Page 50 - Cell biology PDC 2024

 All information for 3-D structure is contained in the linear
sequence of amino acids

Translation of proteins

• It is the decoding of mRNA into a protein
• The newly synthesized mRNA formed in the nucleus goes to the

cytoplasm through the nuclear pore

• Translation is done by means of the ribosomes found in the

cytoplasm

• Transfer RNA (tRNA) carries amino acids from the cytoplasm to

the ribosome.

• Every three adjacent bases in an mRNA molecule are called codon

and they code for one specific amino acid.

• Each tRNA has 3 nucleotides that are complementary to the codon

in mRNA and each tRNA codes for a different amino acid.

• The tRNA carrying the correct amino acid goes to the ribosome

and put this exact amino acid to the growing polypeptide chain.

• Amino acids are joined together to make finally a protein

What happens is that: the small ribosomal subunit attaches to the mRNA
molecule and at the same time an initiator tRNA (that will put the first
amino acid) recognizes and binds to a specific codon sequence on the
same mRNA molecule, then the large ribosomal subunit joins them.

The ribosome has 2 sites, the P site and the A site. The initiator tRNA
resides in the P site leaving the A site open. When a new tRNA molecule
recognizes the next codon sequence on the mRNA, it attaches to the open
A site. A peptide bond is formed connecting the amino acid of the tRNA
in the P site to the amino acid of the tRNA in the A binding site.

As the ribosome moves along the mRNA molecule, the tRNA in the P
site is released and the tRNA in the A site is translocated to the P site.
The A binding site becomes empty again until another tRNA that
recognizes the new mRNA codon takes the vacant position. This
continues again and again and the amino acid chain grows.

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