If there are $81$ million bases in the $RNA$ of a human cell,calculate the total number of introns present in $cDNA$.

Given below are the two statements.
Statement $I$: Only one strand in the transcription unit functions as a template and is called the antisense strand.
Statement $II$: The non-template strand of the transcription unit is called the sense strand.
In the light of the above statements,choose the correct answer from the options given below.

Which enzyme is primarily required for the process of transcription?

What do the processes $1$ and $2$ represent in the following sequence?
$TAC \, AAG \, GCG \, AUA \, CGA$
$\downarrow (1)$
$AUG \, UUC \, CGC \, UAU \, GCU$
$\downarrow (2)$
$Met - Phe - Arg - Tyr - Ala$

What does $X$ represent in the following diagram?

Which of the following is used as a substrate by $\text{RNA}$ polymerase and polymerises in a template-dependent fashion?