this is part one of the chapter 8 lecture this chapter is all about microbial genetics in part one which is this lecture um we're going to talk about DNA replication transcription translation and also mutations so big picture what is genetics that brings us to a few different things one is called the central dogma of molec biology which I'll show you what that is right now mutations are something that we're going to talk about and mutations are changes in DNA and not all mutations are bad some of them are detrimental some of them can actually be uh like a survival Advantage for the microb some of them don't really matter they're neutral so we'll talk about that um and then we're going to talk also about gene expression that's controlled by operons now we have haven't learned what what an operon is yet but we're going to learn it in this lecture and whenever we say gene expression or if I say a gene is being expressed that means that a gene is being used to make a protein and that brings us back to that first point here central dogma of biology basically states that in order to make a protein for whatever function that protein has inside of of the cell everything starts from the genes so it all has to begin with the DNA from the DNA the cell makes RNA and then from that RNA the cell makes protein and that protein will do whatever its function is whatever it's supposed to do this is the typical chain of events whether that protein is going to be a channel whether the protein is going to be a certain type of enzyme whatever it's going to be um it always follows this order so even though you're saying okay this is a protein and that's DNA they're two completely different organic compounds they have they're kind of intertwined so what happens if there's a mutation like I said A mutation is a change in the DNA it's an alteration of the DNA sequence so if the DNA is mutated then the MRNA is going to be mutated and if the RNA is mutated then the protein is going to be mutated and the function's going to be off maybe it'll have a different function maybe it won't function but everything basically gets thrown off okay so altering the genes of bacteria or kind of messing with gene expression in bacterial cells helps us get a lot of information so knowing how bacteria work their processes how they express their genes can help us figure out out um how they cause disease so that we can work on preventing it um treating diseases what drugs we can develop and we can even manipulate bacterial genes and gene expression for our own benefit um so a lot of times we've talked about previously how bacteria reproduce so fast right they divide so fast their population doubles so fast and so efficiently so if for example I'm trying to make a certain type of product in the lab and sell it whatever it is it could be like medication or insulin or whatever it might be um I can insert that Gene into bacteria and it can make that product for me and it'll make a bunch of it CU it's so many cells and then I can use that um for example in like Pharmaceuticals there are other ways too but we'll learn about other ways later on okay so some vocabulary to in introduce us to all of these processes the first term here is genetics genetics is the study of genes and it's not just knowing what that Gene looks like it's also knowing okay what information does that Gene carry what is it about what information is going to be expressed what protein is it going to code for all of that is genetics and then chromosomes those are structures that carry the DNA they contain the DNA they're made up of genes um and so if you recall eukariotic chromosomes were linear whereas bacterial chromosomes were a single circular chromosome and we're going to see that again in this lecture genes are SE uh segments of DNA sequences of DNA and I like I said they code for proteins okay in other words they encode proteins everything starts with the DNA and then if you say the g Genome of something it's all the genes inside that cell so if we say the human genome it's all the genes that humans carry if I say the Genome of eoli then it's all the genes that eoli cells carry so just some terminology to get us started okay so we mentioned the central dogma is going from DNA to RNA to protein so this has to do with the genetic code the genetic code is basically the processes that we're going to look at in this video that takes us from nucleotides to amino acids if you recall the building blocks of DNA were nucleotides right the building blocks of proteins were amino acids so how do these come together how do we kind of translate from the language of nucleic acids to the language of proteins cuz they're totally different building blocks totally different organic compounds so going from DNA to protein it's a big pathway and it's called the genetic code a couple of other terms here that um you've probably learned in previous classes genotype versus phenotype when you think of genotype think of the genes that the cell is carrying phenotype think of the physical expression of the gene like for example if I have Gene a and that codes for brown eye color the gene a is the genotype the color of my hair that I expressed that you can see the physical trait is the brown hair okay so like I mentioned um a minute ago bacteria have a single circular chromosome and the chromosome is of course made up of the genes made up of the DNA and there are also these proteins associated with the DNA molecule that help it do all of its function which we'll see in a second now normally when we think of the flow of genetic information or passing genes we kind of think of it as passing down genes right so parents pass down their genes to their offspring and then those offsprings will pass it down to the Next Generation and to the next and so on this is called vertical Gene transfer going from parent to offspring to the next Offspring through generations vertical Gene transfer in part two of this lecture we're also going to learn about another process called called horizontal Gene transfer so um you'll see that later on okay so we're going to talk about a lot of processes a lot of steps in this chapter it's really important to keep them separate so the first process is DNA replication when when would DNA need to be replicated if I'm a bacterial cell what in what circumstance would I be replicating my DNA if you said binary fishing or cell division that's correct if you recall when we looked at those steps that diagram um in a previous chapter of binary fishing we saw that one of the major first steps is the parent cell makes a copy of its DNA so that when it splits it has identical daughter cells right when it splits into two cells so DNA replication is a really important thing when it comes to cells dividing and reproducing so before we get into the steps of DNA replication we do have to get into the details of the DNA molecule some of which we've learned before so DNA forms a double helix okay remember it's double stranded and it's in this helical coiled shape now this is what a DNA molecule looks like now if you recall it's made up of nucleotides right so each nucleotide has a sugar a phosphate and a base right so all of these nucleotides they join together to make the DNA molecule so here I want you to see that this strand right here and this strand right here this is called the backbone of DNA and the backbone is made up of the sugars and the phosphates and since we're talking about DNA the sugar is deoxy ribos and in the center here kind of sticking out sticking inside um between these strands that's where the nitrogenous bases are these are the a the T the C the G and these base pairs between them are actually hydrogen bonds and um between a and t you have two hydrogen bonds between G and C you have three hydrogen bonds that's how it always is so once again this is one strand this is another strand the backbone of DNA is made up of deoxy ribos and phosphate and then the middle consists of the bases that base pair with each other through hydrogen bonding another thing we want to learn about DNA is that the strands are anti-parallel notice in this strand this end is called the five Prime end and this end is called the thre Prime end it's the opposite for this other strand the three prime end is up here five Prime end is up here so they're parallel but they're going in reverse Direction so we say that the strands are anti-parallel and the Order of these bases whatever order it may be is going to be the genetic instructions remember we're if we're trying to make um for example if we're trying to make a protein from a DNA the sequence of these bases the order is going to determine what protein is going to be made okay all right so let's go over now again DNA replication which is um done during cell division or binary fion now for DNA replication to occur the DNA double strands they have to separate from each other and so once these strands separate from each other so you have one original strand here one original strand here or you can call it a parent Strand and so each of these parent strands are going to get a complementary strand so let's go over those steps remember we have one DNA molecule and we want to double it right we want to replicate it so first thing that happens is the strands need to relax there are two enzymes that come come in and relax the strands these are Topo isomerase and gyas and then a third enzyme comes in called helicase and it separates those strands and this creates a replication fork think of like a fork in the road so here is the regular DNA molecule everything's together and then the strands relax and they separate so notice that now we have this parent strand here and this parent strand here and now this is creating a replication fork okay all right then a really really big enzyme like the main player comes in and this is called DNA polymerase remember a polymer is basically a big molecule right so DNA polymerase is going to polymerize DNA in other words is going to synthesize a DNA molecule and remember DNA strands are made up of nucleotides joining together so DNA polymerase is an enzyme that comes in and it keeps adding nucleotides to the new DNA strand building a new complementary strand now when we say complementary strand this is what we mean so for example if I have a t a a g c c just an example if this is my parent strand so I'm going to call this the OG strand okay so this is the original Strand and that serves as a template we are basically making a complimentary strand to this so my new strand is going to be so this is going to be my new is going to be complimentary so what's the complimentary base pair to a it's going to be T complimentary base pair to T is going to be a so if you keep going it would be t t complimentary to G you have C and then you have G G okay so I know that it's not a straight line but you get the point all right so one thing you want to keep in mind is that the synthesis of newly of new strands always is made in the five Prime to three prime Direction so this new strand of DNA that the cell is making is always made in the five Prime to three prime Direction and DNA polymerase can't start on its own DNA polymerase requires an RNA primer basically like a tiny short piece of RNA to come in and initiate the process so this is what it looks like this image is pretty helpful so here's my DNA double helix like normal and then the strands relax and they separate and here's a replication fork right okay so here the dark purple is my parent strand the original Strand and and then this light purple is the newly synthesized strand the newly synthesized strand is always going to be made in the five Prime to 3 Prime Direction so keep that in mind it's always going to be five Prime to 3 Prime now in order for this replication to start we need RNA primer to kind of start the process once it starts the process then DNA plumis can come in and it can start adding nucleotides to each other now remember we're making a new strand here and a new strand here so there are two types of strands that are made this one is called the leading strand the leading strand is synthesized towards the replication fork so you can see the arrow it's being synthesized toward the replication fork DNA polymerase is just adding adding adding okay but still five Prime to three prime and then the other strand is the lagging strand that you can see here it's being synthesized Siz again 5 Prime to 3 Prime and you can see the DNA polymerase joining those nucleotides now keep in mind or you can see actually from this picture the leading strand is continuous it's just one smooth strand all ready to go however the lagging strand which is synthesized away from the fork notice that it's in fragments it's kind of choppy that's because it's Le it's being made away from the replication fork so DNA polymerase keeps having to jump off and come in and keep adding the nucleotides so there's some gaps here it's very choppy so we say that the lagging strand is discontinuous and each of these fragments that are made we call them okazaki fragments at the end of this process there's another enzyme that comes in called DNA ligase and it basically joins these fragments together to make it look like a continuous strand so now at the end you have twice the amount of DNA which will be contributing to the cell division okay so one more time going over the steps here I have my DNA and it wants to be replicated right so the cell wants to replicate the DNA so that it can divide and it can have two copies so Topo isomerase and gyas relax the strands helicase separates the strands and now you have a replication fork each parent strand serves as a template for the newly synthesized strand two types of newly synthesized strands are made the leading strand is synthesized towards the replication fork and it's continuous the lagging strand is synthesized away from the replication fork and it's discontinuous okay um and so it creates these okazaki fragments and remember that in order for DNA to DNA polymerase to make that new DNA strand it requires an RNA primer to first come attach and initiate the process at the end DNA ligase seals these okazaki fragments up and glues them together so everything's like continuous another thing you want to keep in mind is that newly synthesized strands are always synthesized in the 5 Prime to 3 Prime Direction so this is DNA replication now most bacterial DNA replication is bir directional so if you go back to this image notice that you have a fork here and you have a fork here because it's a circular DNA which is like this image right here whenever you open it up you act you actually get two forks one here and one here so two replication forks so for that reason we say that D bacterial DNA replication is bir directional it's going in two directions and each offspring cell is going to receive one copy of the DNA right the two identical daughter cells each have a copy of that original DNA and replication is also proof red so DNA polymerases the enzyme DNA polymerase has proofreading abilities so it can come in and just double check hey maybe there's a base pair that's not matching up maybe an a is accidentally base pairing with a c whatever it might be um it has a level of proof reading it can't fix everything but it can come in and just review because you don't want a mutated DNA to be transferred okay so remember that that's its own process that's DNA replication so whenever you're studying this study it separately so if I were you and I'm going to study this chapter I would study DNA replication I would know the steps the purpose then I would take a break and then I would study the next process then I would take a break and study the next process because it's really easy to mix everything up because we're talking about the same compounds we're just doing the cell is just doing different things with those compounds okay so moving on to RNA and protein synthesis so whenever if we go back to the central dogma the process of going from DNA to RNA is called transcription and going from RNA to protein is called translation so now we're going to go through the process of transcription and the process of translation and remember this has to happen in order for the cell to make any type of protein it has to start from the DNA that's why DNA is so important and it's so protected cuz without it can't really make too many things okay so let's review RNA structure really quickly remember RNA is another nucleic acid similar to DNA however it's sugar is ribos instead of deoxy ribose um and so that's why it's called ribo acid it is single stranded whereas DNA is double stranded and it contains uricel instead of thymine okay and speaking of RNA there are different types of RNA inside of the cell and all of them contribute to protein synthesis so we have ribosomal RNA or R RNA which makes up part of the ribosomes and we already know ribosomes function is to make protein we have Transfer RNA or TRNA just by the name alone you know that it transfers so it actually transports amino acids in order to put them together to make proteins at the end of this whole process because remember the point is to make protein whatever that protein may be and then the third type of mRNA and the most abundant is messenger RNA the MRNA whenever we're talking about oh in transcription DNA so RNA is made we're talking about the MRNA so that's kind of like the middleman between the DNA and the protein so it carries information from DNA to the ribosomes for a protein to be synthesized so it starts with transcription remember in transcription you start with DNA and you're making essentially a complementary RNA strand to that DNA okay so I'm going to just draw this in the previous slide so for example if my DNA strand okay I'm starting with a DNA and let's say it's t c g g a a c just for example so that's my DNA what I'm doing in transcription is I'm making an mRNA complement to it so my mRNA is going to be complementary to my DNA meaning the base pairs are going to match up but remember instead of T we have U so T would be complimentary to a c is complimentary to g g is complimentary to C again G is complimentary to C and then a is going to be complimentary to U right and so this is what the MRNA strand would look like and it's pretty simple that's basically what it is but this time since we're making RNA the main enzyme here is going to be RNA polymerase your polymerizing RNA you're synthesizing RNA so this process right here is transcription okay so in proc carots so we're going to talk about transcription procariotas first again you're synthesizing a complementary RNA Strand and the RNA strand is an mRNA transcription begins at a specific sequence of DNA right before the gene um and that's called a promoter sequence it's basically your start site that's the site where transcription Begins for a certain Gene transcription and the synthesis of that new mRNA strand is again five Prim to 3 Prim Direction and only one of the DNA strands gets transcribed okay so DNA strands remember you have two of them only one of them is used for transcription when does transcription end just like how we had a promoter sequence that initiated the process we also have a Terminator sequence in the DNA that will end the process of transcription okay so if you look at this image right here again we have the DNA and in transcription we make an mRNA complement to the DNA so this green strand right here is mRNA and you can see it's complimentary and it's being made and the enzyme here again is RNA polymerase okay now that was transcription but remember that's the first step in order to get to proteins there's one more process which is translation and you're literally translating the language of nucleic acids to the language of proteins their building blocks are different so how are they going to kind of match up so how does the MRNA basically make proteins how does it help it happen each group of three mRNA nucleotides just think of like bases so each group of three bases codes for a specific type of amino acid remember there are 20 different types of amino acids and we have codons that can basically code for any of those amino acids so that brings us to the genetic code the genetic code is basically like the translation between mRNA language and protein language so here if let's say I have a three bases and remember it's three so every three is a codon so if let's say I have auu I can see that it codes for the amino acid isoline if I have CAC it codes for the amino acid histadine if I have ggu it codes for the amino acid glycine so the genetic code this table kind of puts it all together so it can literally be translated so there is a start codon and there are stop codons the start codon is basically the signal that begins the translation process so the start codon is going to be the first codon at the beginning of every protein synthesis and the start codon is Aug whenever a protein is finished being made and it's complete and it's ready to go we also have nonsense codons or in other words stop codons we have three stop codons UAA u a and UA so these stop codons literally stop protein synthesis or in other words stop translation and the codons of mRNA are read sequentially meaning you go in order so if let's say I have mRNA here and it's u a so that's one codon yuuu that's the next codon so whatever amino acid is quoting for this comes first then the next amino acid then the next okay all right so let's go over the process now mRNA is the transcript that we just made right at the end of transcription now we're going to see how TRNA and r RNA come into play so let's go through the steps so this right here this strand is my mRNA the one that we just made from the DNA ribosomes come in the large and small ribosomal subunit assembles on the MRNA and the TRNA comes in notice that the TRNA has a really weird structure it has a weird shape to it and it literally does look like a t so the TRNA has two components that are important for us to remember on the bottom here it has an anti-codon an anti-codon is complimentary to the codon so over here I have my start codon Aug and I have my complimentary anticodon on my first TRNA molecule which is UAC another thing on the TRNA molecule at the top here is the amino acid so the TRNA comes in holding the corresponding amino acid and it brings it so let's look at the steps everything assembles right and notice that there are these three spaces over here we call them sites we have the arrival site or a site the P site in the middle and we have the E site or I call it the exit site the first TRNA that comes in is going to sit at the P site the rest of them arrive at the a site like the arrival site so it comes in and remember the start codon is always the same and it codes for the amino acid methionine make sure you remember that you're not responsible to memorize all the amino acids but you do need to know the first one is methionine and that's what the start codon codes for is methionine as the amino acid so that's always going to be first beginning of every protein and then the next TRNA comes in the next TRNA molecule has an anti-codon that's complementary to the second on here in sequence right the next codon over it comes in and it arrives in the a site and it's holding the next amino acid these two amino acids join together through peptide bonds to start making the chain of amino acids or in other words start making the protein and then they kind of shift over the one in the middle goes to the E site the one in the a site goes to the P site so you're always just like shifting one SE heat over and then the next TRNA arrives at the aite this one again anti-codon complimentary at the bottom holding the next amino acid at the top right and then these are going to peptide bond with each other and so again your amino acid chain is growing the one that was at the East Side exits they shift one over the next one comes in right and so each time TR is coming in you're building that amino acid chain or that polypeptide chain with peptide bonds okay all right then whenever a stop codon is reached that's a nonsense codon it doesn't code for any amino acids so that's the signal to terminate the process that's the signal that says hey this protein is complete it's done and so everything disassembles and your new protein is ready to go that's the process of translation now translation in bacteria um Can Happen simultaneously with transcription so even if the MRNA is just made and it's not finished being made the codons are already starting to be translated into proteins very very efficient very very fast but it's also important to remember that everything's happening in the same place in a bacterial cell right there's no there are no organel so there's no nucleus there's no GGI so everything's in the same room so and everything can happen simultaneously very very quickly and together eukaryotic cells are different so let's talk about some things um about eukaryotic cells one is that the genes are different the chromosome or the DNA in bacterial cells all of it is called coding DNA all of it can code for different types of proteins however you carotic organisms the DNA has a lot of fillers so there's parts of the DNA that do code for proteins but there's also parts of the DNA that don't code for anything so they're just like filler DNA so they don't do anything they're just there the parts that do code for proteins are called exons the parts that do not code for proteins are called introns and so what has to happen is you want to get rid of the introns you don't want to translate anything that's useless remember the cells are very smart with their energy they don't just waste it so there are these proteins called snrnps which stands for small nuclear ribonuclear proteins they will come in and remove the introns and join the exons together so let's look at that process here I have my DNA right DNA gets transcribed into my mRNA notice that there's exons and introns right right then my snrnps will come in they'll remove those introns and they'll stick all all the exons together so now this whole thing is coding all of it can code for different proteins so this is called splicing and this is an extra step that happens to the MRNA before the MRNA even leaves the nucleus remember eukariotic cells have organel the DNA does not leave the nucleus it's really important as we can see right it's like sets the stage for everything to happen so the DNA does not leave the nucleus so transcription happens in the nucleus and mRNA leaves after it's mature and then translation happens in the cytoplasm so it's a little bit different okay moving on to another subject kind of and remember I'm going to remind you one more time study these processes separately so study DNA replication separately transcription separately translation separately you can kind of look at the bigger picture and how they're all involved with each other but if you're learning individual steps separate them because they start to kind of all mix together okay so I mentioned a minute ago that cells do not like to waste energy cells are not going to express genes if they don't need to they're not going to waste their time they're only going to express genes that they actually need genes that are always expressed they're always needed are called constitutive genes so these are basically like the DNA polymerase the cells are always going to want to divide so they're always going to need DNA polymer so that one is constantly being made however there are genes that are only going to be expressed if they're needed like depending on the environment so if I'm a bacterial cell and I'm in an environment and I see that I have to make more of a certain protein I can express that Gene if I'm in an environment where there's a protein that I no longer need to make then I can not do transcription I can turn off a gene so these genes that are not constituted constitutive they are called inducible genes or repressible genes inducible genes are genes that can be turned on induction turns on gene expression it turns on transcription so normally these genes are off but they can be induced normally these genes are off but they can be turned on repression is the opposite to repress something means to block it so repression is going to block gene expression it's going to inhibit transcription from even happening and so repressors are proteins that repress okay now now these with repression it's going to be on a gene that's normally on so the gene is normally on but it can be turned off the gene is normally being expressed but it can be repressed so induction is the action and the protein that does it is the inducer repression is the action and the protein that does it is a repressor and one more time genes that are always on on can be repressed genes that are off can be induced this is something that can get complicated so make sure you sit with it you understand and you're able to explain it and make sense of it okay now we're going to Define that term I mentioned earlier which is the operon so there is the promoter site that initiates transcription on the DNA okay there's also an operator site which is a sequence of DNA that controls the transcription so it's kind of like the supervisor it's kind of like the manager um setting that gene expression whether it's going to happen or not together operator sites and promoter sites are called the operon so it's basically a region in the DNA made up of promoters and operators that are in charge of gene expression okay and they're in charge of transcription so we're going to use one example of an operon and this example is going to be an inducible operon if it's inducible that means it's normally off the genes are not transcribed or expressed unless there's an inducer turning it on okay in this example um this is called the lack operon and it has to do with lactose lactose can be can serve as a nutrient if lactose if a bacterial cell wants to use lactose from their environment and break it down and use it for energy then they need enzymes to break the lactose down if there's lactose in my environment and I want to break it down I have to express the enzymes to break it down right but if there's no lactose around am I going to need the enzymes for breaking down lactose no I don't need it and I'm not going to waste my energy making them right I only I'm going to make them if there's lactose there and I need it so when lactose is not there like we mentioned normally the gene is off so normally there's a repressor that's bound to the gene bound to the operon that is blocking transcription the gene is off however in the presence of lactose lactose acts as an inducer this inducer which in this case the lactose is going to bind to the repressor and not allow the repressor to block transcription so it's kind of like blocking the blocker it's inhibiting the inhibitor so it doesn't allow the repressor to block transcription anymore and so the Gene gets expressed so once again the gene is normally off there's normally a repressor on it if lactose is present then it will go and it'll bind to the repressor and it will basically turn off the repressor it won't let the repressor do its job and so now the gene will be turned on okay so that's the lack operon and that's an inducible operon there is another example which is a repressible operon I'm not going to ask you about the example the only example for operons is the lack operon but you do need to know this first bullet point repressible operons these are genes that are normally on but they can be turned off if they're not needed so that's a repressible operon so it could be either one now another way to turn genes off is by methylating it so adding a methyl group just like how we have like functional groups like Amino groups or phosphate groups adding a methyl group to the nucleotides actually turns genes off off okay it'll turn off transcription and if I'm a parent cell and I divide and I have Offspring cells they can actually inherit the methylated genes those off genes but it's not a permanent change The Offspring cells the daughter cells can take that those methyl groups off and turn those genes back on so this is just another way of controlling gene expression the last two ways of controlling gene expression has to do with posttranscriptional control post meaning after so these are ways to modify the RNA in order to stop translation and the protein not be made so far we looked at changes in the DNA and how the DNA can be controlled um and genes can be turned on and off but post-transcriptional control involves the steps after transcription so there's one uh one the ribos switch the ribos switch is one part of the MRNA molecule that can actually bind to another molecule and it causes the MRNA to change its structure and if that happens translation is blocked the process ends it stops another way is using micro rnas micro rnas basically are specific types of rnas that can base pair with the MRNA to make it double strand remember mRNA is not supposed to be doubl stranded so the cell will see this and it'll break it down with enzymes it'll destroy it so the proteins again won't be made these are things that can be done if let's say there's a mutation you can't save it you can't fix the mutation then you would try to stop the process because the cell doesn't know how the protein is going to act maybe it's going to react with things it's not supposed to it could be um it could be a big problem okay so the last part of this lecture of this part one of this lecture is mutations mutations are alterations in the sequence of DNA they're permanent changes in the DNA and like I mentioned earlier mutations can be neutral where they don't really affect anything they can be beneficial they can cause the bacteria to survive better or they can be harmful and they can cause harm or detriment to the cell things that cause mutations we call them mutagens and mutations can happen randomly these would be called spontaneous mutagen so if it's not like a physical or chemical mutagen specifically causing that mutation mutations can happen all the time spontaneously and that happens a lot especially in bacterial cells because they replicate so fast and they reproduce so fast they're prone to more mutations all right different types of mutations so um base substitution or we can call that a point mutation is a change in just one base of the DNA maybe an a is switched with a t or a c is switched with an a whatever it might be now if that point mutation if that base substitution results in a change of an amino acid like the amino acid was supposed to be glycine but now because of that base change the amino acid is loosing that is called a Mis sense mutation when the amino acid changes so for example here it was supposed to be glycine but there was a mistake here and now it's sering it totally changes the protein now if the base substitution same thing happens but it ends up creating a stop codon so one of those three stop codons then the protein is truncated meaning the protein was normally supposed to be this long but now because of this base change um it ended up in the stop codon so now the protein's really short and again the function has been defective um another type of mutation these are called frame shift mutation that's when um nucleotide pairs it could be two nucleotides or more are basically inserted or deleted or removed from the MRNA and so this basically shifts the reading frame so if for example here I had remember you have codons right so we have these three these three these three these three if for example this a got removed it's totally Shifting the frame so now this was supposed to be lysine which it still is this is supposed to be fenal alanine but totally different amino acid now glycine totally different amino acid it kind of shifts everyone in One Direction doesn't have to be removal it could be insertion too and it could be five Amino uh it could be five nucleotides okay the last part of this video is just mentioning an example of a chemical mutagen which is nitrous acid nitrous acid is a chemical mutagen that causes adenine to bind with cytosine instead of thyine meaning a will bind with C but it's not supposed to right it's supposed to bind with T so this is a mutation that's caused by nitrous acid okay this concludes part one of this chapter and then we'll go over part two which is about um horizontal Gene transfer