Regents Biology 2009-2010

MutationsChanges to DNA

Regents Biology

Mutations■ Changes to DNA are called mutations

◆ change the DNA◆ changes the mRNA◆ may change protein◆ may change trait

DNA TACGCACATTTACGTACG

mRNA AUGCGUGUAAAUGCAUGC

aa

aa

aa

aa

aa

aa

aa

protein

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Types of mutations■ Changes to the letters (A,C,T,G bases) in

the DNA◆ point mutation

■ change to ONE letter (base) in the DNA■ may cause change to protein, may not

◆ frameshift mutation■ addition of a new letter (base) in the DNA

sequence■ deletion of a letter (base) in the DNA■ both of these shift the DNA so it changes how

the codons are read■ big changes to protein!

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Point Mutations ■ One base change

◆ can change the meaning of the whole protein

THEFATCATANDTHEREDRATRAN

THEFATCARANDTHEREDRATRAN

THEFATCATENDTHEREDRATRAN

OR

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Point Mutations ■ Missense mutation = changes amino acid

AUGCGUGUAUACGCAUGCGAGUGA

MetArgValTyrAlaCysGluStop

AUGCGUGUAUACGUAUGCGAGUGA

MetArgValTyrValCysGluStop

Doesthis

changethe

protein?DEPENDS…

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Sickle cell anemia■Hemoglobin protein in red blood cells

◆ limits activity, painful & may die young

Normalround cells

Misshapen

sickle cells

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Point Mutations ■ Silent mutation = no change to protein

AUGCGUGUAUACGCAUGCGAGUGA

MetArgValTyrAlaCysGluStop

AUGCGUGUAUACGCUUGCGAGUGA

MetArgValTyrAlaCysGluStop

Does this change

the protein?Why not?

The code has

repeats in it!

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Point Mutations ■ Nonsense mutation = change to STOP

AUGCGUGUAUACGCAUGCGAGUGA

MetArgValTyrAlaCysGluStop

AUGCGUGUAUAAGCAUGCGAGUGA

MetArgValStop

Really destroyed

that protein!

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Frameshift Mutations ■ Add or delete one or more bases

◆ changes the meaning of the whole protein

THEFATCATANDTHEREDRATRAN

THEFATCANTANDTHEREDRATRAN

THEFATCAANDTHEREDRATRAN

OR

Add one!

Delete one!

Does this change

the sentence?

A LOT!

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Frameshift Mutations ■ Addition = add one or more bases

AUGCGUGUAUACGCAUGCGAGUGA

MetArgValTyrAlaCysGluStop

AUGCGUGUAUACGUCAUGCGAGUGA

MetArgValTyrValMetArgValA

Does this change

the protein?A LOT!

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Frameshift Mutations ■ Deletion = lose one or more bases

AUGCGUGUAUACGCAUGCGAGUGA

MetArgValTyrAlaCysGluStop

AUGCGUGUAUACGAUGCGAGUGA

MetArgValTyrAspAlaSerGA

Does this change

the protein?A LOT!

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Cystic fibrosis■ Broken salt channel in cells

◆ gene codes for a protein channelthat allows salt to flow across cell membrane■ broken protein doesn’t work as channel

■ doesn’t allow salt out of cell, so water doesn’t flow out either

■ thicker & stickier mucus coating around cells

■ mucus build-ups in lungs & causes bacterial infections

■ destroys lung function

◆ without treatment children die before 5; with treatment can live past their late 20s