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Mistakes in the code

Mistakes in the code. Review:. What does DNA look like? How is DNA for a new cell 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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Mistakes in the code

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  1. Mistakes in the code

  2. Review: • What does DNA look like? • How is DNA for a new cell 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?

  3. Observed trait DNA mRNA protein translation protein function ( ex. enzyme activity) transcription 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

  4. Questions • Mitosis and Meiosis are about replicating the DNA in somatic and sex cells. Mistakes in these processes can cause permanent changes in the DNA. • Can you inherit mistakes from Mitosis? Meiosis? Q. We’ve studied transcription, translation, and replication. A mistake in which of these processes would result in a permanent mutation?

  5. Mistakes can be inherited • If a DNA mistake in sperm or egg cell production is not corrected, the new sequence of DNA is passed on to offspring. • Over generations, mutations accumulate and species can slowly change their appearance.

  6. Mutations Mutation- a change in the DNA nucleotide sequence Mutations can be silent (have no/neutral effect) Cause subtle differences (both harmful & beneficial) Cause dramatic effects on observed traits in individuals (Usually harmful)

  7. 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 GG C UC U AA 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 GG C UA U AA G U amino acid sequence: Met -- Ala -- Iso -- Ser T

  8. 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 AC G UA U AC 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 AA G UA U AC G U amino acid sequence: Leu -- Ser -- Ile -- Arg

  9. 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 A C C G A T G A T T C A Inserting one or more nucleotides T A C C G A G A T T C A Deleting one or more nucleotides

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

  11. How much variation in DNA exists between 2 people? Hemoglobin (beta) gene sequence from person A

  12. How much variation in DNA exists between 2 people? Hemoglobin (beta) gene sequence from person B

  13. 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.

  14. 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

  15. 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)

  16. 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.

  17. 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.

  18. Questions • Which type of mutations had the biggest effect on the protein sequence? WHY? • Which type of mutations had the smallest effect on the protein sequence? WHY? • Which examples would you predict to have the biggest effects on a trait? WHY? • Which examples would you predict to have the smallest effects on a trait? WHY? • What is a possible explanation for the occurrence of these mutations?

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