protein targeting to the chloroplast

Question 1

What is the chloroplast targeting sequence?

Answer 1

transit peptide

Question 2

Is a transit peptide at the N-terminus of the protein?

Answer 2

yes

Question 3

Plants must send different proteins to their mitochondria and chloroplasts, which means that…

Answer 3

the targeting sequences for these organelles also need to be different.

Question 4

Like the mitochondrial sequence, the chloroplast transit sequence has a region that forms an

Answer 4

alpha helix (has hydroxylated AAs near N-terminus)

Question 5

The protein is moved across the outer chloroplast membrane, and then the inner membrane, through a pair of translocation channels known as

Answer 5

TOC (transporter outer chloroplast membrane) and TIC (transporter inner chloroplast membrane)

Question 6

does this process require ATP?

Answer 6

yes

Question 7

The chloroplast targeting sequence is cleaved by a

Answer 7

stromal processing peptidase (SPP), releasing the protein into the stroma of the chloroplast.

Question 8

If the final destination of the protein is the thylakoid lumen (interior compartment of the chloroplast)

Answer 8

-The protein will be transported into the stroma, as described above.
- The N-terminal targeting sequence is immediately followed by a
second signal sequence, which is revealed when the N-terminal
chloroplast targeting sequence is cleaved.
- The protein moves into the thylakoid lumen, the second signal
sequence is cleaved, and the protein folds into its final 3D conformation.