nükleosit

A nucleotide is a molecule composed of three parts: a phosphate group, a five-carbon sugar called a pentose, and a nitrogenous base. These nitrogenous bases are classified into two types: purines (adenine and guanine) and pyrimidines (cytosine, thymine, and uracil). In DNA, the sugar is deoxyribose, and the bases are adenine, guanine, cytosine, and thymine. In RNA, the sugar is ribose, and the bases are adenine, guanine, cytosine, and uracil.

Nucleotides are the fundamental building blocks of nucleic acids, namely DNA and RNA. DNA, or deoxyribonucleic acid, is a double-stranded helix that carries the genetic instructions for the development, functioning, growth, and reproduction of all known organisms. RNA, or ribonucleic acid, is typically single-stranded and plays various roles in gene expression, including messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). The sequence of nucleotides in DNA and RNA determines the genetic code.

Beyond their role in nucleic acids, nucleotides also have other crucial functions in the body. Adenosine triphosphate (ATP) is the primary energy currency of the cell, powering numerous biochemical reactions. Cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) act as important second messengers in cellular signaling pathways, mediating responses to hormones and other extracellular signals. Nucleotides are also components of coenzymes such as nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD), which are essential for metabolic processes like cellular respiration and photosynthesis.