Question

Imagine a single DNA strand containing a section with the following base sequence: \(5^{\prime}\) -GCATTGGC-3'. What is the base sequence of the complementary strand? (The two strands of DNA will come together in an antiparallel fashion: that is, \(5^{\prime}\) - \(\mathrm{TAG}=3^{\prime}\) will bind to \(3^{\prime}\) - \(\mathrm{ATC}-5^{\prime}\).)

Short answer

The base sequence of the complementary strand is \(3^{\prime}\) - GCCAATAG - \(5^{\prime}\).

Step-by-step solution

Identify the given DNA strand base sequence

The given DNA strand section has the base sequence: \(5^{\prime}\) - GCATTGGC - \(3^{\prime}\).

Determine the complementary base sequence

To find the complementary base sequence, we will use the base pairing rules. Replace each base with its complementary base in the given sequence: G -> C C -> G A -> T T -> A T -> A G -> C G -> C C -> G So, the complementary base sequence is: CTAAACCG

Reverse the order of the complementary base sequence to make it antiparallel

As DNA strands are antiparallel, reverse the order of the complementary sequence: Original complementary sequence: CTAAACCG Reversed complementary sequence: GCCAATAG

Write the final complementary strand

Now our complementary strand is complete, with the base sequence: \(3^{\prime}\) - GCCAATAG - \(5^{\prime}\) So, the base sequence of the complementary strand is \(3^{\prime}\) - GCCAATAG - \(5^{\prime}\).

Key concepts

DNA Structure

Deoxyribonucleic acid, or DNA, serves as the blueprint for all living organisms, storing the genetic instructions for the development, functioning, growth, and reproduction of all known lifeforms. The structure of DNA is often referred to as a double helix, resembling a twisted ladder.

Each 'rung' of the ladder is made up of two nitrogenous bases paired together. These bases are attached to a sugar molecule (deoxyribose) and a phosphate group, creating a nucleotide. The double helix is composed of two long strands of nucleotides connected by these bases. The sugar and phosphate groups form the backbone of the structure, on each strand, and are joined by strong covalent bonds.

The sequence of bases along a DNA strand encodes valuable genetic information. Understanding the DNA structure is crucial in fields such as genetics, forensics, and molecular biology.

Base Pairing Rules

The base pairing rules are fundamental to understanding DNA structure and function. These specific rules dictate how bases on opposite strands of DNA bond with each other. In DNA, there are four types of nitrogenous bases: adenine (A), thymine (T), guanine (G), and cytosine (C).

According to the base pairing rules:

• Adenine always pairs with thymine (A-T)
• Guanine always pairs with cytosine (G-C)

These pairs are held together by hydrogen bonds, which, while weaker than covalent bonds, play a crucial role in maintaining the double helix structure. The base-pairing mechanism ensures accurate DNA replication, a process essential for cell division and growth. It is also pivotal in DNA repair and transcription processes.

Antiparallel DNA Strands

When exploring DNA structure, it's necessary to understand the orientation of the two strands composing the double helix; they are antiparallel. This means that while one strand runs in a 5' to 3' direction, the complementary strand runs in a 3' to 5' direction. The numbers refer to the position of the carbon atoms in the deoxyribose sugar.

The 5' end of a strand is characterized by a phosphate group attached to the fifth carbon of the sugar ring, while the 3' end has a hydroxyl group attached to the third carbon. This antiparallel arrangement is essential for many biological processes, including DNA replication and transcription, as it allows enzymes to read the sequences and synthesize new strands accurately.

This property of DNA was clearly demonstrated in the given exercise, wherein the base sequence of one strand dictated the sequence of the other, once the rules of base pairing and antiparallel orientation were applied.