How does Transcription of proteins work?

Question

transcription is the a process in protein synthesis and this will outline the process

Answer 1

In eukaryotes, transcription is the process by which our cells use information in DNA to synthesize RNA. So, DNA serves as a template for RNA. This process occurs in the nucleus of the cell.

The first step is Initiation: RNA polymerase binds to the promoter (a region of DNA that has a certain nucleotide sequence called the TATA box which indicates the starting point of transcription) with the help of lots of proteins called transcription factors.

The second step is Elongation: Once RNA polymerase binds to the promoter, it begins moving down the DNA and unwinding it. It reads the template DNA strand in the 3' --> 5' direction, but synthesizes an RNA transcript in the 5' --> 3' direction. The RNA transcript is complimentary to the template DNA strand, except RNA has uracil instead of thymine.

The third step is Termination: Once the RNA polymerase has finished elongating the sequence of DNA, the RNA transcript that was synthesized is released, and the RNA polymerase detaches from the DNA.

After transcription, the RNA transcript will be modified and altered so that it can be ready for translation. Translation will then synthesize proteins using the information in the RNA transcript.

Answer 2

Hello!

Before I answer your question, I want to clarify the difference between transcription and translation. Transcription is the process of synthesizing an mRNA strand from a DNA template, and is the first step in the process that (typically) produces a functional protein product. Translation is the process of producing a protein (well, initially a polypeptide) from an mRNA that has been produced by transcription. The distinction between transcription and translation is very important, because in the case of transcription, you're really just making a short lived mRNA copy of your DNA genetic code (you're "transcribing" but the language stays essentially the same). In translation, on the other hand, you are "translating" the nucleic acid code into an amino acid chain (you're changing the actual "language" from nucleic acids to amino acids, hence the term "translation). So although they sound similar, transcription and translation are really completely different.

So how does translation of proteins work? I'm not sure what level of information you need, but basically there's three different main players in translation:

1. The messenger RNA (mRNA) which is carrying the information needed to produce the protein in the form of a nucleic acid sequence.
2. Transfer RNAs (tRNAs). These are the actual "translators" of the translation process. They are basically strands of RNA with an amino acid sticking off the end and a special complementarity determining region consisting of three nucleotides that recognizes its complementary three nucleotide region on an mRNA. these tRNAs serve as the bridge between the genetic code and the protein product.
3. Ribosomes: These are like the assembly lines for protein production. They grab onto an mRNA, and feed it through a the biological version of an assembly line belt, allowing the tRNAs to swoop in and attach amino acids to create a growing chain.

There is one other key point to understand, which is that our genetic code is read in triplets. By now, you are probably aware that our RNA, including our mRNA, is composed of four basic subunits (called nucleotides). these subunits have identical phosphate and ribose sugar backbones, but differ in the nitrogenous bases they have attached. for RNA, these nitrogenous bases are Adenine, Guanine, Uracil, and Cytosine. So what's the deal with the triplet code? Well, lets look at the other possibilities:

1. Singlet code: each RNA nitrogenous base corresponds to a single amino acid. so for example, Adenine might correspond to the amino acid proline, guanine might correspond to asparagine, and so on. The problem with the singlet code concept is that you only have four nitrogenous bases, whereas you have 20 amino acids that make up your proteins. This means that each different nucleotide would have to correspond to 5 different amino acids if you wanted to cover the full gamut. Obviously, if you want consistent protein production that is no way going to work. Every polypeptide produced would be a mess of different amino acids, and the chance of getting exactly the right sequence to produce the desired functional protein would be very slim. This code is just too simple.
2. Doublet code: Here, instead of a single nitrogenous base corresponding to an amino acid, you read two amino amino acids in sequence and correspond that to an amino acid. for example, AG might correspond to methionine, whereas GA corresponds to alanine, and GC corresponds to leucine. This is better than the singlet model, but has the same problem. How many ways can you combine four different amino acids together into pairs? We could construct the whole sample space, but it's a bit time consuming, so lets just do it the simple way with multiplication: There's 4 different possibilities for the first spot of a doublet (G, A, U, C) and four possibilities for the second spot, so 4*4 = 16 different combinations. Clearly, this is still not enough different combinations to ensure a unique sequence for every amino acid, so the doublet code won't work.
3. The triplet code is the next progression, where every three nucleotide sequence corresponds to an amino acid. So maybe AUG corresponds to methionine, CUU corresponds to leucine, and so on. Each spot in this triple codon has four different possible nitrogenous bases, so the number of different arrangements for a three nucleotide code is 4*4*4 = 64. That's more than enough to code for the 20 amino acids used in protein production, and in fact allows for a lot of redundancy in the genetic code, which turns out to be a good thing.

With those main players in mind, lets walk through the process. A freshly transcribed and processed mRNA emerges from the nucleus. It has a 5' cap and a polyA tail, which both helps to prevent degradation and facilitates recognition by ribosomes. A ribosomal subunit binds the mRNA, assembles a fully functioning ribosome, and scans along the mRNA from 5' to 3' until it hits the first AUG. Again, AUG is shorthand for a nucleotide sequence of Adenine-Uracil-Guanine. It signals the beginning of translation (also known as the Open Reading Frame, or ORF) as well as coding for the amino acid, methionine. When the ribosome hits the first AUG, it starts pulling in tRNAs, which are carrying the amino acids that will be used to produce the protein. Different tRNAs carry different amino acids and have different anti-codons which recognize their complementary triplet codon sequences on the mRNA. They are the ones really doing the "translating" and they are the ones primarily reading the information contained in the mRNA sequence and converting that to an amino acid sequence. The mRNA is processed through ribosome; as each triplet is read by a tRNA, an amino acid is added to the end of a growing chain and the mRNA is pushed further through the ribosome by three nucleotides to allow the next nucleotide triplet to be translated. This goes on until the ribosome hits a stop codon, which signals the closure of the ORF and the end of translation. The ribosome is dissasembled and the mRNA is released.

That's the skeletal outline of translation. I skipped a bunch of stuff, as I'm not sure what level you're learning at and don't want to overwhelm you with information. If you want to see this with visuals (which helps me a lot) I highly recommend the AmoebaSisters on Youtube. https://www.youtube.com/watch?v=oefAI2x2CQM

It basically covers everything I talked about here, but with cartoons!