Molecular Basis of Genetic Inheritance and DNA Function
Types of Biological Reproduction
Sexual reproduction is performed by specialized cells called gametes. This process involves two individuals, where each one contributes sex gametes from the progenitor. In contrast, asexual reproduction involves no gametes and only one parent from which the offspring originate.
The Role of Genetic Information
Certain cellular components contain the instructions for each organism to develop its own characteristics of its kind. This information, known as genetics, is contained in a substance called deoxyribonucleic acid (DNA), which is localized in chromosomes within the cell nucleus. DNA is the material carrier of genetic genes.
Chemical Composition of DNA
DNA is a chemical that belongs to the group of nucleic acids. Specifically, the constituents of DNA are nucleotides. Every nucleotide is made by the union of:
- One molecule of phosphoric acid
- One monosaccharide (deoxyribose)
- One nitrogenous base (adenine A, guanine G, cytosine C, and thymine T)
In these pairings, A = T and C = G. The nucleotides join together to form long chains of nucleic acids, where phosphoric acid joins two consecutive monosaccharide nucleotides.
The Watson and Crick Model
According to the model of Watson and Crick, each DNA molecule is composed of two long nucleotide chains that are parallel and wound around an axis, forming a double helix. Genetic information resides in the specific order of the nucleotides in the DNA.
DNA Duplication and Replication
For daughter cells to receive the same genetic information as the mother cells, exact copies of the DNA must be made. This process, called DNA duplication or replication, starts with the unwinding and separation of the two chains that form the molecular structure. Each chain serves as a template for the synthesis of another string due to the coupling of additional nitrogenous bases. The result is the formation of two daughter DNA molecules that are exactly alike. Through DNA mirroring, genes are passed down through families.
DNA and Protein Synthesis
DNA carries information on how amino acids (the molecules that form proteins) must be positioned. The difference between proteins is due to the placement of these amino acids. Each DNA fragment that governs the synthesis of one protein is called a gene, which is responsible for the appearance of a particular character. Protein synthesis is the process by which genetic information is expressed in cells.
The Function of RNA
In addition to DNA, all cells contain another nucleic acid: ribonucleic acid (RNA). Its composition is similar to DNA but with some differences: its nucleotides contain ribose instead of deoxyribose. Furthermore, instead of the nitrogenous base thymine, RNA has uracil (U). RNA consists of only a single nucleotide chain. DNA directs both RNA and protein production.
The Genetic Code
The order of nucleotides in the DNA of a gene determines the order of amino acids in the corresponding protein. This correspondence between amino acids and nucleotides is called the genetic code. It is a triplet code: each amino acid is determined by a group of three nucleotides called a triplet or codon.