Question

The sequence one strand of a DNA double helix is: \(*\) ATGGCTACAA Beginning at the \(*\) end, what is the complimentary sequence?

Short answer

Answer: The complementary DNA sequence is TACCGATGTT.

Step-by-step solution

Identify the nucleotide pairs

In DNA, we have the following pairs: - Adenine (A) with Thymine (T) - Cytosine (C) with Guanine (G)

Read the given strand

Read the given DNA strand from the \(*\) end: ATGGCTACAA

Find the complementary sequence

Determine the complementary nucleotide for each nucleotide in the given strand: A -> T T -> A G -> C G -> C C -> G T -> A A -> T C -> G A -> T A -> T

Write the complementary strand

Write down the complementary strand in the same order as the given strand: TACCGATGTT The complementary DNA sequence is TACCGATGTT.

Key concepts

Understanding Nucleotide Pairs

The molecular structure of DNA is composed of nucleotides, which are the building blocks of genetic information. Nucleotides themselves consist of three components: a sugar molecule (deoxyribose), a phosphate group, and a nitrogenous base. There are four types of nitrogenous bases in DNA: adenine (A), thymine (T), cytosine (C), and guanine (G).

One of the fundamental principles of DNA structure is the pairing of these bases. As established by the pairing rules, adenine always pairs with thymine, and cytosine pairs with guanine. This means that if one strand of a DNA double helix has a sequence that reads ATG, the complementary strand will read TAC. This specific pairing is critical because it ensures that genetic information is accurately copied and transferred during processes like DNA replication and cell division.

Base Pairing in Practice

Using the original exercise example of the DNA sequence ATGGCTACAA, we can apply the base pairing rules step by step. The complementary sequence starting from the 5' to 3' direction will be TACCGATGTT, which accounts for each base's corresponding partner as outlined in the nucleotide pairing: A with T and C with G.

Decoding the DNA Double Helix

The DNA double helix is a remarkable structure discovered by James Watson and Francis Crick in 1953. It resembles a twisted ladder, where the sugar-phosphate backbones represent the sides of the ladder, and the nucleotide pairs form the rungs. The double helix is antiparallel, with one strand running in the 5' to 3' direction and the other in the 3' to 5' direction, denoting the orientation of the deoxyribose sugar.

As the two strands twist around each other, they create a stable structure that protects the genetic code. The helical shape allows DNA to be compactly stored in the nucleus of cells while still being accessible for replication and transcription. The exercise example explores one strand of the DNA helix and asks for the complementary strand, illustrating how both strands need to be understood in the context of this double helix configuration to replicate and express genetic information effectively.

Functionality and Stability

Hydrogen bonds between the base pairs add to the helix's stability, and this pairing also facilitates the error-checking and repair mechanisms that are crucial to maintaining genetic fidelity. The double helix is not just a structure but also the physical representation of the living cell's ability to maintain and reproduce its genetic blueprint accurately.

Unraveling the Genetic Code

The genetic code is the set of rules by which information encoded within genetic material (DNA or RNA) is translated into proteins by living cells. Proteins are the workhorses of the cell, carrying out a myriad of functions necessary for life. The genetic code is universal, meaning with few exceptions, it operates the same way in almost all organisms.

The code is composed of codons, which are sequences of three nucleotides that correspond to a specific amino acid (the building blocks of proteins) or a stop signal during protein synthesis. The sequence one strand of a DNA double helix, such as the exercise's example, is a part of the genetic code that, when transcribed and translated, results in a specific protein with a unique function in the organism.

Translating the Code

For example, the initial segment ATG commonly serves as a start codon, signifying the beginning of a protein-coding region. Following the rules of the genetic code, enzymatic machinery within the cell reads codons in a strand of mRNA (which is transcribed from the DNA template) and assembles amino acids in the corresponding sequence to form a protein. The process of decoding the genetic information into a functional protein is central to the life of a cell and the organism as a whole.