Explain the “life” of a secreted protein molecule - trace the pathway in a cell by which a secreted protein, such as an antibody, would be produced in an animal cell, starting in the nucleus. Solution Cells secrete proteins for their own cytosol or for release into surrounding extracellular fluid. These secretions may include various hormones, digestive enzymes, antibodies, mucus etc. The transcription process (conversion of DNA to mRNA) occurs inside the nucleus. This newly formed mRNA is translated into proteins in the cytosol at cellular structures called ribosomes.the ribosome remains in the cytosol if the protein has to be used within the cell, whereas if it is destined for secretion outside the cell, the signal sequence (first few amino acids) is synthesized on the ribosome and then the ribosome docks at the rough endoplasmic reticulum (RER) for completion of protein synthesis. Proteins enter and cross endoplasmic recticulum (ER) membrane co-translationally (i.e., they cross ER during synthesis of polypeptide). In the lumen of ER, proteins undergo glycosylation and molecular chaperones aid in the process of protein folding. Misfolded proteins are retrotranslocated to the cytosol, where they are degraded by a proteasome action. The vesicles with correctly folded proteins then enter the golgi appratus where further posttranslational modifications occur including cleavage and functionalization. When the protein moves through the entire Golgi apparatus, it buds off as secretion vesicles. Now, with the help of cell\'s cytoskeleton, it moves towards the edge of the cell and attaches itself to the membrane. Eventually, vesicle fuses with the cell membrane releasing its contents out of the cell through the process of exocytosis. This secretion pathway is followed for all protein molecules including antibodies..

1. Explain the “life” of a secreted protein molecule - trace the pathway in a cell by which a secreted
protein, such as an antibody, would be produced in an animal cell, starting in the nucleus.
Solution
Cells secrete proteins for their own cytosol or for release into surrounding extracellular fluid.
These secretions may include various hormones, digestive enzymes, antibodies, mucus etc.
The transcription process (conversion of DNA to mRNA) occurs inside the nucleus. This newly
formed mRNA is translated into proteins in the cytosol at cellular structures called ribosomes.the
ribosome remains in the cytosol if the protein has to be used within the cell, whereas if it is
destined for secretion outside the cell, the signal sequence (first few amino acids) is synthesized
on the ribosome and then the ribosome docks at the rough endoplasmic reticulum (RER) for
completion of protein synthesis. Proteins enter and cross endoplasmic recticulum (ER)
membrane co-translationally (i.e., they cross ER during synthesis of polypeptide). In the lumen
of ER, proteins undergo glycosylation and molecular chaperones aid in the process of protein
folding. Misfolded proteins are retrotranslocated to the cytosol, where they are degraded by a
proteasome action.
The vesicles with correctly folded proteins then enter the golgi appratus where further
posttranslational modifications occur including cleavage and functionalization. When the protein
moves through the entire Golgi apparatus, it buds off as secretion vesicles. Now, with the help of
cell's cytoskeleton, it moves towards the edge of the cell and attaches itself to the membrane.
Eventually, vesicle fuses with the cell membrane releasing its contents out of the cell through
the process of exocytosis.
This secretion pathway is followed for all protein molecules including antibodies.