Question

Draw the full structure of the RNA dinucleotide UA.

Short answer

Draw ribose sugars, attach uracil and adenine, and connect them via a phosphodiester bond.

Step-by-step solution

Identify the RNA Bases

RNA consists of four different nucleobases: adenine (A), uracil (U), cytosine (C), and guanine (G). For UA, we are dealing with uracil and adenine.

Draw the Ribose Sugar

RNA nucleotides are made up of a ribose sugar. Draw the ribose sugar, which is a five-carbon sugar with OH groups on the 2' and 3' carbons and a substituent at the 1' carbon where the base will attach.

Attach Uracil to the Ribose

Attach uracil to the ribose sugar by forming a glycosidic bond between the 1' carbon of the sugar and the nitrogen atom in position 1 of the uracil base. Uracil has a structure similar to thymine, with a double bond in the positions 4 and 5 and carbonyl groups at positions 2 and 4.

Phosphodiester Bond Formation

Form a phosphodiester bond between the 3' carbon of the ribose sugar of uridine (with uracil attached) and the 5' phosphate group of the second ribose sugar, which will connect uracil to adenine. This phosphate group forms a bridge between two sugars in the dinucleotide.

Attach Adenine to the Ribose

For the second nucleotide, connect adenine to the ribose sugar. The glycosidic bond will form between the 1' carbon of the second ribose and the nitrogen at position 9 on the adenine molecule. Adenine has a double-ring structure with positions containing nitrogen at 1, 3, 7, and 9.

Key concepts

Nucleotide

A nucleotide is a fundamental building block of RNA. It consists of three main components: a nitrogenous base, a five-carbon sugar, and a phosphate group. The nitrogenous bases in RNA are adenine (A), uracil (U), guanine (G), and cytosine (C).
A nucleotide in RNA is formed by linking these components together in a specific structure. The phosphate group connects to the 5' carbon of the ribose sugar, while the nitrogenous base attaches to the 1' carbon of the ribose, forming a linkage called a glycosidic bond.
Each nucleotide connects to another through phosphodiester bonds, forming the RNA strand's backbone. Understanding nucleotides helps in comprehending how RNA can encode genetic information and participate in protein synthesis.

Ribose Sugar

Ribose sugar is an essential component of RNA and holds the entire structure together. It is a pentose, or five-carbon sugar, characterized by the presence of hydroxyl groups (-OH) at the 2' and 3' positions.
This is crucial because the 2' hydroxyl group differentiates RNA from DNA, which contains deoxyribose sugar without the 2' hydroxyl. The ribose sugar forms the backbone of RNA by connecting with both the nitrogenous base and phosphate group.
At the 1' carbon, the base attaches to the ribose, and at the 5' carbon, the phosphate group links, allowing nucleotide chains to link through phosphodiester bonds. The arrangement and bonding of ribose sugar are essential for RNA’s structure and function.

Phosphodiester Bond

Phosphodiester bonds are the links that hold nucleotides together within the RNA strand. They form between the 3' carbon atom of one ribose sugar and the 5' phosphate group of the next ribose.
The creation of phosphodiester bonds results in a nucleotide chain known as a nucleic acid strand, essential for RNA structure. These bonds provide stability and strength to the RNA backbone.
This linkage ensures that the genetic message encoded in RNA remains intact and accurately transmitted during processes like protein synthesis. Understanding how phosphodiester bonds function is vital for grasping RNA’s role in genetic coding and expression.

Glycosidic Bond

A glycosidic bond is a type of covalent bond that connects the ribose sugar to the nitrogenous base in a nucleotide. In RNA, this bond forms between the 1' carbon of the ribose and a nitrogen atom in the base.
For example, in the nucleotide UA, uracil is attached via a glycosidic bond to the ribose in uridine, and adenine connects to ribose similarly. These bonds are crucial as they help define the nucleotide's identity and properties.
The strength and specificity of glycosidic bonds allow the RNA molecule to maintain its structural integrity while carrying the genetic code. This facilitates various important cellular processes including transcription and translation.