L19 Secretory Pathway Flashcards
How is lipid asymmetry achieved and maintained in cell membranes?
Flippases and Floppases
Scramblases
Vesicle Trafficking
What is a key example of membrane lipid asymmetry?
Red Blood Cell Membrane:
Negatively charged phospholipids, such as phosphatidylserine, are predominantly located in the cytosolic leaflet (inner leaflet) of the red blood cell membrane.
What enzymes maintain phosphatidylserine asymmetry in the red blood cell membrane?
- Flippases (specifically, translocases): These enzymes move phosphatidylserine from the outer leaflet to the inner leaflet of the membrane.
- Scramblases: These enzymes catalyze the bidirectional movement of phospholipids between leaflets, tending to randomize lipid distribution.
Is the composition of membrane bound organelles same between different cell types?
No - The composition of membrane bound organelles
is different between different cell types
What is the ER like in terms of its structure?
The Endoplasmic Reticulum (ER) is a dynamic network that is constantly breaking and reforming. This dynamic nature is essential for its diverse functions within the cell.
Where is the ER connencted to?
Nuclear envelope
What does ER form?
ER forms hollow tubes and flattened sacs. The chambers are cisternae
What are the two types of ER?
Rough (RER) outer membrane covered in ribosomes
Smooth (SER) no ribosomes
What are the 4 functions of the ER?
- Quality control
- Synthesis
- Storage
- Detoxification
What happens to newly synthesized proteins?
Proteins destined for secretion or incorporation into membranes must be translocated into the Endoplasmic Reticulum (ER).
What is the role of chaperone proteins in protein folding?
Chaperone proteins assist in the proper folding of newly synthesized proteins by guiding them into their correct three-dimensional (tertiary and quaternary) structures.
What are the key functions of the Endoplasmic Reticulum?
- Synthesis of proteins destined for secretion or membrane insertion.
- Quality control of protein folding.
What is the function of the smooth endoplasmic reticulum?
storage and detoxification
What is the SER responsible for? (5)
- Synthesis of phospholipid and cholesterol
- Steroid hormone production
- Synthesis and storage of glycerides
- Synthesis and storage of glycogen
- Important role as a calcium store
Explain calcium signalling in Acinar cells?
Zymogen granules contain enzymes important for digestion: Stimulation – Ca2+ release – Vesicle fusion – enzyme release.
Explain transport from ER to Golgi.
- Transport between ER and Golgi in the form of vesicles and tubules
- The vesicles bud off the ER and are received by the Golgi
- Anything in the lumen or the membrane of the vesicle will be transported to the new compartment
What is the role of protein coats in vesicle formation?
- Vesicle formation is often mediated by a protein coat.
- This coat provides mechanical strength and helps to shape the forming vesicle.
- However, the coat must be discarded before the vesicle can fuse with its target membrane.
What are the three types of vesicle coats?
- Clathrin
- COPI
- COPII
How do vesicles reach the correct target ?
Through SNARE - soluble N-ethylmaleimide-sensitive factor adaptor protein receptor
What are the two types of SNARE?
Two types
v-SNAREs : vesicle SNARES- found in the vesicle membrane.
t-SNARE: target SNARES found in the membrane of the target membrane
What is the SNARE complex in nerve terminals?
In nerve terminals, the SNARE complex is a helical bundle of proteins involved in the docking and fusion of synaptic vesicles with the presynaptic membrane. It typically consists of three components.
What are the adaptations of Golgi apparatus?
Golgi apparatus is composed of flattened discs – also called cisternae
The cisternae communicate with the ER and cell membrane by use of vesicles and tubules
What are the three primary functions of the Golgi apparatus?
- Modification and packaging of secreted proteins
- Renewal and modification of the plasma membrane
- Delivery of material to other organelles,
especially the endocytic pathway
Explain the structure of Golgi?
The Golgi is a highly structured organelle. Vesicles released from the ER bind to the cis face and are then processed and leave from the trans face of the organelle.
What is the major sorting station for newly made proteins?
The trans - golgi network.
