Transcript Translation - Olympic High School

Mistakes in the code
Review:
• What does DNA look like?
• How is DNA made?
• How does DNA instruct the cell to make
proteins?
• What determines the order of amino acids in a
protein?
• What happens if you change an amino acid in
the sequence of a particular protein?
• Why?
Mutations
Mutation- a change in the DNA
nucleotide sequence
Mutations can be silent (have no effect),
cause subtle, or dramatic effects on
observed traits in individuals
How does your DNA determine
your traits?
DNA
mRNA
protein
Observed
trait
Remember:
1. Traits are determined by the functions of proteins
2. Protein function is determined by protein shape
3. Protein shape is determined by amino acid sequence
Mutations can change the amino
acid sequences of proteins
TACCGAGATTCA
mRNA sequence:
AU G G C U C UAAG U
amino acid sequence: Met -- Ala -- Leu -- Ser
DNA sequence:
DNA sequence:
TA T T C A
TACCGAG
AU G G C U A UAAG U
amino acid sequence: Met -- Ala -- Iso -- Ser
mRNA sequence:
How does this mutation change the
amino acid sequence?
(Original)
AAT G CATAT G CA
mRNA sequence:
UUACGUAUACGU
amino acid sequence: Leu -- Arg -- Ile -- Arg
DNA sequence:
(Mutated)
AAT T CATAT G CA
mRNA sequence:
U UAAG UAUAC G U
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
Your Turn
• Complete the “Mutations practice”
worksheet. 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.
Questions
1. Which type of mutations had the biggest effect
on the protein sequence? WHY?
2. Which type of 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?
5. What is a possible explanation for the
occurrence of these mutations?
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.
Consequences of mutations…
• As a result of mutations, small differences
exist between 2 organisms 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 – For any trait in a population there
is variation within that trait as a result of small
sequence differences (DNA
Amino Acids)
Genetic diseases
• Most changes are harmless, but some can
cause specific diseases.
• One way to determine whether a disease
is inheritable is to trace the family history
of a disease by creating a type of family
tree called a pedigree.
• One inheritable disease caused by a
specific substitution (or “point”) mutation is
sickle cell anemia.
Questions
Q. We’ve studied transcription, translation, and
replication. A mistake in which of these
processes would result in a permanent mutation?
•
•
Mitosis and Meiosis are about replicating
the DNA. Mistakes in these processes
can cause permanent changes in the
DNA.
Can you inherit mistakes in either of
these processes? Why/why not?
Mistakes can be inherited
• If a mutation in sperm or egg DNA is not
corrected, the new sequence of DNA is
passed on to offspring.
• Over generations, mutations accumulate
and species can slowly change their
appearance.