The Ribosome And Its Importance As You Have Not Seen It Before
By ribosome, all living cells proteins are synthesized.
It's a large macromolecule composed of ribonucleic acids (ribosomal RNAs (rRNA)) and proteins.
It has a complex asymmetric quaternary structure.
To synthesize protein, the ribosome must have
(1) an order determining the sequence of amino acids in the polypeptide chain of protein,
(2) the amino acid substrate that the protein is made
(3) energy.
The function of the Ribosome 
  • The ribosome is responsible for forming peptide bonds, i.e. for the polymerization of amino acid residues into the polypeptide chain.
  • Deoxyribonucleic acid (DNA) "from the cell genome" gives the program which starts the sequence of amino acid residues in a polypeptide chain.
  • Genes, which are sections of the double-stranded DNA, work as templates for synthesizing single-stranded RNA molecules. 
  • The synthesized RNA species are complementary replicas of just one of the DNA chains. 
  • The process accomplished by the enzyme RNA polymerase and called transcription.
  • In all eukaryotic cells, and in some prokaryotic cells, Transcripted RNA may undergo some additional changes called processing in which certain parts of the nucleotide sequence may be excised from RNA or altered (edited).
  •  The mature RNA called messenger RNA (mRNA) and serves as a program, or template, which determines the amino acid sequence in the synthesized protein.
  • Briefly, the flow of information from DNA to ribosomes is mediated by gene transcription and RNA processing, resulting in the formation of mRNA. 
  • Usually done in the nucleus
  • note: DNA and ribosome are found in the same place, so as a result the ribosome can reach mRNA and start to synthesize proteins during transcription; this is called coupled transcription-translation.
  • Proteins consist of amino acids. BUT free amino acids are not used in syncretization of the ribosome.
  • Using mRNA as a program the ribosome translates mRNA from the nucleotide state into the amino acid state of polypeptide chains.

In molecular terms, we can say that while moving along the mRNA, the ribosome specifically selects appropriate tRNA (transfer amino acids to ribosome to form the chain) parts from the medium. 
The specificity of the amino acid the residue of a corresponding tRNA selected by the ribosome is made by the combination of nucleotides in a corresponding stretch of mRNA associated with the ribosome.
"the nucleotide combinations that determine, or code, each of the 20 natural amino acids" is known as nucleotide triplets or called codons.
So, the passing of mRNA through the ribosome establishes an order of entering the various amino acids carried by tRNA into the ribosome.
This order depends on the sequence of codons along the mRNA.
The amino acid residue of each selected tRNA attached covalently to the growing polypeptide chain by the ribosomal machinery.
All of this results in the bit-by-bit formation of the polypeptide chain, according to the program of mRNA.
BY \DR.WAHBA AHMED