Question

Draw the full structure of the DNA dinucleotide AG.

Short answer

Draw adenine and guanine, attach them to deoxyribose sugars, connect sugars via phosphate groups.

Step-by-step solution

Understand DNA Nucleotide Structure

Each nucleotide in DNA consists of three components: a phosphate group, a sugar molecule (deoxyribose), and a nitrogenous base. To draw the dinucleotide AG, we need to carefully connect these components.

Identify the Nitrogenous Bases

The nitrogenous bases for the dinucleotide AG are adenine (A) and guanine (G). Adenine and guanine are purines, which means they have a double-ring structure.

Draw the Sugar and Phosphate Backbone

Start by drawing the sugar-phosphate backbone. Each nucleotide has a deoxyribose sugar connected to a phosphate group. Connect the 5' carbon of one deoxyribose sugar to the phosphate group, and link this phosphate to the 3' carbon of the next nucleotide's deoxyribose sugar.

Attach the Nitrogenous Bases

Attach the adenine base to the 1' carbon of the first deoxyribose sugar and the guanine base to the 1' carbon of the second deoxyribose sugar. Ensure these bases are correctly oriented facing each other across the sugar-phosphate backbone.

Connect the Nucleotides

Link the 3' carbon of the adenine nucleotide's sugar to the phosphate group of the guanine nucleotide's sugar to complete the dinucleotide structure. This forms a phosphodiester bond, which is typical in DNA structure.

Key concepts

Nucleotide Components

DNA, known as deoxyribonucleic acid, is made up of simpler units called nucleotides. Nucleotides are the building blocks of DNA, and each one contains three critical components:

• **Phosphate Group**: This is a phosphorus atom bonded to four oxygen atoms. The phosphate group is crucial because it connects to the sugar of the next nucleotide, forming a chain.
• **Sugar Molecule**: In DNA, the sugar is called deoxyribose. It is a five-carbon sugar, which provides a framework around which the nucleotide components are organized.
• **Nitrogenous Base**: There are four main bases in DNA—adenine (A), thymine (T), cytosine (C), and guanine (G). These bases are responsible for encoding genetic information.

Understanding these components is important because each nucleotide connects with others to form the long, double-helix structure of DNA. The unique sequences of the nitrogenous bases enable DNA to store vast amounts of information.

Purine Bases

In DNA, the nitrogenous bases can be divided into two categories: purines and pyrimidines. The purine bases include adenine (A) and guanine (G). Both are characterized by their double-ring structure.

The double-ring structure of purines makes them larger compared to pyrimidines, which only have a single ring. These bases are essential because they pair with specific pyrimidine bases through hydrogen bonds, allowing the DNA strands to hold together in a precise double-helix shape.

• Adenine (A) pairs with thymine (T) in DNA.
• Guanine (G) pairs with cytosine (C).

This pairing is crucial for DNA replication and the transmission of genetic information from one generation to the next. By accurately pairing these bases, cells can duplicate DNA faithfully.

Sugar-Phosphate Backbone

The structure of DNA is supported by a sugar-phosphate backbone. This backbone is essential because it provides structural stability and integrity to the DNA molecule.

The backbone is composed of alternating deoxyribose sugar and phosphate groups. These components form a continuous chain through strong covalent bonds. Here's how they are connected:

• The sugar, deoxyribose, has five carbon atoms, labeled as 1'-5'.
• The phosphate group is attached to the 5' carbon of one sugar and links to the 3' carbon of the next sugar.

This 5' to 3' orientation is critical. It dictates the direction in which DNA is read and replicated. The continuity of the sugar-phosphate backbone ensures that the DNA's structure remains consistent and protected while carrying genetic information along its length.

Phosphodiester Bond

A key feature in DNA's structure is the type of bond that links its nucleotides together, known as the phosphodiester bond. These bonds are essential to the formation of the DNA's sugar-phosphate backbone.

The phosphodiester bond is formed through a reaction between the hydroxyl group on the 3' carbon of one deoxyribose sugar and the phosphate group attached to the 5' carbon of another sugar. This reaction releases a molecule of water, exemplifying a dehydration synthesis process.

• This bond makes the DNA stable and resilient, allowing it to withstand the various forces and conditions it may encounter within the cell.
• The strength of the phosphodiester bond makes it challenging to break under normal conditions, protecting DNA from degradation.

By maintaining this robust linkage, the DNA can effectively store genetic information over long durations without losing its integrity. Each bond connects sequential nucleotides, forming a continuous strand of genetic information.