Question

Discuss the role of hydrogen bonding in (a) collagen and (b) DNA.

Short answer

Hydrogen bonds stabilize collagen's triple helix and DNA's double helix by linking chains in collagen and nucleotide pairs in DNA.

Step-by-step solution

Understanding Collagen Structure

Collagen is a protein found in connective tissues, and it has a triple helical structure. Each helix is made up of three polypeptide chains that are tightly packed to form a left-handed helix. Hydrogen bonding is essential in maintaining this structure.

Explaining Hydrogen Bonding in Collagen

In collagen, hydrogen bonds stabilize the triple helix by forming between the backbone amide groups of the polypeptide chains. These bonds occur primarily between the NH group of Glycine (which constitutes every third residue) and the C=O group of Proline residues on adjacent chains, helping to hold the helices together tightly and providing structural strength.

Understanding DNA Structure

DNA has a double helix structure composed of two polynucleotide strands twisted around each other. The sides of the helix are formed by a sugar-phosphate backbone, while the interior contains paired nitrogenous bases.

Explaining Hydrogen Bonding in DNA

In DNA, hydrogen bonds play a crucial role in base-pairing between the two strands of the helix. Adenine (A) pairs with Thymine (T) via two hydrogen bonds, and Cytosine (C) pairs with Guanine (G) via three hydrogen bonds. These bonds provide the stability necessary to maintain the double helix structure and allow the strands to separate during processes such as replication and transcription.

Key concepts

Collagen Structure

Collagen is a vital structural protein predominantly found in various connective tissues. This protein is characterized by its unique triple helical structure. Imagine it as three individual polypeptide chains that are twisted together to form a robust left-handed helix. This configuration is meticulously held together and stabilized by hydrogen bonds.
These hydrogen bonds predominantly occur between the backbone amide groups of these chains. The repetitive sequence in collagen, usually Glycine-X-Y, where X and Y are often Proline or Hydroxyproline, facilitates this bonding. Specifically, Glycine, being a small amino acid, fits perfectly within the helix and allows for tight packing.

• Hydrogen bonds occur between the NH group of Glycine and the C=O group of an adjacent Proline residue.
• This bonding is repeated along the length of the collagen molecule.
• These interactions imbue collagen with its tensile strength, crucial for its role in tissues like tendons and skin.

The integrity provided by these bonds is essential for collagen's structural role, ensuring it maintains form and function under stress.

DNA Double Helix

The DNA double helix is one of biology's most iconic structures, consisting of two complementary strands coiled around each other. These strands are composed of nucleotides that include a phosphate group, a sugar molecule, and a nitrogenous base.
The sides of the helix, often likened to a ladder's rails, are made of alternating sugar and phosphate molecules, while the rungs consist of paired nitrogenous bases. The twist in the double helix is stabilized by hydrogen bonds.

• The nitrogenous bases include Purines (Adenine, Guanine) and Pyrimidines (Thymine, Cytosine).
• Hydrogen bonds form between the paired bases, Adenine with Thymine and Cytosine with Guanine.
• This base-pairing and the accompanying hydrogen bonds are critical in maintaining the integrity of the genetic material.

Hydrogen bonding, therefore, plays a fundamental role in the stability and function of DNA, allowing it to maintain its specific sequence needed for genetic storage and information transfer.

Protein Stabilization

Proteins are the workhorses of cells, and their function is highly dependent on their structure. The three-dimensional shape of a protein, termed its tertiary structure, is stabilized by various types of interactions, with hydrogen bonding being one of the most critical.
In proteins, hydrogen bonds occur between different parts of the polypeptide chain or between different chains altogether. These bonds contribute significantly to maintaining the protein's structure and, consequently, its function.

• In the secondary structure, such as alpha-helices and beta-pleated sheets, hydrogen bonds form between the carbonyl oxygen and amide hydrogen of the peptide backbone.
• These interactions are responsible for the formation of the regular, repetitive structures seen in many proteins.
• Hydrogen bonding can also occur with side chains, assisting in folding the protein into its final stable structure.

Overall, hydrogen bonds are indispensable in protein folding and stability, helping the molecule maintain its desired shape to perform specific biological functions effectively.

Base-Pairing

Base-pairing is a foundational concept in molecular biology, crucial for the structure and function of nucleic acids such as DNA. It involves specific hydrogen bonding between pairs of nitrogenous bases, which form the steps of the DNA ladder.
These specific pairings are rules-driven: Adenine pairs with Thymine, and Cytosine pairs with Guanine. These base-pairs are stabilized by hydrogen bonds:

• Adenine and Thymine are connected by two hydrogen bonds.
• Cytosine and Guanine, however, form three hydrogen bonds, making this pair slightly more stable.

Through these pairings, DNA can replicate accurately, as each strand serves as a template for creating a new, complementary strand. This precise matching ensures that genetic information is faithfully transmitted across generations, underscoring the importance of hydrogen bonding in genetic fidelity and information transfer.