A gene is a specific section on the DNA. It is a carrier of hereditary information and, in interaction with other genes, controls the totality of bodily processes. Gene alterations can be harmless as well as cause serious malfunctions in the organism.
What is a gene?
Genes, as specific sections on DNA, are the basic units of the entire hereditary system. The totality of all genes found in the organism is called the genome. Their interaction guarantees any vital functions of the organism. The individual gene provides the basis for the complementary copy in the form of a ribonucleic acid (RNA). This RNA in turn mediates the translation of the genetic code into the amino acid sequence of a protein. Thus, a transfer of the information stored in the hereditary material takes place from DNA to RNA to enzymes and structural proteins. Each gene stores specific hereditary information, which finds its expression in certain characteristics or functions of the organism. Each species of organism has a characteristic number of genes, although their quantity says nothing about the complexity of the living being. For example, humans contain 35,000 genes.
Anatomy and structure
As a section on DNA, a gene, like all DNA, is characterized by a sequence of base pairs on a double helix. DNA (deoxyribonucleic acid) is a chain molecule of nucleotides, each of which in turn consists of a nitrogen base, a sugar molecule (in this case, deoxyribose), and a phosphoric acid residue. For a single strand of DNA, the four nitrogen bases adenine, guanine, thymine and cytosine are available. However, the particular sugar molecule necessitates the construction of a double helix strand, with the individual nitrogen bases facing the corresponding complementary bases. The sequence of nitrogen bases in the DNA stores the genetic information as a genetic code. If the double helix splits during cell division, the respective single strands are completed again to form a double strand. In eukaryotes (organisms with a cell nucleus), the DNA molecules are packaged in protein. The entire structure is called a chromosome. Humans have 23 pairs of chromosomes, with one chromosome coming from each parent. This means that the genes for the same functions are opposite each other as alleles. Within the gene there are coding (exon) and non-coding (intron) sections. The exons contain the genetic information necessary for the organism. The introns are often old information that is no longer active. Thus, within genes, exons are responsible for transcribing the necessary genetic code into the amino acid sequence of proteins.
Function and tasks
Genes are first responsible for storing all the necessary genetic information for the functions of the organism. Furthermore, they are responsible for passing this information on to subsequent cells during cell division or transmission to the next generation of organisms. Gene activity can occur through a variety of mechanisms. During transcription, the genetic information is first transferred to an RNA. This translates the genetic code into the amino acid sequence of the protein as part of protein biosynthesis. However, not all information must always be equally available. For example, in certain phases of the organism’s activity, special enzymes or hormones are increasingly required, while other proteins are not needed. A complicated regulatory mechanism then either stimulates or blocks genes for protein biosynthesis. This can be achieved by the attachment and detachment of specific proteins on certain DNA segments. During cell division, the entire genetic code must be transferred from the initial cell to the subsequent cell generation. In the process, the double helix of DNA splits into single strands. However, each single strand is completed again into a double strand by the addition of nucleotides with complementary nitrogen bases. However, errors, so-called mutations, can occur in the process, leading to a change in the genetic information. To avoid mutations, the organism in turn has a highly efficient repair system. Through these processes, the genetic code is passed on to the next generation largely unchanged. However, if an altered gene is nevertheless inherited, this can lead to a serious genetic disease.
Diseases and complaints
When altered genes are transmitted, serious diseases of the same organism or genetic diseases of subsequent generations may result. For example, the occurrence of cancer is often the result of gene alterations during cell division. Usually, the immune system will kill the altered cell. However, under special conditions, such as a high mutation rate caused by environmental factors, the immune system can become overwhelmed, with unregulated cell growth setting in. More familiar in connection with gene mutations, however, is the occurrence of genetic diseases. Often only individual genes are affected. Depending on which functions or which characteristics the gene stands for, a wide variety of diseases can occur. Each person contains two genes for the same function, since they come from both parents. For example, there are genetic diseases that are inherited in an autosomal recessive manner. Here, the disease only occurs if both parents inherit an altered gene. Examples of these diseases are cystic fibrosis, phenylketonuria or cleft lip and palate. Other diseases are inherited in an autosomal dominant manner, such as Huntington’s disease, Marfan syndrome or retinoblastoma. In these cases, it is sufficient to pass on a gene from a sick parent. Some diseases, such as diabetes, have only a genetic disposition and are significantly dependent on environmental conditions or lifestyle.
