Protein translocators:
- imported mitochondria and chloroplast proteins
o most have a signal sequence at the N-terminal that allows them to
enter a specific organelle.
o Proteins destined for either organelle are tra
...
Protein translocators:
- imported mitochondria and chloroplast proteins
o most have a signal sequence at the N-terminal that allows them to
enter a specific organelle.
o Proteins destined for either organelle are translocated simultaneously
across both inner and outer membranes as specializes sites where the
two membranes contact each other.
o Each protein is unfolded as it is transported and its signal sequence is
removed after translocation is complete.
o Chaperone proteins- also assist in pulling the protein across the two
membranes and fold it back once it is inside.
o The insertion of the transmembrane proteins into the inner
membrane is guided by signal sequences in the protein that start and
stop the transfer across the membrane like the insertion for proteins
in the ER membrane.
Mitochondrial protein translocator process:
1. the mitochondrial signal sequence on a mitochondrial protein is
recognized by a receptor on the outer mito membrane.
2. This receptor is associated with a protein translocator
a. This complex diffuses laterally in the outer membrane until it
encounters the inner membrane translocator.
3. The two translocators then transport the protein across both membranes
unfolding the protein in the process.
4. The signal sequence is finally cleaved off by signal peptidase in the
mitochondrial matrix.
Same process for chloroplasts and the chaperone proteins pull the protein across
membranes and help refold.
Proteins enter peroxisomes from both the cytosol and the endoplasmic reticulum:
Peroxisomes: these organelles are present in all eukaryotic cells, and break down a
variety of molecules such as alcohol, fatty acids, and toxins.
they acquire the bulk of their proteins from the cytosol from selective
transport.
A short sequence of 3 amino acids serves as an import signal for many
peroxisomal proteins.
This signal is recognized by receptor proteins in the cytosol.
They enter via protein translocators called peroxins.
o But the do not need to unfold to enter
Most peroxisomal proteins come from the cytosol, some come via vesicles
that bud from the ER.
Proteins enter the endoplasmic reticulum while being synthesized.
- the endoplasmic reticulum- serves as an entry point for proteins destined
for other organelles as well as the er itself.
9
[Show More]
