Problem 80 - Chemistry The Science in Context

Question

If the sequence of one strand of DNA is \(5^{\prime}\) ATTGCCA \(3^{\prime}\) what is the sequence (in the \(\left.5^{\prime} \text { to } 3^{\prime} \text { direction }\right)\) of the other strand?

Step-by-Step Solution

Answer

Answer: The sequence of the complementary DNA strand in the 5' to 3' direction is 5' TGGCAAT 3'.

Step 1: Write down the sequence of the first DNA strand

The sequence of the given DNA strand is \(5^{\prime}\) ATTGCCA \(3^{\prime}\).

Step 2: Complementary base pairing

Find the complementary bases for the given strand using the base pairing rules, which are adenine (A) pairs with thymine (T) and guanine (G) pairs with cytosine (C).

Step 3: Write down the complementary bases for the original sequence

The complementary bases for the original DNA sequence are: - A pairs with T - T pairs with A - T pairs with A - G pairs with C - C pairs with G - C pairs with G - A pairs with T So the complementary sequence is TAACGGT.

Step 4: Write the sequence of the complementary DNA strand from 5' to 3'

The given sequence is written in the 5' to 3' direction. To write the complementary strand in reverse (from the 5' to 3' direction), read the complementary sequence from Step 3 in reverse order. The sequence of the complementary DNA strand in the \(\left.5^{\prime} \text { to } 3^{\prime} \text { direction }\right)\) is \(5^{\prime}\) TGGCAAT \(3^{\prime}\).

Key Concepts

Complementary Strand

In DNA, the concept of a complementary strand refers to a sequence that pairs with another DNA strand by following specific base pairing rules. This process is like finding a best friend for each nucleotide.
Understanding these pairings is crucial for DNA replication and transcription. In any DNA sequence, adenine (A) will always pair with thymine (T), and guanine (G) will always pair with cytosine (C). Let's consider a given sequence: if one strand reads 5' ATTGCCA 3', its complementary strand would automatically be determined as 3' TAACGGT 5'. This happens because:

• A pairs with T
• T pairs with A
• G pairs with C
• C pairs with G

These rules ensure the double-helix structure is stable and allows DNA to carry genetic information accurately from generation to generation.

Nucleotide Sequence

A nucleotide sequence is the order of nucleotides in a DNA molecule. Nucleotides are the building blocks of DNA and consist of a sugar, phosphate group, and a nitrogenous base. In a sequence, each nucleotide is represented by a letter:

• A for adenine
• T for thymine
• G for guanine
• C for cytosine

These letters come together to form long strands of genetic information. In the original DNA strand, represented as 5' ATTGCCA 3', each letter signifies a specific nucleotide in the sequence.
Since every organism's DNA can be unique in its combination of these sequences, understanding this provides insights into genetic differences, hereditary, and potential for research in fields like genetics and medicine.

5' to 3' direction

The 5' to 3' direction describes the orientation of the DNA strand and is fundamental to how DNA replication occurs. Every DNA strand has a directionality determined by the chemical orientation of the sugar-phosphate backbone. You can think of it as a one-way street that dictates the flow of genetic information. The number 5' (five prime) denotes the fifth carbon in the sugar of a nucleotide, which is attached to a phosphate group, while 3' (three prime) denotes the third carbon in the sugar, which has a hydroxyl group (-OH). DNA synthesis and repair processes happen from the 5' end to the 3' end. In genetic communication, it is essential to define the direction because sequences like 5' ATTGCCA 3' can imply different information when read backwards. Thus, DNA is always written and often read in the 5' to 3' direction to maintain consistency and accuracy in biological processes.