Hi chimichurri!
Let me try and explain how operons/genes work.
Firstly, remember that a gene is a section of DNA that codes for a specific protein. Of course, genes are found in both eukaryotes and prokaryotes. A gene will code for multiple amino acids, forming a polypeptide chain that can be folded to form a functional protein. An operon is generally only found in prokaryotes, and its a cluster of linked genes that all share a common promoter and operator, and are transcribed at the same time. Generally, all of these genes are related by function (i.e. biochemical process that they are a part of). Now, the genes in the operon are structural genes (genes that don't code for regulatory proteins, but instead proteins needed for structure or cellular functioning). The trp operon (that you need to know about from the study design) consists of multiple structural genes and has a structure like the following:
3' end - Promoter - Operator - Leader (TrpL) - Attenuator - TrpE - TrpD - TrpC - TrpB - TrpA - Trailer - 5' end
TrpE to TrpA are your important structural genes. As we know, genes code for many amino acids, so an operon is not going to just code for amino acid. It is easy to think that the trp operon codes only for one amino acid, that being tryptophan (since the process can be quite confusing to understand). However, the trp operon actually codes for multiple polypeptides, each structural gene being transcribed and translated to form different proteins (specifically enzymes) that are required to produce tryptophan. Here are some details on the enzymes formed (don't need to know the specifics, but it can be helpful in understanding how it works).
- TrpE and TrpD -> Form enzyme Anthranilate synthase, which converts chorismate (found in the cell) into anthranilate.
- TrpC -> Forms enzyme Indole-3-glycerol-photosphate synthase, which converts anthranilate into indole-3-glycerol-photosphate.
- TrpB and TrpA -> Forms enzyme Tryptophan synthase, which converts indole-3-glycerol-photosphate into tryptophan.
(Requires lots of energy, meaning the process needs to be tightly regulated via attenuation and repression mechanisms).
To put it simply, the enzymes are produced to convert certain chemical products into tryptophan, with each enzyme consisting of many amino acids that form polypeptides and therefore are folded into functional proteins (i.e. enzymes). Hopefully that makes sense.
With directions, it can be quite confusing. RNA polymerase (not pre-mRNA) reads the strand in a 3' to 5' direction, forming an mRNA strand (mRNA for prokaryotes, but pre-mRNA for eukaryotes) that is 5' to 3' (due to complementary nature of DNA transcription). DNA replication is the same, as DNA polymerase reads the strand from 3' to 5' and writes a new DNA strand from 5' to 3'. I remember it like this: "When we study, we read up on a topic (3' to 5'), and then you write it down (5' to 3')". That said, google makes it kind of confusing by saying that DNA is read 5' to 3', but I'm assuming that it is referring to the fact that whilst the template strand being copied in a complementary manner is the 3' to 5' direction, the actual coding strand that is being replicated is 5' to 3' (which is why the created DNA or RNA strand is always written in a 5' to 3' direction). I might be wrong about that though. Not sure if that makes sense, since I'm still trying to wrap my head around how it works haha.
