True about DNA structure: (PGI Nov 2010)
**Core Concept:** DNA structure and its key components.
DNA stands for Deoxyribonucleic Acid, which is a long, twisted, and coiled molecule that carries the genetic instructions for life. It consists of two strands that are twisted around each other to form a double helix structure. The DNA molecule is composed of four nucleotides: adenine (A), thymine (T), guanine (G), and cytosine (C). These nucleotides are linked together in pairs: A always pairs with T, and G always pairs with C. This pairing is called base pairing and is crucial for the proper functioning of DNA as a genetic code.
**Why the Correct Answer is Right:** DNA is a double helix structure, where the two strands are held together by hydrogen bonds between complementary base pairs (A-T and G-C). This unique structure allows DNA to replicate itself during cell division, ensuring that genetic information is accurately passed on to the next generation of cells. The correct answer refers to the double helix structure and base pairing, which are essential for DNA replication and gene expression.
**Why Each Wrong Option is Incorrect:**
A. False: DNA is not a single chain; it is a double helix structure.
B. False: DNA does not consist of a single nucleotide type; it is composed of four nucleotides.
C. False: DNA does not only consist of sugar and phosphate groups; it also contains the four nucleotides.
D. False: DNA does not replicate itself continuously; it undergoes replication during cell division.
**Clinical Pearl:** Understanding the structure and function of DNA is essential for medical professionals, as it is the basis of genetics and heredity. Knowledge of this core concept will enable physicians to discuss genetic disorders, drug therapies, and medical interventions that involve DNA and gene manipulation.