Mistakes in the code

Review: What are some features of DNA? How is DNA for a new cell made? How does DNA instruct the cell to make proteins (The Central Dogma of biology)? 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?

How does your DNA determine your traits? mRNA protein Observed trait transcription translation protein function ( ex. enzyme activity) 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 is determined by nucleotide sequence

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 in somatic and sex cells. Mistakes in these processes can cause permanent changes in the DNA. Can you inherit mistakes from Mitosis? Meiosis?

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.

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)

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 mRNA sequence: A U G G C U A U A A G U amino acid sequence: Met -- Ala -- Iso -- Ser T

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

3 types of mutations T Point or Substitution Insertion Deletion 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

Consequences of mutations… As a result of mutations, differences exist between within a species DNA sequence!

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

Example of a point mutation that exists between 2 people? Hemoglobin (beta) gene sequence from person A

Example of a point mutation that exists between 2 people? Hemoglobin (beta) gene sequence from person B

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. Students discuss in partners/small group Discuss briefly as class Students write answers INDIVIDUALLY (no talking answers to question on notecard and pass in for assessment)

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. https://www.youtube.com/watch?v=ZvnhZI-GZS4 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.

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 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?