UBC BIOL 200 CH 5 EXAM QUESTIONS
AND ANSWERS GRADED A+ 2026
What does the Endomembrane System (EMS) consist of? - ANS ER, Golgi apparatus,
Lysosomes, Endosomes, and Secretory Vesicles.
Once proteins enter the EM system, they can return to the cytosolic compartment. -
ANS False.
What are the three major subdivisions of the EMS? - ANS 1) secretory pathway
2) lysosomal pathway
3) endocytic pathway
Proteins entering the EMS can only enter through the start of each pathway and can only leave
once they reach the final destination for that pathway. - ANS True
All proteins targeted to the same destination carry the same signal encoded in their protein
sequence. - ANS True
How does a protein "find" its receptor? - ANS There is a specific protein receptor that
corresponds to each type of targeting signal. The protein has a sequence encoded in its amino
acid backbone.
@COPYRIGHT 2026/2027 ALL RIGHTS RESERVED
1
, Where is synthesis of proteins that later enter the ER initiated? - ANS On free ribosomes in
the cytosol.
What part of the protein allows it to be targeted to the ER? - ANS A sequence of hydrophobic
amino acids near the amino terminal end of the growing polypeptide.
What happens to proteins that are inserted completely into the ER? - ANS They are not
soluble (not membrane) proteins and are destined for secretion or transfer to lysosomes.
What happens to proteins that are inserted partially into the ER? - ANS May be destined for
the ER, membranes of another organelle (Golgi, lysosomes, or endosomes), or the plasma
membrane (PM). Always stay within the membrane once inserted into the ER membrane.
When does ER targeting occur? - ANS Once the ER signal sequence is recognized by the signal
recognition particle (SRP).
What happens when the SRP binds the ER signal sequence on the protein? - ANS The SRP
binds to an SRP receptor in the ER membrane.
Once the SRP binds the SRP receptor, what happens? - ANS The ribosome attaches to the
ribosome receptor, which also functions as the translocation channel.
Once the ribosomes binds to its ER receptor (the translocation channel) what happens? -
ANS The SRP is displaced and recycled.
How many transfer sequences do soluble proteins need? Where is it found? - ANS Only one;
Always on the N-terminus.
What removes the signal sequence of a soluble protein? Where does that signal seem to stay? -
ANS signal peptidase; embedded within the ER membrane.
@COPYRIGHT 2026/2027 ALL RIGHTS RESERVED
2
AND ANSWERS GRADED A+ 2026
What does the Endomembrane System (EMS) consist of? - ANS ER, Golgi apparatus,
Lysosomes, Endosomes, and Secretory Vesicles.
Once proteins enter the EM system, they can return to the cytosolic compartment. -
ANS False.
What are the three major subdivisions of the EMS? - ANS 1) secretory pathway
2) lysosomal pathway
3) endocytic pathway
Proteins entering the EMS can only enter through the start of each pathway and can only leave
once they reach the final destination for that pathway. - ANS True
All proteins targeted to the same destination carry the same signal encoded in their protein
sequence. - ANS True
How does a protein "find" its receptor? - ANS There is a specific protein receptor that
corresponds to each type of targeting signal. The protein has a sequence encoded in its amino
acid backbone.
@COPYRIGHT 2026/2027 ALL RIGHTS RESERVED
1
, Where is synthesis of proteins that later enter the ER initiated? - ANS On free ribosomes in
the cytosol.
What part of the protein allows it to be targeted to the ER? - ANS A sequence of hydrophobic
amino acids near the amino terminal end of the growing polypeptide.
What happens to proteins that are inserted completely into the ER? - ANS They are not
soluble (not membrane) proteins and are destined for secretion or transfer to lysosomes.
What happens to proteins that are inserted partially into the ER? - ANS May be destined for
the ER, membranes of another organelle (Golgi, lysosomes, or endosomes), or the plasma
membrane (PM). Always stay within the membrane once inserted into the ER membrane.
When does ER targeting occur? - ANS Once the ER signal sequence is recognized by the signal
recognition particle (SRP).
What happens when the SRP binds the ER signal sequence on the protein? - ANS The SRP
binds to an SRP receptor in the ER membrane.
Once the SRP binds the SRP receptor, what happens? - ANS The ribosome attaches to the
ribosome receptor, which also functions as the translocation channel.
Once the ribosomes binds to its ER receptor (the translocation channel) what happens? -
ANS The SRP is displaced and recycled.
How many transfer sequences do soluble proteins need? Where is it found? - ANS Only one;
Always on the N-terminus.
What removes the signal sequence of a soluble protein? Where does that signal seem to stay? -
ANS signal peptidase; embedded within the ER membrane.
@COPYRIGHT 2026/2027 ALL RIGHTS RESERVED
2
