Biological information is contained in a genetic language common to all organisms

Biological information is contained in agenetic language common to all organisms

Cells are the basic building blocks of organisms, but even a single cell is complex, with many internal structures and many
functions that depend on information. The information required
for a cell to function and interact with other cells—the “blueprint” for existence—is contained in the cell’s genome, the sum
total of all the DNA molecules it contains. DNA (deoxyribonucleic acid) molecules are long sequences of four different subunits called nucleotides. The sequence of the nucleotides contains genetic information. Genes are specific segments of DNA
encoding the information the cell uses to make proteins (Figure
1.4). Protein molecules govern the chemical reactions within
cells and form much of an organism’s structure.
By analogy with a book, the nucleotides of DNA are like
the letters of an alphabet. Protein molecules are the sentences.
Combinations of proteins that form structures and control biochemical processes are the paragraphs. The structures and
processes that are organized into different systems with specific
tasks (such as digestion or transport) are the chapters of the
book, and the complete book is the organism. If you were to
write out your own genome using four letters to represent the
four nucleotides, you would write more than 3 billion letters.
Using the size type you are reading now, your genome would
fill about a thousand books the size of this one. The mechanisms
of evolution, including natural selection, are the authors and
editors of all the books in the library of life.

1.4 DNA Is Life’s Blueprint The instructions for life are contained in
the sequences of nucleotides in DNA molecules. Specific DNA nucleotide
sequences comprise genes. The average length of a single human gene
is 16,000 nucleotides. The information in each gene provides the cell with
the information it needs to manufacture molecules of a specific protein.  

All the cells of a multicellular organism contain the same
genome, yet different cells have different functions and form
different structures—contractile proteins form in muscle cells,
hemoglobin in red blood cells, digestive enzymes in gut cells,
and so on. Therefore, different types of cells in an organism must
express different parts of the genome. How cells control gene
expression in ways that enable a complex organism to develop
and function is a major focus of current biological research.
The genome of an organism consists of thousands of genes.
If the nucleotide sequence of a gene is altered, it is likely that
the protein that gene encodes will be altered. Alterations of
the genome are called mutations. Mutations occur spontaneously; they can also be induced by outside factors, including chemicals and radiation. Most mutations are either harmful or have no effect, but occasionally a mutation improves the
functioning of the organism under the environmental conditions it encounters. Such beneficial mutations are the raw material of evolution and lead to adaptations.

Ref:  Life The Science of Biology