Question

Assertion: The initiation step of protein synthesis in prokaryotes and eukaryotes has several differences.
Reason: They both form mRNA-tRNA complexes with smaller subunits of ribosomes.
A. If both assertion and reason are true and the reason is the correct explanation of assertion.
B. If both assertion and reason are true and the reason is not the correct explanation of assertion.
C. If assertion is true but the reason is false
D. If both the assertion and reason are false
E. If the assertion is false but the reason is true.

Answer 1

Hint: Process by which proteins are derived from RNA is called translation. The sequence of amino acids in the protein is determined by the sequence of nitrogen bases in the amino acid. These amino acids are joined together by peptide bonds in a protein chain.

Complete answer: Process of translation is seen in both prokaryotes and eukaryotes. But they are different in some steps. As the nucleus is absent in prokaryotes, transcription and translation are coupled in them. But in eukaryotes, mRNA produced after transcription is taken out from the nucleus to the cytoplasm. Translation in eukaryotes takes place in the cytoplasm. The first step in the process of translation is initiation. For the initiation to take place, several initiation factors are needed for both prokaryotes and eukaryotes. Eukaryotes have more number of initiation factors than prokaryotes. Ribosomes are the cellular factories responsible for the translation. In prokaryotic translation, 70S ribosomes are involved. In eukaryotes, it is 80S ribosomes that perform translation. Prokaryotic mRNA has a special type of sequence called Shine Dalgarno sequence to which the ribosome binding takes place. It is absent in eukaryotes. In eukaryotes, this function is done by a sequence called the Kozak sequence. The initiation complex formed at the end of initiation is also different in prokaryotes and eukaryotes. The smaller subunit of ribosomes binds with the mRNA in both prokaryotes and eukaryotes. Larger subunits of ribosomes have two binding sites for tRNA. So during the mRNA-tRNA complex formation, both the subunits of ribosomes are involved. So the reason is incorrect and the assertion is correct.
Hence, the correct option is C.

Note: Genetic information for protein synthesis is coded in a DNA molecule. A single amino acid is determined by an order of three nitrogen bases. So, it is a three-letter code and the sequence of three bases determining a single amino acid is called codon. There are 64 codons for all naturally occurring amino acids.