Test: Translation (NCERT) - NEET MCQ

DNA Replication: DNA replication is the process by which a cell makes an identical copy of its DNA. It occurs during the cell cycle to ensure that each daughter cell receives a complete set of genetic instructions. DNA replication is a highly accurate process in which the DNA double helix is unwound, and each strand serves as a template for the synthesis of a complementary strand. 

Transcription: Transcription is the process by which a segment of DNA is used as a template to synthesize a complementary RNA molecule. It is the first step in the central dogma of molecular biology, which describes how genetic information is used to produce proteins. In transcription, an enzyme called RNA polymerase reads the DNA template and assembles a single-stranded RNA molecule, known as messenger RNA (mRNA), by matching RNA nucleotides to the DNA template. 

Translation: Translation is the process in which the information contained in an mRNA molecule is used to synthesize a protein. This process occurs at ribosomes, cellular structures that serve as the protein-manufacturing factories. During translation, the mRNA is read in sets of three nucleotides called codons. Each codon corresponds to a specific amino acid, the building blocks of proteins. 

UAA is a nonsense codon. It signals for polypeptide chain termination. Hence, only 24 amino acids chain will be formed.

During translation, a (RNA) is specifically linked to an amino acid, this process takes place under the direction of an enzyme, aminoacyl tRNA synthetase that is extremely specific, i.e., recognises only one amino acid. (RNA) complexed with amino acid is called as charged tRNA. The process is referred to a charging or aminoacylation of tRNA.

Translation is the process of polymerisation by which the triplet base sequence of a mRNA guides the linking of a specific sequence of amino acids to form a polypeptides (protein) on ribosomes. Each tRNA is specific to an amino acid, as tRNAs are added to the sequence, amino acids are linked together by peptide bonds, eventually forming a protein that is later released by the tRNA.

 codon is a sequence of three nucleotides on an mRNA strand that encodes a specific amino acid. 
Sixty-four different three nucleotide combinations (codons) can be made using the four nucleotides in mRNA (43 = 64 combinations).
Following are the codons that represent Valine and proline respectively.
Valine: GUA, GUC, GUG, GUU
proline:  CCT, CCC, CCA, CCG

• In order to form a peptide bond, a certain quantity of energy is required.
• The first phase in this process is known as charging of tRNA.
• It is also known as Aminoacylation of tRNA.
• In this process, the amino acids are activated in the presence of ATP and are linked to their cognate tRNA.

mRNA has some additional sequences that are not translated and are referred as untranslated regions, (UTRs). The UTRs are present at both 5 end (before start codon) and at 3-end (after stop codon). They are required for efficient translation process.

Aminoacyl tRNA synthetase is an enzyme that attaches the appropriate amino acid onto its tRNA. This step  is called as the charging of the tRNA with appropriate amino acid to the anti-codon arm. The mRNA is hence attached to the tRNA and a small sub unit of the ribosome is assembled primarily which is the cellular factory that is responsible for the translation of mRNA to proteins.For initiation the ribosome binds to the mRNA at the start codon that is recognized by the initiator tRNA. The larger sub-unit of the ribosome has two sites for subsequent amino acids to bind and thus be close enough to each other to form a peptide bond. Hence, acting as a catalyst for the peptide bond formation. This linking is the process of the peptide bond formation between two successive amino acids and the formed polypeptide chains with multiple peptide bonds exits from the ribosome. 

mRNA has some additional sequences that are not translated and are referred as untranslated regions (UTRs). The UTRs are present at both the 5'-end (before the start codon) and the 3'-end (after the stop codon). They are required for an efficient translation process.

1. (i) mRNA has more elaborate 3-dimensional structure due to extensive base-pairing:
   This statement is incorrect. mRNA typically doesn't have an elaborate 3D structure due to extensive base-pairing. While it does have regions of secondary structure, its primary function is to carry genetic information from DNA to the ribosome. The 3D structure of mRNA is less complex compared to tRNA.

2. (ii) tRNA has more elaborate 3-dimensional structure due to extensive pairing:
   This statement is correct. tRNA molecules have a highly intricate 3D structure, often described as a "cloverleaf" in 2D, due to extensive intramolecular base-pairing. This structure is essential for its role in translation, where it helps in recognizing codons and delivering the appropriate amino acids.

3. (iii) tRNA is usually smaller than mRNA:
   This statement is correct. tRNA molecules are much smaller than mRNA. A typical tRNA is around 70-90 nucleotides in length, while mRNA molecules can be several thousand nucleotides long.

4. (iv) mRNA bears anticodon but tRNA has codons:
   This statement is incorrect. The anticodon is part of tRNA, not mRNA. The tRNA carries the anticodon, which is complementary to the codon on the mRNA during translation. The mRNA carries the codons, which are sequences of three nucleotides that specify the amino acid to be added to the growing polypeptide chain.

Thus, the correct answer is (b) (ii) and (iii).