Question

The number of hydrogen bonds formed between in the sequence of a stretch of a double helical DNA 5'ATGCCTAA3' is (a) 15 (b) 19 (c) 29 (d) 12

Short answer

The correct number of hydrogen bonds formed is not an option provided.

Step-by-step solution

Understand DNA Base Pairing

Double helical DNA consists of two strands that run in opposite directions. The bases on one strand pair with bases on the complementary strand. Adenine (A) pairs with Thymine (T) forming two hydrogen bonds, and Cytosine (C) pairs with Guanine (G) forming three hydrogen bonds.

Identify Pairing for the Given Sequence

Given the sequence 5'ATGCCTAA3', determine the complementary base on the opposite strand: A pairs with T, T pairs with A, G pairs with C, C pairs with G, C pairs with G, T pairs with A, A pairs with T, A pairs with T.

Count the Number of Each Pair Type

The complementary sequence will be 3'TACGGATT5'. Count each base pair: A-T pairs twice, T-A pairs twice, G-C pairs once, and C-G pairs twice.

Calculate the Total Hydrogen Bonds

Calculate the hydrogen bonds: Each A-T pair forms 2 hydrogen bonds: 4 (from 2 A-T pairs). Each T-A pair forms 2 hydrogen bonds: 4 (from 2 T-A pairs). Each G-C pair forms 3 hydrogen bonds: 3 (from 1 G-C pair), and each C-G pair forms 3 hydrogen bonds: 6 (from 2 C-G pairs). Total = 4 + 4 + 3 + 6 = 17.

Key concepts

Hydrogen Bonds

Hydrogen bonds play a vital role in the structure of DNA, providing stability to the iconic double helix shape. These bonds form between certain nitrogenous bases in the middle of the helix, ensuring that the two strands of DNA stick together securely.

In DNA, hydrogen bonds form between the complementary bases: Adenine (A) pairs with Thymine (T), and this pairing involves the formation of two hydrogen bonds. On the other hand, Guanine (G) pairs with Cytosine (C), which is slightly stronger due to the formation of three hydrogen bonds. These bonds are not as strong as covalent bonds, but their combined effect across the entire DNA molecule provides significant stability.

Hydrogen bonds are crucial for the replication and transcription processes. When DNA needs to replicate or transcribe, these bonds momentarily break, allowing the DNA strands to unwind and serve as templates. Once the process is done, the hydrogen bonds reform, restoring the structure of DNA. Understanding how hydrogen bonds work can help us comprehend more about genetic encoding and mutations.

Double Helix Structure

The double helix structure of DNA resembles a twisted ladder, a design that efficiently packs a large amount of genetic information in a compact form. This iconic structure was first identified by Watson and Crick, who described how two long strands of DNA wind around each other to form the helix.

The two strands of the double helix run in opposite directions, making them antiparallel. Each strand is composed of a sugar-phosphate backbone, with nitrogenous bases sticking out towards the center, where they pair with complementary bases from the opposite strand. This antiparallel orientation is crucial for the formation of stable hydrogen bonds between bases.

The double helix model facilitates replication and repair. Its design allows for easy separation of the strands, enabling enzymes to copy each strand's information accurately. These features make the double helix structure uniquely efficient for storing and replicating genetic data, ensuring that living organisms can reproduce and maintain genetic consistency across generations.

Complementary Base Pairing

Complementary base pairing is a fundamental principle governing DNA structure and function, ensuring accurate transmission of genetic information. This idea describes how specific bases on one strand of DNA pair with specific bases on the complementary strand.

In DNA, adenine (A) always pairs with thymine (T), and guanine (G) pairs with cytosine (C). This specific pairing is due to molecular shape and hydrogen bonding properties, which ensure that only these pairs fit together perfectly in the structure.

Complementary base pairing allows a single strand of DNA to act as a template for creating a new, complementary strand. This is vital for DNA replication, ensuring each new cell receives the exact genetic code. It also contributes to DNA repair mechanisms, where errors in the sequence can be identified and corrected by recognizing mispaired bases.

This concept also helps to explain how DNA can encode complex information and why mutations can have such a significant impact if the wrong base pair is incorporated during the replication process. Understanding complementary base pairing is essential for genetics, molecular biology, and understanding how genetic diseases occur.