PROTEIN SYNTESIS
Protein:A protein is simply a long chain of amino acids linked
together by bonds. There are only twenty amino acids consisting of
carbon, hydrogen, nitrogen, oxygen, and two that contain sulfur.when a
protein is in a water-based environment, the hydrophobic amino acids
fold inwards while the hydrophilic remain on the outside. (This process
is aided by chaperone proteins)
Protein Synthesis:The basic
process of making proteins in cells is called protein synthesis. It is
with this ability of the cell that its genetic makeup is defined.
Protein is synthesized in the body in four distinct stages that
involves both the DNA and the RNA.Proteins are very much needed in the
body to provide amino acids which in turn build new proteins.While
protein synthesis involves a large part of the cell, its main stages
take place in the nucleus and ribosome.
Closer Look:
1.Transcription:This is where
the sequence of nucleotides present in the double helix DNA form are
transcribed into a single strand of messenger RNA.So that you will
understand the vast amount of work that is present in this step, let''s
look at some numbers.Every three nucleotides will become the
instructions for just one amino acid. There are1,200nucleotides in just
one gene in a strand of DNA.This means that 400 amino acids would have
to be produced to represent one gene in one strand of DNA.Considering
the huge number of genes in the body, it is easy to appreciate just how
many nucleotide combinations there are that will eventually encode
amino acids.
2.Transferal:In this stage,an
amino acid activating enzyme attaches an amino acid to one end of
transfer RNA,also called an adaptor molecule.On the other end of the
adaptor is a specific three-nucleotide code which will be used when the
adaptor reaches the mRNA.Since there are twenty different kinds of
amino acids, there are also twenty different kinds of adaptors and
amino acid activating enzymes.To simply say that an adaptor and an
amino acid are connected is an oversimplification of the process.
1:An ATP molecule docks on the
activating enzyme in a place specially prepared for it (think of this
space as a reserved parking place).
2:An amino acid then parks in the next space which was also prepared especially for it.
3:The ATP molecule and the
amino acid drift closer together until they bond, thereby releasing two
phosphates. At this point, the amino acid is energized.
4:The adaptor then comes and
parks in the space next to the amino acid (as you may have guessed, the
place was also reserved especially for the adaptor).
5:The adaptor comes closer to the amino acid until they bond.
6:Energy from the ATP molecule is transferred into this bond and the ATP molecule is released.
7:The activating enzyme finally releases the adaptor with the amino acid attached to one end.
3. Translation: At this
point,one amino acid is attached to an adaptor.Remember that it takes
many amino acids to make up one protein.Therefore, there must be a way
to link these amino acids into a single protein in order to complete
protein synthesis.This is where the ribosome comes in which is so good
at producing proteins that is often termed a"protein factory."The
ribosome"reads"the nucleotide code and associates it with the proper
amino acid.Again, let''s look at the mechanisms of this system closer.
A:A messenger RNA attaches to the smaller subunit of the ribosome
B:The first adaptor comes and matches the first three nucleotides of the messenger.
C:The larger subunit of the ribosome attaches to the smaller subunit.
D:A second adaptor enters a second dock to the left of the first adaptor.
E:The backbone links of the two amino acids present at the ends of the adaptors link.
F:The messenger moves right
causing the first adaptor to drop off, leaving an empty space to the
left of the second adaptor. It is important to understand that this
adaptor has two amino acids at its G:The process repeats itself as
new adaptors arrive, link their amino acid chains, and then push off
the previous adaptor. This causes the adaptor''s amino acids to grow.
H:The last triplet on the messenger RNA will not be able to find an adaptor that fits it; this signals STOP.
I:The ribosome releases the mRNA and the amino acid chain has grown to a protein.
J:In order to facilitate this process, many ribosomes work at once to produce proteins.
Summary:
Therefore, protein synthesis is a fairly complex process where amino
acids are connected together to form a protein. The distinguishing
aspect of this process is that each different order of amino acids
causes a different protein to be produced.