Question

If the sequence of a segment of DNA in one strand is \(5^{\prime}-\mathrm{CGCAACTAC}-3^{\prime},\) what is the sequence of the corresponding segment in the opposite strand? a. \(5^{\prime}-\) GCGTTGATG-3 \(^{\prime}\) b. \(3^{\prime}-\mathrm{ATACCAGCA}-5^{\prime}\) c. \(5^{\prime}-\mathrm{ATACCAGCA}-3^{\prime}\) d. \(3^{\prime}-\) GCGTTGATG-5 \(^{\prime}\)

Short answer

The sequence of the corresponding segment in the opposite strand is \(5^{\prime}-\mathrm{GCGTTGATG}-3^{\prime}\) or choice a. However, usually, the sequence on the opposite strand should be given in the 3' to 5' direction, not in the 5' to 3' direction. So, there might be an error in the question or possible options.

Step-by-step solution

Identifying the Base Pairing

Determine the base pairs according to the rule. Cytosine (C) pairs with Guanine (G), Adenine (A) pairs with Thymine (T). Therefore the new sequence becomes \(5^{\prime}-\mathrm{GCGTTGATG}-3^{\prime}\)

Reversing the Sequence

The sequence formed should be in the 3' to 5' direction since it is on the opposite strand. Hence flip the sequence from 3' to 5' direction. Therefore, the new sequence becomes: \(3^{\prime}-\mathrm{GATGTTGCG}-5^{\prime}\).

Recognizing the Correct Answer

Identify the correct choice from the given options. The resulting sequence does not match with any of the options given. But considering the DNA base pairing rules if the exercise expects the answer in 5'-3' direction then the correct DNA sequence is \(5^{\prime}-\mathrm{GCGTTGATG}-3^{\prime}\).

Key concepts

Nucleotide Sequence

The nucleotide sequence is the fundamental building block of DNA, comprised of a chain of nucleotides connected together. Each nucleotide contains three components: a sugar molecule (deoxyribose), a phosphate group, and one of four nitrogenous bases—adenine (A), thymine (T), guanine (G), or cytosine (C).

The sequence of these bases along a DNA strand encodes genetic information, much like letters forming words and sentences in a language. This genetic 'text' dictates the synthesis of proteins, which perform most life functions in organisms. When depicting a nucleotide sequence, it's crucial to pay attention to the directionality; DNA strands are antiparallel, with one running 5' to 3' (five prime to three prime) and the other 3' to 5'. The numbers refer to the carbon atoms of the sugar molecule, to which the phosphate and bases are attached.

In educational settings, understanding the orientation and sequence of nucleotides is fundamental for grasping concepts like DNA replication and transcription. It also plays a pivotal role in other exercises, like identifying complementary strands or mutations.

Complementary Strands

Complementary strands refer to the two polynucleotide chains of DNA that run in opposite directions and are bound together by hydrogen bonds between paired bases. The beauty of this system lies in its simplicity and specificity: adenine always pairs with thymine, and guanine always pairs with cytosine.

DNA's double helical structure consists of a 'right' strand and a 'left' strand, each serving as a template for the other. The orders of bases on one strand determine the order on the complementary strand, thanks to the base pairing rules. This principle is so critical that it underpins life's ability to replicate itself and pass genetic information from one generation to the next.

To illustrate, given a segment of DNA with the sequence 5'-CGCAACTAC-3', we can determine its complement using the base pairing rules. For every cytosine (C) in the original sequence, there will be a guanine (G) on the opposite strand, and vice versa. Similarly, for every adenine (A), there will be a thymine (T) opposite to it, and so on. If you were to physically write out the sequence, the complementary segment would be facing in the opposite direction, reading 3'-GCGTTGATG-5'.

DNA Replication

DNA replication is the biological process by which an exact copy of a DNA molecule is created, ensuring that each new cell receives a full set of chromosomes during division. It's characterized by several key steps, which involve unwinding the DNA helix, separating the strands, and synthesizing two new daughter strands using the original strands as templates.

Enzymes like DNA helicase unwind and separate the strands, while DNA polymerase synthesizes the new DNA by adding nucleotides to complement the existing ones on the template strand. Importantly, DNA polymerase can only add nucleotides to the 3' end of a preexisting strand of DNA. This continuous assembly on one strand is known as the leading strand, while the other strand, called the lagging strand, is constructed in short segments, later joined together.

The DNA replication process is semiconservative, which means that each of the two resulting DNA molecules will have one old strand, called the template strand, and one newly synthesized strand. This mechanism ensures the genetic consistency throughout cell divisions, which is vital for the growth, development, and maintenance of organisms. Understanding these complex interactions and the roles of various enzymes is crucial for comprehending how life perpetuates its genetic material.