Question

Write the complementary base sequence for each of the following DNA segments: a. \(-\mathrm{G}-\mathrm{A}-\mathrm{C}-\mathrm{T}-\mathrm{T}-\mathrm{A}-\mathrm{G}-\mathrm{G}-\mathrm{C}-\) b. \(-\mathrm{T}-\mathrm{G}-\mathrm{C}-\mathrm{A}-\mathrm{A}-\mathrm{A}-\mathrm{C}-\mathrm{T}-\mathrm{A}-\mathrm{G}-\mathrm{C}-\mathrm{T}-\) c. \(-\mathrm{A}-\mathrm{T}-\mathrm{C}-\mathrm{G}-\mathrm{A}-\mathrm{T}-\mathrm{C}-\mathrm{G}-\mathrm{A}-\mathrm{T}-\mathrm{C}-\mathrm{G}-\)

Short answer

a. -CTGAATCCG- b. -ACGTTTGATCGA- c. -TAGCTAGCTAGC-

Step-by-step solution

Understand DNA Base Pairing Rules

In DNA, each base pairs with a specific partner: adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G).

Write the Complementary Sequence for Segment a

Given the sequence \(-\text{G}-\text{A}-\text{C}-\text{T}-\text{T}-\text{A}-\text{G}-\text{G}-\text{C}-\), the complementary bases are identified as follows:* G pairs with C* A pairs with T* C pairs with G* T pairs with A* T pairs with A* A pairs with T* G pairs with C* G pairs with C* C pairs with GSo the complementary sequence is \(-\text{C}-\text{T}-\text{G}-\text{A}-\text{A}-\text{T}-\text{C}-\text{C}-\text{G}-\).

Write the Complementary Sequence for Segment b

Given the sequence \(-\text{T}-\text{G}-\text{C}-\text{A}-\text{A}-\text{A}-\text{C}-\text{T}-\text{A}-\text{G}-\text{C}-\text{T}-\), the complementary bases are identified as follows:* T pairs with A* G pairs with C* C pairs with G* A pairs with T* A pairs with T* A pairs with T* C pairs with G* T pairs with A* A pairs with T* G pairs with C* C pairs with G* T pairs with ASo the complementary sequence is \(-\text{A}-\text{C}-\text{G}-\text{T}-\text{T}-\text{T}-\text{G}-\text{A}-\text{T}-\text{C}-\text{G}-\text{A}-\).

Write the Complementary Sequence for Segment c

Given the sequence \(-\text{A}-\text{T}-\text{C}-\text{G}-\text{A}-\text{T}-\text{C}-\text{G}-\text{A}-\text{T}-\text{C}-\text{G}-\), the complementary bases are identified as follows:* A pairs with T* T pairs with A* C pairs with G* G pairs with C* A pairs with T* T pairs with A* C pairs with G* G pairs with C* A pairs with T* T pairs with A* C pairs with G* G pairs with CSo the complementary sequence is \(-\text{T}-\text{A}-\text{G}-\text{C}-\text{T}-\text{A}-\text{G}-\text{C}-\text{T}-\text{A}-\text{G}-\text{C}-\).

Key concepts

complementary base sequence

DNA is composed of two strands that wind around each other to form a double helix. Each strand in the DNA helix is made up of nucleotides. Nucleotides have one of four bases: adenine (A), thymine (T), cytosine (C), or guanine (G). One of the key principles of DNA's double helix structure is complementary base pairing. This means that the sequence of bases on one strand directly determines the sequence on the other strand because each base pairs specifically with another. Adenine pairs with thymine, and cytosine pairs with guanine. This complementary relationship ensures the stability and integrity of the genetic code and allows for accurate replication of DNA during cell division.

adenine-thymine pairing

In DNA, adenine (A) always pairs with thymine (T). This is due to the ability of these bases to form hydrogen bonds with each other. Specifically, an adenine-thymine pairing involves two hydrogen bonds. The consistent pairing of adenine with thymine is crucial for the accurate replication and transcription of genetic material. If A did not always pair with T, the information stored in DNA could become corrupted, leading to errors in protein synthesis and cellular function.
Understanding A-T pairing is essential when writing complementary base sequences. For instance, if one strand of DNA has a sequence including adenine, you will know that the corresponding position on the complementary strand must be thymine.

cytosine-guanine pairing

Similar to adenine and thymine, cytosine (C) always pairs with guanine (G) in DNA. This pairing is due to the formation of three hydrogen bonds between cytosine and guanine, making the C-G pair slightly more stable than the A-T pair. The specific pairing of cytosine with guanine is vital for maintaining the DNA's double helix's structural integrity. When determining a complementary sequence, each cytosine in one strand must pair with a guanine in the other strand and vice versa.
For example, in the provided DNA segment \(-C-G-A-T-G-C-\), each C would pair with a G, each G with a C, providing the complementary sequence corresponding to the original nucleotides.

nucleotide sequences

Nucleotide sequences are the order of nucleotides in a DNA strand. Each nucleotide consists of one base (A, T, C, or G), a sugar molecule, and a phosphate molecule, forming the backbone of DNA. The specific sequence of nucleotides encodes genetic information. During replication, transcription, and translation, the nucleotide sequences determine the specific amino acids used in proteins.
To construct a complementary DNA sequence, follow these steps:

• Identify each base in the original sequence.
• Replace each base with its pair (A with T, T with A, C with G, G with C).
• Ensure the new sequence aligns correctly to mirror the original strand's direction.

The consistent following of these rules ensures accurate genetic replication and expression.