Problem 79 - Chemistry: The Central Science

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'-TAG-3' will bind to \(3^{\prime}\)-ATC-5'.)

Step-by-Step Solution

Answer

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

Step 1: Identify the given base sequence

The given base sequence is \(5^{\prime}\)-GCATTGGC-3.

Step 2: Write out the complementary base pairs

Using the base-pairing rules (A-T and C-G), replace each base in the given sequence with its complementary base. The complementary base pairs are as follows: G -> C C -> G A -> T T -> A T -> A G -> C G -> C C -> G

Step 3: Construct the complementary strand

Now, arrange the complementary bases in the same order as the original sequence, keeping in mind that the two strands of DNA come together in an antiparallel fashion: \(5^{\prime}\)-CGTAACCG-3.

Step 4: Write out the final complementary base sequence

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

Key Concepts

Complementary DNA Strand

When looking at DNA, you'll often hear about its ‘complementary’ strands. DNA is made up of two strands that wind around each other to form a double helix. Each strand is made up of a sequence of nucleotides. These nucleotides are identified by their bases: adenine (A), thymine (T), cytosine (C), and guanine (G). The concept of complementary strands refers to how each base on one strand pairs with a specific base on the opposing strand.

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

This complementary base pairing ensures that if you know the sequence of one strand, you can easily determine the sequence of the other strand. It’s like having a molecular pattern that simply fits together perfectly. Using this complementary rule, in our given DNA sequence, the complement to the provided sequence 5'-GCATTGGC-3' becomes 5'-CGTAACCG-3'. Each base on the original strand matches directly with its partner on the complementary strand.

Antiparallel Orientation

DNA strands are not only complementary but also have an antiparallel orientation. This means that one strand runs in a 5' to 3' direction, while its complementary strand runs in the opposite 3' to 5' direction. It’s a bit like two roads running alongside each other, but in opposite directions. This arrangement is crucial because DNA replication and many of its biological processes depend on this orientation. When a DNA polymerase enzyme synthesizes a new strand, it reads the template strand in the 3' to 5' direction, assembling the newly-synthesized strand in the 5' to 3' direction. In the context of our exercise, given 5'-GCATTGGC-3', the complementary strand is written as 5'-CGTAACCG-3' in a manner that respects this antiparallel characteristic, ensuring the ends correctly align as 5'/3' and 3'/5'.

Base Sequence

The base sequence of a DNA strand is fundamental to genetic information. It dictates everything from the production of proteins to the transfer of genetic code in living organisms. This sequence of bases encodes genes and instructions, much like letters and words create sentences and meaning in a language. The sequence is always read in the 5' to 3' direction, which is why, if you are given a sequence, it is typically written as such. The specific order of A, T, C, and G bases carries critical instructions that can influence everything from an organism's physical traits to susceptibility to diseases. In our exercise's sequence 5'-GCATTGGC-3', each letter corresponds to a nucleobase that fits precisely with its complementary base on the opposite, antiparallel strand. Understanding the base sequence helps in determining not just the complementary strand but also in understanding the broader biological roles the particular sequence plays.