Question

What will be the complementary strand of the given DNA strand \(5'-TAGGCAT-3'\)?
• \(5'-ATCCGTA-3'\)
• \(3'-TAGGCAT-5'\)
• \(3'-ATCCGTA-5'\)
• \(5'-AUCCGUA-3'\)

• A. \(1\)
• B. \(2\)
• C. \(3\)
• D. \(4\)

Hint:

DNA complementary base pairing: \[ A \leftrightarrow T \] \[ G \leftrightarrow C \] Also remember: \[ 5' \rightarrow 3' \] pairs with: \[ 3' \rightarrow 5' \] DNA strands are always antiparallel.

Answer 1

The Correct Option is C

Concept:
DNA consists of two complementary strands arranged in: \[ Antiparallel orientation \] This means:
• One strand runs from \(5' \rightarrow 3'\)
• The complementary strand runs from \(3' \rightarrow 5'\) DNA base pairing follows strict rules known as: \[ Chargaff's base pairing rules \] The complementary bases are: \[ A \leftrightarrow T \] \[ G \leftrightarrow C \] Thus:
• Adenine pairs with Thymine
• Guanine pairs with Cytosine

Step 1: Writing the given DNA strand carefully.
The given strand is: \[ 5'-TAGGCAT-3' \] We now find the complementary bases one by one.

Step 2: Applying complementary base pairing rules.
\[ T \rightarrow A \] \[ A \rightarrow T \] \[ G \rightarrow C \] \[ G \rightarrow C \] \[ C \rightarrow G \] \[ A \rightarrow T \] \[ T \rightarrow A \] Therefore the complementary sequence becomes: \[ ATCCGTA \]

Step 3: Writing the strand in antiparallel direction.
Since DNA strands are antiparallel: \[ 5' \rightarrow 3' \] pairs with: \[ 3' \rightarrow 5' \] Hence the complementary strand must be written as: \[ 3'-ATCCGTA-5' \]

Step 4: Checking all options carefully.
Option (1): \[ 5'-ATCCGTA-3' \] Correct bases but wrong direction. Option (2): \[ 3'-TAGGCAT-5' \] This is simply the original strand reversed incorrectly. Option (3): \[ 3'-ATCCGTA-5' \] Correct complementary sequence and correct antiparallel orientation. Hence this is correct. Option (4): \[ 5'-AUCCGUA-3' \] Contains uracil (\(U\)), which is found in RNA, not DNA. Hence incorrect.

Step 5: Final conclusion.
The complementary DNA strand is: \[ \boxed{3'-ATCCGTA-5'} \] Hence, the correct answer is: \[ \boxed{(3)} \]