Endoplasmic Reticulum
How are Lipids synthesised in the smooth ER and what are the examples of lipids?
- By enzymes of the smooth ER - oils, steroids, and new membrane phospholipids. -Steroids produced by SER in animal cells : sex hormones of vertebrates - various steroid hormones secreted by the adrenal glands.
How does smooth ER detoxify drugs and poisons?
-By enzymes of SER - Detoxification usually involves adding hydroxyl groups to drug molecules - Making them more soluble and easier to flush from the body.
How does the rough ER play a role in the intracellular transport of proteins in the cell?
1. After secretory proteins are formed, they depart from the ER wrapped in vesicle called transport particles. 2. Transport vesicles containing modified proteins are transported to the Golgi apparatus.
How are secretory proteins formed in the rough ER?
1. 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. 2. The new polypeptide folds into its functional shape as it enters the ER lumen. - Most secretory proteins are glycoproteins 3. The carbohydrates are attached to the proteins in the ER lumen by enzymes built into the ER membrane.
Describe the structure of Rough Endoplasmic Reticulum
1. Consists of cisternae - interconnected system of membrane-bound flattened sacs - continuous with the outer membrane of nucleus 2. Has many ribosomes on the outer surface of its membrane
How does the rough ER produce membrane phospholipid?
1. Enzymes built into the ER membrane assemble phospholipids from precursors in the cytosol. 2. The ER membrane expands, and portions of it are transferred in the form of transport vesicles to other components of the endomembrane system.
Describe the structure of Smooth Endoplasmic Reticulum
1. Lacks ribosome on the outer surface of its membrane 2. System of interconnected tubules
How does the smooth ER act as a storage of calcium ions and what is the importance of it?
1. SER stores and releases calcium ions for muscle contraction. 2. In muscle cells, The SER becomes modified to form sarcoplasmic reticulum surrounding the muscle myofibril 3. The SER membrane pumps calcium ions from the cytosol into the ER lumen. 4. When a muscle cell is stimulated by a nerve impulse, calcium ions rush back across the ER membrane into the cytosol and trigger the contraction of the muscle cell. 5. In other cell types, calcium ion release from the smooth ER triggers different responses - The secretion of vesicles carrying newly synthesized proteins.
List down the functions of the rough ER
1. Secretion of proteins 2. Intracellular transport of proteins 3. Membrane factory of cell 4. Production of membrane phospholipid
List down the functions of the smooth ER
1. Site of metabolism of carbohydrate 2. Synthesis of lipids 3. Detoxification of drugs and poisons 4. Storage of calcium ions
How does the rough ER function as the membrane factory for the cell?
1. The RER grows in place by adding membrane proteins and phospholipids to its own membrane. 2. As polypeptides grow from the ribosomes, they are inserted into the ER membrane itself and anchored there by their hydrophobic portions.
What is cisternae?
A network of membranous tubules and sacs
What cells are abundant in rough ER?
Rapidly growing cells and secretory cells E.g pancreatic cells
What is the difference between Rough ER and Smooth ER
Ribosomes are found on the surface of rough ER. Smooth ER has no ribosomes on its surface.
Examples of drugs metabolised by smooth ER
Sedative phenobarbital and other barbiturates
The ER membrane and lumen contain enzymes
TRUE
The Endoplasmic Reticulum forms an intracellular transport system and cytoplasmic skeleton
TRUE
What is the ER lumen/cisternal space?
The internal compartment of the ER
What are secretory vesicles?
Transport vesicles that carries material to plasma membrane to be secreted from the cell by exocytosis
What are transport vesicles?
Vesicles in transit from one part of the cell to another.
What cells are abundant in smooth ER?
cells involved in lipid and steroid hormone Synthesis - cells of testes and ovaries Cells involved in detoxification - liver cells
