DNA Structure, Function, and Mutations
DNA Composition
DNA is a biomolecule composed of carbon, hydrogen, oxygen, nitrogen, and phosphorus. It is a polynucleotide made of repeating units called nucleotides (deoxyribonucleotides). DNA stores and transmits hereditary information, forming the molecular basis of heredity.
Chemically, DNA consists of:
- A pentose sugar (deoxyribose).
- A nitrogenous base (adenine, guanine, cytosine, or thymine).
- A phosphate group.
DNA Structure
Primary Structure
The primary structure of DNA is the sequence of nucleotides in the chain.
Secondary Structure
The secondary structure is the double helix model proposed by Watson and Crick in 1953.
- Two antiparallel polynucleotide strands coil around the same axis.
- Nitrogenous bases are paired (A with T, G with C) via hydrogen bonds.
- The helix has a diameter of 2.0 nm and a distance of 0.34 nm between base pairs.
Mutations
Hugo de Vries introduced the term “mutation” in 1901 to describe a genetic change resulting in a new trait.
Types of Mutations
Genome Mutations
Affect the number of chromosomes (polyploidy, haploidy, aneuploidies).
Chromosome Mutations
Alter chromosome structure.
Gene Mutations
Change the nucleotide sequence.
Causes of Mutations
Spontaneous Mutations
Occur naturally.
Induced Mutations
Caused by mutagens.
Mutagens
- Physical Mutagens: Ionizing radiation (X-rays) and non-ionizing radiation (UV rays).
- Chemical Mutagens: Nitrous acid, alkylating agents, base analogs, intercalating substances.