a high volume of protein as enzymes. Many of the proteins are produced in quantity in the cells of the pancreas and the digestive tract and function as digestive enzymes. Proteins are produced for the plasma membrane, Golgi apparatus, secretory vesicles, plant vacuoles, lysosomes, endosomes and the endoplasmic reticulum itself.
Some of the proteins are delivered into the lumen or space inside the ER whilst others are processed within the ER membrane itself. In the lumen some proteins have sugar groups added to them to form glycoproteins.
Some have metal groups added to them. It is in the rough ER for example that four polypeptide chains are brought together to form haemoglobin.
Protein quality control section It is also in the lumen that an amazing process of quality control checking is carried out. Proteins are subjected to a quality control check and any that are found to be incorrectly formed or incorrectly folded are rejected. These rejects are stored in the lumen or sent for recycling for eventual breakdown to amino acids.
A type of emphysema a lung problem is caused by the ER quality control section continually rejecting an incorrectly folded protein. The protein is wrongly folded as a result of receiving an altered genetic message. The required protein is never exported from the lumen of rough ER.
Rigorous quality control plays a part in cystic fibrosis A form of cystic fibrosis is caused by a missing single amino acid, phenylanaline, in a particular position in the protein construction. The protein might work well without the amino acid but the very exacting service provided by the quality control section spots the error and rejects the protein retaining it in the lumen of the rough ER.
In this case the customer the person with cystic fibrosis loses out completely due to high standards when a slightly poorer product would have been better than no product at all. They are conveyed in vesicles or possibly directly between the ER and Golgi surfaces. It is found fairly evenly distributed throughout the cytoplasm. Smooth ER is devoted almost exclusively to the manufacture of lipids and in some cases to the metabolism of them and associated products. In liver cells for example smooth ER enables glycogen that is stored as granules on the external surface of smooth ER to be broken down to glucose.
Smooth ER is also involved in the production of steroid hormones in the adrenal cortex and endocrine glands. Smooth ER — the detox stop Smooth ER also plays a large part in detoxifying a number of organic chemicals converting them to safer water-soluble products.
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