Trafficking

Question 1

What order do proteins destined for the inner membrane of the mitochondria go through translocators?

Answer 1

TOM
TIM 23
TIM 22 or
OXA if synthesised in mitochondria

Question 2

how are matrix proteins imported into the mitochondria?

Answer 2

Hsp70 keeps unfolded, through TOM, ATP-dependent release from Hsp70.

TIM23, requires energy from H+ gradient.

mitochondrial Hsp70 high affinity for unfolded polypeptide chains, ATP - dependent pulling.

matrix peptidase cleaves SS

Hsp60 cycles of ATP binding & hydrolysis help folding.

Question 3

Describe the mitochondrial signal sequence.

Answer 3

N-terminal

Amphiphatic alpha helix with +ve residues on one side and uncharged on other.

Question 4

what is the retrieval signal for resident ER proteins and soluble ER proteins?
What is notable about KDEL affinity?

Answer 4

KKXX (binds COP1 coats)
KDEL (binds receptors)
high affinity at acidic pH i.e. near Golgi.

Question 5

what are the signal sequences?

Answer 5

Nucleus - rich in arg & lys (anywhere)
Mitochondria - N-terminal amphiphatic alpha helix
Peroxisome - C-terminal SKL
ER - 8 hydrophobic aas at centre.
Retrieval -
KKXX (transmembrane)
KDEL (soluble)

Question 6

describe the nuclear pore complex.

Answer 6

column subunits form bulk of pore wall
ring subunits have cytosolic & nuclear faces
annular form centre of pore
lumenal span membrane & anchor NPC to membrane

the nucleporins have unstructured domains lining central pore. with FG repeats, preventing anything larger than 60kDa passing through.

Question 7

what is the role of peroxisomes?

Answer 7

breakdown of long chain FAs via B-oxidation 
synthesise plasmolagen (major phospholipid of myelin).

Question 8

outline peroxisomal transport.

Answer 8

peroxins
Pex5 is SS receptor
accompanies cargo into peroxisomes
cycles back out dependent on ATP.

Question 9

outline the steps in co-translational transpirt of proteins into the ER.

Answer 9

signal recognised by srp
transient translation block (ribosome binds ER)
srp binds receptor on er, recruiting Sec61 translocator
srp + receptor released
sec61 transfers polypeptide across membrane.
signal peptidase cleaves ss.