3 - Protein targeting to mitochondria

Where are 99% of mitochondrial & chloroplasts proteins encoded at?

Nuclear genes

What are imported proteins?

Protein coded by nucleus, when inside mitochondria / chloroplast

Which AA’s do mitochondrial signal sequences normally have high contents of?

Arg / Ser / Thr

Mitochondrial signal sequence normally have high content of Arg & Ser / Thr. Where is this sequence located?

At N-terminus

Mitochondrial signal sequence normally have high content of Arg & Ser / Thr. How long is this sequence?

20-80 AA long

What % of mitochondrial / chloroplasts proteins are synthesised within the organelle?

1%

Where are soluble proteins located?

Lumen of organelle of endomembrane system

Where are integral membrane proteins located?

Embed into lipid bilayer

What is a common feature of an endoplasmic reticulum targeting signal?

Stretch of 8+ hydrophobic AA residues ~near N-terminus

Ribosomes synthesising proteins without a signal sequence would remain free in the_____?

Cytosol

What is the concept of co-translation?

All proteins are made by free ribosomes in the cytoplasm, but not all ribosomes move to the ER and attach to it during translation.

What does SRP do in the cytosol?

Binds ER signal sequence as it emerges from ribosome / translation paused / SRP binds to SRP receptors in the ER membrane

What does the ER signal sequence bind to, to open channel?

Sec61 translocator

What is Co-translational translocation?

Translocation, protein movement across ER membrane / occur same time as translation

What is the Sec61 channel?

Multi-subunit complex of protein forming a channel in the ER membrane