Question

What are the sites for protein synthesis inside the cell?

Answer 1

Hint: Protein synthesis takes place when translation of m-RNA takes place. After transcription, m-RNA moves out of the nucleus.

Complete answer: Protein synthesis is a very important step of “Central dogma of life”.
Do you know about “Central dogma of life”?
Let me explain, “Central dogma of life” includes two processes : transcription and translation. All life forms exist due to these two processes. Transcription is the process in which DNA converts into m-RNA and in translation m-RNA converted into protein.

Coming back to the question, Proteins are synthesised in ribosomes. Ribosomes are the organelle present in both eukaryotic and prokaryotic cells. But they are a little bit different from each other. Prokaryotic cells have 70S ribosomes and eukaryotic cells have 80S ribosomes.
Ribosomes have two subunits, one large sub-unit (50S for prokaryotic and 60S for eukaryotic cell) and a smaller subunit (30S for prokaryotic and 40S for eukaryotic cell). Each subunit of ribosomes consist of ribosomal RNA (rRNA) and many ribosomal proteins. Ribosomes are also called protein factories or translational apparatus.
 So, translation takes place in-between these two sub-units, t-RNA reads the m-RNA and adds amino acids accordingly.
Now, these ribosomes are present in bounded states as well as in free states. In bounded state they are present on the surface of rough endoplasmic reticulum and in free state they are present in cytoplasm.
So, we can conclude that protein synthesis or translation of m-RNA to protein takes place in ribosomes and these ribosomes are present on rough endoplasmic reticulum and cytoplasm.

Additional Information: Endoplasmic reticulum are the organelles present in prokaryotic and eukaryotic cells these are of two types, Smooth Endoplasmic reticulum (SER) and Rough Endoplasmic reticulum (RER). RER are responsible for mainly protein production and SER are responsible for fat production.

Note: Remember central dogma of life, that is, transcription is conversion of DNA to m-RNA and translation is conversion of m-RNA to proteins.