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KVPY Sample Paper KVPY Stream-SX Model Paper-16

  • question_answer
    In an experiment, the \[{{\operatorname{PO}}_{4}}\] groups of the phospholipids facing the lumen of the endoplasmic reticulum (ER) are labelled. If in the course of time, the ER buds off vesicles which fuse with the cell membrane, the label will be found:

    A) On the \[{{\operatorname{PO}}_{4}}\] groups of cell membrane facing extracellular fluid.

    B) On the \[{{\operatorname{PO}}_{4}}\] groups of cell membrane facing cytosol.

    C) Only on inner lumen of ER.

    D) On both inner and outer laminae of ER.

    Correct Answer: A

    Solution :

    The phospholipid molecule generally consists of two hydrophobic fatty acid "tails" and a hydrophilic "head" consisting of a phosphate group. In ER, the hydrophilic head is facing the lumen. When ER buds off vesicles, labelled \[P{{O}_{4}}\] group will be facing the lumen of the vesicle. When this vesicle fuses with plasma membrane, its surface facing lumen will face the extracellular fluid. So, phosphate group also face the extracellular fluid.


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