28 Questions
Which type of endoplasmic reticulum is studded with ribosomes?
Rough endoplasmic reticulum (RER)
What connects the endoplasmic reticulum to the nuclear envelope?
Extensive network of folded membranes
What is the function of the smooth endoplasmic reticulum (SER)?
Lipid biosynthesis
How can the two basic kinds of endoplasmic reticulum interchange in a cell?
Depending on changing metabolic needs
Which process is responsible for the transfer of oligosaccharides to polypeptides in the ER lumen?
Oligosaccharyl transferases
Which of the following is NOT a chaperone involved in facilitating proper protein folding in the ER?
Proteasome
What stabilizes the structure of secretory proteins and membrane proteins in the GER?
Disulfide bonds
How are abnormally folded proteins handled in the ER?
Exported for degradation in the cytosol via the ubiquitin-proteasome pathway
What determines whether proteins are translocated into the ER cotranslationally or posttranslationally?
Sequence of the protein
Where do soluble proteins destined for the ER lumen or secretion pass completely?
ER lumen
What is required for posttranslational protein insertion into the ER membrane?
ATP
What facilitates the export of proteins from the ER to the Golgi?
Transport vesicles
What response is activated to prevent proteotoxicity in the ER under conditions of ER stress?
Unfolded protein response (UPR)
What is associated with pathophysiological conditions such as ischemia, diabetes, and neurodegenerative diseases?
ER stress
What maintains ER function by selectively transporting ER resident proteins back to the ER?
KDEL receptors
What process is activated under severe and prolonged ER stress, leading to cell death?
Apoptosis
Which type of endoplasmic reticulum is involved in the biosynthesis of steroid hormones?
Smooth ER (SER)
In which cells is Smooth ER (SER) abundant and involved in the biosynthesis of steroid hormones?
Leydig’s cells, adrenal cortex cells, and corpus luteum cells
Which type of endoplasmic reticulum is involved in the breakdown of dietary lipids in the small intestine and the absorption of fatty acids and monoglycerides?
Smooth ER (SER)
Which type of endoplasmic reticulum is involved in the detoxification of drugs and toxic chemicals in liver cells?
Smooth ER (SER)
What is the principal site of production of lipoprotein particles in the liver?
Smooth ER (SER)
In which cells is Granular ER (GER) well developed and prominent?
Protein-secreting cells
Who formulated the signal hypothesis, explaining the mechanism of protein synthesis in Granular ER (GER)?
Günter Blobel and David Sabatini
What is the function of Sarcoplasmic Reticulum (SR) in muscle cells?
Regulates muscular contraction
What is the function of Smooth ER (SER) in neuronal synapses?
Regulating calcium ions
What are the small closed vesicles formed when tissue disrupts ER?
Microsomes
What type of endoplasmic reticulum lacks ribosomes and is not involved in protein synthesis?
Smooth ER (SER)
What is the function of Smooth ER (SER) in liver cells?
Breakdown of glycogen into glucose
Study Notes
Endoplasmic Reticulum (ER) Structure and Functions
- Homogenization of tissue disrupts ER, leading to the formation of small closed vesicles called microsomes
- Smooth ER (SER) lacks ribosomes, has tubular or vesicular form, and is not involved in protein synthesis
- SER has diverse functions in specialized cells, including biosynthesis of lipids, lipid transport, and biosynthesis of steroid hormones
- SER is the principal site of production of lipoprotein particles in the liver and contains enzymes for lipid synthesis
- SER is involved in the breakdown of dietary lipids in the small intestine and the absorption of fatty acids and monoglycerides
- SER contains enzymes for the biosynthesis of steroid hormones and is abundant in Leydig’s cells, adrenal cortex cells, and corpus luteum cells
- In liver cells, SER is involved in detoxifying drugs and toxic chemicals and in the breakdown of glycogen into glucose
- A special type of smooth ER, called Sarcoplasmic Reticulum (SR), is found in muscle cells and regulates muscular contraction
- In neuronal synapses, SER is involved in regulating calcium ions similar to muscle cells
- Granular ER (GER) is involved in protein synthesis and is prominent in cells for protein secretion
- GER appears as parallel membrane-limited flattened sacs or cisternae, and is well developed in protein-secreting cells
- The mechanism of protein synthesis in GER is explained by the signal hypothesis, formulated by Günter Blobel and David Sabatini in 1971, and elaborated by Blobel and his colleagues between 1975 and 1980. Günter Blobel was awarded the Nobel Prize in Physiology in 1999 for this discovery.
Test your knowledge on the structure and functions of the Endoplasmic Reticulum (ER) with this quiz. Explore the roles of Smooth ER (SER), Granular ER (GER), and Sarcoplasmic Reticulum (SR) in various cellular processes, including protein synthesis, lipid biosynthesis, and calcium regulation.
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