2017/162 101 MANIALE Internal Letue QUESTION 3 diagram below shows components of

Question

2017/162 101 MANIALE Internal Letue QUESTION 3 diagram below shows components of the endomembrane system in a cell and the pathway taken by a protein that is secreted from a eukaryotic cell. nucleus 6 eticnlum Label the diagram on the six indicated arrows to show the components of the (3 marks) Explain how a protein destined for secretion is recognised and inserted into the 4 marks) b) lumen of the endoplasmic reticulum. How do the components labelled by arrow 4 in the diagram above move to the part labelled by arrow 5? (1 mark) How are proteins modified in the secretory pathway shown above and where do these reactions occur? d) (2 marks) Page 4 of 8

Explanation / Answer

a) 1) nuclear membrane

2) rough endoplasmic reticulum.

3) golgi body

4) secretory vesicles

5) plasma membrane.

6) ribosome.

b) protein that are secretory or reside in the endoplasmic reticulum use the co-translational translocation pathway. the N-terminal signal peptide of the protein being recognized by a signal recognition particle (SRP) and synthesis pauses and the ribosome-protein complex is transferred to an SRP receptor on the ER. the signal sequence is then cleaved from the nascent polypeptide when translocated into the membrane of the ER.

c) via constitutive secretory pathway.

d) In golgi complex protein are modified and sent for the different location.

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