Download What is a mutation?

Bellringer 10.29.12
1. Three consecutive bases in mRNA are known
as what?
2. Three consecutive bases in tRNA are known
as what?
3. How many codons are there?
4. How many amino acids?
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Mutations in DNA
Mutations
• What is a mutation?
• Any change in a DNA sequence
• What is a mutagen?
– External things that can change DNA
• What 4 things can cause a mutation?
1.
2.
3.
4.
Mistakes in DNA replication
radiation
chemicals
high temperatures
Types of Mutations
–Point Mutations or Substitutions:
bases are mismatched
Correct DNA
GAG
CTC
Point mutation
GCG
CTC
Correct mRNA
Correct AA
CUC
mutated mRNA
CGC
Leucine
Wrong AA
Arginine
A should pair with T, but instead G is mismatched to T
Mutations
• Example: Sickle Cell Anemia
•
http://evolution.berkeley.edu/evolibrary/article/0_0_0/mutations_06
Mutations
• Frame-shift Mutation: when bases are added
or removed, all of the CODONS that follow the
mutation will be altered.
Example
THE DOG SAW THE CAT
or
THD OGS AWT HEC AT
Insertion: one or more new bases are inserted into a
gene.
Correct DNA:
ATA
TAT
CCG
GGC
TGA
ACT
Correct mRNA:
UAU
GGC
ACU
Tyrosine
Glycine
Correct amino acids:
Threonine
Extra inserted base shifts how we read the codons (3
bases), which changes the amino acids
Frameshift mutation
in DNA:
ATG
TAC
ACC
TGG
GTG
CAC
A
T
Mutated mRNA:
UAC
UGG
CAC
U
Wrong amino acids:
Tyrosine Tryptophan Histadine
Deletion- One or more bases are deleted.
Rate of Mutations in Human Gametes
• In humans, mutation rates range from
about 1 in 100,000 - 1,000,000 gametes.
• A mutation in a gamete
is inherited by the offspring
Results of Mutations
• Missense : ANY mutation that changes the
codon and makes a different amino acid in the
protein
• Nonsense : ANY mutation that changes a
codon into one of the STOP codons
• Silent : ANY mutation that causes no change
in the protein and cannot be detected without
sequencing the gene
Repairs
• Proofreading enzymes
are able to repair some
damages to DNA
Effects of Mutations
Only 1-2% of
people in the
world have red
hair!!!
1. Harmful—can cause
diseases
2. Helpful—can provide
protection or a new trait
(bacteria can mutate
against our antibiotics,
helpful for them)
3. Neutral—nothing happens
because the same protein
is still made
Mutations to control genes can transform one
body part into another. Scientists have studied
flies carrying Hox mutations that sprout legs on
their foreheads instead of antennae!
Mutations in Humans
Sickle Cell Anemia
http://evolution.berkeley.edu/evolib
rary/article/0_0_0/mutations_06
Name Mutations
http://www.nature.ca/genome/04/0
413_e.cfm
On a separate sheet of paper…
• Copy on of the following sequences:
– ATC GAT GTC ACC AAT ATG
– ATG CGA CTA TGG GAC CCC
– TGA GTT TTA CCG GGA AGA
Change the sequence to mRNA
Change the sequence to tRNA
Perform a frame-shift mutation (insertion or deletion)
to the original sequence
Change the new sequence to mRNA
Change the new sequence to tRNA