Transcription And Translation Essay Ap Bio

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We are going to continue our discussion of molecular genetics with the topics of transcription and translation.0002

Before we delve into the details, I am going to give you an overview of the process.0011

Recall that the central dogma of molecular biology is the flow of information from DNA to RNA to protein.0015

The genetic information is contained on DNA.0029

A transcript is made of RNA and this is then, transported.0033

A particular type of RNA, mRNA is transported into the cytoplasm, where it is translated into polypeptide and forms of protein.0039

This process, therefore, is called transcription.0050

The use of a DNA template to form RNA, and the process of going from RNA using that RNA transcript to form a protein is translation.0055

When a protein is made based on the information contained in DNA, we say that the gene has been expressed.0071

A person might carry a gene for red hair, and that is just the gene.0079

But the actual protein that makes the hair color red, when that is made, we say the gene is expressed. It is expressed in the form of red hair.0086

Now, looking at these names, transcription and translation, recall that DNA is made from nucleotides. The nucleotide monomers form a polynucleotide.0095

RNA is also made from nucleotide monomers.0108

There are slight differences between DNA and RNA, but the essential code is the same.0112

Therefore, a DNA template is simply copied. It is transcribed to make the RNA.0117

That is much difference between RNA and protein, so with DNA, you are working with nucleotides, with RNA, with nucleotides.0125

With protein, it is an amino acid sequence.0132

In order to go from this one type of code - nucleotides - to another code - amino acid sequence - is actually translation.0135

You are not just copying something. You are actually taking the information and translating it into a different form.0145

We are going to discuss transcription first, and to understand transcription, you need to have RNA structure down.0154

Again, this is a topic that was covered under the nucleic acid and protein lecture earlier on, but I am going to review the essentials right now.0160

Unlike DNA, RNA molecules are single stranded.0169

Another difference between RNA and DNA is that they contain uracil instead of thymine.0173

The essential structure is the same, though.0180

RNA consists of nucleotides. It is a nucleotide sequence, and looking at what a nucleotide is, there is a pentose sugar; so that is a 5-carbon sugar.0182

In the case of RNA, the sugar is ribose.0194

In DNA, this oxygen is gone. It is deoxygenated.0198

It is deoxyribose, so this is ribonucleic acid.0202

The second element is a nitrogenous base.0206

And recall that there are two sets of nitrogenous bases- the pyrimidines, which contain a 6-membered ring, and they are cytosine, thymine and uracil.0210

In RNA, you will find uracil. In DNA, you will find thymine, and cytosine is found in both.0224

For RNA, we are just going to have C and U.0233

The second type of nitrogenous base is the purines.0236

These contain a 6-membered ring fused to a 5-membered ring and consist of G and C, adenine and - excuse me - guanine and cytosine, so C, U, G, C.0243

The other thing to be aware of besides the differences between RNA and DNA is the types of RNA.0267

There are multiple types of RNA. Three main ones we will be focusing on.0275

One is messenger RNA. The other is ribosomal RNA, and the third is transfer or tRNA.0279

Messenger RNA is the type of RNA that is used for translation.0289

It is the transcript to make a protein.0297

Ribosomal RNA is not used to make a protein. The rRNA is itself, the product.0303

Ribosomes are composed largely of ribosomal RNA, so these are component of ribosomes.0309

tRNA or transfer RNA delivers amino acids to the ribosome during translation, and we will be going into detail about all three types of these as we go along.0323

We are going to start out mainly focusing on mRNA. All three of these would be transcribed.0340

DNA would be used as a template to form all three types, but as we talk about transcription, I am going to focus on mRNA.0345

And then, we are going to follow that process of transcription with translation.0352

Transcription is the process through which RNA is synthesized using a DNA molecule as a template.0359

There are three phases. Initiation, elongation and termination are the three phases.0368

We are going to go through each of these phases starting out with initiation.0375

Initiation begins with the binding of RNA polymerase to the promoter region.0379

The region on DNA, where this gets started, is known as promoter.0385

Here, we have the DNA double helix, and you see it is separated out here in order to allow transcription to occur.0392

Transcription for a particular gene occurs using only one of the DNA strands as a template.0401

In this case, here we have DNA, DNA, and then, in brown, it is the RNA; and you can see that this RNA strand is using this DNA as the template.0408

This is the template strand. Another name for template strand, we sometimes call it the sense strand, and the other is the antisense strand.0420

During initiation - I will put this right here - the RNA polymerase binds to the promoter region.0430

Promoter regions are also known as TATA boxes because they have the sequence T-A-T-A.0447

Initially, where this promoter region is, the RNA polymerase binds, is slightly upstream of where the first actual nucleotide will be transcribed.0459

Things start out, RNA polymerase binds to this promoter region, and then, slightly pass that, we will get the actual transcription of RNA.0471

In addition to RNA polymerase, there are other factors that bind to this promoter region.0487

If you take it together, the RNA polymerase plus other proteins known as transcription factors,0493

what you have is something called the transcription initiation complex.0506

And the job of these transcription factors is to help the RNA polymerase bind to the correct region.0516

We have RNA polymerase plus transcription factors. All that binds together to the promoter region to get things started.0525

And it is known as a transcription initiation complex.0531

In eukaryotes, there is actually a different type of RNA polymerase for each of those three types of RNA that I mentioned- tRNA, rRNA and mRNA.0535

We are focusing right now in messenger RNA.0550

The one that is used to transcribe DNA into what will become messenger RNA is known as RNA polymerase II.0551

RNA Pol II transcribes DNA into what is eventually messenger RNA.0559

This has occurred. This binding has occurred.0566

The transcription initiation complex has bound.0569

The next thing that needs to happen is the double helices to unwind.0571

And again, helicases are involved in this unwinding, this separating out so that the RNA can use the template strand.0575

Now, for a particular gene, the same strand is always used as a template.0584

Let's look at this DNA and say that there is a gene here that is being transcribed.0589

Well, that is what is happening, and we see that this is the template strand.0594

There might be another gene over here that needs to be transcribed, and this strand may be the template for that.0599

So, the same template is used for a particular gene, but it might be a different strand that is used for another gene, so that is initiation.0606

The next thing that needs to happen is elongation.0617

The initiation complex has bound. RNA polymerase is ready to go.0619

It is bound to the template strand. These other factors are bound.0623

We found the TATA box. The helix has been separated.0628

What is going to happen is that RNA polymerase is going to proceed in the 5' to 3' direction, just like DNA polymerase.0632

And it is going to form a strand of RNA that is complementary to the template strand.0641

Remember that complementary means that we would have G and C. Those two are complementary.0645

And with DNA, when we would say "OK, A is complementary with T", for RNA we do not have T. We have U.0656

For RNA, it is going to be A, U, G, C as complementary nucleotides.0666

Looking here at what I mean, this is the template strand for this situation.0672

This is the RNA strand. RNA polymerase is going to seed T, and that is going to tell it to add A for the nucleotide in the growing RNA strand.0681

For C, the complementary strand is going to be G. For G on the template, we are going to have C.0692

For A, if this was DNA synthesis, we would have T, but it is not. It is RNA synthesis, so instead, we are going to have U, G, C.0701

A on the DNA gives me U, A, T and so on, and recall that we just produced one strand.0713

We do not need a double helix. RNA is just single-stranded.0725

You will also notice that this is the same sequence almost as the antisense strand.0731

It is complementary to this template strand or sense strand.0736

And it is the same as antisense not a 100% the same because you will see here, I have AA GG CC T.0739

There is no T here. There is U instead, CC and U instead of T and so on.0748

OK, the first step was initiation transcription complex - excuse me - transcription initiation complex bound to the template strand.0756

Ch. 17- Transcription and Translation The central dogma of biology is DNA makes RNA. RNA makes protein and protein runs the cell. So, DNA is responsible, or is called the blueprint, for everything in the cell. The first step of translation, which is the synthesis of RNA under the direction of DNA, is called initiation. The promoter of a gene, which typically extends “upstream from the start point”, signals the start of RNA synthesis. In addition to serving as a binding site for RNA polymerase and determining where transcription stars, the promoter determines which of the two strands of the DNA helix is used as the template. The TATA box is an important DNA sequence of the promoter that assists in the binding of RNA polymerase. A collection of proteins called transcription factors help RNA polymerase to bind to the promoter and signal the beginning of transcription. The completed assembly of transcription factors and RNA polymerase 2 bound to the promoter is called the initiation complex. During the next step, elongation, the RNA polymerase begins to move along the DNA, untwisting the double helix, 10 to 20 bases at a time. The double helix immediately reforms and the RNA strand begins to peal away. As this happens, RNA polymerase adds nucleotides to the 3’ end of the growing RNA molecule. Polymerase reads 3’ to 5’, but adds 5’ to 3’. A gene can be transcribed simultaneously by several RNA polymerases, which will increase the amount of mRNA that is produced. The third step of transcription is called Termination. This step differs in prokaryotes and eukaryotes. In prokaryotes, the polymerase stops transcription at the end of the terminator, causing the polymerase to detach from the DNA and release the transcript, which is available for immediate use as mRNA. In eukaryotes, the pre-mRNA is cleaved from the growing chain while the polymerase continues to transcribe the DNA, a specific sequence AAUAAA in the pre-mRNA. Eventually the polymerase falls of the DNA, signaling the end of transcription. Next, the eukaryotic pre-mRNA must be modified during RNA processing. First, the 5’end is capped with a modified version of of a guanine nucleotide, forming a 5’ cap. A poly-A-tail, which is the addition of 50 to 250 adenine nucleotide, is added to the 3’ end of a mRNA molecule. These two modifications seem to facilitate the export of mRNA, protect mRNA from hydrolytic enzymes in the cytosol, and facilitate the attachment of ribosomes to the 5’ end of the RNA to begin translation. Next, non-coding nucleotides, called introns, need to be cut out.

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