BIO206H5 Lecture Notes - Lecture 22: Signal Recognition Particle, Stem-Loop, Signal Peptidase

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1 Oct 2016

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The endoplasmic reticulum: most extensive membrane system in eukaryotic cell, continuous with outer membrane of nucleus, smooth and rough er (+/- ribosomes) Luminal space: a space that is distinct from the cytoplasm. Transport of proteins into the er: er is site of protein entry for er + other destinations. Secretion: mrna in cytosol, ribosomes bound to rer synthesize proteins for the endomembrane system and plasma membrane. Nature of the signal that is carried by the protein determines where it goes in the cytoplasm. Normal elongation happens until a certain sequence is found at the n-terminus which is recognized as a signal recognition particle signal sequence. Soluble protein translocation: signal sequence bound to channel, protein threaded through as loop, gtp required, signal sequence cleaved, translocation channel opens sideways, peptide is released into er e. g. preprolactin (pituitary hormone)proteins that. Signal peptidase hydrolyzes peptide bonds and it recognizes a particular amino acid sequence and cuts the protein at a particular aa residue.

Related Questions

1. The histones that form the core of the nucleosome get into the nucleus by which of the following?

a) Passive diffusion through nuclear pores

b) Selective and facilitated active transport through nuclear pores

c) Ribosomes located in the nucleus synthetize histones in the nucleus

d) Histones are made at the ER membrane and then diffuse to the nucleus

2. Membrane proteins that belong to the golgi, lysosome, or plasma membrane first pass through which organelle before reaching their final subcellular destination?

a) The golgi apparatus

b) The smooth ER

c) The nucleus

d) The ER membrane

e) The ER lumen

3. Where in the cell would a ribosomal protein be located if it has had its nuclear export signal inactivated (non-functional or non-existent).

a) The protein would be found in the ER lumen

b) The protein would remain in the nucleus

c) The protein would be secreted

d) The protein would remain in the cytoplasm

e) The protein would be in the ER membrane

4. Where would be the final destination of a protein if it contained a NLS anywhere in the protein sequence (and which is exposed to the cytoplasm after protein folding) but also contained an ER signal sequence at the carboxy terminus?

a) The ER lumen

b) The nucleus

c) The cytoplasm

d) The inner nuclear membrane

e) The ER membrane

5. The sequence K-D-E-L serves as a retention/retrieval signal for ER proteins.

a) True

b) False

6. The following are true for both cell membrane proteins and secretory proteins EXCEPT?

a) Precursors of the mature proteins contain signal sequence.

b) Both types of proteins contain stop-transfer sequences

c) Both types of proteins enter the ER while being synthetized

d) Both types of proteins pas through the golgi apparatus

e) Both are carried by clatherin-coated vesicles

7. If you isolate a regulated secreted protein from a secretory/storage vesicle and inject it into the cytosol, is will?

a) Be secreted through channels in the plasma membrane

b) Be taken up into secretory vesicle and secreted

c) Remain in the cytosol until it is degraded

d) Be taken up into the rough ER and follow the secretory pathway

goldmanatee250

Imagine that you have engineered a set of genes , each encoding a protein with a pair of conflicting signal sequences that specificy different compartments. If the genes were expressed in a cell, what signal would win and why?

1) A) Signals for import into ER would beat signals for import int the nucleus. What is the reasonable explanation?

1) The nuclear transport receptor is more efficient than the signal recognition particle (SRP)

2) The ER signal near the N-terminus will be exposed before the nuclear signal during protein synthesis and thus recognized by SRP before the nuclear signal is even available

3) the nuclear signal near the middle of the sequence will be exposed before the ER signal during protein synthesis and thus recognized by the nuclear transprot protein before the ER signal is active.

4) the SRP is more efficient than the nuclear transport receptor.

B) Signals for import into ER would beat signals for import into peroxisomes. What is the reasonable explanation?

1) The peroxisome transport proteins are more efficient than the signal recognition particle (SRP)

2) The ER signal near the N-terminus will be exposed before the peroxisome signal during protein synthesis and thus recognized by SRP before the peroxisome signal is even available

3) peroxisome proteins are transported by vesicles not by transport proteins.

4) the SRP is more efficient than the peroxisome transporter.

C) Signals into the mitochondria and retention into the ER? Which would win? Reasonable explanation as to why?

1)Mitochondria

2)ER

and

1) The mitochondrial transport protein is more efficient than the signal recognition particle (SRP)

2) The ER signal near the N-terminus will be exposed before the mitochondrial signal during protein synthesis and thus recognized by SRP before the mitochondrial signal is even available

3) the mitochondrial signal near the N-terminus of the sequence will be exposed before the ER retention during protein synthesis and thus recognized by the SRP before the ER signal is active

4) the signal for retention of a protein in the ER is at the C-terminus and not recognized until import into the ER begins

rosesnail820

please help me answer theses questions correctly

1/ Which of the following are required for one-pass transmembrane proteins?

I. N-terminal signal sequence

II. Binding of SRP to the SRP receptor

III. Presence of stop-transfer sequence

IV. Presence of start-transfer sequence

a) I and III

b) I, II, and III

c) II, III, and IV

d) I, II, III, and IV

___________________

2/ Which of the following statements about the signal-recognition particle (SRP) is FALSE?

a) The SRP binds to the ER signaling sequence after the entire protein has been translated by the ribosome.

b) The SRP cycles between the ER membrane and the cytosol.

c) The SRP is required for peptides destined for either the ER membrane or ER lumen.

d) The SRP recognizes the signal sequence at the N-terminus of the newly forming polypeptide.

______________________

3) t-SNARES are _____.

a) found on the cytosolic side of the vesicle membrane.

b) necessary for recognition and transport of proteins into the nucleus.

c) usually located on the target membrane.

d) necessary for vesicle formation.

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BIO206H5 Lecture Notes - Lecture 22: Signal Recognition Particle, Stem-Loop, Signal Peptidase

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