DNA is made up of molecules called nucleotides. Each nucleotide contains a phosphate group, a sugar group and a nitrogen base. The four types of nitrogen bases are adenine (A), thymine (T), guanine (G) and cytosine (C). The order of these bases is what determines DNA’s instructions, or genetic code. Human DNA has around 3 billion bases, and more than 99 percent of those bases are the same in all people.
Similar to the way the order of letters in the alphabet can be used to form a word, the order of nitrogen bases in a DNA sequence forms genes, which in the language of the cell, tells cells how to make proteins. Nucleotides are attached together to form two long strands that spiral to create a structure called a double helix. If you think of the double helix structure as a ladder, the phosphate and sugar molecules would be the sides, while the bases would be the rungs. The bases on one strand pair with the bases on another strand: adenine pairs with thymine, and guanine pairs with cytosine.
DNA molecules are long — so long, in fact, that they can’t fit into cells without the right packaging. To fit inside cells, DNA is coiled tightly to form structures we call chromosomes. Each chromosome contains a single DNA molecule. Humans have 23 pairs of chromosomes, which are found inside the cell’s nucleus.
GPSC Notes brings Prelims and Mains programs for GPSC Prelims and GPSC Mains Exam preparation. Various Programs initiated by GPSC Notes are as follows:-- GPSC Mains 2024 Tests and Notes Program
- GPSC Prelims Exam 2024- Test Series and Notes Program
- GPSC Prelims and Mains 2024 Tests Series and Notes Program
- GPSC Detailed Complete Prelims Notes