Question

In a DNA molecule, the double helix is held together by hydrogen bonds. How many hydrogen bonds are between a guanine (G) base and a cytosine (C) base in DNA?

Short answer

There are three hydrogen bonds between a guanine (G) base and a cytosine (C) base.

Step-by-step solution

Identify Base Pairs in DNA

In DNA, there are four types of nitrogenous bases: adenine (A), thymine (T), guanine (G), and cytosine (C). These bases form pairs to connect the two strands of the DNA double helix. Guanine (G) always pairs with cytosine (C), while adenine (A) pairs with thymine (T).

Understand Hydrogen Bonding Between Base Pairs

The pairing of bases is held together by hydrogen bonds. Adenine and thymine form two hydrogen bonds, whereas guanine and cytosine form three hydrogen bonds.

Determine the Number of Hydrogen Bonds

Since guanine (G) and cytosine (C) pair together, there are three hydrogen bonds between them. This property helps stabilize the DNA structure more than the adenine and thymine pair due to the additional bond.

Key concepts

Nitrogenous bases

In the DNA molecule, nitrogenous bases serve as the fundamental building blocks. These bases are essential for the genetic information coding. There are four main types of nitrogenous bases in DNA: adenine (A), thymine (T), guanine (G), and cytosine (C). These bases are known as 'complementary' bases because they pair in specific ways:

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

This specific pairing is crucial to maintaining the DNA's structure and ensuring accurate genetic information transmission. Each pair connects the two strands of the DNA double helix through hydrogen bonds, forming a stable structure. The specific pairing rules, known as "Chargaff's rules," ensure that DNA replicates precisely during cell division. Imagine these bases as letters in a genetic alphabet, spelling out the instructions for every living organism.

Guanine-Cytosine Pairing

Guanine-cytosine pairing is a vital aspect of the DNA structure. Among the nitrogenous bases, guanine and cytosine have a special connection because they form a pair through three hydrogen bonds. This three-bond connection is:

• Stronger and more stable than the adenine-thymine pair, which has only two hydrogen bonds.
• Crucial for maintaining the integrity and stability of the DNA molecule.

The increased number of hydrogen bonds in guanine-cytosine pairs means that regions of the DNA with higher G-C content are more stable under conditions that might otherwise disrupt DNA strands. This quality is particularly important in the areas of DNA that code for essential functions or in organisms that must survive extreme environments. In essence, the guanine-cytosine pairing is like extra glue holding the DNA strands together, ensuring the molecule's robustness.

DNA Structure

DNA is famous for its double helix structure. This shape is like a twisted ladder – the sugar-phosphate backbones form the sides, while the nitrogenous bases form the rungs, held together by hydrogen bonds. Understanding its structure helps in grasping how DNA functions:

• The helical shape allows for compact storage of genetic information.
• The complementary base-pairing ensures accurate replication during cell division.
• The sequence of bases encodes genetic instructions crucial for life.

The double helix model, proposed by James Watson and Francis Crick, revolutionized the field of genetics. This specific arrangement allows cells to store considerable amounts of information efficiently and transcribe it to create proteins necessary for life. Each time a cell divides, the DNA unzips the helical strands and replicates, making sure each new cell has identical genetic instructions. Simply put, DNA's structure is fundamental to life's processes, encoded with the data necessary for every organism to function.