Protein Synthesis

Translation Process

• Translation proceeds in the 5' to 3' direction.
• The start codon for all protein synthesis is AUG, which codes for methionine.
• Specific stop codons (UAG, UAA, UGA) signal the termination of protein synthesis during translation.
• The process of modifying specific amino acid side chains after translation is called post-translational modification.

tRNA and Amino Acids

• The enzyme responsible for covalently linking amino acids to tRNA is aminoacyl-tRNA synthetase.
• The molecule that carries the appropriate amino acid to the site of synthesis on the ribosomal complex is tRNA.
• Aminoacyl-tRNA synthetases attach amino acids to tRNA and edit for correct pairing.
• The family of enzymes required for attaching amino acids to tRNA is aminoacyl-tRNA synthetases.

mRNA and Codons

• The molecule that carries the code in triplicate is mRNA.
• The components required for translation are mRNA, tRNA, ribosomes, amino acids, and energy.
• There are three codons (UAG, UAA, UGA) that code for termination/stop codons.

Consequences of Mutations

• Altering the nucleotide sequence in the coding region of mRNA can change the amino acid sequence of the protein.
• Frameshift, missense, and nonsense gene mutations can alter the reading frame of the mRNA and the protein synthesized from it.

Initiation and Elongation

• Initiation factors play a crucial role in translation initiation.
• The mechanism by which tRNA recognizes more than one codon for a specific amino acid is through wobble base pairing.
• Eukaryotes use the scanning mechanism to recognize the start codon.
• The AUG codon on mRNA signals the start of protein synthesis and codes for methionine.
• The codon UAA on mRNA signals the end of protein synthesis and does not code for an amino acid.

Prokaryotes and Eukaryotes

• The Shine-Dalgarno sequence is involved in translation initiation in prokaryotes.
• The mRNA cap and poly-A tail are involved in translation initiation in eukaryotes.
• Free ribosomes are found in the cytoplasm of eukaryotes.

Protein Synthesis and Folding

• Protein factors involved in initiation, elongation, and termination of protein translation include initiation factors, EF-Tu-GTP, and release factors.
• The sequence of amino acids determines how a protein will fold.
• The initiation codon is recognized by the ribosome and plays a crucial role in translation initiation.
• tRNAi is distinguished from internal AUG-tRNA by its ability to initiate protein synthesis.
• Bacterial tRNAi carries methionine.
• The 30S subunit prevents the premature binding of the large subunit during initiation.
• EF-Tu-GTP plays a crucial role in elongation by bringing aminoacyl-tRNA to the ribosome.