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Biochemistry Molecular Genetics b73c8653

Proteins destined for secretion from eukaryotic cells have which of the following in common?

A
An N-Terminal Methionine in the Mature Protein Is - Very likely; A Signal Peptide Located at - Carboxy terminus; Synthesized on Which Type of Ribosome? - Rough; Embedded Within the ER Membrane? - Yes
B
An N-Terminal Methionine in the Mature Protein Is - Very likely; A Signal Peptide Located at - Amino terminus; Synthesized on Which Type of Ribosome? - Cytoplasmic; Embedded Within the ER Membrane? - No
C
An N-Terminal Methionine in the Mature Protein Is - Very likely; A Signal Peptide Located at - Carboxy terminus; Synthesized on Which Type of Ribosome? - Rough; Embedded Within the ER Membrane? - Yes
D
An N-Terminal Methionine in the Mature Protein Is - Unlikely; A Signal Peptide Located at - Amino terminus; Synthesized on Which Type of Ribosome? - Rough; Embedded Within the ER Membrane? - No
High-Yield Explanation
Proteins destined for secretion contain a signal sequence at the N-terminal end that causes the ribosomes on which they are being synthesized to bind to the SRP, which transfers the mRNA-ribosome complex to the RER. As they are being produced, they enter the cisternae of the RER, where the signal sequence, including the initial methionine, is removed. It is thus unlikely that the mature protein will contain an N-terminal methionine. Carbohydrate groups can be attached in the RER or the Golgi. Secretory vesicles bud from the Golgi, and the proteins are secreted from the cell by the process of exocytosis. If the proteins have a hydrophobic sequence that embeds in the membrane, they remain attached to the membrane and are not secreted and become membrane-bound proteins.

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