What is protein targetting? Illustrate the same with reference to transport of proteins to plasma membrane. (UPSC 2017, 20 Marks, )

प्रोटीन लक्ष्यीकरण क्या है? प्रोटीन के प्लाज्मा झिल्ली तक परिवहन के संदर्भ में इसे स्पष्ट करें। (What is protein targeting? Illustrate the same with reference to transport of proteins to plasma membrane.)