hello everyone Today we're going to be covering um energy and cellular metabolism Another name for this chapter this topic is protein synthesis Okay here are the C lows that coordinate with this um topic These are the objectives that you should know by the time you finish this lecture Identify the importance of a gene Identify the starting point of a gene Identify the process involved in protein synthesis Understand and explain transcription and translation in depth Understand the importance of the genetic code Identify the start and the stop codons Identify the various types of RNAs utilized in protein um synthesis Okay Of course these are broad um objectives that you should know Okay So protein synthesis it's a way that your body actually will make a protein So protein synthesis involves two processes Step one or the first process is transcription The second process is called translation So the first is transcription Second is translation Now let's look at transcription What is transcription doesn't transcription sound like transcribe so you're actually writing something So what are you writing in one hand you have DNA You're looking at the DNA and creating or making basically mRNA which is messenger RNA Okay Now where does transcription occur you guys know DNA is found in the nucleus and it cannot leave the nucleus Therefore transcription has to occur within the nucleus Now let's look at translation Translation sounds like you're basically decoding something right basically that's what translation is Via transcription you just created a mRNA Now mRNA is basically formed or found not sorry mRNA just basically contains codes So translation is looking at mRNA reading all the codes and making sense out of it and making a protein So translation is you're looking at mRNA reading the hidden codes in there making a protein Where does translation occur within the cytoplasm okay So right here you see your DNA right here you see mRNA and right here you see protein So what was the process that allowed to look at a DNA and make mRNA out of it so what was the first step of protein synthesis so the first step is transcription which occurred if you guys recall in the nucleus Now we have mRNA in hand and you're going to look at it to make a protein What was that process called translation And if you guys recall translation occurs within the cytoplasm Okay Now let's talk about a gene What is a gene gene is a recipe to make a protein So one gene codes or gives you the instructions to make one protein So think of it this way DNA is a recipe book and each recipe is a gene Okay so here's my double stranded DNA So as you can see it has multiple gene 1 2 3 4 5 6 seven seven genes at the moment Let's say this gene tells you instructions how to make a protein called actin Let's say this gene gives you instruction how to make let's say lipase which is a protein this gene let's say gives you instructions how to make a protein called meiosin etc So you can see all of these genes are found in the DNA okay and each gene is um a recipe for a different protein found in our body So during transcription as I said you are looking at uh DNA and making MRI correct now to be more precise you're not looking at the entire DNA you're not looking at the entire thing let's say your body needs actin do you think you're going to look at the entire DNA to make that mRNA no you're just going to look at this gene specific so let's say you have a recipe book you want to make chicken parmesan do you think you're going to read the entire uh book all of the recipes No at that time you're only going to focus on the recipe that is for chicken parmesan Same concept Now as you saw what is a gene it's a specific segment of a DNA It's still DNA So how does the machinery of the uh protein synthesis know where does the gene start where does the gene stop this is why we have other molecules that kind of identify the starting point and the end point of a gene Let's look at a starting point of a gene It is called a promoter Promoter signifies the starting point of a gene It tells the machinery this is where the gene starts So right here we have the entire DNA These pink letters right here is actually the gene But this portion t a ta the tataw that is actually the promoter As you can see it's found right before the gene right where the gene starts So this is the promoter and it identifies the starting point of a gene Now as we have a promoter that identifies a starting point Let's look at terminator which identifies the end of the gene So again this pink or purple letters are basically the gene right here That was called the promoter Good job What is this portion called this is basically the terminator And as you can see it's at the end of the gene Okay And so it identifies the end of the gene So when the machinery comes across this it knows that the gene has ended Now the promoter is usually not active It's dormant or silent Only when it's time to create that protein in question does the promoter actually get activated Okay So imagine um if you don't if a soul not soul sorry if a store is not having a sale are they going to advertise sale no right right same concept if our body does not need that protein or doesn't need to make that protein at the moment it's not going to basically activate the promoter because what does activation of the promoter mean to the body or to the machinery it tells the machinery okay it's time to make that protein So only when it's time to make that protein does the promoter get activated Rest of the time it's asleep Okay it's lazy So what activates the promoter okay what causes the promoter to basically get up okay what kicks it out of bed that is the transcriptional factor So transcriptional factor will actually cause the promoter to get activated and this in turn will tell the machinery of transcription to basically let's start working So what is transcriptional factors transcriptional factors are usually hormones and they're only released by the body when it's time to produce a protein If you do not need to produce um actin that specific transcription factor for actin will not get produced and secreted Okay let's look at the steps of transcription Okay so transcription has several steps and they are in order We will go through each step and talk about it more in depth but right now here's outline First one is promoter activation meaning you activate the promoter Second step is enzyme entry and binding Okay Third step production of the mRNA which is immature Release of the MR mRNA which is still immature Then you have to edit the mRNA Okay and then release the mRNA By editing the mRNA you're causing the immature to transform into a mature And then once the mature one has formed you release it Okay So let's talk about each step more in depth So right here you can see we have the DNA right now Can you identify basically the promoter no it's basically silent But your body actually needs the protein to be made Let's say this gene stands for actin Okay So when it's time to make actin the transcription of factor TF stands for transcriptional factor Example hormone it will come in and it will bind to the promoter Now we can see because the transcriptional factor is bound to the promoter primar has been activated Okay and that basically tells the machinery it's time to make action So what happens once the promoter has been activated basically the necessary enzyme the worker that actually creates the mRNA comes to play So this is an enzyme called RNA polymerase RNA polymerase RNA polymerase is an enzyme that's going to actually look at the DNA or the gene and actually put down the complimentary nucleotides So the RNA polymerase is going to come and bind to the total box or the promoter and it's going to cause the gene to unwind Only the gene unwinds not the entire DNA Once the chain has basically been unwind unbound what's going to happen the RNA polymerase think of him as a little person he's actually going to look at every single nucleotide and put the complimentary nucleotide down So he's going to walk through basically the gene So the first nucleotide he finds in the gene is a T So he looks at a T and puts the complimentary down which is a A He walks over looks at a a puts a complimentary down and puts a U down Remember it's a U not a T Because a RNA does not contain tying You're making mRNA Therefore it's a U Ursil It will move forward Look at a C put a G down Move over look at a C again put another G down Move over look at a A put a U So the RNA polymerase keeps on doing that It keeps on placing the complimentary nucleotides down and this is creating the mRNA as the RNA form is going through it finally comes across the terminator Okay And this coming across the terminator it tells it that basically we're done creating the mRNA We have come to the end of the chief So what happens when it comes to the promo uh sorry what happens when it comes to the terminator So let's see from the beginning because the transcriptional factor bound to the promoter promoter is activated that calls the RNA polymerase to come in play RNA polymerase moves across moves through the gene creating the mRNA Now it comes across basically the um terminator and when it does that it knows this is the end of a gene So everything goes it separate ways basically um the gene closes up you can see the tata box basically um shuts down the RNA polymerase the enzyme is degraded and the transcriptional factor also is degraded Okay So everything goes in separate ways And this right here is a primary mRNA or another name is immature mRNA Now immature mRNA is basically the reason we call it immature is because it contains material that we need to chop out Think of it like you want to write a paper Do you think you're going to write a paper and submit it no You're first going to have a dough draft right and don't you have to basically modify that rough rough draft to create your final piece same concept So think of a immature as basically your rough draft and a mature one as your final draft So why is the um mRNA we just created why is it immature because as I said it contains junk information It contains information which codes for something and it contains stuff that is basically um useless Okay So right here we have the immature mRNA or the primary mRNA we made As you can see it has two different sections So it has these light gray areas which is called intron and that is the junk information it does not code for anything And then you have these dark blue areas Those are important information because it actually has codes to make a protein So of course we have to get rid of the junk information So mature mRNA should only contain important information no junk So we have to remove the inron and keep all the axons So the first step is removal of the inrons Okay And then putting the exons together So after you create the immature mRNA the mRNA has to go through basically editing process MRNA editing or post transcriptional editing Okay Or post transcriptional modification So there are various names mRNA editing the editing process post- transanscriptional editing or post- transanscriptional modification It just means you modifying the mRNA to make it from immature to mature So what are the two things that you have to do to cause it to go from immature to mature so first is of course removal of the inron As we talked about this is junk information you have to get rid of it Second thing is adding a cap in the tail Where did transcription occur in the nucleus Where does translation occur within the cytoplasm So how does when the mature mRNA when it enters the cytoplasm how does the machinery of translation know where is uh where is the beginning of the mRNA versus where is the end this is why you add a cap and a tail As you guys know cap go in the head which is your front part of mRNA and the tail goes at the bottom which is your end of your mRNA So let's look at the editing process more in detail So the first step you have this immature mRNA because it has exxons and introns So the first step or the first um thing that happens is splyosomes which are group of enzymes and their function is to just cut out the inrons They act like scissors So splicosomes basically cuts away these like gray areas and puts all of the important stuff together So as you can see in this right here you do not have any influence All you have is excellence That's the first step of the editing process Once you have done this then you go into the second one which as I mentioned you add a cap and a tail So cap goes to the front end Okay here's a cap and you add it to the front end of the mRNA What is a cap it's a metal group Okay it's a chemical group Methyl group is a chemical group And the second part is to add a tail So tail goes at the bottom So at the end of the mRNA you add a tail What is the tail it's a polyatil So multiple adenine molecules put together When I say multiple it's about 25 adenine nucleotides put together And when the machinery comes across that it knows this is basically the um tail Okay Once the post-transcriptional modification has occurred meaning you have removed the inrons and put the exxons together and second you have put a cap in the tail the methyl group and the polyatail Once those two things are done then you are done with transcription You have produced a mature mRNA This mature mRNA will leave the nucleus enter the cytoplasm and now transcription has ended translation starts Okay Now a mature RNA have nucleotides The three nucleotides together is called a codon So a mature mRNA is just made up of codes or codons So as you can see these three nucleotides together is called a codon These three is another codon These three another codon another codon another codon another codon So all it is is bunch of codons put together Every three nucleotides makes one codon So it basically contains a message in codes Now what is the importance excuse me What is the importance of a codon a codon represents a amino acid One codon means one amino acid Example aug is a codon and it represents amino acid called methyomine Now a genetic code is 64 codons but we only have 20 amino acids Okay So one codon can only represent one amino acid but that amino acid can be coded by multiple codons I know that sound confusing So let's say you have leucine that is an amino acid So leucine is an amino acid Leucine can be coded by multiple codons So here's one amino acid A UU can code for leucine CCC can code for leucine UU can code for leucine or CGC can code for lucine So as you can see multiple codon can represent one amino acid but ccc will always code for lucine CCC cannot code for anything else but lucine Same thing a uu can code for lucine but nothing else So one codon means one amino acid always But that amino acid in turn can be represented by multiple codons Now of course I don't expect you to know all 64 codons Heck I don't either But there are four important ones that you do have to know about What are the four you have to know a UG UA U A UA Those are the four that you have to memorize Now why do you have to memorize them because they are the start and the stop codons So AUG is a start code on meaning it codes or signifies the starting point of the mRNA It starts off translation AUG is always the first nucleot first codon in mRNA What does AUG stand for the amino acid methionine So if aug is always the first codon and it coats on methionine methionine is always the first amino acid in a protein UAA U A UA those three are stock codons The reason they're considered stock codons because these three do not code for any amino acid And therefore because they do not code for any amino acid when the machinery comes across any three or any one of these it's going to know that this is the end of mRNA and translation ends Now is the mRNA going to help all three no It's only going to contain one out of three Some mRNA will contain this others will contain this Just depends on which one Okay Okay So now we're going to actually talk about translation more in depth So translation is you're looking at mRNA the codons and making protein because you're putting down complimentary um amino acids and as you guys know a chain of amino acids is called a polyeptide chain which is a primary structure of a protein Um where does translation occur in the cytoplasm what are the three steps of translation initiation elongation and termination So now we're going to go through and talk about each step in detail Now there are three different types of RNAs that you need to make translation You need mRNA which stands for messenger which we just made via transcription You need tRNA okay which stands for transfer and you need RNA which is called the ribosomal RNA Now let's look at each RNA more in depth So function of RR RNA holds and moves along the RNA during translation So think of RRNA as basically pieces that hold mRNA in place So think of a let's say a burger okay you have the patty right in the middle You have the lettuce tomatoes and you have the two buns right the two buns okay would basically be the RNAs Okay the patty would actually be the mRNA and then the lettuce tomatoes all of that would be the tRNA Now uh rRNA looks at each codon and allows the appropriate amino acid to be placed down because of the tRNA Now let's look at rRNA more in uh depth So here is the ribosome The reason it's called ribosomal because ribosomes contain the RRNA So here is basically the ribosome The ribosome or the rnas have two main um components or subunits It has a large subunit and a small subunit Large subunit and a small subunit These are usually separate They're not together Only time these two components come together is during translation So here's the the um the top of the bun Here's the bottom of the bun and the blue that's the mRNA This is where the mRNA would be As you can see it's holding it in place Now the small subunit is a 40S And yes you have to know the numbers The large unit is 60S 60 cents per size So large subunit is 60s small subunit is 40s Why is this important when you go into microbiology bacteria also have ribosomes But their ribosomes the size are different They have a 30 and a 70s So when you take antibiotics likein they are targeted towards ribosomes but they are targeted against 70 or 30s and therefore they don't harm other ribosomes They only harm bacterial ribosomes Now to get a closer look the large subunit has two distinct sites It has a p site and a a site A site is to allow the tRNAs to enter the T I just wrote T the tRNAs to come in and the P to allow the tRNAs to exit Now what is the importance of tRNA in translation they are the mole that carry the amino acids okay in the process So let's look at uh tRNA in depth So here is a tRNA As you can see it looks like a T right it looks like a T Now tRNA has two arms It has antic-codon arm and it has a amino acid arm So antic-codon arm and amino acid arm Amino acid arm has the amino acid Okay Where the antic-codon arm is used So the codon and the antic-codon can come together So example let's say this is the antic-codon g a u So it's there So the tRNA can bind to the codon on the mRNA So so the codon and the mRNA would be ca So when the appropriate tRNA comes in it's able to bind to it because as you know C and G get attracted A and T get attracted A and U get attracted So this allows the tRNA to basically bind to the mRNA and it's carrying the amino acid right here So CTA can code for the amino acid So whatever amino acid CTA the codon codes for this is amino acid it's holding here So example So on the mRNA you have the codon aug So what what is going to be the anticodonum right here so this tion can bind to this codon What do you think so A would bind with Q U will bind with A and G will bind with C So this tRNA that can bind with this codon the antic-codon would be U A C What amino acid would you have here a UG is a start codon and it codes for the amino acid methionine So methionine would be right here Okay So think of anticodon and a codon as basically velcro One is the rough side one is the furry side and they can bind together Same concept Okay Okay So now since we kind of laid the foundation of the um RNA needed let's talk about the three steps of translation Initiation elongation termination Let's look at initiation first Initiation is just getting everything to come together It's like when you're going to cook you kind of get all of your ingredients out and put them down Same concept initiation is you're just getting all the material setting it up so you can basically start translation So the ribosome comes together binds to basically the mRNA and it's going to bind to the first codon which is aug and therefore the tRNA that can actually bind to aug would come in with methionine Okay So example So here is basically the mRNA So you can see the ribosomes come and bind to AUG Sorry I kind of do that wrong Let me do it up here So the aug So here's a ribosome Here's the A site looking at the AUG Here's a P site So this tarn comes in which can bind to the AUG So it has anticodon U AC It's holding the amino acid methionate As soon as this comes or sets up we're done with initiation We're going to go into the next part which is elongation So elongation is basically where the polyeptide chain is getting longer Elongation stands for elongating So what happens is this ribosome complex moves one codon over Okay When it moves one codon over the new tRNA comes And once the new tRNA comes and the amino acid makes a bond As soon as the amino acid makes a bond the old one leaves the ribosome moves over one more And when it moves up over the new tRNA comes in The amino acids make a link The old one leaves then the ribosome complex moves over Does that make sense i know it's hard to visualize and we'll do a visual visualization during class So this is basically elongation You can see the polyeptide chain is just basically getting longer Okay The last part is termination In termination is basically just tells you that translation has ended Okay So when the ribosome is moving along and it comes across the stop codon UAA UAG UG any one of those it knows this is end of translation Why are those the stop code on because they do not code for any amino acid So as soon as the ribosome comes across the stop codon it knows it's time to finish It's done with this shift So ribosome complex breaks apart The large goes away the small goes away There's no more tRNA coming in And what happens to this polyeptide chain it actually goes into the rough ER and this is where it's going to obtain a secondary tertiary and maybe quantitary structures after which it will go into goji apparatus do the refining process and then you have created a protein So this was basically the step of termination Termination is just ribosome and um the slot subunit small subunit going its separate ways and the polyeptide chain released so it can go into the ER and at that point translation has ended and we are done with transcription and translation which are the two steps or two processes for basically protein synthesis This is just um the image of translation al together That's it If you have any questions let me know