Understanding DNA Complementarity

The question asks us to find the complementary DNA strand for a given coding sequence: 5′ – GTATTACG – 3′.

DNA consists of two strands that run in opposite directions, known as antiparallel orientation. One strand runs from the 5' end to the 3' end, and its complementary strand runs from the 3' end to the 5' end.

The bases in DNA pair specifically:

• Adenine (A) pairs with Thymine (T)
• Guanine (G) pairs with Cytosine (C)

These pairing rules are based on the formation of hydrogen bonds between the bases (A-T form two hydrogen bonds, C-G form three hydrogen bonds).

Generating the Complementary DNA Strand

We are given the coding sequence:

\(5′ – \text{G T A T T A C G} – 3′\)

To find the complementary strand, we will apply the base pairing rules to each base in the given sequence and write them in the antiparallel direction.

Let's go base by base from the 5' end of the given strand:

• For G, the complementary base is C.
• For T, the complementary base is A.
• For A, the complementary base is T.
• For T, the complementary base is A.
• For T, the complementary base is A.
• For A, the complementary base is T.
• For C, the complementary base is G.
• For G, the complementary base is C.

So, the sequence of complementary bases in the same order as the coding strand (5' to 3') would be C A T A A T G C.

However, the complementary strand runs in the antiparallel direction (3' to 5'). Therefore, we write this complementary sequence starting from the 3' end.

Given strand: \(5′ – \text{G T A T T A C G} – 3′\)

Complementary strand: \(3′ – \text{C A T A A T G C} – 5′\)

Evaluating the Options

Now let's look at the provided options:

1. 5′ – CUTUUTGC – 3′: This contains 'U' which is Uracil, found in RNA, not DNA. Also, the sequence is not complementary.
2. 3′ – CATAATGC – 5′: This sequence matches the complementary strand we derived (3′ – C A T A A T G C – 5′).
3. 3′ – CUTUUTGC – 5′: This contains 'U' (Uracil), which is not present in DNA.
4. 5′ – CTUTTUGC – 3′: This contains 'U' (Uracil) and the orientation is incorrect for a complementary strand if the original is 5' to 3'.

Based on our derivation, the correct complementary strand is 3′ – CATAATGC – 5′.

Revision Table: Key Concepts in DNA Complementarity

Additional Information on DNA Structure and Function

DNA, or deoxyribonucleic acid, is the molecule that carries genetic information in most organisms. Its double helix structure is fundamental to its function.

Structure of DNA

• Each strand is a polymer of nucleotides.
• A nucleotide consists of three parts: a deoxyribose sugar, a phosphate group, and a nitrogenous base (A, T, C, or G).
• The two strands are held together by hydrogen bonds between the complementary bases.
• The sugar-phosphate backbone forms the outer structure of the helix, while the bases are stacked inside.
• The antiparallel nature of the strands is crucial for DNA replication and transcription.

Importance of Complementarity

The complementary nature of the DNA strands is essential for several biological processes:

• DNA Replication: During replication, each strand serves as a template for the synthesis of a new complementary strand, ensuring accurate duplication of genetic material.
• Transcription: In transcription, one strand of DNA (the template strand) is used to synthesize a complementary RNA molecule.
• DNA Repair: The complementary strand can be used as a template to repair damage in the other strand.

Understanding how to find the complementary strand is a basic but important skill in molecular biology and genetics.