Intracellular components Flashcards
What kind of protein trafficking occurs on the nuclear membrane?
Gated transport
What are the three types of protein trafficking?
Gated transport, protein translocation, vesicular transport
How long, generally, are signal sequences
15-60 amino acids
What is the function of a signal peptidase
to cleave the signal sequence from the finished protein after the complete sorting process
What is the signal sequence for a protein destined for the ER?
5-10 nonpolar amino acids on the N-terminal sequence
What is the signal sequence for a protein destined for the mitochondria?
positively charged amino acids that alternate with hydrophobic ones
What is the signal sequence for a protein destined for peroxisomes?
3 characteristic amino acids at their C-terminus
How much of the cell’s volume is occupied by membrane-enclosed compartments?
50%
What proteins help the precursor mitochondrial protein stay unfolded in the cytosol?
Chaperone proteins fo the hsp70 family
Within the mitochondria, where is the H+ ion concentration the greatest?
the intermembrane space
What proteins help the unfolded protein fold when within the mitochondria?
mitochondrial hsp60
Describe the difference between Co-translational and post-translational import of proteins into the ER.
Co- ribosome with half-baked protein attaches to the translocator and finishes protein synthesis, while funneling through the growing protein. Post- protein is completed by the time it gets to the translocator on the ER membrane.
What types of proteins are fully translocated into the lumen of the ER?
water-soluble
What guides a protein undergoing translation to the ER membrane?
signal recognition particle (SRP)
What does the SRP bind to?
the ER signal sequence and the large ribosomal subunit, and later to the SRP receptor
What is true about all ER signal sequences?
They have 8 nonpolar amino acids at the center.
Where does the SRP attach on the large ribosomal subunit?
the elongation factor site, pausing translation
What is a common ER translocator?
Sec61
how many subunit comprise Sec61?
3
What triggers the opening of the pore in Sec61>
ER signal sequence binding
What are the three ways a transmembrane protein integrates in the ER membrane?
- via a cleaved ER signal sequence
- via an internal signal sequence that leads to C-terminus in the lumen
- via an internal signal sequence that leads to T-terminus in the lumen
Why, if there are more positively charged amino acids before the hydrophbic sequence, does the C-terminus enter the lumen?
The positive charge is attracted to the negative charge in the cytosol, causing it to stay outside.
What would be included in the amino acid sequence of a Multipass protein in the ER membrane?
multiple start and stop transfer sequences.
Where are the three most likely destinations for a water-soluble protein?
lumen of the ER, another organelle, or secretion
What is an SRP made of ?
six polypeptide chains bound to a single, small RNA molecule
The SRP’s signal sequence bind site is lined by what hydrophobic residue?
methionine
