Question

Draw the structural formula for the tetradeoxynucleotide CGTA.

Short answer

The structure of CGTA is a linear sequence of four nucleotides: Cytosine, Guanine, Thymine, and Adenine, connected in a 5' to 3' orientation with a sugar-phosphate backbone.

Step-by-step solution

Identify Nucleotides

The tetradeoxynucleotide CGTA is made up of four deoxyribonucleotides: Cytosine (C), Guanine (G), Thymine (T), and Adenine (A). Each of these nucleotides consists of three components: a phosphate group, a deoxyribose sugar, and a nitrogenous base (either C, G, T, or A).

Understand Bonding Orientation

DNA nucleotides always connect in a 5' to 3' direction. The phosphate group of one nucleotide connects to the 3' carbon of the deoxyribose sugar of the next nucleotide. This forms the backbone of the DNA strand.

Start Drawing from the 5' End

Begin with the 5' phosphate group connected to the deoxyribose sugar of the first nucleotide, Cytosine (C). Draw the nitrogenous base (a single ring for C) attached to the 1' carbon of deoxyribose.

Add Second Nucleotide

Link the 3' carbon of Cytosine's deoxyribose to the 5' phosphate of Guanine. Draw Guanine (a double-ring structure) attached to its deoxyribose sugar.

Add Remaining Nucleotides

Continue adding Thymine and then Adenine. Link each 3' carbon to the next 5' phosphate group, ensuring each nitrogenous base (a single ring for Thymine and a double ring for Adenine) is attached to the 1' carbon of its deoxyribose.

Complete and Check Structure

Finish by ensuring the tetradeoxynucleotide chain runs 5'-C-G-T-A-3'. Check that each deoxyribose, phosphate, and nitrogenous base is correctly linked in the 5' to 3' direction.

Key concepts

Nucleotide Structure

Nucleotide structure is fundamental to understanding DNA. A nucleotide consists of three main components:

• A phosphate group
• A deoxyribose sugar
• A nitrogenous base

These building blocks connect to form the chains of DNA. The phosphate group is negatively charged, contributing to the DNA's overall negative charge.
The deoxyribose sugar is a five-carbon sugar, differing from ribose by the absence of one oxygen atom, hence the "deoxy" prefix. The nitrogenous base can be a purine, such as Adenine (A) and Guanine (G), or a pyrimidine, like Cytosine (C) and Thymine (T). In the tetradeoxynucleotide CGTA, C, G, T, and A represent these bases. The specific sequence of the nitrogenous bases encodes genetic information.

Phosphate Backbone

The phosphate backbone is the supporting structure of DNA, providing a stable framework that supports its function and structure. It consists of alternating phosphate groups and deoxyribose sugars linked together. Each nucleotide connects through its phosphate group to the 3' carbon of the neighboring sugar, forming a continuous "chain."
Two key things to remember:
1. The sequence runs from the 5' end to the 3' end of the DNA strand. This directionality is crucial for many biological processes, such as DNA replication and transcription. 2. The phosphate bonds between the 3' carbon and the phosphate group are strong and resist cleavage, which helps protect the integrity of the DNA strand.
This structure not only aids in the proper linkage of nucleotides but also allows the flexibility and twist of the DNA double helix.

Nucleotide Pairing

Nucleotide pairing is the mechanism by which the two strands of DNA are held together, ensuring accurate genetic replication. In the context of CGTA, each base pairs with a complementary partner on the opposite DNA strand. This occurs via hydrogen bonding, which stabilizes the structure of DNA.
- Cytosine (C) pairs with Guanine (G) through three hydrogen bonds. - Thymine (T) pairs with Adenine (A) through two hydrogen bonds.
This specific pairing is known as complementary base pairing, and it's essential for DNA's double helix structure. The precise pairing ensures that the genetic code is preserved during DNA replication, as each half of the DNA double helix can serve as a template for reconstructing its pair.

Deoxyribose Sugar

Deoxyribose sugar is an essential component of the nucleotide structure in DNA. This sugar is a five-carbon molecule, distinguished from ribose by the absence of one oxygen atom at the 2' position, hence the "deoxy" in deoxyribose. This sugar plays a pivotal role in linking the phosphate group and the nitrogenous base.
The carbons of deoxyribose are numbered 1' through 5':

• The 1' carbon attaches to the nitrogenous base.
• The 3' carbon is where the next nucleotide's phosphate group binds.
• The 5' carbon is bonded to the current nucleotide's phosphate group.

This unique linkage provides the backbone of the DNA, facilitating the directional flow from the 5' end to the 3' end. Deoxyribose's structural arrangement allows DNA to maintain its functional and structural integrity while protecting the genetic information within each cell.