Problem 79 - Chemistry The Central Science In Si Units

Question

Imagine a single DNA strand containing a section with the following base sequence: \(5^{\prime}\) -AGTTACTGG-3'. What is the base sequence of the complementary strand?

Step-by-Step Solution

Answer

The complementary sequence is 3'-TCAATGACC-5'.

Step 1: Understand DNA Base Pairing

DNA strands are made up of nucleotides, each containing one of four bases: adenine (A), thymine (T), cytosine (C), and guanine (G). The bases on opposite strands of DNA pair with each other in a specific manner: adenine with thymine (A-T) and cytosine with guanine (C-G).

Step 2: Determine the Complementary Sequence

Given the original sequence is 5'-AGTTACTGG-3', find the complementary bases for each base in this sequence: - A pairs with T - G pairs with C - T pairs with A - T pairs with A - A pairs with T - C pairs with G - T pairs with A - G pairs with C - G pairs with C.

Step 3: Construct the Complementary Sequence Order

DNA strands are antiparallel, meaning they run in opposite directions. The original strand runs from 5' to 3', therefore the complementary strand starts from the 3' end to 5' end. The complementary sequence is therefore: 3'-TCAATGACC-5'.

Key Concepts

Nucleotide Bases

DNA is composed of building blocks known as nucleotide bases, which play a crucial role in genetic encoding. Each nucleotide consists of a sugar, a phosphate group, and a nitrogenous base. The four types of nitrogenous bases in DNA are adenine (A), thymine (T), cytosine (C), and guanine (G). These bases pair in a specific manner which is essential for the structure and function of DNA.

Here is a simple way to remember the pairs:

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

This pairing is facilitated by hydrogen bonds between the bases, which help stabilize the DNA structure. Understanding these pairs is key when constructing a complementary strand of DNA from a given sequence.

Complementary Strands

When discussing DNA, a central concept is that of complementary strands. DNA is double-stranded, meaning it has two polynucleotide chains that are paired together. These strands are complementary because each base on one strand pairs with a specific base on the other strand, following specific base pairing rules.

The original exercise involves finding a complementary strand for a specific DNA sequence. Here's how a complementary strand is built:

• Begin by examining each base in the original strand.
• Match each base with its partner: A with T, T with A, C with G, and G with C.
• Construct the complementary sequence by writing down these paired bases.

For example, if you start with the strand 5'-AGTTACTGG-3', the complementary bases would be 3'-TCAATGACC-5'. This pairing ensures that genetic information is precisely duplicated during DNA replication.

Antiparallel DNA

DNA strands are described as being antiparallel, which means they run in opposite directions. Understanding antiparallel orientation is essential when constructing complementary strands. Each strand has two ends, labeled 5' (five prime) and 3' (three prime), based on the carbon numbers in the DNA's sugar backbone.

In an antiparallel configuration:

• One strand runs from the 5' to the 3' direction.
• The complementary strand runs from 3' to 5'.

This antiparallel arrangement is vital for several biological processes, including DNA replication and protein synthesis. In the original exercise, the sequence 5'-AGTTACTGG-3' is paired with its complementary strand, which is formed by writing the complementary bases in the opposite direction: 3'-TCAATGACC-5'. This ensures that the genetic code is accurately passed on to future cells.