The cell is the fundamental unit of all living organisms. Its constituent parts are made up of molecules. A typical cell has a diameter of one three-hundredth of a millimeter. Every cell represents a highly organized structure responsible for the shape and function of an organism.
An adult human has 100,000,000,000,000 cells. The life of a cell depends on the combined activity of thousands, possibly even hundreds of thousands, of different protein molecules.
Protoplasm is the basic substance of all living cells. It is not a uniform substance but a mixture of numerous chemical compounds, a system of substances capable of nourishing and reproducing itself. Enzymes are effective substances that enable the exchange of matter within a cell without being altered themselves. They are composed of long chains of amino acids. The sequence of individual components determines the working capability of individual enzymes.
In the nucleus of the cell there is a DNA molecule, the central record with all the instructions for organizing and operating the entire organism.
Deoxyribonucleic acid (DNA) has the shape of a double helix. The sequence of nucleotides along these strands represents the language of life. During reproduction, the helices are separated by a specific protein, and then both halves synthesize identical copies of one another from the nucleotide-building material floating in the viscous fluid of the cell nucleus. Apart from the ability to replicate itself, DNA directs the activity of a cell (known as metabolism) by synthesizing another nucleic acid, RNA, which acts as a “messenger” that goes outside the nucleus to the periphery where it controls the formation of a certain enzyme at the right time and in the right place. DNA in the cell “knows” what needs to be done, while RNA transmits the “instructions” received from DNA to other parts of the cell. Once everything is complete, one enzyme molecule is created, which governs a specific aspect of the cellular system.
The human DNA ladder is a billion nucleotides long. The vast majority of nucleotide combinations are meaningless. Namely, they would initiate the synthesis of a protein that serves no useful function. Only an exceptionally small number of nucleic acid molecules are useful for a complex life form such as a human. Yet, the number of useful nucleic acid combinations is astonishingly large, likely far greater than the total number of protons and electrons in the universe.
Approximate age of living beings on Earth
– Sponges – over 580 million years
– Fish/protofish – 420 million years
– Land plants – 420 million years
– Amphibians – 360 million years
– Insects – 330 million years
– Reptiles – 300 million years
– Conifers – 270 million years
– Mammals – 210 million years
– Birds, flowers – 150 million years
99% of the atmosphere is of organic origin. The sky is made by life.