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Mutation

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  • example: uracilglycosylase--enzyme which removes uracil from DNA.Several proteins are involvedin this process (in prokaryotes these are the products of the 'uvr' genes, for 'UV repair').

Mutation Mutation Presentation Transcript

  • DNA Mutation Presented byMona Othman AlBureikan
  • What are mutations?
  • What are mutations?- Any changes in the DNA sequence of an organism is a mutation.- DNA is made of a long sequence of smaller units strung together. There are four basic types of unit: A, T, G, and C.- Some parts of DNA are control centers for turning genes on and off.- some parts have no function.- And some parts have a function that we dont understand yet.- Organisms have mechanisms such as DNA repair to remove mutations.
  • What are mutations?- Other parts of DNA are genes that carry the instructions for making proteins .- Proteins are long chains of amino acids.- These proteins help build an organism.- Protein-coding DNA can be divided into codons — sets of three bases that specify an amino acid or signal the end of the protein.
  • Classifications of mutations OR Types of Mutation
  • A- Good or bad or neutral.- A harmful mutation Is a mutation that decreases the fitness of the organism.- A beneficial mutation Is a mutation that increases fitness of the organism, or which promotes traits that are desirable.- A neutral mutation Has no harmful or beneficial effect on the organism. Such mutations occur at a steady rate, forming the basis for the molecular clock.
  • B- Somatic or germline
  • C- Spontaneous or Induced Mutations - Most mutations are spontaneous, rather than being induced by a mutagen. - Spontaneous mutation ; A mutation occurring in the absence of mutagens, usually due to errors in the normal functioning of cellular enzymes.
  • Spontaneous MutationsThese mutations can be caused by:• Tautomerism – A base is changed by the repositioning of a hydrogen atom, altering the hydrogen bonding pattern of that base resulting in incorrect base pairing during replication.• The ability of a molecule to exist in more than one chemical form is called tautomerism .• All the four common bases of DNA (A, G, C and T) have unusual tautomeric forms, which are rare.
  • Spontaneous Mutations- Depurination – In molecular genetics, depurination is an alteration of DNA in which the purine base (adenine or guanine) is removed from the deoxyribose sugar by hydrolysis of the beta-N-glycosidic link between them.- Loss of a purine base form an apurinic site (AP site). where the sugar phosphate backbone remains and the sugar ring has a hydroxyl (-OH) group in the place of the purine.
  • Spontaneous Mutations• Deamination – Hydrolysis changes a normal base to an atypical base containing a keto group in place of the original amine group.
  • Spontaneous Mutations- Slipped strand mispairing - Denaturation of the new strand from the template during replication, followed by renaturation in a different spot lead to insertions or deletions.- (SSM) is a process that produces mispairing of short repeat sequences between the mother and daughter strand during DNA synthesis
  • Induced Mutations• Ingredients that cause mutations are called mutagens. Mutagen is divided into three, namely:1- Mutagenic chemicals like;• Hydroxylamine NH2OH• Base analogs (e.g. BrdU)• Alkylating agents• Agents that form DNA adducts• DNA intercalating agents• DNA crosslinkers• Oxidative damage
  • Induced Mutations Nitrous acid converts amine groups on A and C to diazo groups, altering their hydrogen bonding patterns which leads to incorrect base pairing during replication.
  • Induced Mutations2- Mutagen materials physics like;- Ultraviolet rays. (can cause skin cancer).- Radioactive rays.- Gamma rays.
  • Induced Mutations- Ultraviolet light is absorbed by the nucleic acid bases, and the resulting influx of energy can induce chemical changes.
  • Induced Mutations- The most frequent photoproducts are the consequences of bond formation between adjacent pyrimidines within one strand, and, of these, the most frequent are cyclobutane pyrimidine dimers (CPDs).- T CPDs are formed most readily, followed by T-C or C-T; C-C dimers are least abundant.
  • Induced Mutations3- Mutagen biological substances.suspected viruses and bakeries can cause mutations. Of the virus that can cause mutations is DNA.
  • D- Forward or Reverse Mutations- In an organism when mutations created a change from wild type to abnormal phenotype, then that type of mutations are called forward mutations.- Most mutations are of forward type.- The forward mutations are often corrected by error, correcting mechanism, so that an abnormal phenotype changes into wild type phenotype. Such mutations are called back or reverse mutations.
  • E- Point or frameshift mutations
  • Point mutations- Point mutations also called Single base substitutions are single nucleotide base changes in a genes DNA sequence.- It exchange a single nucleotide for another.- These changes are classified as transitions or transversions.
  • Point mutations- Most common is the transition that exchanges a purine for a purine (A ↔ G) or a pyrimidine for a pyrimidine, (C ↔ T).- Less common is a transversion, which exchanges a purine for a pyrimidine or a pyrimidine for a purine (C/T ↔ A/G).
  • Point mutations- Point mutations that occur within the protein coding region of a gene may be classified into three kinds, depending upon what the erroneous codon codes for: • Silent mutations: which code for the same amino acid. • Missense mutations: which code for a different amino acid. • Nonsense mutations: which code for a stop and can truncate the protein.
  • Point mutationsIllustration of three types of point mutations
  • frameshift mutations- Frameshift mutation is a mutation caused by add or remove one or more DNA bases of nucleotides that is not evenly divisible by three from a DNA sequence.- Insertion or deletion mutations cause frameshift mutations.
  • frameshift mutations• Addition or deletion of one or two bases results in a new sequence of codons which may code for entirely different amino acids. This results in a drastic change in the protein synthesized.
  • DNA Repair• Cells have developed a number of systems designed to repair DNA damage and correct mutations.1- Photoreactivation- For Repair Thymine Dimers by A brief exposure to blue light following UV exposure can reverse the effects of the UV radiation.
  • DNA Repair• An enzyme called photolyase or photoreactivation enzyme (PRE), which cleaves the covalent bonds linking the thymine dimers using the energy from a DNA Repair Pathway. This flow chart shows one way that damaged photon of blue light. DNA is repaired in E. coli bacteria.
  • DNA Repair• 2- Base excision repair The damaged or inappropriate base is removed from its sugar linkage and replaced. These are glycosylase enzymes which cut the base-sugar bond.• 3- Nucleotide excision repair - This system works on DNA damage which is "bulky" and creates a block to DNA replication and transcription. - (UV-induced dimers and some kinds of chemical adducts). - It probably recognizes not a specific structure but a distortion in the double helix.
  • DNA Repair4- Recombinational (daughter-strandgap) repair- This is a repair mechanism whichpromotes recombination to fix thedaughter-strand gap--not the dimer--andis a way to cope with the problems of anon-coding lesion persisting in DNA.- Double Strand Break (DSB) Repair.Shown is an overview of the main stepsand factor requirements for DNA DSBrepair by homologous recombination (left)and non-homologous end-joining (right).
  • DNA Repair• Mismatch repair - This process occurs after DNA replication as a last "spellcheck" on its accuracy. - In E. coli, it adds another 100-1000-fold accuracy to replication. - It is carried out by a group of proteins which can scan DNA and look for incorrectly paired bases (or unpaired bases) which will have aberrant dimensions in the double helix. - The incorrect nucleotide is removed as part of a short stretch and then the DNA polymerase gets a second try to get the right sequence.
  • Nucleotide excision
  • DNA Repair
  • References;http://academic.brooklyn.cuny.edu/biology/bio4fv/page/molecular%20biology/mutations-type.htmlhttp://www.web-books.com/MoBio/Free/Ch7G.htmhttp://www.emunix.emich.edu/~rwinning/genetics/mutat.htmhttp://www.prism.gatech.edu/~gh19/b1510/7mut4.jpghttp://www.ncbi.nlm.nih.gov/books/NBK21240/http://chemistry.gravitywaves.com/CHEMXL153/DNAMutationRepair.htmhttp://www.brooklyn.cuny.edu/bc/ahp/BioInfo/MUT/Mut.Definition.htmlhttp://evolution.berkeley.edu/evolibrary/article/mutations_01http://learn.genetics.utah.edu/archive/mutations/mutatedna.htmlhttp://www-personal.ksu.edu/~bethmont/mutdes.htmlhttp://en.wikipedia.org/wiki/Mutation#Causeshttp://ocw.openhighschool.org/mod/book/view.php?id=8447&chapterid=2327http://www.microbiologyprocedure.com/genetics/mutation/classification-of-mutation.htmhttp://en.wikipedia.org/wiki/Mutation#Causes
  • THE ENDTHANK YOU