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Mutation
- 1. DNA Mutation Presented by Mona Othman AlBureikan
- 3. 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 don't understand yet. - Organisms have mechanisms such as DNA repair to remove mutations.
- 4. 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.
- 5. Classifications of mutations OR Types of Mutation
- 6. 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.
- 7. B- Somatic or germline
- 8. 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.
- 9. Spontaneous Mutations These 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.
- 10. 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.
- 11. Spontaneous Mutations • Deamination – Hydrolysis changes a normal base to an atypical base containing a keto group in place of the original amine group.
- 12. 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
- 13. 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
- 14. 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.
- 15. Induced Mutations 2- Mutagen materials physics like; - Ultraviolet rays. (can cause skin cancer). - Radioactive rays. - Gamma rays.
- 16. Induced Mutations - Ultraviolet light is absorbed by the nucleic acid bases, and the resulting influx of energy can induce chemical changes.
- 17. 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.
- 18. Induced Mutations 3- Mutagen biological substances. suspected viruses and bakeries can cause mutations. Of the virus that can cause mutations is DNA.
- 19. 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.
- 20. E- Point or frameshift mutations
- 21. Point mutations - Point mutations also called Single base substitutions are single nucleotide base changes in a gene's DNA sequence. - It exchange a single nucleotide for another. - These changes are classified as transitions or transversions.
- 22. 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).
- 23. 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.
- 24. Point mutations Illustration of three types of point mutations
- 25. 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.
- 26. 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.
- 27. 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.
- 28. 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.
- 29. 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.
- 30. DNA Repair 4- Recombinational (daughter-strand gap) repair - This is a repair mechanism which promotes recombination to fix the daughter-strand gap--not the dimer--and is a way to cope with the problems of a non-coding lesion persisting in DNA. - Double Strand Break (DSB) Repair. Shown is an overview of the main steps and factor requirements for DNA DSB repair by homologous recombination (left) and non-homologous end-joining (right).
- 31. 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.
- 33. DNA Repair
Hinweis der Redaktion
- 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').