Membrane trafficking Flashcards
Explain the terms exocytosis and endocytosis
Eukaryotic cells continually import materials by endocytosis and secrete intracellular materials by exocytosis. exocytosis-a process by which the contents of a cell vacuole are released to the exterior through fusion of the vacuole membrane with the cell membrane. endocytosis-the taking in of matter by a living cell by invagination of its membrane to form a vacuole.
How are proteins directed to the correct compartment?
Signal sequences behave like address labels and direct the protein to the correct compartment
List the types of intracellular transport?
- Gated transport (e.g. Transport through nuclear pores) 2. Transport across membranes (e.g. import of newly synthesized proteins into ER, import of proteins into mitochondria) 3. Vesicular transport (e.g. inter-organellar transport) add pic
How are proteins imported into the nucleus? And what type of transport is this?
Example of gated transport Nuclear proteins are imported by so-called import receptors that recognise nuclear localisation signals as the ‘address label’. add pic
What happens when a ribosome happens to be making a protein with an ER signal sequence?
When a ribosome happens to be making a protein with an ER signal sequence, the signal sequence directs the ribosome to the ER membrane. Many ribosomes bind to each mRNA forming a polyribosome. At the end of each round of protein synthesis, the ribosomal subunits are released and rejoin the common pool in the cytosol add pic
Proteins destined for other organelles are first imported to what organelle
Endoplasmic recticulum
What happens to misfolded or unassembled proteins ?
Unassembled or misfolded proteins are retained in the ER and exported back into the cytosol where they are degraded Many diseases result from blocked ER exit due to misfolding, e.g. Cystic Fibrosis add pic
Explain vesicular transport in cells?
in the pic below , the inward endocytic pathway (green arrows) extracellular molecules are ingested (endocytosed) in vesicles derived from the plasma membrane and are delivered to endosomes and lysosomes. add pic
Where do further protein modification occur?
Golgi apparatus Many of the sugar chains that are added in the ER undergo further modifications in the Golgi. On some proteins, more complex oligosaccharide side chains are added and removed by a series of enzymes that reside in sequence as the protein passes through the Golgi stack.
What are the cis and trans face in the golgi apperatus?
The Golgi stack has two distinct faces, an entry face (or cis face) and an exit, or trans face.
List the secretory and exocytic pathway?
add pic
What is constitutive secretion?
A steady stream of vesicles buds from the trans golgi network and fuses with the plasma membrane to release its contents.
What is regulated secretion?
The products are concentrated and stored the secretory vesicles until an extracellular signal stimulates secretion
What is pinocytosis
the ingestion of liquid into a cell by the budding of small vesicles from the cell membrane.
Name the types of endocytosis?
Receptor-mediated endocytosis Pinocytosis (fluid phase) Phagocytosis (fluid / particles e.g. microbes)
Explain the formation of clathrin-coated vesicles?
Vesicles that bud off from membranes have a distinctive protein coat on their cytosolic surface and are therefore called coated vesicles. After budding the coat is shed, allowing the vesicle to interact with the membrane to which it will fuse
Clathrin-coated vesicles have an outer coat made up of the protein clathrin. They bud from the trans-Golgi network on the outward secretory pathway and from the plasma membrane on the inward secretory pathway.
