Summary

This document is a lecture on mutations, focusing on DNA, its structure, and related processes. It provides an overview of the topic, including details of how DNA works and explaining different types of mutations with examples.

Full Transcript

Mutations Esmaili 1 DNA DNA 2 DNA stands for deoxyribose nucleic acid This chemical substance is present in the nucleus of all cells in all living organisms DNA controls all the chemical changes which take place in cells The k...

Mutations Esmaili 1 DNA DNA 2 DNA stands for deoxyribose nucleic acid This chemical substance is present in the nucleus of all cells in all living organisms DNA controls all the chemical changes which take place in cells The kind of cell which is formed, (muscle, blood, nerve etc) is controlled by DNA The kind of organism which is produced (buttercup, giraffe, herring, human etc) is controlled by DNA DNA molecule 3 DNA is a very large molecule made up of a long chain of sub-units The sub-units are called nucleotides Each nucleotide is made up of a sugar called deoxyribose a phosphate group -PO 4 and an organic base Ribose & deoxyribose 4 Ribose is a sugar, like glucose, but with only five carbon atoms in its molecule Deoxyribose is almost the same but lacks one oxygen atom Both molecules may be represented by the symbol The bases 5 The most common organic bases are Adenine (A) Thymine (T) Cytosine (C) Guanine (G) Nucleotides 6 The deoxyribose, the phosphate and one of the bases Combine to form a nucleotide PO4 adenine deoxyribose At the energy below than 15 eV, LEEs can break a DNA strand via the formation of a transient molecular anion (TMA) (i.e., resonant electron capture) of a DNA subunit (e.g., base, deoxyribose, phosphate and structural water). They often lead to the formation of transient molecular anions (TMAs), and their decay by auto ionization or dissociation accompanied by bond dissociation. 9 Radiation /Heavy Particle Damage Radiation Damage: mostly indirect (OH radicals, electrons, etc.) https://clinicalgate.com/basics-of-radiation- therapy-2/ Electron-Induced Damage: Transient Anions http://www.isa.au.dk/networks/eipam/radam-research.html The mean free path of the majority of the LEEs varies from 0.1 to 10 nm, they can produce clustered damage within DNA. 11 Joined nucleotides 7 PO4 A molecule of DNA is formed by millions of nucleotides joined PO4 together in a long chain PO4 PO4 sugar-phosphate + bases backbone 8 In fact, the DNA usually consists of a double strand of nucleotides The sugar-phosphate chains are on the outside and the strands are held together by chemical bonds between the bases 2-stranded DNA 9 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 Bonding 1 10 The bases always pair up in the same way Adenine forms a bond with Thymine why ? AdenineandThymine have a favorable configuration for theirbonds. They both have to -OH/-NH groups which can form hydrogen bridges. Adenine Thymine and Cytosine bonds with Guanine why ? Cytosine Guanine Bonding 2 11 PO4 PO4 adenine thymine PO4 PO4 cytosine guanine PO4 PO4 PO4 PO4 Pairing up 12 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 PO4 14 THE DOUBLE HELIX bases sugar-phosphate chain Genetic code 1 19 The sequence of bases in DNA forms the Genetic Code A group of three bases (a triplet) controls the production of a particular amino acid in the cytoplasm of the cell The different amino acids and the order in which they are joined up determines the sort of protein being produced Coding 21 For example Cytosine Adenine Codes for Valine Thymine Cytosine (C) Guanine (G) Codes for Alanine Adenine (A) 20 Each amino acid (Serine, Cysteine, Valine, Glycine and Alanine) is coded for by a particular triplet of bases Triplet code 22 This is known as the triplet code Each triplet codes for a specific amino acid CGA - CAA - CCA - CCA - GCT - GGG - GAG - CCA - Ala Val Gly Gly Arg Pro Leu Gly The amino acids are joined together in the correct sequence to make part of a protein Ala Val Gly Gly Arg Pro Leu Gly DNA and enzymes 23 The proteins build the cell structures They also make enzymes The DNA controls which enzymes are made and the enzymes determine what reactions take place The structures and reactions in the cell determine what sort of a cell it is and what its function is So DNA exerts its control through the enzymes Genes 24 A sequence of triplets in the DNA molecule may code for a complete protein Such a sequence forms a gene There may be a thousand or more bases in one gene Definition A mutation is a change in an organism’s DNA – Silent mutations are changes that do not result in a change to the organisms phenotype –Mutations that occur in germ cells (sperm, eggs) are passed on to offspring –Mutations in somatic (body) cells may be harmless, or may result in disease such as cancer Chromosoma l Mutations A Point Mutation Resulting in Nonsense A Point Mutation: An Analogy the red dog bit the tan cat theredmogbitthetancat This point mutation changes the meaning, resulting in nonsense A Point Mutation Resulting in Missense A Point Mutation: An Analogy the red dog bit the tan cat the red hog bit the tan cat This point mutation changes the meaning, resulting in missense An Insertion Mutation in a Gene An Insertion Mutation: An Analogy the red dog bit the tan cat theredrdogbitthetanca This insertion mutation changes the reading frame A Deletion Mutation in a Gene An Deletion Mutation: An Analogy the red dog bit the tan cat t h e r e d o g b i t t h e t a n c a t _ This deletion mutation changes the reading frame In the aqueous solution, methionine, cystine, threonine, histidine and arginine were proved to be more radiosensitive while cysteic acid, tyrosine, alanine and proline were relatively radioresistant.

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