·信号肽的准确定义？？？？急急急

刚背过 是北大版生物化学上的
信号肽-指在新合成的多肽链中用于指导蛋白质跨膜运输的氨基酸残基序列

信号肽，即Signal Peptide，它是一段由3-60个氨基酸组成的短肽序列，它是引导新合成蛋白质被输送至目的地点的识别信号。它也被称为靶标信号。
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选译自WIKIPEDIA，这里是原文：

A signal peptide is a short (3-60 amino acids long) peptide chain that directs the post-translational transport of a protein. Signal peptides may also be called targeting signals, signal sequences, transit peptides, or localization signals.

The amino acid sequences of signal peptides direct proteins (which are synthesized in the cytosol) to certain organelles such as the nucleus, mitochondrial matrix, endoplasmic reticulum, chloroplast, apoplast and peroxisome. Some signal peptides are cleaved from the protein by signal peptidase after the proteins are transported.
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signal sequence is the sequence of amino acide ,usually N-terminal , responsible for the co-t