ER, Vesicular Transport, Cotranslational Import

Question 1

what is the function of the rough er

Answer 1

protein synthesis, modification, and transport
synthesis of membrane phospholipids
glycosylation of proteins
addiction of carbohydrate chains

Question 2

where does protein translation begin

Answer 2

on free ribosomes

Question 3

what are the two ways protein translation happens

Answer 3

1) completed on free ribosomes

2) completed by ribosomes associated with rough er

Question 4

describe protein translation that’s completed on free ribosomes

Answer 4

• cytosolic proteins
• peripheral membrane proteins
• proteins are targeted to the nucleus, mitochondria, peroxisomes, and chloroplasts

Question 5

where are cytosolic proteins translated

Answer 5

free ribosomes

Question 6

where are peripheral membrane proteins translated

Answer 6

free ribosomes

Question 7

where are the proteins translated at free ribosomes targeted to

Answer 7

nucleus, mitochondria, peroxisomes, chloroplasts

Question 8

describe protein translation that occurs on ribosomes associated with the rough er

Answer 8

• secretory proteins
• integral membrane proteins
• soluble proteins associated with inside (lumen) of the endomembrane system (ie proteins that fuction within the er, Golgi, and lysosomes)

Question 9

where are secretory proteins translated

Answer 9

ribosomes on rough er

Question 10

where are integral membrane proteins translated

Answer 10

ribosomes on rough er

Question 11

where are pertains that function in the endomembrane system (the er, golgi, lysosomes) translated

Answer 11

ribosomes on rough er

Question 12

how is the site of translation determined

Answer 12

they are targeted by a signal sequence

Question 13

where is the signal sequence located

Answer 13

proteins contain the signal sequence which determines where they are translated

Question 14

where on proteins is the signal sequence located

Answer 14

located on its amino-terminus

Question 15

what does the signal sequence contain

Answer 15

the signal sequence contains several consecutive hydrophobic amino acids

Question 16

what does the signal sequence do

Answer 16

the signal sequence directs synthesis to ER

Question 17

how does the signal sequence work

Answer 17

proteins move through a channel into ER

Question 18

what is another term for the process that comes after the signal sequence

Answer 18

cotranslational import

Question 19

what terminus comes out of the ribosome first

Answer 19

the N-terminus comes out first (because it goes in first)

Question 20

what terminus goes in ribosome first

Answer 20

the N-terminus

Question 21

describe the four steps of cotranslational protein import

Answer 21

1) signal recognition particle
2) targeting of translation complex to er
3) SRP is released and ribosome binds to the translocon
4) polypeptide enters the ER and is translated

Question 22

describe the first step of cotranslational protein import

Answer 22

1) signal recognition particle

the signal recognition particle (SRP) binds to the signal sequence, and translation STOPS

Question 23

describe the second step of cotranslational protein import

Answer 23

2) targeting of translation complex to ER

SRP/RIBOSOME +MRNA/NEW POLYPEPTIDE

Question 24

describe the third step if cotranslational import

Answer 24

3) SRP is released and ribosome binds to the translocon

- protein synthesis resumes

Question 25

describe the fourth step of cotranslational import

Answer 25

4) polypeptide enters the ER (through traslocon) and is translated
- signal sequence is cleaved off
- chaperone folds protein

Question 26

what are the two options a protein targeted to the ER lumen (after it is finally synthesized and folded) has?

Answer 26

1) is retained in the ER lumen (if that’s where it functions)
2) is transported from the ER to the Golgi complex for further modification and is delivered to distal parts of the biosynthetic/secretory pathway. (final destination could be outside of the cell)

Question 27

once in the ER, a protein is now part of the ________, and may ultimately become a part of a compartment, or be secreted

Answer 27

once in th ER, a protein is now part of the biosynthetic/secretory endomembrane system and may ultimately become a part of a compartment, or be secreted

Question 28

example fo a 12 pass protein

Answer 28

CFTR

Question 29

odd number pass protein will end up:

Answer 29

on the oposite side of the membrane as it started

Question 30

even number pass protein will end up:

Answer 30

on the same side of the membrane as it started