Which best describes the structure of a dna molecule
The Correct Answer and Explanation is:
The structure of a DNA molecule is best described as a double helix.
Explanation:
DNA (deoxyribonucleic acid) is the molecule that carries genetic information in living organisms. Its structure was first described by James Watson and Francis Crick in 1953, with the help of X-ray diffraction data from Rosalind Franklin. The DNA molecule has a unique and intricate structure, often described as a double helix, which resembles a twisted ladder.
The DNA molecule is made up of two strands that run in opposite directions and are twisted around each other. These strands are composed of repeating subunits called nucleotides, each consisting of three components:
- A phosphate group
- A deoxyribose sugar molecule
- A nitrogenous base
The nitrogenous bases are the key to the genetic code and come in four varieties:
- Adenine (A)
- Thymine (T)
- Cytosine (C)
- Guanine (G)
The two strands of DNA are held together by hydrogen bonds between complementary nitrogenous bases: adenine pairs with thymine, and cytosine pairs with guanine. This complementary base pairing ensures the accurate transmission of genetic information during cell division.
The strands of DNA run in opposite directions, which is referred to as antiparallel orientation. One strand runs from the 5′ (5-prime) end to the 3′ (3-prime) end, while the other strand runs in the opposite direction, from 3′ to 5′. This orientation is crucial for the proper functioning of enzymes that replicate and transcribe DNA.
The two intertwined strands of DNA form a right-handed double helix, giving the molecule its characteristic twisted structure. This helical shape is stabilized by hydrophobic interactions between the stacked nitrogenous bases inside the helix and hydrogen bonds between the complementary base pairs. The double helix structure of DNA is vital for its ability to store and transmit genetic information in cells.