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Molecular Genetics

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Molecular Genetics. Mutations. What is a mutation?. With your group, represent non-linguistically what you think a mutation is. Mutations. “Changes in the DNA sequence that are inherited” Can have a negative consequence, no consequence, or a positive consequence. Silent Mutations.

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Presentation Transcript
what is a mutation
What is a mutation?
  • With your group, represent non-linguistically what you think a mutation is
mutations
Mutations
  • “Changes in the DNA sequence that are inherited”
  • Can have a negative consequence, no consequence, or a positive consequence
silent mutations
Silent Mutations
  • Has no consequence (neither good nor bad)
  • Can happen in 2 ways:
  • A mutation occurs in an intron, which is spliced out during mRNA processing.
  • A mutation occurs in the DNA which does not change the amino acid
silent mutations example
Silent Mutations - Example

Example of #2:

5’ – AUG AAG UUU GGC UAA – 3’

Met Lys Phe Gly Stop

5’ – AUG AAG UUU GGU UAA – 3’

Met Lys Phe Gly Stop

Original (normal) mRNA

Mutated (Base C changed to U) mRNA

But no change in amino acid

missense mutations
Missense Mutations
  • A change in a nitrogenous base leads to a change in the amino acid produced.

5’ – AUG AAG UUU GGC UAA – 3’

Met Lys Phe Gly Stop

5’ – AUG AAG UUU AGC UAA – 3’

Met Lys Phe Ser Stop

Original (normal) mRNA

Missense mutation (G base changed to A)

= A different amino acid

nonsense mutations
Nonsense Mutations
  • A change in a nitrogenous base leads to a premature stop codon

5’ – AUG AAG UUU GGC UAA – 3’

Met Lys Phe Gly Stop

5’ – AUG UAG UUU GGC UAA – 3’

Met Stop

Original (normal) mRNA

Nonsense mutation (A base changed to U)

= Premature stop codon

classification
Classification
  • Missense and Nonsense mutations arise because of a base pair substitution
  • In other words, the nitrogenous base itself may change, but the number of nitrogenous bases don’t change
deletion mutations
Deletion Mutations
  • One or more bases are deleted

5’ – AUG AAG UUU GGC UAA – 3’

Met Lys PheGly Stop

5’ – AUG AAG UUG GCU AA – 3’

Met Lys LeuAla

Original (normal) mRNA

Deletion of the base “U”

= The “reading frame” shifts, and new amino acids result

insertion mutations
Insertion Mutations
  • The addition of one or more bases

5’ – AUG AAG UUU GGC UAA – 3’

Met Lys Phe Gly Stop

5’ – AUG UAA GUU UGG CUA – 3’

Met Stop

Original (normal) mRNA

Insertion of the base “U”

= The “reading frame” shifts, and a stop codon results. This frameshift insertion cause a nonsense mutation

classification1
Classification
  • Frameshift mutations occur because of insertions or deletions
  • All of these mutations (missense, nonsense, insertions, deletions) are called point mutations meaning that they occur only with one base pair
classification2
Classification
  • Another category of mutations involves large segments of DNA
  • These are called chromosomal mutations

TRANSLOCATIONS

INVERSIONS

how do mutations arise
How do mutations arise?
  • What causes mutations?
  • List examples
  • Spontaneously
  • Mutagenic agents (chemicals that cause mutations, e.g. X rays, UV radiation, cosmic rays, chemicals)
try it
Try It!

The following strand of mRNA represents the “normal” (aka wild type) strand.

5’ – AUG GGG UUU AUC CUA UAG – 3’

This strand is hit by UV radiation and turns into:

5’ – AUG GGG UUG AUC CUA UAG – 3’

  • Write the amino acid sequences for both strands
  • What kind of mutation occurred? Be very specific.
  • What would happen if the “UUG” changed into “UAG”?
gel electrophoresis
Gel Electrophoresis
  • Is a procedure used to separate DNA fragments
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