The statement is correct.Because of degeneracy codons, mutations at third base of usually do not result into any change in phenotype.On the other hand, if codon is changed in a way that now it specifies another  amino acid it may alter the protein function as it happens in case of \(\beta \) - globulin of haemoglobin, protein where a substitution of valine instead of glutamic acid causes changes in its structure and function, and resulting into sickle-cell trait.

(i) (a) Hydrogen bonds.
(b) Purine base
(c) Deoxyribose sugar.
(ii) 'd' represents 5' end of the chain,

1. Lactose is the inducer for lac operon. The active form of lactose binds to the repressor protein and brings about a conformational change in the repressor.
2. As a result, the repressor is inactive, i.e. it cannot bind to the operator.
3. This provides access of the RNA polymerase to structural genes and transcription and production of enzymes continue and metabolism of lactose takes place.
4. In its absence, the repressor is active and binds to the operator, thereby switching off the process.

1. In prokaryotes, the mRNA does not require any processing to become active.
2. Transcription and translation occur in the same compartment-cytosol, as there is no well-defined nucleus. So coupling of transcription and translation is possible.
3. The mRNA has to be processed before becoming active (splicing is necessary).
4. Since nucleus and cytoplasm are well separated, in eukaryotes the RNA has to be transported to the cytoplasm for translation.
5. So coupling of transcription and translation is not possible.