Summary
Highlights
Chromosomes contain long strands of DNA, which are wound up into themselves. These strands have sequences called genes that code for specific polypeptides or proteins. The central dogma of biology explains how information flows from genes to proteins. The first step, transcription, converts DNA into messenger RNA (mRNA). The second step, translation, converts mRNA into protein, which is the focus of this video.
In eukaryotic cells, DNA is transcribed into pre-mRNA by RNA polymerase. This pre-mRNA undergoes processing where introns are removed, and a cap and tail are added, forming mature mRNA. This mRNA then travels to a ribosome for translation. In prokaryotic cells, there's no nuclear membrane or processing step; mRNA is directly used for translation.
Ribosomes are the sites of translation, composed of proteins and ribosomal RNA (rRNA). The ribosome moves along the mRNA from the 5' end to the 3' end, reading the information. Every three nucleotides on the mRNA form a 'codon', which codes for a specific amino acid. There are 64 possible codons, which is more than enough to code for the 22 standard amino acids. AUG is the start codon, coding for methionine and signaling the ribosome to begin translation.
Out of the 64 codons, 61 code for amino acids, and three are 'stop codons' (UAA, UAG, UGA) that signal the ribosome to stop translation. Transfer RNA (tRNA) molecules are crucial for matching codons to amino acids. Each tRNA binds to a specific amino acid at one end and has an 'anticodon' at the other end, which is complementary to a specific mRNA codon. This ensures the correct amino acid is brought to the ribosome for polypeptide synthesis.
The ribosome has three sites: the A-site (aminoacyl-tRNA binding site), the P-site (peptidyl-tRNA binding site), and the E-site (exit site). The appropriate tRNA, carrying an amino acid, first binds to the A-site. A peptide bond then forms between the amino acid in the A-site and the growing polypeptide chain in the P-site. The ribosome then shifts, moving the tRNA with the polypeptide chain to the P-site, and the now empty tRNA to the E-site to exit. This process continues until a stop codon is reached, releasing the complete polypeptide.
Translation is a fundamental process constantly occurring in our cells. Antibiotics can target this process; for example, they can disrupt the function of bacterial ribosomes without harming human ribosomes, which are structurally different. This allows antibiotics to stop protein synthesis in bacteria, preventing their growth and survival without negatively affecting the host.