Requirements Introduction to translation of mRNA Genetic code (codon and anticodon) Transfer RNA Ribosome

2. • Requirements
• Introduction to translation of mRNA
• Genetic code (codon and anticodon)
• Transfer RNA
• Ribosome

3. • tRNA
• mRNA
• Ribosome
• Translational factors
1. Initiation factors (IF)
2. Elongation factors (EF)
3. Release factors (RF)

4. • The final step in the expression of genes that encode
proteins is translation.
• The mRNA nucleotide sequence is translated into the
amino acid sequence of a polypeptide chain.
• Protein synthesis is called translation because it is a
decoding process.
• The information encoded in the language of nucleic
acids must be rewritten in the language of proteins.

5. • The genetic code showed that the DNA base sequence
corresponds to the amino acid sequence of the
polypeptide specified by the gene.
• Only 20 amino acids normally are present in proteins,
there must be at least 20 different code words in DNA.
• 64 codon in mRNA that code for 20 amino acid in the
synthesis of polypeptide or protein
• Among them 3 are the stop or nonsense codon (UGA,
UAG, UAA) and 61 are the sense codon (direct amino
acid incorporation into protein) in which 6 are
degeneracy codon.

10. • Amino acids are activated for protein synthesis through a reaction
catalyzed by aminoacyl-tRNA synthetases
Amino acid tRNA ATP ⎯⎯→ aminoacyl-tRNA AMP PPi
• The amino acid is attached to the 3′-hydroxyl of the terminal
adenylic acid on the tRNA by a high-energy bond and is readily
transferred to the end of a growing peptide chain. This is why the
amino acid is said to be activated.
• There are at least 20 aminoacyl-tRNA synthetases, each specific
for a single amino acid and its tRNAs
• Some aminoacyl-tRNA synthetases proofread just like DNA
polymerases do. If the wrong amino acid is attached to tRNA, the
enzyme hydrolyzes the amino acid from the tRNA rather than
release the incorrect product.

11. • The actual process of protein synthesis takes place on
ribosomes that serve as workbenches, with mRNA acting as
the blueprint
• . Procaryotic ribosomes have a sedimentation value of 70S
and a mass of 2.8 million daltons. A rapidly growing E. coli
cell may have as many as 15,000 to 20,000 ribosomes, about
15% of the cell mass.
• Each of the two subunits of the procaryotic ribosome is an
extraordinarily complex structure constructed from one or
two rRNA molecules and many polypeptides
• The region of the ribosome directly responsible for
translation is called the translational domain
• Both subunits contribute to this domain
• The 16S rRNA of the 30S subunit is needed for the initiation
of protein synthesis in Bacteria

12. • Shine-Dalgarno sequence
The Shine-Dalgarno (SD) Sequence is a ribosomal binding site in
bacterial and archaeal messenger RNA, generally located
around 8 bases upstream of the start codon AUG. The
RNA sequence helps recruit the ribosome to the messenger
RNA (mRNA) to initiate protein synthesis by aligning the
ribosome with the start codon.