endoplasmic reticulum

Question 1

4 points about what the endoplasmic reticulum is

Answer 1

network of enclosed tubules
continuous with nuclear membrane
accounts of approximately 50% of cell membranes
involved in protein processing and sorting

Question 2

what is the role of rough ER

Answer 2

synthesis and folding of new proteins

Question 3

what is the role of smooth ER

Answer 3

synthesis of new lipids

Question 4

what does the ER acts as

Answer 4

a major calcium store- which is released upon certain cellular events- e.g. muscle contraction

Question 5

what is the SRP

Answer 5

ER signal recognition particle and is a series of 20 amino acids on the end of a synthesised protein - as its being translated by ribosome

Question 6

what is the defining fetaure of SPR

Answer 6

hydrophobic region

Question 7

what are the 4 stages of co-translational translocation

Answer 7

binding of SRP to signal peptide causing a pause in translation
SRP-bound ribosome attaches to SRP receptor in ER membrane
translation continues and translocation begins
SRP and SRP receptor displaced and recylced

Question 8

what is a translocon

Answer 8

channel to insert polypeptide into ER lumen

Question 9

what is post-translational translocaiton

Answer 9

more common in yeast cells

proteins determined for mitochondria, chloroplasts etc

Question 10

what is co-translational translocation

Answer 10

root by which vast majority of proteins are synthesised in mammalian cells

Question 11

what are 4 stages of post-translational translocation

Answer 11

signal sequence present on polypeptide chain, but not one that binds signal sequence
doesnt bind to ER, as polypeptide chain is translated
chaperone bind to polypeptide
chaperones are family of HSC70

Question 12

what are chaperones(3)

Answer 12

maintain linear polypeptide chain- prevent curling and folding
binds to set 62/63 complex on ER which is closely associated with translocon
acts as a ratchet to pull polypeptide throught he translocon into ER lumen

Question 13

how are soluble proteins produced

Answer 13

single sequence is cleaved off and protein is released into ER

Question 14

how are transmembrane proteins produced(3)

Answer 14

must modify protein
when transmembrane sequence reaches translocon - stops further enrty into lumen and stops transfer sequence
changes confirmation anf pushes polypeptide into cell membrane

Question 15

describe insertion of multi-pass transmembrane proteins

Answer 15

series of start and stop sequences

pushes loop into ER lumen until we reach stop and the translocon changes confirmation and pushes it into cell membrane

Question 16

what is n-linked glycosylation 3

Answer 16

proteins are folded almost immediate as they enter ER lumen - in conjunction with chaperone proteins - formation of di-sulphide bonds

Question 17

what is another modification in ER

Answer 17

apply GPI anchors via a lipid carrier

Question 18

describe the addition of GPI anchors 3

Answer 18

aldysaccharide and ethanol amino head group
precursor molecule in membrane
once protein folded, cleavage and then transfer of GPI anchor via ethanol amine group

Question 19

describe phospholipid synthesis

Answer 19

generated and added to cytosolic side of smooth er

Question 20

what does phospholipid synthesis require 3

Answer 20

cytosolic precursors
glycerol 3 phosphate
fatty acyl coa

Question 21

describe phospholipid ordering in membrane (4)

Answer 21

lipid bilayer of er
phospholipid synthesis adss to cytosolic half of bilayer
scramblase catalyses flipping of phospholipid molecules
symmetric growth of both halves of bilayer

Question 22

describe phopholipid ordering in the plasma membrane (3)

Answer 22

asymettric lipid bilayerof plasma membrane
delivery of new membrane by exocytosis
flippase catalyses flipping of specific phospholipids to cytoplasmic monolayer