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Mutations

Because Stuff Happens. Mutations. A. Mutation Overview. Any change or random error in the nucleotide sequence (either DNA or mRNA) is called a mutation Can occur in any cell in body Gamete : cell that determines sex; sperm or egg cell Mutation passed down to offspring

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Mutations

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  1. Because Stuff Happens Mutations

  2. A. Mutation Overview • Any change or random error in the nucleotide sequence (either DNA or mRNA) is called a mutation • Can occur in any cell in body • Gamete: cell that determines sex; sperm or egg cell • Mutation passed down to offspring • Somatic cell: all other cells • Mutation stays with cell; may be copied in cell replication

  3. Skin cancer is not inherited because it occurs in somatic or body cells

  4. Two types of mutations: • Point mutation: one base is mutated into another (one amino acid change) • Frameshift mutation: one base is added or deleted (all amino acids changed) • Affects may be neutral (no change in expression), positive, or negative (disease or death)

  5. A mutation in the thumb joint changed it to an opposable thumb = positive mutation!

  6. Introns & Exons • Entire DNA strand is 3 billion (3,000,000,000) base pairs • In eukaryotes, divided into two types: • Introns: no coding information (nonsense) • Exons: code for proteins

  7. Why would eukaryotic DNA have so many nonsense base pairs or junk? • Protection – mutation here wouldn’t harm protein (neutral mutation) mutation INTRON EXON INTRON

  8. Before mRNA leaves nucleus - therefore before translation (making proteins from mRNA) - introns must get cut out by process called splicing • Done by specific enzymes called spliceosomes

  9. Point Mutation • Single nucleotide (base, PO4, sugar) changes • Original : The fat cat ate the wee rat. • Mutation: The fat hat ate the wee rat. • Many diseases are result of single point mutation in gene

  10. Sickle cell anemia • Point mutation: aa glutamine mutated into valine • Result: red blood cell changed from round shape to sickle (crescent) shape • Gets stuck on walls of blood vessels & can cause clog

  11. Cystic fibrosis • Point mutation: aa glutamine becomes STOP codon • Result: should be 1480 aa in protein, now only 493 • Mucosal cells produce excess mucus which blocks ducts (tubes linking organs) which causes infections

  12. Frameshift • Any mutation which causes shift of codon sequences or incorrect amino acid number • Caused by two scenarios: • Deletion of nucleotide (base) • Original: The fat cat ate the wee rat. • Mutation: The fat atatet hew eer at. • Insertion of extra nucleotide(s) (base) • Original: The fat cat ate the wee rat. • Mutation: The fat caa tat eth ewe era t. • Many diseases caused by frame-shift mutations

  13. Frameshift

  14. Huntington’s Disease • Mutation: additional CAG in protein • Result: early cell death in brain Huntington’s Disease Normal

  15. Fragile X Syndrome • Mutation: extra GGG codons inserted on X chromosome • Result: mental retardation in males normal

  16. Muscular dystrophy • Mutation: extra CTG or CCTG in muscle protein • Result: deteriorating (weakening) muscles

  17. Tay-Sachs Disease • Mutation: insertion of TACT in exon 11 • Result: enzyme that breaks down fat in central nervous system (brain & spinal cord) defective • Fat accumulates on brain & spinal cord, permanently damaging cells & killing child before age 5

  18. Point vs. Frameshift

  19. Classwork • Mutations worksheet • Use mRNA codes to look up amino acids in proteins • Do the same thing for the mutated mRNAs. • a. Where is the mutation? Either circle it or explain (G is now C or G got deleted/inserted) • b. What is the result? Describe the change to the amino acid(s) .

  20. Homework • Do p. 220 #3-5 • Do p. 222 #1-3, 8, 10-12 • Study for a quiz tomorrow just on central dogma (25 points) • Transcription – DNA to RNA • Translation – RNA to protein • Know the process of transcription and translation (how it happens, where it happens, what happens)

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