Comprehension - L12-L13 Flashcards
In lysosomes, the organelle is surround by what?
A double membrane structure known as the autophagosome
Soluble ER proteins usually contain the signal:
lys-asp-glu-leu (KDEL)
ER membrane proteins also have this retrieval signal:
lys-lys-X-X
What does Mannos 6-Phosphate do?
The residue acts as a sorting signal, directing proteins to the lysosome
What does the GGA adaptor do?
Connects clathrin to the MPRs
What is the MPR?
Transmembrane protein that recognizes and captures proteins with the mannose 6 phosphate signal
In the targeting of lysosomal enzymes to lysosomes, what does the G-protein Arf1-GTP do?
Binds to membrane and initiates formation of the budding vesicles and binding of the other coat proteins and induces membrane curvature when bound to GTP
What are the 3 domains in a GGA adaptor molecule?
Bind Arf1-GTP
Bind Clathrin
Bind to cytosolic tails of the MPR
What do sorting signals do?
Involved in directing proteins to the plasma membrane of polarized cells
In the endocytic pathway, what is bulk-phase endocytosis?
Pinocytosis
Non- specific uptake of extracellular fluids
In the endocytic pathway, what is receptor mediated endocytosis?
Clathrin mediated
Specific molecules bind to receptors on the extracellular surface
What does the AP2 complex do?
Links the cytoplasmic tails of plasma membrane receptors with clathrin
What is dynamin?
A G-protein required for the clathrin coated vesicle to bud from the membrane
- subunits form a ring
- GTP hydrolysis cause the vesicle to cleave and dynamin disassembles
What happens in the recycling pathway of endocytosis?
- Receptors mediate uptake of materials
- Receptors go to early endosome for sorting
- Ligands dissociate due to pH
- Receptors go to recycling component
- Vesicles return receptors to surface to be used again
What happens in the degradation pathway of endocytosis?
- Signal receptors bind ligands
- Goes to early endosome for sorting and matures into late endosome
- Late endosome fuses w lysosome for receptor degredation
What does receptor degradation do?
Prevents the cell from being further stimulated by the hormone/growth factor
What are the 3 filamentous structures of the cytoskeleton?
- Microtubules
- Microfilaments (actin)
- Intermediates
What are the 5 general functions of the cytoskeleton?
- Structural support
- Transport of materials and organelles
- Contraction and motility
- Spatial organization
- Cell division
How are cytoskeletal elements held together?
Weak non-covalent bonds
What are microtubules?
What do they do?
Hollow, unbranched, tubular structures made of tubulin
Cell support and movement
Each is made of 13 protofilaments aligned to form a tube
The alpha-tubulin end is:
The Beta-tubulin end is:
The alpha-tubulin end is: Negative
The Beta-tubulin end is: Positive
What is a centrosome?
A type of micro-tubule organizing centre which initiates microtubule function
Composed of 2 centrioles surrounded by PCM
What do centrosomes dictate?
- # of microtubules
- their polarity
- # of protofilaments
- the time and location of microtubule assembly
The PCM contains gamma-TURC, which is
- Gamma tubulin
- Non-tubulin proteins in a ring
What is stability determined by in microtubules?
- Microtubule interacting Proteins (MAPs)
- +TIPS, which bind at the + end of growing microtubules
- Temperature (cold=disassembly)
How do MAPS increase stability?
- Promote assembly by linking tubulin dimers together
- controlled by presence of phosphate groups
T or F. Beta tubulin is NOT a G-Protein
False. B-tubulin is a G protein: hydrolyzes GTP to GDP after the dimer is added to the microtubule
