[Music] as living organisms reproduce and grow they are constantly replicating DNA with a high degree of peration however there are about once in every billion nucleotides that are replicated and error occurs in the replication process changing the sequence of the nucleotides chemicals called mutagens can increase the chance of such mistakes these errors are called mutations there are two main classes of mutations one is known as base substitution mutation and frame shift mutations cells have evolved several methods to dealing with mutations including photolyases exis repair enzymes and mismatch repair enzymes here we we will see the different types of mutations and the different types of mutagens that cause those mutations we will also see CS different strategies to fight against those mutations let's begin with the different types of mutations first we will see the base substitution mutation base substitution mutations occurs when a single nucleotide replaces another in the DNA sequence base substitution mutations can be further divided into silent mutations msense mutations and non-sense mutations now let's dig deep into each of this type of the mutations the base substitution produces no change in the amino acid sequence of the resulting protein it is a silent mutation due to the overlapping nature of the genetic code and onethird of its all substitutions lead to the silent mutations since there is no change in the amino acid sequence of the protein silent mutations affect the genotype of the organism but not the phenotypic effect next is the missense mutation if a b substitution mutation cause a single amino acid to change to the protein the mutation is missense mutation depending on the nature of the amino acid substitution the missense mutation can be harmful neutral or even beneficial in very rare cases the third type is a nonsense if the base substitution causes a codon to change from one coding amino acid to the stop codon it is a nonsense mutation in general nonsense mutations are harmful since they lead to the premature termination of the protein synthesis now let's look the second type that is a frame shift mutation if nucleotides are inserted into or removed from the DNA sequence the resulting mutation is known as a frame shift mutation because the ribosome translates messenger RNA into the protein by reading the MRNA in three nucleotide codons if one or two nucleotides are removed or inserted the result is a shift in the reading frame of the codons this leads to the change in every amino acid that follows the site for frame shift mutation frame shift mutation usually leads to the non-functional protein production now let's look at the type of frame shift frame shift insertion if one or more bases are added to the DNA sequence causing a shift in the reading frame of the resulting codons the mutation is a frame shift insertion if one or more bases are removed from the DNA sequence causing a shift in the leading frame and the reading frame of the resulting codons the mutation is a frame shift deletion now as we learned about the different types of mechanism to repair the DNA now let's look at the different harmful effects that cause the mutation in the first place for example let's first talk about the ionizing radiation ionizing radiation such as xrays and gamma rays can cause some of the molecules within the cell to lose electrons becoming highly reactive ions and free radicals some of these radical ions or free radicals can combat with the bases of the the DNA resulting in error in the DNA replication and therefore mutations even more seriously three groups can react to the sugar phosphate backbone of the DNA and causing the break in the chromosome second is a non-ionizing non-ionizing radiation in the form of UV light is also mutagenic because it cause adjacent thyine bases to covalently bind to one another producing thyine diers such diers can cause serious harm or death to the cell if they're not repaired since this ders prevent the cells from properly transcribing and replicating such DNA third type is a nucleoside analoges nucleoside analoges are compounds that are structurally similar to normal nitrogenous bases but with different base bearing properties these compounds can become incorporated into growing DNA during replication replacing their related base once Incorporated the nucleotide analog can inhibit further replication or cause mismatching of the figure between the replication for example five bromo urasil is a nucleotide analog of thyine but it often pairs with guanin rather than adinin incorporation of five bromo urasil can therefore lead to a base substitution mutation of a guanine for an adenine some chemical mutagens directly alter the structure of the nitrogenous bases of the DNA for example nitrous acid can chemically alter the adenine base so that the base pair with cytosine rather than thyine during replication this change cause a base substitution mutation in the daughter DNA some chemical mutagens cause small insertions or Del I of nucleotide base pairs which can lead to the frame shift mutations example of such frame shift mutations include acridine which is a Dy commonly used for a mutagen in genetic research benzopyrene which is found in Smoke and shoot and ethidium bromide which is useful for the Laboratories for staining the DNA these chemicals are the right size and have the light right chemical properties to sleep between the Stacked base pairs of the DNA producing a bulge in the molecule during DNA replication this bulge can lead to the insertion or deletion of one or more bases in the newly synthesized DNA