Organelles & Biochemical Compartments Flashcards
How are materials shuttled between organelles?
Small membrane-bounded transport vesicles move through the cytoplasm in a directed manner, often pulled by motor proteins that operate on tracks formed by microtubules and microfilaments of the cytoskeleton. The vesicles fuse with the membrane of the acceptor compartment, which receives the vesicle’s soluble cargo as well as its membranous wrapper.
What is the secretory pathway?
The route by which proteins are synthesized in the ER, modified during passage through the Golgi complex, and transported to various destinations. It is called the secretory pathway because many of the proteins synthesized are destined to be discharged (secreted) from the cell.
Describe constitutive secretion.
During constitutive secretion, materials are transported in secretory vesicles from their sites of synthesis and discharged into the extracellular space in a continual manner. Most cells engage in this process because it contributes to the formation of the extracellular matrix and the plasma membrane.
Describe regulated secretion.
During regulated secretion, materials are stored as membrane-bound packages and discharged only in response to an appropriate stimulus. Examples include hormonal release in endocrine cells, digestive enzyme release, and neurotransmitter release. Materials to be secreted are stored in large, densely packed membrane-bound secretory granules.
How is the endocytic pathway different from the secretory pathway?
Whereas materials move out of the cell by the secretory pathway, the endocytic pathway operates in the opposite direction. By following the endocytic pathway, materials move from the outer surface of the cell to compartments such as endosomes and lysosomes located within the cytoplasm.
How are particular proteins targeted to particular cellular compartments?
Sorting signals are encoded in the amino acids of proteins. These signals are recognized by specific receptors that reside in the membranes of budding vesicles, ensuring that the protein is transported to the appropriate destination.
Describe the technique of autoradiography. What did it aim to study?
The researchers who developed autoradiography wanted to follow the cycle of secretion from start to finish. Autoradiography provides a means to visualize biochemical processes by allowing an investigator to determine the location of radioactively labeled materials within a cell. In this technique, tissue sections containing radioactive isotopes are covered with a thin layer of photographic emulsion, which is exposed by radiation emanating from the tissue. Sites containing radioactivity are revealed under the microscope.
What does a pulse-chase experiment reveal to a researcher?
One can follow the movements of newly synthesized molecules by observing a wave of radioactive material moving through the cytoplasmic organelles of cells. This helps researchers define the biosynthetic and secretory pathway.
What does the green fluorescent protein allow researchers to do?
This protein emits a green fluorescent light. When it is fused to other proteins, it allows researchers to view that protein under a microscope.
What does subcellular fractionation aim to do?
Subcellular fractionation separates vesicles derived from different organelles (nucleus, mitochondrion, plasma membrane, ER, etc).
Define microsome.
A microsome is a membranous vesicle derived from the endomembrane system that forms a heterogenous collection of similar-sized vesicles.
Define cell-free system.
A cell-free system refers to the isolated parts of a cell. They are called cell-free because they do not contain whole cells.
How can a researcher use the process of RNA interference to inhibit the translation of mRNA?
RNAi is a process in which cells produce small RNAs that bind to specific mRNAs and inhibit the translation of these mRNAs into proteins. Researchers can synthesize a collection of these siRNAs that can inhibit any specific gene. Each mRNA represents the expression of a specific gene, therefore, one can find which genes are involved in a process by determining which siRNAs interfere with that process.
What is the difference between rough and smooth endoplasmic reticulum?
Rough ER is defined by the presence of ribosomes bound to its cytosolic surface. Smooth ER does not have these ribosomes.
What are the functions of smooth ER?
- Synthesis of steroid hormones in the endocrine cells of the gonad and adrenal cortex.
- Detoxification in the liver of a wide variety of organic compounds.
- Sequestering calcium ions within the cytoplasm of cells. The regulated release of Ca2+ from the SER of skeletal and cardiac muscle cells triggers contraction.
