Pulsed Field Gel Electrophoresis (PFGE)


DNA, or deoxyribonucleic acid, is the molecule that carries the genetic information of all living organisms. DNA is composed of four types of nucleotides, which are the building blocks of DNA. Each nucleotide consists of a nitrogenous base (adenine, guanine, cytosine, or thymine), a sugar (deoxyribose), and a phosphate group. The nucleotides are linked together by covalent bonds between the sugar and phosphate groups, forming a long chain called a strand. Two strands of DNA are twisted around each other to form a double helix, which is stabilized by hydrogen bonds between the complementary bases on opposite strands. The sequence of bases on one strand determines the sequence of bases on the other strand, and thus the sequence of nucleotides on both strands encodes the genetic information.

DNA is organized into structures called chromosomes, which are located in the nucleus of eukaryotic cells or in the cytoplasm of prokaryotic cells. Each chromosome consists of a single, long molecule of DNA that is tightly coiled and wrapped around proteins called histones. The human genome contains 23 pairs of chromosomes, which collectively carry about 3 billion base pairs of DNA. Each chromosome has a specific number and shape that can be distinguished by staining and microscopy techniques.

DNA is replicated before cell division, so that each daughter cell inherits an identical copy of the genetic material from the parent cell. The process of DNA replication involves unwinding the double helix and separating the two strands by breaking the hydrogen bonds between them. Then, each strand serves as a template for synthesizing a new complementary strand by adding nucleotides according to the base-pairing rules. The result is two identical copies of the original DNA molecule, each consisting of one old and one new strand.

DNA is also transcribed into RNA, which is another type of nucleic acid that plays various roles in gene expression. RNA differs from DNA in having a ribose sugar instead of a deoxyribose sugar, and having uracil instead of thymine as one of the bases. RNA can be single-stranded or double-stranded, depending on its function and structure. The most common type of RNA is messenger RNA (mRNA), which carries the genetic information from DNA to the ribosomes, where it is translated into proteins. Proteins are the molecules that perform most of the biological functions in cells, such as catalyzing reactions, transporting substances, signaling pathways, and regulating gene expression.