Problem 71 - Chemistry: An Atoms-Focused Approach

Question

During the replication of DNA, a segment of an original strand has the sequence T-C-G-G-T-A. What is the sequence of the double-stranded helix formed in replication?

Step-by-Step Solution

Answer

Answer: The complementary DNA sequence is A-G-C-C-A-T.

Step 1: Identify the original DNA sequence

The given DNA sequence is T-C-G-G-T-A.

Step 2: Apply base pairing rules

Using the base pairing rules, determine the complementary bases for the original sequence: - For T (Thymine), the complementary base is A (Adenine). - For C (Cytosine), the complementary base is G (Guanine). - For G (Guanine), the complementary base is C (Cytosine). - For A (Adenine), the complementary base is T (Thymine).

Step 3: Determine the complementary sequence

Applying the base pairing rules to the original DNA sequence T-C-G-G-T-A, we obtain the complementary sequence A-G-C-C-A-T.

Step 4: Write down the double-stranded DNA helix

The double-stranded helix formed during DNA replication is: Original strand: 5'-T-C-G-G-T-A-3' Complementary strand: 3'-A-G-C-C-A-T-5'

Key Concepts

base pairing rules

DNA replication, which is essential for biological inheritance, relies on a pivotal principle known as the base pairing rules. These rules are fundamental for accurately copying genetic information from one cell to its offspring. DNA is composed of four types of nucleotide bases: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G). Understanding which bases pair together is crucial for DNA replication.

Here's how base pairing works during DNA replication:

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

These base pairing rules ensure that each strand of the DNA helix can serve as a template for the formation of its complementary strand. This precise matching process conserves the genetic information from one generation to the next, maintaining the integrity of the organism's code.

This specificity occurs due to hydrogen bonding between each pair, with A-T pairs forming two hydrogen bonds and C-G pairs forming three, contributing to the DNA molecule's stability and accuracy.

complementary bases

In the context of DNA replication, complementary bases play a vital role. Each nucleotide base on one DNA strand pairs with a specific complementary base on the opposing strand, forming what is known as base pairs. This process of pairing is guided by the base pairing rules.

During replication, the sequence on the original DNA strand will direct the formation of the new strand using complementary bases. For instance, in the original sequence T-C-G-G-T-A, each base has a complementary partner:

• **T (Thymine)** becomes **A (Adenine)** on the new strand.
• **C (Cytosine)** turns into **G (Guanine)**.
• **G (Guanine)** switches to **C (Cytosine)**.

These complementary bases ensure that the new strand is an accurate copy of the original, albeit in a complementary fashion.

The fidelity of this complementary base pairing is critical for the correct transmission of genetic instructions. Mistakes in this process can lead to mutations, which might affect an organism's traits or lead to genetic disorders. Therefore, understanding the role of complementary bases helps in grasping how DNA manages to replicate so accurately.

double-stranded DNA helix

The double-stranded DNA helix is a key structural feature of DNA, often visualized as a twisted ladder-like shape. Each "rung" of this ladder consists of two paired nucleotides, bonded together by hydrogen bonds. The two strands run in opposite directions, a feature known as antiparallel.

During DNA replication, each strand of the double helix serves as a template for creating a new complementary strand. As seen in our example with the original sequence T-C-G-G-T-A, the complementary strand produced is A-G-C-C-A-T. These two sequences together form the new double-stranded helix.

This structure is critical to the function of DNA in encoding genetic information. The stability provided by its double-stranded nature protects the genetic material, while its flexibility allows for the necessary processes of replication and transcription. The idea of a double helix model was famously proposed by James Watson and Francis Crick, building a profound understanding of genetic material that forms the foundation of modern molecular biology.

The double-stranded nature also plays a crucial role in the repair of DNA damage, as having a backup of genetic information on the complementary strand allows for errors to be corrected, ensuring genomic stability.