Source: Video and Images Created by Amanda Soderlind
Welcome to this lesson today on translation. Today, we are going to be discussing translation as the second step in protein synthesis, which follows transcription. So in translation, basically what it does is it translates instructions from a single stranded mRNA, this messenger RNA, which was formed from transcription, into proteins. So we're using this strand of messenger RNA that was formed during transcription in the nucleus and has now moved into the cytoplasm, as the template in order to form proteins.
So this occurs in the cytoplasm of the cell. And we have three stages to translation, initiation, elongation, and termination. So we're going to use this diagram here to help describe what these three stages are. So first of all, I'm going to label a couple of things here.
We have our ribosome here. So our ribosome is composed of our large subunit, and our small subunit. And then we also have-- this here is our messenger RNA, or mRNA. OK. So this is the strand of messenger RNA that was formed in transcription, moved out of the nucleus into the cytoplasm, and is now used in order to form proteins.
So basically initiation being the first step, or the first stage in translation, what happens here is that the small and large ribosomal subunit will join together and then initiator tRNA will arrive at the start codon. So the start codon marks the start of a new polypeptide chain. So what happens then is that amino acids can then be added.
So the transfer RNA carries an anticodon. And these anticodons will match up with the strand of messenger RNA using the base pair rules. So you can see here how our messenger RNA will match up with our anticodons. And again, using those original base pair rules.
And then the anticodon is also carrying-- or the transfer RNA, in addition to carrying the anticodon, is also carrying an amino acid. So each of these anticodons codes for certain amino acid. So depending on what our codon is in our messenger RNA, it will bind with a specific anticodon, which then codes for a specific amino acid. So remember these codons are groups of three nucleotides, which code for amino acids.
And then the same thing will happen with this next group of three. So this group of three nucleotides, this codon right here, will match up with a specific anticodon carried by tRNA, which then signals for a certain amino acid. So these amino acids will start building up in this chain called a polypeptide chain.
And these polypeptide chains build proteins. And these amino acids are held together by a peptide bond. So amino acids which form polypeptide chains are held together by peptide bonds. OK. So then the elongation stage is the stage where those amino acids are being built in a chain. The polypeptide chain is growing. And then termination being the last stage of translation is when the stop codon of messenger RNA signals the end of translation, and then that polypeptide chain is complete.
There you go. OK. So this lesson has been an overview on the process of translation as the second step in protein synthesis in which polypeptide chains are built.
