Video Transcript
The diagram provided shows a simplified outline of the process of translation. What is the structure labeled Z? (A) A chain of monosaccharides, (B) a DNA sequence, (C) a polypeptide chain, or (D) an RNA sequence.
All of the proteins of our body are encoded by genes in our DNA. In order for these genes to be expressed to produce these proteins, the gene on DNA must first be transcribed into mRNA. This mRNA sequence can then be translated into a series of amino acids to construct the protein. The process of translation is outlined in this diagram. Let’s go through this diagram in some detail and label the different parts.
Translation begins with an organelle called the ribosome attaching to a molecule of mRNA, as indicated here. You can see the different nucleotides in mRNA as these different-colored boxes. Three nucleotide sequences in mRNA called codons are matched to specific amino acids. These amino acids are carried by a special type of RNA called transfer RNA, or tRNA. This particular tRNA is carrying the amino acid methionine. This amino acid is matched to the codon in mRNA because of the complementary anticodon sequence at the end of this specific tRNA.
Each amino acid is carried by a different tRNA that has a different anticodon. So in the next step, the next tRNA comes in that can bind to the next codon in mRNA. In this case, it’s a tRNA molecule carrying histidine. A peptide bond is formed between the two amino acids by the ribosome. Then, the ribosome moves forward along the mRNA to the next codon. So now, the next tRNA, in this case carrying leucine, can come in. This pushes the empty tRNA molecule out of the ribosome, and another peptide bond is formed between histidine and leucine. This continues until the end of translation, where a special stop codon is reached.
Now, the polypeptide labeled as Z in this diagram can exit the ribosome and fold into a protein. In this example, this polypeptide is only three amino acids long, but typically they are much larger. Therefore, the structure labeled Z in this diagram is a polypeptide chain.
