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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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a mutation overview
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
slide5

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)
introns exons
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
slide8

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

slide9

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
point mutation
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
slide12

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
slide13

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
frameshift
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
slide16

Huntington’s Disease

    • Mutation: additional CAG in protein
    • Result: early cell death in brain

Huntington’s Disease

Normal

slide17

Fragile X Syndrome

    • Mutation: extra GGG codons inserted on X chromosome
    • Result: mental retardation in males

normal

slide18

Muscular dystrophy

    • Mutation: extra CTG or CCTG in muscle protein
    • Result: deteriorating (weakening) muscles
slide19

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
classwork
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) .
homework
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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