everyone this is the third in a series of videos I'm making about the biology and of course is an exam in North Carolina now these videos are meant to help students review essential content in preparation for the biology EOC but they can use as a reference for a lot of basic biology topics if you follow along I encourage you to use the resources linked in the video description and go ahead and subscribe if you like this kind of material so this third video is gonna focus on evolution and genetics which is a huge part almost half of the biology EOC in North Carolina a lot of these topics are good to review by doing practice problems so I encourage you to practice some of these after you're done with the video we're gonna cover essential stand essential standards 3.1 through 3.5 as well as their objectives which include topics like DNA protein synthesis mutations meiosis inheritance patterns effects of environment on gene expression biotechnology genetic engineering bioethics evidence for evolution natural selection disease influence classification systems dichotomous keys and cladograms but keep in mind this video is meant as a review so we won't have time to touch on everything just the simplified essentials we're starting with the structure and function of DNA remember DNA or deoxyribonucleic acid is a nucleic acid and it is made of nucleotides a nucleotide is composed of a phosphate group a sugar and then of course a base which in DNA is a T G or C adenine thymine guanine or cytosine now the sequence of nucleotides in DNA codes for proteins which is key to all the operations that a cell will do and most all cells of an organism have it's the same DNA but that DNA that is expressed will differ so a muscle cell may express different parts of the DNA as opposed to a skin cell or a liver cell but every single salad within an organism's body is going to contain the same genetic code so DNA's structure is a double helix or a twisted ladder and the sides are composed of this phosphate sugar backbone that phosphate group and the sugar and the rungs or the middle parts of the ladder are composed of our complimentary basis so adenine pyramid thymine guanine pairing with cytosine always and these are joined together by hydrogen bonds so this is our double helix here this is the same structure but it's just flipped on its side and untwisted and you see a spared with T's and G's pairs with C always and then this is our base period fools you might want to remember this in a weird way like all teachers can go or Appletree good cookie as long as you remember that eight pairs of T and G pairs with C so if you were asked to write the complementary sequence for a DNA strand what you would do is just make sure you write the base pairing rules so for this one it starts with T a T you would want to write a T a so here's the full strand T pairs with a eight pairs with T T pairs with a GPS OC etc until you make sure you've completed the entire sequence now replication occurs in a specific stage of the cell cycle and allows daughter cells to have an exact copy of DNA so that's gonna happen during S phase remember we went over the cell cycle in another video so go back and watch that if you need more of you so the reason DNA replication has to occur before a cell can divide by mitosis is that we want to maintain the same number of chromosomes in the daughter cells as the parent cells so I want you to think about that if this cell were to split apart without dividing this DNA we would only get half and each daughter cell and if they were to split they would only get half and finally we would have just have my neuts amount of DNA and wouldn't be very good for replicating itself now DNA replication is what we call semi conservative meaning that the DNA is split apart and then a new strand is built off of the old template on each side and we end up with two new strands one with an original strand and one with a brand new strand built off of new nucleotides alright and remember that DNA holds the instructions for proteins in a Cell so if we talk about how to make proteins we need to go from our DNA transcript to mRNA and then the mRNA is going to help build the proteins so cells respond to their environments by producing different types and amounts of proteins and all cells of the organism like we said before are gonna have the same DNA and express different proteins depending on what they need and protein synthesis is just the process by which DNA is translated and transcribed into proteins so it's a fancy way of saying how proteins are made and transcription is going to produce RNA from DNA and then translation is going to produce proteins or an amino acid chain from the RNA and these amino acids are linked by peptide bonds to form polypeptides so we have a lot of different uses for proteins in the body including hormones enzyme chemicals involved in special reactions structural proteins transport proteins and all of these are going to get the jobs done for the organism and the cell and also give the individual the traits that they have so the whole process of protein synthesis again goes from DNA to mRNA to protein and remember the step of transcription is DNA to RNA and translation is RNA to protein sometimes you'll be asked to use a codon chart that's part of the translation process so make sure you google practice questions with codon charts if you're not quite sure how to use them let's move a little bit on the differences between DNA and RNA DNA remember is double-stranded it has a deoxyribose sugar and it uses T or thymine RNA is only single-stranded uses ribose sugar and uses u so in RNA pairing a is gonna pay with you T does not exist in RNA another special thing about RNA is that it can leave the nucleus whereas DNA always stays in the nucleus so if we want to transcribe a sequence now we're gonna instead of just matching the complementary base we're gonna think about what the RNA would be so T still pairs with a so we would put a first but a instead of pairing with T and RNA is gonna pair with you so our complimentary sequence would look like T pairing with a a pairing with you T pairing with a and G's and C they're still the same so you would write out the entire transcribe sequence so if you're asked on the exam to transcribe something make sure you're paying attention and including use if you're asked to just write the complementary sequence you're just right in the DNA pairs so pay attention for that this is the entire process of protein synthesis depicted in one diagram we start with DNA inside the nucleus that DNA is transcribed so a new mRNA template is built off of the DNA that mRNA is going to leave the nucleus and then be translated at the ribosome by these tRNA molecules which are going to bring over amino acids and those amino acids will be linked up to form a protein so I want to talk about mutations mutations can cause can be caused by mistakes in replication transcription translation or other parts of the cell cycle they can also be caused by mutagens things that are going to change up the DNA order things like x-rays you chemicals etc and some of the effects of mutations they can have no effect at all we call those silent mutations the changes could be good they could introduce a new trait within an organism or they could be really bad or it could even cause a genetic disorder or death within the organism so it really depends on how severe the effect is a mutation that introduces a new base for example adds in a little C in the middle of a DNA chain might have a huge effect on the protein because then everything and the reading brain gets shifted down so that makes it a little bit more difficult to create the same protein that we wanted originally so if you think about some questions that you might get were related to me quick to mutations you might be asked like what would likely cause an increase in the frequency of genetic mutations and something like exposure to x-rays would be a good answer for that so understand that mutations are changes in DNA coding and they can be deletions addition substitutions and they can be random or spontaneous and spontaneous and they can be caused by lots of different things so again if there's a mistake in the genetic code then the mRNA has changed and then the structure of the protein is no longer the same so an insertion like we mentioned before would be a big change all right so we're moving forward meiosis I want to talk about briefly it's really important in sexual reproduction so this is how sex cells are formed and then for these are haploid cells is a little bit different than the cells formed from regular cell division in mitosis and meiosis is going to give us lots of genetic variation because of things like independent assortment where the chromosomes line up and homologous chromosomes will line up in different ways randomly and then crossing over will occur during prophase one where the homologous chromosomes were exchanged genetic information and then of course there's random fertilization between whenever sex cell and then whatever sperm cell unites if it's a human or other organisms so remember that in genetic variation mutation is important but these three reasons really from meiosis are some of the more important ones for all of the genetic variation that we have within a population remember within mitosis and meiosis both require DNA replication before they can occur meiosis has two cell divisions way mitosis only has one and meiosis produces gametes or sex cells and meiosis is the only one that involves crossing over crossing over does not happen in mitosis and again it's important to sexual reproduction because it provides genetic variation in the offspring and so that's really something important you need to remember about meiosis some of the patterns of inheritance you might want to review our regular complete dominance which is probably what you've seen in your practice problems with Mendelian genetics codominance where two traits are displayed in the organism incomplete dominance where we have a blend of trades there's also going to be some questions on sex-linked traits and multiple alleles and a good example of multiple alleles that you've probably gone over is blood types so make sure you know how to predict the inheritance patterns of each of these types of traits another thing to review is the influence of environment on genes so for example if identical twin girls are separated at birth and cared for by two different families in two different environments after many years these girls could have different heights in different weights so the cause of these differences is that they probably had a different diet different environmental exposures and different physical activities and the environment does play a role in influencing traits so even if they are identical twins they're not going to be exactly the same because their genes will be expressed in different ways some of the biotech and DNA technology you should you are things like gel electrophoresis transgenic organisms and the human genome project gel electrophoresis is also known as DNA fingerprint and it's used for things like forensic analysis parental testing and looking at evolutionary relationships we can use it to identify different individuals and identify and catalog endangered species transformation is possible because we have the same DNA in all of our organisms and the only difference between the DNA of a dog for example in the DNA of a fly is the sequence of nucleotides so we are able to manipulate different organisms genetic code because the tech because the DNA code is the same now transgenic organisms are used in a lot of different areas but agriculture is a big one including manipulating certain organisms to resist insects pharmaceutical applications such as the production of insulin and bacteria has even been modified to clean up oil spills now what you need to know about the human genome project is that this project was useful in determining whether individuals carry genes for different genetic conditions and it was used a little bit towards developing gene therapy we wanted to map the genes in the human genome now it was not as groundbreaking as we hoped it would be there are a lot of things that we hope to discover with the human genome project it was not to be the cure-all for all diseases but unfortunately it was not that and there's still a lot of work to be done within the realm of DNA technology and the human genome I want to take a quick look at gel electrophoresis in this review now this is what a gel would look like and you might be asked to use a gel in your in your practice problems or any of the test questions and with the gel electric current is applied and the negatively charged DNA moves towards the positive end of the gel which is at this side here and what you can do is you can compare the patterns of the DNA bands and to see which ones match to determine for this case this is a crime scene and you can look at the crime scene and which suspect best matches up with the particular evidence from the crime scene and then you can identify your subject we're talking about evidence for evolution so we're shifting a little bit into our evolution topic there's a lot of different pieces of evidence that scientists use in order to determine evolutionary relationships and how organisms are related to each other one of my just biochemical evidence and this can be related to proteins and DNA we also have embryonic development that we can look at fossil evidence anatomical evidence and these are things like morphology or different physical traits that organisms have and so if you look at two different organisms you might see that they go through similar developmental stages and you can infer from that that they share a common ancestor and if organisms for example have similarities and DNA sequences we could assume that they share a recent common ancestor and that's how we figure out their evolutionary relationship now you definitely definitely want to review natural selection organisms better adapted to their environment are more likely to reproduce and pass on traits to their offspring and so the ones that are more successful are more fit to the environment so species do have a potential to increase number if the environment is a good match for them and there is variation in populations as well but because there's a finite supply of resources we only have we have a struggle for existence and changing environments are going to provide selective presser selective pressure for specific phenotypes and the organisms with the adaptations that are best fit for the environment survive they reproduce they pass on their alleles and then over time this contributes to a change in the population so let's do a quick example with antibiotics so here we have a population and within this population there is variation some of the bacteria in this population are naturally resistant to antibiotics and some of them are not now when the antibiotics are provided what is going to happen is most of the individuals in the population will be killed and only the ones that are have the resistant gene will survive now unfortunately for us if we don't want antibiotic resistant bacteria that's going to provide a good environment for the resistant bacteria to pass on that resistant gene and to grow and to populate the particular environment and so what we have now is an antibiotic resistant population and over time the resistant bacteria the ones that were more fit have survived and reproduced at a greater rate than the non resistant bacteria and you can see similar examples with this with pesticides now you want to also review your classification systems as well the earliest classification systems focused on physical traits and behavior to make inferences about the relationships between organisms but now we have better evidence that shows common genetic history between different organisms so we can look at things like the DNA and we can make better maps and better inferences about which organisms are related and how closely they are related to each other you want to make sure you're able to use a dichotomous key which an example of which is shown here and you want to be able to interpret what's called a cladogram or a phylogenetic tree and looking at these you can determine how closely organisms are related and at which point they've branched off from other categories and groups and make sure you've done a few practice problems with these to review as well alright so that was a very quick review on our evolution in genetics that show up on the biology EOC remember this is a huge chunk of the exam so make sure you go back and practice practice problems that are related to all the topics we've reviewed in this video thank you guys for watching