Problem 30 - Anatomy and Physiology of Animals

Question

In DNA, nucleotide bonding forms a compound with a characteristic shape known as a(n) ___________ . a. beta chain b. pleated sheet C. alpha helix d. double helix

Step-by-Step Solution

Answer

Double helix (d) is the shape formed by nucleotide bonding in DNA.

Step 1: Understanding Nucleotide Bonding

To solve this problem, we need to identify the structure formed by nucleotide bonding in DNA. Nucleotides in DNA pair specifically through hydrogen bonding, leading to a specific three-dimensional configuration.

Step 2: Identifying Nucleotide Structures in DNA

The structure formed by the base pairing of nucleotides in DNA leads to a specific shape known as the double helix. This is a twisted ladder-like structure where the sugar-phosphate backbones form the sides, and paired bases form the rungs.

Step 3: Evaluating the Options

We need to choose from the options given: a. beta chain, b. pleated sheet, c. alpha helix, d. double helix. The only option that describes the characteristic shape of DNA is the double helix.

Key Concepts

Nucleotide Bonding

Nucleotide bonding is the process by which individual nucleotides join to form the backbone of DNA. Each nucleotide consists of three components: a sugar molecule, a phosphate group, and a nitrogenous base. The sugar and phosphate groups link together, creating a chain through covalent bonds, known as phosphodiester bonds. These bonds are strong and form the sturdy sugar-phosphate backbone of the DNA structure.
This backbone supports the sequence of nitrogenous bases, which extend inward like the rungs of a ladder. This arrangement is crucial because it allows the precise and specific interactions essential for the DNA's information-carrying function.

Hydrogen Bonding in DNA

Hydrogen bonding is a type of weak chemical bond, vital to the structure of DNA. It occurs between nitrogenous bases, which are part of the nucleotides forming the DNA. The DNA's double helix structure is stabilized by these hydrogen bonds.
DNA has four types of nitrogenous bases: adenine (A), thymine (T), cytosine (C), and guanine (G). Hydrogen bonds form between complementary bases, with adenine pairing with thymine through two hydrogen bonds, and cytosine pairing with guanine through three hydrogen bonds.
This complementary base pairing enables the double helix to maintain a uniform shape, thereby supporting the replication and transcription of genetic information.

Double Helix Structure

The double helix structure is the iconic shape of the DNA molecule, resembling a twisted ladder. This shape is a result of nucleotide bonding and specific pairing of bases. It was famously discovered by James Watson and Francis Crick in 1953.
The double helix features two parallel strands running in opposite directions, known as antiparallel strands. This means one strand runs 5' to 3', while the opposite strand runs 3' to 5'. The sugar-phosphate backbone forms the helical sides; meanwhile, internally paired bases constitute the "rungs" of the ladder.
This structural configuration allows for the compact and efficient packaging of DNA within cells, and its stability enables reliable genetic inheritance across generations.

Base Pairing in DNA

Base pairing in DNA refers to the specific hydrogen bonds formed between complementary nucleotide bases. Due to specific chemical properties, adenine pairs with thymine and cytosine pairs with guanine. This pairing mechanism ensures accurate genetic replication.
Base pairing is guided by the rules known as Chargaff's rules, which state that the amount of adenine equals thymine, and the amount of cytosine equals guanine in a DNA molecule. This precise matching is essential not only for maintaining the structure of the DNA double helix but also for the correct reading of genetic code during processes like DNA replication and transcription.
Understanding base pairing is fundamental in studying genetics, as it underpins the mechanisms of gene expression and heredity.