Question

What is the structure of DNA? How does it differ from that of RNA?

Short answer

Question: Explain the structure of DNA and compare it with the structure of RNA. Answer: DNA, or Deoxyribonucleic Acid, is a double helix-shaped molecule made up of nucleotides, each consisting of a deoxyribose sugar, a phosphate group, and one of the four nitrogenous bases (Adenine, Guanine, Cytosine, or Thymine). In contrast, RNA, or Ribonucleic Acid, is typically single-stranded and consists of nucleotides with a ribose sugar, a phosphate group, and one of the nitrogenous bases (Adenine, Guanine, Cytosine, or Uracil instead of Thymine). The main differences between DNA and RNA are the double helix structure of DNA, the sugar backbone (deoxyribose in DNA and ribose in RNA), and the replacement of Thymine with Uracil in RNA as a nitrogenous base.

Step-by-step solution

DNA Structure Overview

DNA stands for Deoxyribonucleic Acid and is a double helix-shaped molecule made up of nucleotides. Each nucleotide consists of a sugar molecule known as deoxyribose, a phosphate group, and one of the four nitrogenous bases: Adenine (A), Guanine (G), Cytosine (C), or Thymine (T). The nucleotides are connected by phosphodiester bonds while the nitrogenous bases on each strand form hydrogen bonds with their complementary bases on the other strand (A pairs with T, G pairs with C).

RNA Structure Overview

RNA stands for Ribonucleic Acid and, like DNA, is a polymer made up of nucleotides. Each nucleotide in RNA also consists of a sugar, a phosphate group, and one of the nitrogenous bases. However, RNA's sugar molecule is a ribose instead of deoxyribose. The nitrogenous bases in RNA are Adenine (A), Guanine (G), Cytosine (C), and Uracil (U) – instead of Thymine (T). RNA is typically single-stranded, but can fold into complex structures as a result of base pairing within the same strand.

Identifying Differences Between DNA and RNA

There are three main differences between DNA and RNA: 1. DNA has a double helix structure, while RNA is usually single-stranded. 2. DNA has a deoxyribose sugar backbone, while RNA has a ribose sugar backbone (the difference being an extra oxygen atom in the RNA sugar). 3. Thymine (T) is one of the nitrogenous bases in DNA, while Uracil (U) replaces Thymine (T) in RNA. In both molecules, Adenine (A) pairs with its complementary base, Thymine (T) in DNA, and Uracil (U) in RNA.

Key concepts

DNA Double Helix

When we talk about the structure of DNA, we often refer to its distinctive shape, known as the double helix. This can be visualized as a twisted ladder where the sides of the ladder are a repeated pattern of sugar and phosphate molecules – this is the sugar-phosphate backbone. The rungs of the ladder are the nitrogenous bases.

DNA's double-helix structure allows it to store biological information in a compact and stable form. The two strands of the helix run in opposite directions (antiparallel), and the bases on one strand pair with those on the other strand: Adenine with Thymine and Guanine with Cytosine. These base pairs are held together by hydrogen bonds, allowing for easy unzipping during processes like replication and transcription.

RNA Structure

RNA, though similar in composition to DNA, has a markedly different structure. It is primarily single-stranded and doesn't form a double helix. Instead, RNA molecules can fold into a variety of complex three-dimensional shapes. These structures are possible because of short double-stranded regions formed by hydrogen bonding between complementary bases within the same RNA molecule.

The versatility in RNA's structure allows it to perform many functions in the cell, from being a messenger that carries genetic information for protein synthesis, to catalyzing chemical reactions as a ribozyme. Its structure is less stable than DNA but perfectly suits the temporary roles RNA plays.

Nucleotides

Nucleotides are the basic building blocks of both DNA and RNA. Each nucleotide is composed of three parts: a 5-carbon sugar, a phosphate group, and a nitrogenous base. The sugar-phosphate backbone is formed by the sugars and phosphate groups of adjacent nucleotides bonding together. This creates a chain that is both strong and flexible.

Function of Nucleotides

In DNA, nucleotides store genetic information, while in RNA, they are used to transfer and express that information as proteins. Moreover, the sequence of these nucleotides encodes the genetic instructions for the development and functioning of living organisms.

Nitrogenous Bases

The nitrogenous bases are critical for the storage of genetic information. There are four main bases in DNA: Adenine (A), Guanine (G), Cytosine (C), and Thymine (T); in RNA, Thymine is replaced by Uracil (U).

Base Pairing Rules

Adenine always pairs with Thymine in DNA and with Uracil in RNA, while Guanine pairs with Cytosine. This pairing is what ensures the accurate transfer of genetic information when cells divide and is key to the synthesis of proteins that perform various functions in the body.

Sugar-Phosphate Backbone

The sugar-phosphate backbone forms the framework of both DNA and RNA molecules. In DNA, the backbone is made with deoxyribose sugars, which lack one oxygen atom that is present in the ribose sugars of RNA. This seemingly small difference is elemental, as it gives DNA more stability, making it the preferred storage form of genetic material in cells.

The sequence of the sugars and phosphates is the same in both DNA and RNA, providing the necessary continuity and allowing the nitrogenous bases to project inward towards the helix axis in DNA, or towards the center of the molecule in RNA, to engage in hydrogen bonding and carry on genetic coding duties.