Q4. In NCERT Figure 5.13, the ribosome holds tRNAs on the codons GCA and GUU, and the next codon is AAU. Which amino acid comes next, and what is the anticodon of its tRNA?
AAU codes for asparagine (Asn) in NCERT Table 5.1, and its tRNA has the complementary anticodon 3′-UUA-5′ (5′-AUU-3′ from its 5′ end), as the figure shows (NCERT pages 96 and 99).
Q5. A translational unit, stop codon included, has 330 nucleotides. How many amino acids does its polypeptide have, and how many peptide bonds?
330 ÷ 3 = 110 codons; one is the stop codon, so 109 amino acids, joined by 108 peptide bonds (our arithmetic from NCERT pages 96–99).
Q6. Why are amino acids charged onto tRNAs before translation?
Forming a peptide bond needs energy, so amino acids are first activated in the presence of ATP and linked to their tRNAs; if two such charged tRNAs are brought close enough, peptide-bond formation between them is favoured energetically (NCERT pages 98–99).
Q7. What ends translation, and what happens to the polypeptide?
A release factor binds to the stop codon, which terminates translation and releases the complete polypeptide from the ribosome (NCERT page 99).
Q8. In which state does a ribosome exist as two separate subunits, and when does translation begin?
In its inactive state the ribosome exists as two subunits, a large and a small one; translation begins when the small subunit encounters an mRNA (NCERT page 99). Beyond the NCERT text: initiation factors and the initiator tRNA at the start codon are also needed before the large subunit joins (Wikipedia, “Translation (biology)”, facts in our words).