The start codon (AUG) codes for the amino acid methionine. The start codon is the nucleotide triplet on the mRNA strand that signals the start of the codons to be translated. Each codon triplet binds to a complementary anticodon triplet on a tRNA molecule that carries a corresponding amino acid. 

In the initiation stage of translation, a 5’ cap forms at the 5’ end of the mRNA strand, which is composed of the small ribosomal subunit and initiation factors. Initiation factors are proteins that facilitate the start of translation during the initiation stage. Once this complex is assembled, it “scans” the mRNA strand for the start codon, AUG. The initiator tRNA molecule coding the anticodon UAC and carrying the corresponding amino acid methionine is recruited and binds to the start codon. This makes methionine the first amino acid in the polypeptide chain. The large ribosomal subunit then associates with the complex, placing the methionine tRNA in the P-site of the large subunit. There is an alternative model of initiation in which the mRNA scanning complex does not form at the 5’ end. This model is believed to occur under stress responses.

Antibiotics are able to inhibit protein synthesis in prokaryotes in a number of ways. The specific method of inhibition depends on the antibiotic that is used. Examples of the antibiotics that target translation are rifamycin, linezolid, and tetracyclines. Rifamycin inhibits RNA polymerase and the resulting synthesis of mRNA. Linezolid blocks the formation of the translation initiation complex. Tetracyclines obstruct the aminoacyl “A” site of ribosomes. Inhibiting translation is an effective way to kill bacteria and treat bacterial infections. Antibiotics specifically target prokaryotic cells, ensuring no harm to the host eukaryotic cells. 

There is only one codon that signals the start of translation: AUG. This codon codes for the amino acid methionine so this amino acid will also be at the N-terminus of all proteins, however it may be removed and/or modified later.

The three types of RNA involved in Translation are messenger RNA, transfer RNA, and ribosomal RNA.

Many amino acids have multiple three-nucleotide sequences that correspond with them. If a sequence that codes for leucine (UUA) is mutated by only one letter (to UUG), then it will still form a functional protein, since the mutated sequence also codes for leucine. Redundancy allows occasional mutations to occur without corrupting the amino acid sequence.

DNA polymerase is not involved in the transcription of mRNA to amino acids.

A single three-nucleotide sequence can only code for a single amino acid, although many amino acids can be coded for by multiple nucleotide sequences (redundancy).

Each tRNA contains the anticodon for a specific mRNA codon and carries the amino acid corresponding to that codon to ribosomes during translation. mRNA is produced by transcription from DNA, and ribosomes translate it into proteins. Multiple codons can code for a single amino acid, and so there can be several tRNA anticodons that could be used for a single amino acid.

mRNA, tRNA, and rRNA all play a key role in the synthesis of proteins. tRNA (transfer RNA) is responsible for gathering amino acids in the cytosol and bringing them to the ribosomes when translation is taking place. mRNA (messenger RNA) is the template for translation. rRNA (ribosomal RNA) is a structural element of the ribosomes.

An anticodon is the three-base sequence, paired with a specific amino acid, that a tRNA molecule brings to the corresponding codon of the mRNA during translation. The anticodon sequence is complementary to the mRNA, using base pairs in the anti-parallel direction. tRNA is read 3'-to-5', so the sequence would be 3'-UUG-5'. Keep in mind that adenine binds to uracil in RNA.

Codon:      5'-AAC-3'

Anticodon: 3'-UUG-5'

Anticodons are found on molecules of tRNA. Their function is to base pair with the codon on a strand of mRNA during translation. This action ensures that the correct amino acid will be added to the growing polypeptide chain. A tRNA molecule will enter the ribosome bound to an amino acid. The anticodon sequence will bind to the codon of the mRNA, allowing the tRNA to release the attached amino acid. This amino acid is then added to the peptide chain by the ribosome.