Mutations

From Gene to ProteinHonors Biology

Ms. Kim

Mutations• Mutations–Are changes in the genetic material (DNA)

of a cell2 TYPES

• 1. Point mutations can affect protein structure and function–Are changes in just one base pair of a gene

POINT MUTATIONS• The change of a single

nucleotide in the DNA’s template strand–Can lead to the production of

–an abnormal protein or…–the same protein

Point Mutations• Point mutations within a gene are

called–Base-pair substitutions

• Can result in a mutation (change) that is• harmful• neutral (not harmful or helpful) • beneficial

Substitutions• 2 TYPES–missense (wrong amino acid)• ONLY 1 wrong aa is added to polypeptide…all the

other aa’s are the same – nonsense (prematurely STOP)• The change in DNA leads to an early STOP codon

polypeptide is SHORTEN!!

POINT MUTATION ANALOGY…

• TEMPLATE: THE CAT ATE THE RAT

• POINT MUTATION: THE CAT ATE THE RAT – THE CAT ATE THE BAT What kind of point mutation

is this?• MISSENSE

– THE CAT ATE THE XAT What kind of point mutation is this?• NONSENSE

What is the “wobble” effect? • The last base (nucleotide) in a codon is said to be in the

WOBBLE position.– codon mutation may encode the same amino acid

• Leads to NEUTRAL or SILENT mutations– Not harmful or helpful

• SILENT MUTATIONS• Mutation does not change “end result”…change in DNA

still makes the SAME amino acid• NO noticeable change occurs• a change from AUU to AUC will still encode leucine

What is a neutral mutation? • May or may not affect the resulting protein.– For example, if the codon AAA is mutated to AGA,

arginine would be used in the resulting protein instead of lysine

– These amino acids are chemically similar and may not have a large effect in the protein or its function

– IF this change causes the protein to not function (and be LETHAL to the organism) then it is not a neutral mutation but rather a missense mutation

2. Frameshift Mutations• Insertions and deletions–Are additions or losses of nucleotide pairs in a

gene– produce frameshift mutations• 2 TYPES– Insertions–Deletions

FRAMESHIFT MUTATION ANALOGY…

• TEMPLATE: THE CAT ATE THE RAT

• ADDITION of “B” MUTATION: THE CAT ATE THE RAT – THE CAT BAT ETH ERA T What kind of frameshift

mutation is this?• INSERTION

• SUBTRACTION of “A” MUTATION: THE CAT ATE THE RAT – THE CAT TET HER AT What kind of frameshift mutation is

this?• DELETION• http://highered.mcgraw-hill.com/sites/0072552980/student_vie

w0/chapter9/animation_quiz_5.html

Which is more harmful?• Typically, frameshift mutations are more

harmful BUT some point mutations can be LETHAL–Ex: Tay Sachs and Cystic Fibrosis

Other Types of Mutations• Inversions–“Flip Flops”•Nucleotides trade places on each

strand• Deletions (2+ nucleotides)–Many nucleotides are deleted at once

Causes of Mutations• Inherited mutations– From mom and dad

• Spontaneous mutations–occurs during DNA replication

• Environmental mutations (Mutagens)–physical or chemical agents that can cause

mutations• Ex: Sun, viruses, chemicals

Belgian Blue Cattle (so beefy….)

The Belgian Blue has a natural mutation in myostatin gene, which codes for protein that inhibits muscle development and fat deposition (creates very lean meat).

Piedmontese cattle (still so beefy…)