3: Chapter 11 (part 1) - Protein Sorting and Transport

1) endoplasmic reticulum

2) Golgi apparatus

3) endosomes

4) lysosomes

what are the 4 components involved in protein processing and are conneted via vesicular transport

endoplasmic reticulum (ER)

The _____________________ is a network of membrane-encolsed tubules and sacs

cisternae

______________ are sacs in the ER that extend from nuclear membranes throughout the cytoplasm

rough ER

ribosomes on the outer surface of the ER make up the _______________________

smooth ER

the ____________________ is where lipid metabolism takes place

chase

a ___________________ occurs when samples of amino acids are incubated for different lengths of time

1) ER

2) Golgi apparatus

3) secretory vesicles

4) outside the cell (cell exterior)

the 4-step pathway, known as the secretory pathway, occurs as follows:

translation

in eukaryotic cells, initial protein sorting takes place while ________________ is in progress

free ribosomes

proteins synthesized on ________________ stay in the cytosol or are transported to the nucleus and other organelles

membrane-bound ribosomes

proteins synthesized on ________________ are translocated directly into the ER through a translocon

cotranslational translocation

during ____________________, proteins move into the ER during their synthesis on membrane-bound ribosomes

membrane-bound ribosomes

during cotranslational translocation, proteins move into the ER during their synthesis on _____________________________

posttranslational translocation

during _____________________________, proteins move into the ER after translation has been completed on free ribosomes

free ribosomes

during posttranslational translocatioin, proteins move into the ER after translation has been completed on ____________________

cotranslational

on the __________________ pathway, ribosomes are targeted to the ER by a signal sequence at the amino terminus which is removed when the growing polypeptide chain enters the ER

signal sequence

during the cotranslational pathway, ribosomes are targeted to the ER by a _________________ at the amino terminus which is removed when the growing polypeptide chain enters the ER

in vitro

the role of signal sequences in targeting proteins to correct locations was determined by _____________________ preparations of rough ER

larger

Blobel and Sabatini found that translation of secretory proteins on free ribosoes retained the signal sequences and were slightly ________________________

proteolytic cleavage

when vesicles derived from ER were added, the signal sequences were removed by ____________________________

20

signal sequences are about ___________ amino acids long

hydrophobic residues; amino

signal sequences include a stretch of ______________ residues, and are usually located at the _________________ terminus of the polypeptide chain

signal recognition particle (SRP)

Step 1 of contranslational pathway: as the signal sequence emerges from the ribosome, it is recognized and bound by the ___________________________________

membrane

Step 2 of cotranslational pathway: the SRP escorts the complex to the ER _______________ where it binds to the SRP receptor

translocon

Step 3 of cotranslational pathway: the SRP is released, the ribosome binds to the _________________, and insertion of the signal sequence opens the translocon

peptidase

step 4 of cotranslational pathway: translation resumes and the signal sequence is cleaved by signal _______________

translocation

step 5 of cotranslational pathway: continued translation drives _________________ of the growing polypeptide chain across the membrane

lumen

step 6 of cotranslational pathway: the completed polypeptide chain is released within the ER ____________________________

alpha-helical; hydrophobic

membrane-spanning regions are usually composed of ______________ regions with _______________ amino acids

exterior

the lumen of the ER is topologically equivalent to the ___________ of the cell

cell surface

domains of membrane proteins that are exposed on the ______________________ correspond to regions of polypeptide chains that are translocated into the ER lumen

amino terminal signal sequence

some proteins have a ________________ sequence, which occurs during cleavage by a signal peptidase during translocation through the translocon

transmembrane alpha helix

the ______________ is in the middle of protein and halts translocation and anchors the polypeptide in the membrane

internal transmembrane sequences

many proteins are inserted directly into the ER membrane by ___________________ sequences

SRP

internal transmembrane sequences are recognized by _____________, but not cleaved by signal peptidase

laterally

the transmembrane alpha helices exit the translocon ________________ laterally and anchor proteins in the ER membrane

multiple times

proteins that span the membrane ________________ are inserted as a result of a series of transmembrane sequences with alternating orientations