Exam 3: Transolcation

Question 1

Where does transport in or through the endomembrane system start?

Answer 1

in the ER

Question 2

What do ALL proteins that start in the ER contain?

Answer 2

ER Signal Sequence, consisting of at least 8 hydrophobic amino acids

Question 3

What are 3 steps to ER translocation of water soluble, non transmembrane proteins?

Answer 3

1. the SRP receptor associates with a protein translocator
2. the amino acid chain will be directly translocated into the ER lumen as translation is occuring
3. the signal sequence is cleaved, and the protein is released

Question 4

What occurs with stop/start sequences in water soluble, non transmembrane proteins?

Answer 4

ER signal sequence is taken to ER translocator protein, and the START end stays in place in the translocator as the rest get pushed through with the C-terminal the last thing to grow through the ER Translocator protein

Question 5

do the start/stop-transfer regions stay in the membrane as translation occurs or outside?

Answer 5

they stay in the membrane and form an alpha helix

Question 6

What happens in translocation with a single-pass transmembrane protein?

Answer 6

the protein will release the N-Terminal side into the ER lumen and cleave the ER signal sequence (cleaves the start-transfer sequence)

Question 7

What happens wihen the translocator protein encounters a stop transfer sequence?

Answer 7

1. release initial ER signal sequence into the MEMBRANE (B/C ER signal sequences are HYDROPHOBIC*)
2. holds on to the STOP transfer sequence
3. stops moving the protein through the pore and any AA going from the stop transfer to the end will remain outside the ER (in the cytosol)
4. wehn protein is fully translated, the STOP transfer region will also be released into the ER membrane

Question 8

Where does the endomembrane pathway start ?

Answer 8

at the ER

Question 9

What occurs in the ER?

Answer 9

1. proteins are synthesized AT the ER membrane
2. some initial modifications on proteins occur in the ER
   *any COVALENT modification to a protein occurs in the ER, and enzymes for these modifications are ONLY found in the ER

Question 10

What happens if a chaperone protein CANT fix a protein?

Answer 10

the protein is exported and degraded

Question 11

Where do receptors recognize the ER retention signal/KDEL AA sequence?

Answer 11

the ER and Golgi

Question 12

Which side of the golgi is the CIS side and which is the TRANS?

Answer 12

the side FACING the ER in the cis side/entry side, and the side FACING the plasma membrane is the trans side/exit side

Question 13

What do lysosomes help with?

Answer 13

1. digesting many of the molecules ingested by cells
2. maintains a low pH because many of the hydrolyzing enzymes are only functional at low pH
3. contain transporters in their membrane that allow for expoet of useful metabolites such as AAs, sugars and nucleotides into the cytosol

Question 14

What process is started by vesicle budding?

Answer 14

assembly of a coat protein

Question 15

What are 2 functions of the coat protein?

Answer 15

1. shape the membrane into a bud
2. capture molecules for further movement

Question 16

Constituted vs Regulated Secretion

Answer 16

-constitutive transport vesicles release their contents automatically, while regulated secretory vesicles only release content upon perceiving a signal
-constitutive transport tends to contain low concentrations of proteins while secretory vesicles contents tend to aggregate–combine–resulting in very high concentrations in each vesicle

Question 17

How do you know if a START transfer sequence is cleaved?

Answer 17

if you have an INTERNAL start transfer (ER SS), nothing is cleaved