Question

If one strand of a DNA has the sequence ATGCTTCA, sequence of the bases in complementary strand is:

• A. CATTAGCT
• B. TACGAAGT
• C. GTACTTAC
• D. ATGCGACT

Answer 1

The Correct Option is B

The objective is to determine the sequence of the complementary DNA strand, given one strand's sequence as ATGCTTCA.

Underlying Principle:

DNA's double helix structure is maintained by base pairing rules: Adenine (A) pairs with Thymine (T), and Guanine (G) pairs with Cytosine (C).

Procedural Breakdown:

Step 1: Document the provided DNA strand sequence.

\[ \text{Given Strand: } 5'\text{-ATGCTTCA-}3' \]

Step 2: Identify the complementary base for each nucleotide according to pairing rules.

• A pairs with T.
• T pairs with A.
• G pairs with C.
• C pairs with G.

Step 3: Determine the complementary base for each position in the original sequence.

• Position 1 (A): Complement is T.
• Position 2 (T): Complement is A.
• Position 3 (G): Complement is C.
• Position 4 (C): Complement is G.
• Position 5 (T): Complement is A.
• Position 6 (T): Complement is A.
• Position 7 (C): Complement is G.
• Position 8 (A): Complement is T.

Step 4: Construct the complementary strand sequence. Note that DNA strands are antiparallel; the complementary strand runs 3' to 5' if the given strand runs 5' to 3'.

\[ \begin{array}{rc} \text{Given Strand:} & 5' - \text{A T G C T T C A} - 3' \\ & \quad \ ||\ ||\ ||\ ||\ ||\ ||\ ||\ || \\ \text{Complementary Strand:} & 3' - \text{T A C G A A G T} - 5' \end{array} \]

Conclusion:

The complementary DNA strand sequence is TACGAAGT.