week 7: Intracellular compartments Flashcards
Where are proteins made?
Made in the cytoplasm then transported to the organelles
What are the 3 mechanisms for protein transportation
- through nuclear pores
- transport across membranes
- transport via vesicles through the endomembrane system
what is a signal sequence
a specific sequence of amino acids which tells the cell where that protein belongs
what is the transport of proteins through nuclear pores
- nuclear membrane has many pores
- proteins are trafficked between the nucleus and the cytoplasm through nuclear pores
- aided by receptor proteins that trap the proteins & delivers them to the pore complex
Do nuclear pores transport fully folded proteins?
Yes
How does the transport of protein into the nucleus work?
Transport receptors in the cytosol bind to the nuclear signal sequences on the proteins.
receptors interact with the nuclear pore fibrils and direct the protein transport
Does the transport of protein into the nucleus via transport receptors require energy
yes
what is the transport of proteins across membranes into organelles?
A signal sequence at the N-terminus of the protein allows the protein to enter the mitochondrion
The protein is transported across both the inner and outer membranes, and it is transported in the unfolded state
Chaperone proteins aid this process & help the refolding of the protein once inside the mitochondrion
The signal sequence is removed once the protein is inside the mitochondrion
what are chaperone proteins?
they aid in the process of transport of proteins across membranes and help the refolding of the protein once inside the mitochondrion
What is the transport of proteins through the endomembrane system?
Proteins travel through vesicles
what is the endoplasmic reticulum
serves as an entry point for proteins destined for other parts of the cell.
proteins enter the ER and will move through the cell in membrane-bound vesicles never going into the cytosol
What are the two proteins made in the ER?
- water-soluble - stay in ER lumen
2. Membrane-bound - these stay within ER membrane
where does the translation of all proteins begin?
ribosomes in the cytosol except for protein that are destined for the ER have a signal sequence
what are soluble proteins
water-soluble ( hydrophilic) and so can enter the watery lumen of ER
how are soluble proteins translated
translated through translocator channels in the ER membrane
signal sequence stays bound to translocator & the rest of the protein is threaded through into lumen
once complete, the signal sequence is cleaved off by peptidase enzyme
How are membrane-bound proteins translated
translated through translocator channels in the ER membrane
Proteins are destined to stay in the membrane.
have one or more hydrophobic regions that slide into the ER membrane once translated
the hydrophobic region starts and stops the signal
what is the transport of proteins through the endomembrane system
proteins are synthesised in the ER and transported through vesicles
Transport vesicles form when a small part of the ER membrane buds off
what protein is involved in vesicle budding?
clathrin is involved in forming the vesicle. It coats the outside of the vesicle creating the shape
how does clathrin make a vesicle?
Clathrin forms a basket-like network around the vesicle, and this involves other accessory proteins eg. adaptins, dynamin
how do clathrin-coated vesicles form?
form from Golgi and also the plasma membrane (endocytosis)
what are the Golgi stacks of membrane?
proteins move through the stacks from the cis Golgi network closer to the nucleus, to the trans-Golgi network closer to the plasma membrane
what is protein secretion
secretory proteins are released via exocytosis
What is constitutive secretion
continually supplies the plasma membrane with newly synthesised lipid and proteins
- continual or unregulated
e. g albumin, immunoglobins, collagen
what are regulated secretion
proteins are stored in vesicles until an extracellular signal stimulates their secretion
requires extracellular signal for secretion
e.g insulin, neurotransmitters
