Lecture 2

Question 1

Microsomes

Answer 1

Forms from rough ER (when disrupted)
-can be used to be studied in vitro
-ER can’t be isolated as they turn into microsomes when they’re disrupted

Question 2

Transcription Systems

Answer 2

-Exploits

Question 3

Translation Systems

Answer 3

Rabbit reticulocyte has high concentration machineriy

Question 4

Uses for Transcription/Translation systems

Answer 4

-be used to confirm mobility of protein
-bind particular antibody
-study co-translation translocation to ER

Question 5

ER Signal Sequences

Answer 5

-Hydrophobic Stretch with 1 or so basic residue (Arg or Lys)
-Ala-X-Ala|Y cleavage site of small uncharged residue

Question 6

Function of ER Signal Sequence

Answer 6

-Drives co-translation translocation of protein into ER lumen
-SRP helps stop translation and target to ER
-recognize by Sec61 which is part of the translocon

Question 7

Signal Recognition Particle (SRP)

Answer 7

-recognizes ER signal sequence
-Is recognized by SRP Receptor on surface of ER
-stops translation
-requires Ras-like GTPase to recognize SRP and SR

Question 8

BiP (Binding Protein)

Answer 8

-drives POST-translational translocation into ER
-normally in ATP form but becomes hydrolyzed to ADP as peptide becomes incorporated ADP
-pulls peptide out of translocon ratchet motion
-ADP to ATP releases the peptide

Question 9

Transmembrane ER proteins

Answer 9

-hydrophobic anchor that acts as stop-transfer sequence
-uncleaved signal sequence would lead to continuous growth and just end up out to the cytosol

Question 10

Signal anchor sequence

Answer 10

acts as both as signal and anchor sequence

Question 11

Translocon (Sec channel)

Answer 11

has a plug and lateral gate which allows transmembrane proteins to fold laterally into the membrane