DNA 
In all organisms, the coded instructions for specifying the characteristics of the organism are carried in DNA.  The genetic code is contained in the four nitrogenous bases of DNA; adenine, guanine, cytosine, and thymine. These bases are often indicated only by using their beginning letters A, G, C, and T.   Each individual DNA strand serves as a template or model for the formation of other DNA molecules by replication.

RNA
DNA codes for the formation of RNA in the nucleus of the cell.  RNA is short for another kind of nucleic acid called ribonucleic acid.   RNA is very similar in structure to DNA except for three small differences.   These differences include the fact that RNA is a single stranded molecule, lacks the base thymine (T) as it is replaced by the base uracil (U), and its five carbon sugar ribose has one more oxygen atom than the sugar in DNA.    Three different types of RNA exist, mRNA or messenger RNA, tRNA or transfer RNA, and rRNA or ribosomal RNA. 

Protein Synthesis
Cells store and use coded information. The genetic information stored in DNA is used to direct the synthesis of the thousands of proteins that each cell requires.  The chemical and structural properties of DNA are the basis for how the genetic information that underlies heredity.   DNA is encoded in the sequence of nitrogenous bases which directs the formation of proteins in the cell.  How does this process work?   First, the DNA code is copied on to the mRNA (messenger RNA) codon.   A codon is a sequence of three nitrogenous bases.   This process is called transcription.   This mRNA codon is then carried from the nucleus out to the ribosome.  Messenger RNA attaches to another kind of RNA called tRNA (transfer RNA).  Transfer RNA attaches to amino acids and carries them to the ribosome.    This assembly of amino acids due to the code provided to RNA by the original DNA molecule is what produces proteins for the cell.  Remember a protein is a long molecule formed from amino acid subunits.

Protein Synthesis

In summary, the code of DNA directs the synthesis of RNA, which in turn directs the making of proteins on the ribosomes.    This is sometimes referred to as being the central dogma or idea of biology.  There are 64 possible combinations of triplets (sequences of 3 nitrogenous bases) which code for the 20 different possible amino acids.    As the DNA of different organisms and most individuals (except for identical twins) is different, this means the proteins produced by different humans and other organisms exhibit differences.    It is these differences which make us unique individuals.

The work of the cell is carried out by the many different types of molecules it assembles, mostly proteins. Protein molecules are long, usually folded chains made from 20 different kinds of amino acids in a specific sequence. This sequence influences the shape of the protein. The shape of the protein, in turn, determines its function.

Offspring resemble their parents because they inherit similar genes (DNA sequences) that code for the production of proteins that form similar structures and perform similar functions.

Cell Regulation
Cell functions are regulated.  Regulation occurs both through changes in the activity of proteins and through the selective expression of individual genes, as humans and other organisms have genes which direct the expression of other genes.   This regulation allows cells to respond to their environment and to control and coordinate cell growth and division.