Question

What will be the sequence of RNA synthesized using the following DNA template strand?
5'-GTCTAGGCTTCTC-3'

• A. 5'-GAGAAGCCUAGAC-3'
• B. 5'-GUCUAGGCUUCUC-3'
• C. 5'-CAGAUCCGAAGAG-3'
• D. 5'-CUCUUCGGAUCUG-3'

Hint:

Always write down the template strand in the $3' \to 5'$ direction first.
This makes writing the complementary $5' \to 3'$ RNA strand straightforward and prevents directionality errors.
Remember that RNA contains Uracil (U) instead of Thymine (T).

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks us to find the sequence of the RNA molecule synthesized from a given DNA template strand.
The template strand is read by RNA polymerase in the $3' \to 5'$ direction to synthesize RNA in the $5' \to 3'$ direction.
The bases in the RNA are complementary to those in the DNA template strand.

Step 2: Key Formula or Approach:
To find the complementary RNA strand:
1. Complementary base pairing rules apply: Adenine (A) pairs with Uracil (U) in RNA, Thymine (T) pairs with Adenine (A), Cytosine (C) pairs with Guanine (G), and Guanine (G) pairs with Cytosine (C).
2. The RNA strand is synthesized antiparallel to the DNA template strand.
Thus, the $5'$ end of the RNA is complementary to the $3'$ end of the DNA template.

Step 3: Detailed Explanation:
Let's write down the given DNA template strand:
\[ 5'\text{-GTCTAGGCTTCTC}-3' \]
To easily construct the complementary RNA strand in the standard $5' \to 3'$ direction, we first write the DNA template in the $3' \to 5'$ direction:
\[ 3'\text{-CTCTTCGGATCTG}-5' \]
Now, we find the complementary RNA bases starting from the $5'$ end (which corresponds to the $3'$ end of the DNA template):
- Cytosine (C) at $3'$ end of DNA pairs with Guanine (G) at $5'$ end of RNA.
- Thymine (T) pairs with Adenine (A).
- Cytosine (C) pairs with Guanine (G).
- Thymine (T) pairs with Adenine (A).
- Thymine (T) pairs with Adenine (A).
- Cytosine (C) pairs with Guanine (G).
- Guanine (G) pairs with Cytosine (C).
- Guanine (G) pairs with Cytosine (C).
- Adenine (A) pairs with Uracil (U).
- Thymine (T) pairs with Adenine (A).
- Cytosine (C) pairs with Guanine (G).
- Thymine (T) pairs with Adenine (A).
- Guanine (G) at $5'$ end of DNA pairs with Cytosine (C) at $3'$ end of RNA.
Putting these together from $5'$ to $3'$ gives:
\[ 5'\text{-GAGAAGCCUAGAC}-3' \]

Step 4: Final Answer:
Therefore, the sequence of the synthesized RNA is 5'-GAGAAGCCUAGAC-3', which matches option (A).