Download Mutated

How is the amino acid sequence
determined?
• The mRNA
• Each codon is a code for one amino acid
DNA sequence:
TACCGAGATTCA
mRNA sequence:
AUGGCUCUAAGU
amino acid sequence: Met -- Ala -- Leu -- Ser
Whole Process Video
Notes on Mutations
LT: Understand the different types of mutations
and why some are worse than others.
Mutations
Mutation- a change in the DNA nucleotide
sequence
Mutations can cause subtle or dramatic effects
on observed traits in individuals
How does your DNA determine your traits?
DNA
mRNA
protein
Observed
trait
Remember:
•Traits are determined by the functions of proteins
•Protein function is determined by protein shape
•Protein shape is determined by amino acid sequence
Amino Acid sequence determines the 3-D
protein shape
• Interactions between amino acids cause folding
and bending of the chain
Examples:
– positive (+) and negative (-) parts of amino acids are
attracted to each other.
– hydrophobic regions are attracted to each other
• Folding
http://www.stolaf.edu/people/giannini/flashanimat/proteins/hydrophobic%20force.swf
•
Structure levels
http://www.stolaf.edu/people/giannini/flashanimat/proteins/protein structure.swf
Mutations can change the amino acid
sequences of proteins
TACCGAGATTCA
mRNA sequence:
AUGGCUCUAAGU
amino acid sequence: Met -- Ala -- Leu -- Ser
DNA sequence:
+
DNA sequence:
-
TACCGAG
TATTCA
AUGGCUAUAAGU
amino acid sequence: Met -- Ala -- Iso -- Ser
mRNA sequence:
+
How does this mutation change the amino
acid sequence?
(Original)
AATGCATATGCA
mRNA sequence:
UUACGUAUACGU
amino acid sequence: Leu -- Arg -- Ile -- Arg
DNA sequence:
(Mutated)
AATTCATATGCA
mRNA sequence:
UUAAGUAUACGU
amino acid sequence: Leu -- Ser -- Ile -- Arg
DNA sequence:
3 types of mutations
Substitution
TA T T C A
TACCGAG
Substituting one nucleotide for another.
Insertion
TACCGA G
T ATTCA
Inserting one or more nucleotides
Deletion
TACCGA GATTCA
Deleting one or more nucleotides
Practice
• Complete both sides of the “Mutations
practice”. You will learn how some mutations
can affect the amino acid sequence of
proteins
• Consider how severe of an effect each
mutation would have on the ability of the
protein to function.
1. Which mutations had the biggest effect on the
protein sequence? WHY?
2. Which mutations had the smallest effect on the
protein sequence? WHY?
3. Which examples would you predict to have the
biggest effects on a trait? WHY?
4. Which examples would you predict to have the
smallest effects on a trait? WHY?
Different types of mutations happen
Substitution
TA T T C A
TACCGAG
Insertion
TACCGA G
T ATTCA
Deletion
TACCGA GATTCA
Frameshift mutations
•
•
One or more than one nucleotide can be added
or deleted with insertion and deletion
mutations.
If the number of nucleotides is not a multiple of
3, it is called a frameshift mutation.
1. Why do we call this a frameshift mutation?
2. Can substitution mutations cause frameshifts?
Explain why or why not.
Nonsense mutations
• The introduction of a stop codon where it
doesn’t belong
• Results in a shorter, unfinished protein
Consequences of mutations…
• If a mutation in sperm or egg DNA is not fixed,
the new sequence of DNA is passed on to
offspring.
• Over generations, more mutations
accumulate.
• As a result, differences occur between
people’s DNA sequences!
How much variation in DNA exists between
2 people?
Hemoglobin (beta) gene sequence from person A
How much variation in DNA exists between
2 people?
Hemoglobin (beta) gene sequence from person B
How much variation in DNA exists between
2 people?
• About 1 in every 1,000 nucleotides is different
between 2 people
• (0.1% difference means 99.9% identical)
• We have about 3 billion nucleotides in all, so
that means there are about 3 million
nucleotide differences between 2 people
What is the observed effect of mutations?
•
No Effect
(think about it: are there 3 million differences between 2 people?)
– Why?
1. Some mutations code for the same
amino acid
2. Most mutations are in sequences of
DNA between genes.
• Variation – there are a variety of traits in a
population.
• Genetic disease
Genetic diseases
Many alleles are harmless, but some can cause
specific diseases. They can be dominant or
recessive. To determine whether a disease is
genetic, we trace the family history of a
disease by creating a type of family tree called
a pedigree.
Environmental Causes of Mutations
•
Mutagens - substances that cause mutations
(changes in DNA sequence)
–
•
Ex: cigarette smoke, UV light, x-rays, nuclear
radiation, BPA, etc.
Carcinogen – cancer causing substance
(mutation in a gene linked with cancer)
Reading pgs. 436-437
3a. In what ways do mutations affect
organisms?
Changes the message sent by the DNA – can make it so the
protein does not function or RARELY makes it function better
b. How can mutations occur?
Spontaneously, or through MUTAGENS – chemicals or agents
that cause mutations in your DNA (cigarette smoke, UV
radiation, BPA, etc.)
c. Why can mutations in gametes have a
different effect than mutations in nongamete
cells?
Nongamete cells do not pass on their instructions to offspring –
they only affect the individual. Mutations in gametes will be
passed on to offspring.
DNA and Evolution
• We saw in previous chapters that fossils show
us how organisms have changed over time.
• We can use DNA to examine patterns of
evolution.
DNA and Evolution
• A hemoglobin molecule complex consists of 2
protein chaings – an alpha chain and a beta
chain.
• There are 146 amino acids in the beta chain of
hemoglobin.
• We are going to examine the beta hemoglobin
sequences of 8 different species to try to
identify the relationship between these 8
species.
DNA and Evolution
• Count the differences between the sequences
for species I and II, I and III, I and IV, etc.
• Make a class list on the board.
• How many of the 146 amino acids in the beta
chain of hemoglobin do the two most similar
sequences share?
• How many do the two least similar sequences
share?
DNA and Evolution
•
•
•
•
•
•
•
•
The first 7 species are primates:
I – Human
II – Chimpanzee (Great Ape)
III – Gorilla (Great Ape)
IV – Common Gibbon (“lesser” Ape)
V – Rhesus Monkey (old world monkey)
VI – Squirrel Monkey (new world monkey)
VII – Ring-tail lemur (Prosimian)
DNA and Evolution
• Which group of primates is least similar to the
others? Prosimians are least similar
• Are gorillas more similar to humans, or to
chimpanzees?
• Which 2 species have the fewest differences
(most similar sequences)? Label them on Tree
A in the blanks indicating closest similarity.
• Which third species is most similar to the first
2? Label them on Tree A.
DNA and Evolution
• What position shows the common ancestor of
Chimpanzees and Humans?
• Position 4 shows the common ancestor of
which species?
• Is the Old World Monkey more closely related
to the Gorilla or to the New World Monkey?