Basics
The DNA molecule froms the base of all life. Thanks to it cells multiply, organisms grow and genetic traits are passed from parents to children. The DNA molecule consists of two strands coiled into a helix. On each of two strands successive bases bind; there are four types of bases, complementary pairs: adenine (A) binds with thymine (T), cytosine (C) with guanine (G). Thus, if a strand fragment contains the sequence CTAAAGG, the complementary sequence on the other strand is GATTTCC.
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The DNA molecule consists of two strands coiled in a helix on which there are four types of complementary bases linked in pairs. Adenine (A) binds with thymine (T), cytosine (C) with guanine (G). |
An inherited trait like hair color is encoded by a gene, which is a segment of DNA. The set of genes form the genetic code, for humans it has some 20 000 genes spread over 3 billion base pairs.
The genetic code plays an important role in protein synthesis. The gene is copied by an intermediate messenger, called messenger RNA, a process known as transcription. RNA migrates to specific units called ribosomes, where it is translated into a chain of amino acids, thus forming the corresponding protein. For example, the gene that encodes the hair color of a person determines the production of melanin, the pigment responsible for this color.
The ribosome reads the messenger RNA by sequences of three base pairs, each sequence is translated into an amino acid (there are twenty of them in living organisms). This is attached to the amino acid chain already translated the same way, just as an additional pearl is attached to a necklace. The sequence of base pairs in a gene determines the sequence of amino acids, therefore the structure of proteins. An average-sized protein contains about 300 amino acids, which means we can get 20300 different types of proteins, which is a huge number. This explains why proteins, the building blocks of the living organisms, have such varied functions: oxygen transport, muscle contraction, chemical messengers, tissue structure. Besides water, proteins represent 40% of the human body weight.
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Protein synthesis: the DNA gene sequence is copied into messenger RNA (1). The messenger RNA leaves the nucleus and migrates into the cytoplasm where it encounters a ribosome (2). The ribosome reads the messenger RNA in the order of its sequence and links the amino acids to form the protein (3). |
Living organisms have key components (cells, genes, proteins) that enable growth and reproduction. One of the goals of biological research in recent decades is to understand how these components interact, one main area being the relationship between DNA, RNA and proteins.
The traditional approach of biology research has been to isolate a small number of biological components to understand their structure and function. But this reductionist approach is limited since biological systems are multi-scale and multi-level: most genes, proteins and other components perform their functions within a complex network of interactions with positive and negative feedback loops. In general, a given biological function or a specific disease is not completely controlled by a single gene and conversely, a gene can determine several biological functions.
It is to understand increasingly complex biological systems as a whole that a new discipline called systems biology has emerged. It benefits from advances in investigative techniques of molecular biology but also mathematical modeling and computer simulation.
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