The central dogma of molecular biology:
DNA makes RNA makes protein.
Here the process begins.
Transcription factors assemble at a
specific promoter region along the DNA.
The length of DNA following the
promoter is a gene
and it contains the recipe for a protein.
A mediator protein complex arrives
carrying the enzyme RNA polymerase.
It maneuvers the RNA polymerase into place
inserting it with the help of other factors
between the strands of the DNA
double helix.
The assembled collection of
all these factors
is referred to as the
transcription initiation complex,
and now, it is ready to be activated.
The initiation complex requires contact 
with activator proteins,
which bind to specific sequences of DNA 
known as enhancer regions.
These regions may be
thousands of base pairs distant
from the start of the gene.
Contact between the activator proteins 
and the initiation complex
releases the copying mechanism.
The RNA polymerase unzips a
small portion of the DNA helix
exposing the bases on each strand.
Only one of the strands is copied.
It acts as a template
for the synthesis of an RNA molecule
which is assembled one sub-unit at a time
by matching the DNA letter code
on the template strand.
The sub-units can be seen here entering 
the enzyme through its intake hole
and they are joined together
to form the long messenger RNA chain
snaking out of the top.
Once a gene has been located and
transcribed into mRNA
it must first be edited before it
can be translated into a protein.
This editing process is called splicing.
It involves removing non-coding regions 
called introns,
leaving only the protein coding exons.
In the cell, the introns are removed
by special enzymes
which recognize specific sequences.
These enzymes cut and rejoin the coding
regions for translation into protein.
The job of this mRNA is to
carry the genes message
from the DNA out of the nucleus
to a ribosome
for production of the particular protein 
that this gene codes for.
There can be several million
ribosomes in a typical eukaryotic cell.
These complex catalytic machines use 
the mRNA copy of the genetic information
to assemble amino acid building blocks 
into the three-dimensional proteins
that are essential for life.
Let's see how it works.
The ribosome is composed of one large 
and one small sub-unit.
that assemble around
the messenger RNA
which then passes through the ribosome 
like a computer tape.
The amino acid building blocks,
that's the small glowing red molecules,
are carried into the ribosome attached to 
specific transfer RNAs,
that's the larger green molecules also 
referred to as tRNA.
The small sub-unit of the ribosome 
positions the mRNA
so that it can be read in groups of three
letters known as a codon.
Each codon on the mRNA matches a 
corresponding anticodon
on the base of a transfer RNA molecule.
The larger sub-unit of the
ribosome removes each amino acid
and joins it on to the growing protein chain.
As the MRNA is ratcheted through
the ribosome,
the mRNA sequence is translated
into an amino acid sequence.
There are three locations inside the ribosome,
designated the A site, the P site, and the
E site.
The addition of each amino acid is a three step cycle.
First, the tRNA enters the ribosome
at the A site
and is tested for a codon - anticodon match
with the mRNA
Next, provided there is a correct match,
the tRNA is shifted to the P site
and the amino acid it carries is added to 
the end of the amino acid chain.
The mRNA is also ratcheted on
three nucleotides or one codon.
Thirdly, the spent tRNA is moved to the E site
and then ejected from the ribosome to be
recycled.
As the protein synthesis proceeds
the finished chain emerges from
the ribosome.
It folds up into a precise shape determined
by the exact order of amino acids.
Thus the central dogma explains how the 
four-letter DNA code is
quite literally turned into flesh and blood.
