Which organelle is responsible for the synthesis of proteins?

Question

BlackTom AI · Accepted Answer

Ribosomes are the cellular machines that translate messenger RNA (mRNA) sequences into polypeptide chains, so the correct choice is c. Ribosomes.

1) Relevant knowledge points and concepts
- Gene expression has two main stages: transcription (DNA → mRNA) and translation (mRNA → protein).
- Translation is carried out by ribosomes, complexes of ribosomal RNA (rRNA) and proteins.
- Ribosomes occur free in the cytosol (making cytosolic proteins) and bound to the rough endoplasmic reticulum (ER) (making secreted or membrane proteins).

2) Step-by-step reasoning
- DNA in the nucleus is transcribed to mRNA.
- The mRNA exits the nucleus to the cytoplasm.
- Ribosomes bind to the mRNA, read codons (triplets of nucleotides), and recruit transfer RNAs (tRNAs) that bring specific amino acids.
- Peptide bonds form between successive amino acids, elongating the polypeptide until a stop codon ends translation.
- The result is a newly synthesized protein that may fold or be modified further.

3) Calculations
- No numerical calculations are required for this conceptual question.

4) Why the correct answer is correct
- Ribosomes directly perform translation, the chemical assembly of amino acids into proteins, making them the organelle (or complex) responsible for protein synthesis.

5) Why the other options are incorrect
- a. Lysosome: involved in intracellular digestion and breakdown of macromolecules, not synthesis.
- b. Smooth ER: synthesizes lipids and detoxifies; lacks ribosomes and is not the primary site of protein synthesis (rough ER with bound ribosomes handles many proteins).
- d. Mitochondria: produce ATP through cellular respiration; they have their own ribosomes for a few mitochondrial proteins but are not the cell’s primary protein-synthesis organelle.

Conclusion: The correct answer is c. Ribosomes, which matches the provided answer.

Which organelle is responsible for the synthesis of proteins?单项选择题

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