BIO 320 Lecture Notes - Lecture 6: Nuclear Membrane, Oligosaccharide, Transferase

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10 Jan 2017

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Ribosomes are in the cytosol, proteins are synthesized in the cytosol. Some proteins will remain in the cytosol, some proteins will be secreted and need to follow the secretory pathway through organelles to reach the extracellular space. Signal sequences are found within the protein"s sequence and direct the protein to its final destination. Endoplasmic reticulum (er): first stage of the secretory pathway. It extends from the outer nuclear membrane throughout the cell: rough endoplasmic reticulum: ribosomes associated with the outer surface of the er. *being associated with the er has important role for protein synthesis previously we have mentioned that nascent polypeptide chains (proteins being synthesized) will start forming secondary structures as they leave the ribosome. However, if the ribosome is perfectly placed right next to a channel in the er membrane, it can immediately start pushing the nascent polypeptide chain through the channel: co-translational translocation. Er signal sequence: n-terminus hydrophobic residues, 8+ always!

Related Questions

3. For each alternative ending to the following sentence, indicate why the ending is false: 4 pts

âProteins destined to enter the rough endoplasmic reticulum _______â

a. are transported into the ER after their synthesis is complete.

b. are synthesized on free ribosomes in the cytosol.

c. cross the membrane in a folded state.

d. must be proteins that will be secreted from the cell.

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

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29 Most proteins destined to enter the endoplasmic reticulum _________.

(a) are transported across the membrane after their synthesis is complete.

(b) are synthesized on free ribosomes in the cytosol.

(d) are keep binding to Signal recognition particle (SRP) while they are translated.

30 Which of the following choices reflects the appropriate order of locations through which a protein destined for the plasma membrane travels?

(a) lysosome â endosome â plasma membrane

(b) ER â lysosome â plasma membrane

(d) ER â Golgi â plasma membrane

31 Which of the following statements about vesicle budding from the Golgi is false?

(a) COPII can initiate vesicle budding on Golgi membrane.

(b) Some vesicles budded from Golgi membranes move towards ER.

(d) Clathrin molecules act at the cytosolic surface of the Golgi membrane.

32 Which of the following statements is false?

(a) The signal sequences on mitochondrial proteins are first bound to translocator on outer membrane after translation.

(b) Most mitochondrial proteins are not imported from the cytosol but are synthesized inside the mitochondria.

(c) Chaperone proteins in the mitochondria facilitate the movement of proteins across the outer and inner mitochondrial membranes.

(d) Mitochondrial proteins cross the membrane in their unfolded state.

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BIO 320 Lecture Notes - Lecture 6: Nuclear Membrane, Oligosaccharide, Transferase

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