Mutationsor "DNA out of control'

Mutations (p. 262)What are mutations?• Mutations are changes in the DNA sequence

that are inherited.Do mutations have negative, neutral or positive

side effects on an organism?

Where do mutations occur? somatic (body) cells gametes (reproductive cells)

Causes of mutations

Changes to the base pair sequence of genetic material (either DNA or RNA) that are:Spontaneous• copying errors in the genetic material during

cell division Mutagenic• exposure to UV radiation, natural background radiation, chemical mutagens, or viruses

See pg 265 for more info!

Cancer Diagnosis/Treatment

When can mutations occur?

Result of Point MutationsIn order of increasing severity:

1. silent mutationchanges between 2 codons for the same amino acid GCU GCC

Ala Ala2. missense mutationthe coded amino acid changes to a different AGA AGUAmino acid Arg Ser

3. nonsense mutationchanges the coded amino acid to a stop codon UAU UAA

Tyr STOP

4. frameshift mutationchanges the reading frame GCU AGU AAU GCU AGA AU

Ala Ser Asp Ala Arg

Types of Mutations

1) Substitution: exchanging of one nucleotide for another does notchange reading frame, but changes codon• (silent, missense, nonsense mutations)

2) Deletion: loss of one or more nucleotides changes the

reading frame (frameshift mutation)

3)Insertion (Addition):

• gain of one or more nucleotides• changes the reading frame (frameshift

mutation)

Summary

Chromosomal Mutations

1) Translocation:-a section of DNA moves from one chromosometo another-can inactivate a gene if the section is part ofan exon or promoter

2) Inversion:-a section of DNA from one strand exchanges

with an section of DNA from the other strand-can inactivate a gene if the section is part of anexon or promoter

Cancer and Disease

• Knudson’s Two-Hit Theory• Carcinogenesis (development of cancer) requires:• Activation of oncogenes (genes that promote cell

growth and division)• Deactivation of tumour suppressor genes (genes

that prevent cell growth and division or cause programmed cell death – apoptosis)

• Both alleles (two-hit) must be affected• If one is normal, it will still make the correct

protein

At each checkpoint, the cell undergoes screening to make sure it is healthy. If a mutations is found the cell will undergo apoptosis. Sometimes mutations go undetected, continue to replicate andcan form cancer.

• http://www.youtube.com/watch?v=mHOX43-4PvE

• stop at 1:13

• Homework pg 262-265 • #19-24

• Homework• Page 259-263• Questions1-7