Problem 83 - Chemistry Matter and Change

Question

DNA Replication One strand in a DNA molecule has the following base sequence. What is the base sequence of the other strand in the DNA molecule? $$\mathrm{C}-\mathrm{C}-\mathrm{G}-\mathrm{T}-\mathrm{G}-\mathrm{G}-\mathrm{A}-\mathrm{C}-\mathrm{A}-\mathrm{T}-\mathrm{T}-\mathrm{A}$$

Step-by-Step Solution

Answer

The complementary base sequence is \( \text{G-G-C-A-C-C-T-G-T-A-A-T} \).

Step 1: Understand Base Pairing Rules

DNA consists of two strands that pair together following specific base pairing rules. Cytosine (C) pairs with Guanine (G), and Adenine (A) pairs with Thymine (T). Understanding these rules is crucial to determine the complementary strand.

Step 2: Write the Given Base Sequence

The given sequence is \( ext{C-C-G-T-G-G-A-C-A-T-T-A} \). This sequence represents one strand of the DNA molecule.

Step 3: Determine the Complementary Base Sequence

For each base in the given sequence, write its complementary base using base pairing rules: C pairs with G, G pairs with C, T pairs with A, and A pairs with T. Therefore: - C pairs with G - C pairs with G - G pairs with C - T pairs with A - G pairs with C - G pairs with C - A pairs with T - C pairs with G - A pairs with T - T pairs with A - T pairs with A - A pairs with T

Step 4: Compile the Complementary Sequence

Using the complementary bases determined for each position, the sequence of the other strand is:\( ext{G-G-C-A-C-C-T-G-T-A-A-T} \).

Key Concepts

Base Pairing Rules

In DNA replication, the base pairing rules are fundamental for the process of creating two identical double-stranded DNA molecules. The DNA structure is composed of nucleotides, each consisting of a sugar, a phosphate group, and a nitrogenous base. There are four types of nitrogenous bases in DNA: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G).

According to the base pairing rules:

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

These pairing rules are due to the size and chemical properties of the bases. The complementary base pairing leads to the formation of hydrogen bonds, which hold the two strands of DNA together. This specific pairing is essential for the accuracy of DNA replication, ensuring that each new strand is an exact replica of the original.

Complementary Base Sequence

A complementary base sequence is the sequence of bases on the opposing DNA strand that matches each base according to the base pairing rules. When DNA replicates, each strand serves as a template to guide the formation of a new complementary strand.

To find the complementary sequence of a given DNA strand, you match each base with its complementary counterpart:

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

For example, if you are given the DNA sequence: C-C-G-T-G-G-A-C-A-T-T-A, the complementary sequence would be determined by switching each base accordingly, resulting in: G-G-C-A-C-C-T-G-T-A-A-T. This process ensures that the DNA strands are complementary but not identical, allowing for correct replication.

Nucleotide Pairing

Nucleotide pairing refers to the process of aligning nucleotides through base pairing rules during DNA replication. Each nucleotide within a DNA strand is matched with a complimentary nucleotide from the template strand to form a stable structure.

Understanding nucleotide pairing is essential for grasping how genetic information is accurately copied and passed on during cell division. The nitrogenous bases in nucleotides form hydrogen bonds with their complementary bases on the opposite strand:

• The A-T pair usually forms two hydrogen bonds
• The C-G pair forms three hydrogen bonds, providing greater stability

The number of hydrogen bonds affects the strength and stability of the DNA molecule, which is why G-C rich regions tend to be more stable than A-T rich regions. Precise nucleotide pairing ensures the faithful replication of DNA, which is crucial for healthy cell function and organism development.