[DNA passes on genetic information]
DNA carries genetic information that is passed down from parent to offspring, from cell to cell. DNA exists inside each of about 60 trillion cells in the bodies. The nucleus of a human cell is approximately 0.005-0.008 mm with it containing about 2 meters of DNA chain (approx. 6 billion pairs of bases).
The structure of DNA is represented as double helix, composed of biopolymer strands of nucleotides as seen in the diagram. There are four types of nucleic bases that constitute nucleotides, and the sequence of these bases determines the types of proteins and the volume and location for its production, resulting in varying physical characteristics in the nature of the materials.
DNA is condensed in body cells, wrapping around a type of bundled protein called histones, forming chromosomes. There are 23 pairs of chromosomes, coupling ones of maternal and paternal origins, in each cell (22 pairs of autosomes and 1 allosome). These are divided into X chromosomes and Y chromosomes. In humans, with the combination of XX creating a female individual while XY creates a male.
It is said, however, only 2% of the entire nucleobase will amount out of the 3 trillion that actually carries genetic coding in the chromosomes of the human DNA. The remaining parts are called non-coding regions, considered to be insignificant. However, recent findings suggest that this non-coding region contains some vital coding in humans such as regulating gene expressions.
Genes are located in specific positions in chromosomes, and research to decipher exact coding in the entire chromosome was pursued (the Genome Project) to draw up an atlas of human genome, also known as the Human Genome Map. Following such a development, there is now a post-human-genome project underway to initiate further explorations based on the findings.
Cells are the smallest unit of life in human activity. The continuation of life and growth depends entirely on cell division (self reproduction). As a cell divides to multiply, it needs to produce a copy of its DNA in order for the mother cell (original cell) to give it to it’s offspring (newly created cells). DNA duplication is thought to require an extraordinary amount of nucleotides. There are two methods of generating nucleotides within a human body, and nuclei reserve many nucleotides within themselves. It has been reported that this function to generate nucleotides dwindle in tandem with aging, suggesting a relationship between the decline of nucleotides and aging processes.
Our bodies are endowed with the “DNA repairing mechanism” to ensure correct sequences of nucleobases in the reproduction process by, for example, removing misaligned strings or repairing damaged DNA with reactive oxygen species. Misaligned genes become a cause of failure to produce appropriate types of proteins, leading to be a possible cause to illnesses or mutate cells into cancer cells.
[Protein synthesis based on DNA's genetic coding]
RNA's major function is to synthesize proteins by linking amino acids based on DNA's coding information. While RNA is composed of nucleotides, just like DNA, nucleobases are similar but not quite the same; adenine (A), guanine (G) and cytosine (C), with the fourth being uracil (U). The overall structure is significantly different from that of DNA. While DNA has a double helix, RNA has a single strand.
RNA has three types: messenger RNA (mRNA), transfer RNA (tRNA) and ribosomal RNA (rRNA). They collaborate with DNA in protein synthesis, as seen in the diagram. There are about 20 kinds of amino acids that form proteins. New proteins are generated within the body using ingested amino acids to create about 100,000 different types of proteins. The nucleobase sequences in the chromosomes direct the constellation of the amino acids where a triad of bases joins together with one amino acid. The process of protein synthesis is as follows:
(1) The double helix of DNA disintegrates, and necessary parts are copied onto mRNA. (Transcription)
(2) The mRNA provides the information and tRNA collects necessary amino acids. When tRNA delivers the amino acids to rRNA inside the cell, rRNA links these amino acids with ribosomes, which are essentially proteins, to synthesize necessary types of proteins. (Translation)
[Regulation of gene expressions]
Our bodies consist of approximately 60 trillion cells, all different in shapes and sizes as well as functions, and each one of them contains an entire set of genetic information within its nucleus. The cells are able to perform their unique roles and constitute some particular functions in a concerted working function because each cell activates a different combination of genes within the entire copy of genetic information contained in itself. To say genes function or express means that mRNA is synthesized based on the genetic coding to generate proteins. Our bodies are constantly making adjustments to maintain the inner equilibrium to adapt to the changes in the external environment or internally within the body. Genes are regulated by various mechanisms in terms of the timing, location, and expression. Many have thought that the critical regulation of gene expression takes place at the transcription stage (when mRNA is created from genes) for most genes. The recent discovery of the strain of RNA that is not involved in the protein synthesis (non-coding RNA or ncRNA) has led to the new findings about some post-transcription regulatory functions to exist (RNA interference). Since the completion of deciphering the human genome, RNA has been found to “regulate gene expressions” as one of it's vital functions.