Module 2: Lesson 2 Flashcards
What are the components to vesicle transport?
Vesicle budding and fusion.
What is the endomembrane system?
All of the organelles that exchange membranes and luminal contents by vesicular transport. They consist of the ER and nuclear envelope, Golgi, endosomes, lysosomes, miscellaneous sorting compartments, and lots of different vesicles.
What happens to membrane topology when vesicles bud and fuse?
Topology is preserved.
How does the budding and fusion of vesicles work?
Transport vesicles bud from one compartment and fuse to another compartment. Lumenal proteins and membrane proteins transfer from a donor to a target compartment, including membrane.
Why does a cell need specialized machinery to bud and fuse vesicles?
Bending membranes is energetically unfavorable.
What to coat proteins assist with?
Sorting molecules, forming spherical vesicles, avoiding non-specific fusion with other membranes, and regulation of vesicle movement on microtubules.
What drives vesicle budding?
Coat proteins
What are the types of coated vesicles?
Clathrin-coated, COPI-coated, and COPII-coated vesicles.
What are the steps of clathrin-coated vesicle budding?
- Cargo molecules bind to cargo receptors; 2. On the opposite side of the membrane, receptors are bound by adaptin proteins, which mediate clathrin binding; 3. Dynamin-GTP proteins assemble around the base, cleave GTP, and pinch the vesicles from the membrane; 4. After budding, the coat proteins are removed; 5. The “coat-free” vesicle can fuse with its target membrane.
What is the structure of clathrin and what kind of energy does it contain?
Clathrin is made up of a heavy chain and a light chain that multimerize into an energetically-favorable basket-like structure. Its subunits contain potential energy.
What is dynamin and what is its function?
Dynamin is a GTP-binding protein that forms a ring around the neck of a forming vesicle. It hydrolyzes GTP to pinch off vesicles from donor membranes.
What steps of vesicle budding are energetically unfavorable?
Clathrin forming a network on the cytosolic surface of membranes to induce membrane curvature and budding, disrupting the membrane bilayer to pinch off the vesicle, and coat protein disassembly.
What provides energy for coat protein disassembly?
Hsc70 proteins, which are ATPases, provide energy from disassembly and also restore potential energy to clathrin for the next round of vesicle budding.
What does selectivity of vesicular transport depend on?
The protein displayed on the surface of the transport vesicles.
What are the three steps of vesicle transport and fusion?
Tethering, docking, and fusion.
What are Rab GTPases?
Rab proteins in their active GTP-bound form bind the vesicle membrane and recruit other proteins that mediate vesicle transport, often using the cytoskeleton like railroad tracks. They use GTP/GDP as a molecular switch.
Rab proteins also act as tethering proteins.
What are SNARE proteins and what are their function?
SNARE proteins catalyze the fusion of the vesicle and targeted membranes through the binding of vesicle SNAREs (v-SNAREs) to target membrane SNAREs (t-SNAREs).
What determines which vesicles can fuse with which targeted membranes?
The combination of Rab GTPases, tethering proteins, and SNARE proteins.
Why does the cell need specialized machinery to bud and fuse vesicles?
Bending membranes is energetically unfavorable.
What are the molecular machines that drive vesicle fusion, and why?
SNARE proteins, which contain potential energy to coil into a bundle. When the energy breaks the hydrogen bonds of water, it can be squeezed out and the membranes get close enough to fuse.
What provides energy for SNARE protein disassembly?
NSF, an ATPase, provides energy for SNARE protein disassembly and restores potential energy to the SNARE for the next round of vesicle fusion.
