Functional Difference Between Smooth and Rough Endoplasmic Reticulum

Related Posts:

Functional Difference Between Smooth and Rough Endoplasmic Reticulum (Campbell Biology)

Source: Urry, Lisa A.. Campbell Biology (p. 104). Pearson Education. Kindle Edition.

Campbell Biology

Smooth Endoplasmic Reticulum

The smooth ER functions in diverse metabolic processes, which vary with cell type. These processes include synthesis of lipids, metabolism of carbohydrates, detoxification of drugs and poisons, and storage of calcium ions.

Enzymes of the smooth ER are important in the synthesis of lipids, including oils, steroids, and new membrane phospholipids. Among the steroids produced by the smooth ER in animal cells are the sex hormones of vertebrates and the various steroid hormones secreted by the adrenal glands. The cells that synthesize and secrete these hormones—in the testes and ovaries, for example—are rich in smooth ER, a structural feature that fits the function of these cells.

– What does smooth endoplasmic reticulum synthesize?

Other enzymes of the smooth ER help detoxify drugs and poisons, especially in liver cells. Detoxification usually involves adding hydroxyl groups to drug molecules, making them more soluble and easier to flush from the body. The sedative phenobarbital and other barbiturates are examples of drugs metabolized in this manner by smooth ER in liver cells. In fact, barbiturates, alcohol, and many other drugs induce the proliferation of smooth ER and its associated detoxification enzymes, thus increasing the rate of detoxification. This, in turn, increases tolerance to the drugs, meaning that higher doses are required to achieve a particular effect, such as sedation. Also, because some of the detoxification enzymes have relatively broad action, the proliferation of smooth ER in response to one drug can increase the need for higher dosages of other drugs as well. Barbiturate abuse, for example, can decrease the effectiveness of certain antibiotics and other useful drugs.

– What is the effect of barbiturate abuse to certain antibiotics?

The smooth ER also stores calcium ions. In muscle cells, for example, the smooth ER membrane pumps calcium ions from the cytosol into the ER lumen. When a muscle cell is stimulated by a nerve impulse, calcium ions rush back across the ER membrane into the cytosol and trigger contraction of the muscle cell. In other cell types, release of calcium ions from the smooth ER triggers different responses, such as secretion of vesicles carrying newly synthesized proteins.

Rough Endoplasmic Reticulum

Many cells secrete proteins that are produced by ribosomes attached to rough ER. For example, certain pancreatic cells synthesize the protein insulin in the ER and secrete this hormone into the bloodstream. As a polypeptide chain grows from a bound ribosome, the chain is threaded into the ER lumen through a pore formed by a protein complex in the ER membrane. The new polypeptide folds into its functional shape as it enters the ER lumen. Most secretory proteins are glycoproteins, proteins with carbohydrates covalently bonded to them. The carbohydrates are attached to the proteins in the ER lumen by enzymes built into the ER membrane.

After secretory proteins are formed, the ER membrane keeps them separate from proteins in the cytosol, which are produced by free ribosomes. Secretory proteins depart from the ER wrapped in the membranes of vesicles that bud like bubbles from a specialized region called transitional ER. Vesicles in transit from one part of the cell to another are called transport vesicles.

– What do you call the ribosomes that are found in cytosol?

In addition to making secretory proteins, rough ER is a membrane factory for the cell; it grows in place by adding membrane proteins and phospholipids to its own membrane. As polypeptides destined to be membrane proteins grow from the ribosomes, they are inserted into the ER membrane itself and anchored there by their hydrophobic portions. Like the smooth ER, the rough ER also makes membrane phospholipids; enzymes built into the ER membrane assemble phospholipids from precursors in the cytosol. The ER membrane expands, and portions of it are transferred in the form of transport vesicles to other components of the endomembrane system.

– What does rough endoplasmic reticulum make besides protein?


Urry, Lisa A.. Campbell Biology. Pearson Education. Kindle Edition.

Related Research

Research Article: Endoplasmic Reticulum Redox State Is Not Perturbed by Pharmacological or Pathological Endoplasmic Reticulum Stress in Live Pancreatic β-Cells

Date Published: November 8, 2012 Publisher: Public Library of Science Author(s): Irmgard Schuiki, Liling Zhang, Allen Volchuk, Jeffrey L. Brodsky. Abstract: Accumulation of unfolded, misfolded and aggregated proteins in the endoplasmic reticulum (ER) causes ER stress. ER stress can result from physiological situations such as acute increases in secretory protein biosynthesis or pathological conditions that … Continue reading

Research Article: PARM-1 Is an Endoplasmic Reticulum Molecule Involved in Endoplasmic Reticulum Stress-Induced Apoptosis in Rat Cardiac Myocytes

Date Published: March 18, 2010 Publisher: Public Library of Science Author(s): Koji Isodono, Tomosaburo Takahashi, Hiroko Imoto, Naohiko Nakanishi, Takehiro Ogata, Satoshi Asada, Atsuo Adachi, Tomomi Ueyama, Hidemasa Oh, Hiroaki Matsubara, Arnold Schwartz. Abstract: To identify novel transmembrane and secretory molecules expressed in cardiac myocytes, signal sequence trap screening was performed in rat neonatal cardiac … Continue reading

Research Article: Wnt traffic from endoplasmic reticulum to filopodia

Date Published: February 22, 2019 Publisher: Public Library of Science Author(s): Naushad Moti, Jia Yu, Gaelle Boncompain, Franck Perez, David M. Virshup, Yi Li. Abstract: Wnts are a family of secreted palmitoleated glycoproteins that play key roles in cell to cell communication during development and regulate stem cell compartments in adults. Wnt receptors, downstream … Continue reading

Research Article: Effect of Sec61 interaction with Mpd1 on endoplasmic reticulum-associated degradation

Date Published: January 25, 2019 Publisher: Public Library of Science Author(s): Fabio Pereira, Mandy Rettel, Frank Stein, Mikhail M. Savitski, Ian Collinson, Karin Römisch, Howard Riezman. Abstract: Proteins that misfold in the endoplasmic reticulum (ER) are transported back to the cytosol for ER-associated degradation (ERAD). The Sec61 channel is one of the candidates for … Continue reading