Question

Describe the structure of DNA. Where are the bases, sugars, and phosphates in the structure? Which bases are complementary to one another? How are they held together in the double helix of DNA?

Short answer

DNA is a double helix structure composed of two chains consisting of nitrogenous bases, sugars (deoxyribose), and phosphates. The bases form the inner "rungs" of the ladder, with adenine (A) pairing with thymine (T) and guanine (G) pairing with cytosine (C) through hydrogen bonds. The sugars and phosphates form the backbone of the DNA chain, connected through covalent bonds. This combination of forces provides stability to the DNA molecule and maintains its double helix structure.

Step-by-step solution

Overview of DNA structure

DNA (Deoxyribonucleic Acid) is a molecule made up of two long, twisted chains that consists of four types of nitrogenous bases, sugars, and phosphates. It is arranged in a double helix structure, which resembles a twisted ladder.

Components of DNA

DNA is composed of three main components: 1. Nitrogenous bases: These are adenine (A), guanine (G), cytosine (C), and thymine (T). 2. Sugars: In DNA, the sugar is deoxyribose. 3. Phosphates: These are phosphate groups that connect the deoxyribose sugar molecules.

Positions of the bases, sugars, and phosphates

The positions of these components in the DNA structure can be described as follows: 1. Nitrogenous bases: These are located on the inner part of the DNA double helix, facing each other and forming the "rungs" of the ladder. 2. Sugars: Sugars are attached to the nitrogenous bases and form the backbone of the DNA chain. 3. Phosphates: Phosphates are also part of the backbone, connecting the deoxyribose sugar molecules in a chain.

Complementary base pairing

In the DNA structure, the nitrogenous bases pair up with a specific complement on the opposite strand. Adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C). This pairing is known as complementary base pairing, and it ensures that the genetic information is preserved accurately during replication.

Holding the double helix structure together

The double helix structure of DNA is held together by two forces: 1. Hydrogen bonds: The complementary nitrogenous bases (A-T and G-C) are held together by hydrogen bonds, forming the "rungs" of the ladder. 2. Covalent bonds: The sugar and phosphate molecules in the backbone are connected through covalent bonds. These bonds give the DNA molecule its stability and enable it to maintain its twisted, ladder-like structure, known as a double helix.

Key concepts

Deoxyribonucleic Acid

Deoxyribonucleic acid, or DNA, is the fundamental hereditary material present in all living organisms. It contains the instructions needed for an organism to develop, survive, and reproduce. These instructions are found within the sequence of nitrogenous bases along the DNA strands.

Imagine DNA as a long, spiral staircase that holds the secrets of life. Its structure is like a twisted ladder known as the double helix. The double helix provides a stable framework for the molecule while facilitating the storage and transmission of genetic information across generations.

Complementary base pairing

The rungs of the DNA ladder are formed by pairs of nitrogenous bases, connected in a strict pattern known as complementary base pairing. This means adenine (A) always pairs with thymine (T), and guanine (G) with cytosine (C). This precise pairing mechanism ensures the DNA's double helix is uniform in width and that genetic information can be copied accurately during cell division.

The elegance of complementary base pairing lies in its simplicity and efficiency. When cells divide, the DNA unwinds and each strand serves as a blueprint for a new complementary strand, guaranteeing that each new cell has an exact copy of the DNA.

Double helix

Think of the double helix structure as the DNA's architectural blueprint. It features two strands coiled around each other, providing both stability and flexibility. This formation is paramount for DNA's functions, such as replication and repairing.

The intertwined shape also enables the compact storage of long DNA molecules within the tiny confines of a cell nucleus. If unraveled and stretched out, the DNA from just one human cell would be approximately two meters long! Yet, in its double helix form, it's compact enough to fit neatly inside the microscopic space.

Nitrogenous bases

The secret to DNA's function lies in its four nitrogenous bases: adenine (A), cytosine (C), guanine (G), and thymine (T). These bases are the alphabet of life, spelling out the genetic instructions through their specific order, or sequences, along the DNA strand.

The rules of base pairing—A with T and G with C—ensures that the helical DNA structure maintains a consistent width throughout its length. Also, the hydrogen bonds that form between these bases are not as strong as covalent bonds, allowing them to easily unzip during DNA replication and transcription. Despite their seeming fragility, these bonds are precise and resilient, ensuring the integrity of the genetic code is preserved with high fidelity.