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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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