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Chapter 4: Problem 4

Describe the structure and complementary base pairing of DNA.

Short Answer

Expert verified
Answer: A nucleotide consists of three parts: a sugar molecule (deoxyribose), a phosphate group, and a nitrogen-containing base. The sugar and phosphate groups form the sugar-phosphate backbone, or sides of the DNA double helix ladder, while the nitrogen bases form the rungs. The two strands of the double helix are connected through hydrogen bonds between the nitrogen bases, following complementary base-pairing rules: adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G). This specific pairing ensures the DNA structure is stable and maintains its shape.

Step by step solution

01

Introduction to DNA structure

DNA, or deoxyribonucleic acid, is a molecule that carries genetic information in living organisms. The structure of DNA is a double helix, which resembles a twisted ladder. This shape is due to the fact that it is made up of two strands that run in opposite directions (anti-parallel) and are connected by complementary base pairs.
02

Basic components of DNA - nucleotides

DNA is made up of small subunits called nucleotides. Each nucleotide consists of three parts: a sugar molecule (deoxyribose), a phosphate group, and a nitrogen-containing base. There are four different nitrogen bases in DNA: adenine (A), guanine (G), cytosine (C), and thymine (T).
03

Formation of the DNA double helix

The double helix structure of DNA is formed by the interaction between the sugar-phosphate backbone and the nitrogen bases. The sugar (deoxyribose) and phosphate groups form the backbone or sides of the twisted ladder, while the nitrogen bases form the rungs. The phosphate group of one nucleotide is linked to the sugar molecule of the next nucleotide in a single strand through a covalent bond. This creates a long chain running in one direction, also called the 5' to 3' direction.
04

Complementary base-pairing rules

In the DNA double helix, the two strands are connected by hydrogen bonds between the nitrogen bases. This connection follows specific rules, called complementary base-pairing rules: adenine (A) always pairs with thymine (T), and cytosine (C) always pairs with guanine (G). The A-T and C-G base pairs form two hydrogen bonds and three hydrogen bonds, respectively. This specific base-pairing ensures that the DNA structure is stable and maintains its shape. To summarize, the DNA structure is a double helix formed from two strands connected by complementary base pairs. These strands are made up of nucleotides, which include a sugar, phosphate, and nitrogen base. The complementary base-pairing rules govern the formation of the DNA double helix and ensure its stability.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Nucleotides
In the world of genetics, nucleotides are the building blocks of DNA. Imagine them as the tiny pieces that, when connected together, create the complex molecule known as DNA. Each nucleotide is composed of three main parts: a sugar molecule (named deoxyribose), a phosphate group, and one of four nitrogen-containing bases. These bases are adenine (A), guanine (G), cytosine (C), and thymine (T).

Each component of a nucleotide has an important role:
  • The sugar and phosphate form a strong and stable "backbone" for the DNA strand.
  • The nitrogenous bases allow for specific interactions between the two DNA strands through pairing.
By linking together in long chains, nucleotides form a DNA strand, with the bases extending outwards. This clever design allows them to pair up precisely with complementary bases, giving rise to the complete structure of DNA.
Double Helix
DNA isn鈥檛 just a long straight ladder; it gracefully twists into a spiral known as the double helix. This structure is key to DNA's functionality and stability. Picture a ladder that has been gently twisted, forming a coil or spiral. This double helix shape arises due to the interaction of the nucleotide backbones that run along the sides of the ladder and the paired bases that act like rungs between these backbones.

The double helix consists of two strands of nucleotides that run in opposite directions, known as anti-parallel orientation.
  • The two strands spiral around a central axis, stabilizing the entire molecule.
  • Each twist of the helix contains about ten base pairs, snugly fitted into the groove of the spiral.
The shape of the double helix is not only beautiful but crucial for the efficient packing into chromosomes and proper cell replication.
Complementary Base Pairing
Complementary base pairing is the principle that allows DNA to maintain its double helix structure with a stable and reliable connection. This term describes how each base on one DNA strand pairs specifically with a complementary base on the opposite strand, much like lock and key.

The pairing follows these crucial rules:
  • Adenine (A) pairs only with Thymine (T), forming two hydrogen bonds.
  • Cytosine (C) pairs only with Guanine (G), forming three hydrogen bonds.
This complementary pairing is not random. It relies on the specific attractions and repulsions between the bases, ensuring that the DNA can be copied accurately during cell division. Any change in this pairing can result in mutations, highlighting its critical role in genetic fidelity.
Hydrogen Bonds
The stability and proper functioning of DNA are largely due to hydrogen bonds, a type of weak chemical bond that forms between the complementary bases on opposite strands. Despite being individually weak, many hydrogen bonds together create a stable connection between the DNA strands.

Here's how they work:
  • Each A-T pair forms two hydrogen bonds, just enough to keep them attached yet allow them to separate when necessary, as during replication or transcription.
  • Each C-G pair forms three hydrogen bonds, providing slightly more stability.
The cumulative strength of these bonds throughout the DNA molecule holds the two strands in their helical shape while allowing them to unzip easily when the cell needs to access the genetic information. This dynamic stability is essential for the replication processes that underpin life itself.

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Most popular questions from this chapter

DNA replicates by which of the following models? a. conservative b. semiconservative c. dispersive d. none of the above

Describe the organization of the eukaryotic chromosome.

Portions of eukaryotic mRNA sequence that are removed during RNA processing are ________. a. exons b. caps c. poly-A tails d. introns

The sequence one strand of a DNA double helix is: \(*\) ATGGCTACAA Beginning at the \(*\) end, what is the complimentary sequence?

The RNA components of ribosomes are synthesized in the ________. a. cytoplasm b. nucleus c. nucleolus d. endoplasmic reticulum
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