Mistakes in the code

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Mistakes in the code
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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?

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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

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How does your DNA determine your traits?
Remember

• Traits are determined by the functions of
  proteins
• Protein function is determined by protein shape
• Protein shape is determined by amino acid
  sequence

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Mutations can change the amino acid sequences of
proteins

• DNA sequence T A C C G A G A T T
  C A
• mRNA sequence A U G G C U C U A A G U
• amino acid sequence Met -- Ala -- Leu --
  Ser
• DNA sequence T A C C G A G A T T
  C A
• mRNA sequence A U G G C U A U A A G U
• amino acid sequence Met -- Ala -- Iso --
  Ser

T
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How does this mutation change the amino acid
sequence?

• (Original)
• DNA sequence A A T G C A T A T G
  C A
• mRNA sequence U U A C G U A U A C G U
• amino acid sequence Leu -- Arg -- Ile --
  Arg
• (Mutated)
• DNA sequence A A T T C A T A T G
  C A
• mRNA sequence U U A A G U A U A C G U
• amino acid sequence Leu -- Ser -- Ile --
  Arg

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3 types of mutations
Substitution Insertion Deletion
T
T A C C G A G A T T C A
Substituting one nucleotide for another.
T
G A T T C A
T A C C G A
Inserting one or more nucleotides
T A C C G A
G A T T C A
Deleting one or more nucleotides
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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.

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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?

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Different types of mutations happen
Substitution Insertion Deletion
T
T A C C G A G A T T C A
T
G A T T C A
T A C C G A
T A C C G A
G A T T C A
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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.
• Why do we call this a frameshift mutation?
• Can substitution mutations cause frameshifts?
  Explain why or why not.

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Consequences of mutations

• As a result of mutations, small differences exist
  between 2 organisms DNA sequences!

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How much variation in DNA exists between 2 people?

• Hemoglobin (beta) gene sequence from person A

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How much variation in DNA exists between 2 people?

• Hemoglobin (beta) gene sequence from person B

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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

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What is the observed effect of mutations?

• No Effect
• (think about it are there 3 million differences
  between 2 people?)
• Why?
• Some mutations code for the same amino acid
• 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)

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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.

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Questions
Q. Weve 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?

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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.