Question

(a) Construct a complete transcription unit with promoter and terminator on the basis of the hypothetical coding strand given below :

A T G C A T G C A T A G

(The strand is drawn on a line with arrow heads at both ends and short vertical ticks under each base, for you to complete.)

(b) Write the RNA strand transcribed from the above transcription unit along with its polarity.

Hint:

Promoter goes at the 5 prime end and terminator at the 3 prime end of the coding strand; the RNA is 5 prime AUGCAUGCAUAG 3 prime.

Answer 1

Step 1: Understanding the Concept:
A transcription unit has three parts: a promoter, the structural gene and a terminator. The promoter lies at the \( 5^{\prime} \) end (upstream) of the coding strand, and the terminator at the \( 3^{\prime} \) end (downstream).

Step 2: Write the template strand:
The given coding strand is \( 5^{\prime} \)-ATGCATGCATAG-\( 3^{\prime} \).
The template strand is complementary and antiparallel to it. Using A-T and G-C pairing we get:
\[ 3^{\prime}\text{-TACGTACGTATC-}5^{\prime} \]

Step 3: Part (a) - Construct the unit:
\( 5^{\prime} \)-[Promoter]-ATGCATGCATAG-[Terminator]-\( 3^{\prime} \) (coding strand)
\( 3^{\prime} \)-[Promoter]-TACGTACGTATC-[Terminator]-\( 5^{\prime} \) (template strand)
The promoter is where RNA polymerase binds. The terminator is where transcription stops. Both are marked outside the gene, one at each end.

Step 4: Part (b) - RNA strand:
RNA polymerase reads the template strand in the \( 3^{\prime} \to 5^{\prime} \) direction and builds RNA in the \( 5^{\prime} \to 3^{\prime} \) direction.
RNA has uracil (U) in place of thymine (T). The RNA copies the coding strand, with U for T:
\[ 5^{\prime}\text{-AUGCAUGCAUAG-}3^{\prime} \]

Final Answer:
The unit is promoter, ATGCATGCATAG (coding), terminator, with template \( 3^{\prime} \)-TACGTACGTATC-\( 5^{\prime} \). The RNA is \( 5^{\prime} \)-AUGCAUGCAUAG-\( 3^{\prime} \).