Question

Write the sequence of the complementary DNA strand that pairs with each of the following DNA base sequences: (a) GGTTAC (b) CCCGAA

Short answer

(a) CCAATG (b) GGGTTC

Step-by-step solution

Understand DNA Complementarity

DNA strands are complementary to each other, meaning that they pair in a specific manner: adenine (A) pairs with thymine (T) and cytosine (C) pairs with guanine (G).

Complementary sequence for GGTTAC

To find the complementary strand for the sequence GGTTAC, replace each base with its complement: G pairs with C, T pairs with A, and A pairs with T.

Write the complementary bases

The complementary bases to GGTTAC are: CCAATG.

Complementary sequence for CCCGAA

Similarly, to find the complementary strand for CCCGAA, replace each base with its complement: C pairs with G, and G pairs with C.

Write the complementary bases

The complementary bases to CCCGAA are: GGGTTC.

Key concepts

Complementary DNA Strands

In the world of genetics, DNA strands are known to be complementary. This means that a specific way of pairing exists between the two DNA strands.
Each DNA molecule consists of two strands that coil around each other to form a double helix. These strands are composed of simpler molecules called nucleotides.
Each nucleotide includes one of four bases: adenine (A), thymine (T), cytosine (C), or guanine (G).

• Adenine (A) always pairs with thymine (T)
• Cytosine (C) always pairs with guanine (G)

For example, if one DNA strand has a sequence of 'GGTTAC', the complementary DNA strand will be 'CCAATG'.

DNA Base Pairs

Base pairing is a fundamental aspect of DNA structure. It ensures the stable formation of the DNA double helix.
The bases on one strand of the DNA molecule hydrogen-bond to the bases on the complementary strand to form base pairs.
This complementary base-pairing rule facilitates accurate DNA replication and transcription.

• A-T pairs form two hydrogen bonds.
• C-G pairs form three hydrogen bonds.

By following these rules, you can easily determine the complementary sequence for any given strand. For example, the complementary sequence for 'CCCGAA' is 'GGGTTC'.

Nucleotide Matching

Nucleotide matching is all about understanding the exclusive pairing between the bases. A single nucleotide is made up of three components: a phosphate group, a sugar molecule, and a nitrogen base.
The nitrogen base is what determines the pairing.

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

In DNA synthesis, if one strand of DNA has a cytosine (C), the newly forming complementary strand will have guanine (G) at that position.
This ensures the DNA's integrity and allows cells to pass accurate genetic information during cell division. For the DNA sequence 'GGTTAC', nucleotide matching enables us to determine its complementary strand as 'CCAATG'.