DNA Mutations Worksheet

Name: Page 1 DNA Mutations Worksheet Period: 6 Date: 04 4 21 DNA Mutation Worksheet A mutation is a permanent change of the nucleotide sequence of the genome of an organism, virus, or extra chromosomal DNA or other genetic elements. Only gamete cells (sperm & eggs) will pass on mutations. Mutations are a common natural process occurring in DNA sequences. Think of mutations as “typos” in the DNA code. These “typos” happen about every 100,000 nucleotides. When a human cell is copied and transmitted the exact same sequence of 3 billion nucleotides to its daughter cells. This means there are about 120,000 errors in an average human cell each time it divides. Three ways DNA can be altered when a mutation (change in DNA sequence) occurs. 1. Point Mutation or Substitution — mutation causing replacement of a single base nucleotide with another nucleotide of the genetic material, DNA or RNA. In other words, one base-pair is replace by another. • If a substitution changes the amino acid, it’s called a missense mutation. • If a substitution does not change the amino acid, it’s called a SILENT mutation. • If a substitution changes the amino acid to a “stop,” it’s called a NONSENSE mutation. G C or A G CGTC 2. Insertion — one or more base pairs is added to a sequence. DNA: CGA TGG CGA ATG G mRNA: GCT ACC GCT TAC C 3. Deletion — one or more base pairs is lost from a sequence DNA: CGA TGG CAT GG mRNA: GCT ACC GTA CC There are five possible results 1. Silent mutations — When a base pair is substituted but the change still codes for the same amino acid in the sequence. TCT and TCC both code for the same amino acid, Serine 2. Substitution — When a base is substituted and the new codon codes for a different amino acid. TCT codes for Serine and CCT codes for Proline 3. Premature Stop — When a substitution results in the formation of a STOP codon before all of the codons have been read and translated by the ribosome. DNA: GTG GTC CGA AAC ACC mRNA: GUG GUC CGA AAC ACC Val-Val-Pro-Asn-Thr GTG GTC TGA AAC ACC GUG GUC UGA AAC ACC Val-Val-STOP 4. Codon Deletion or Insertion — When a whole new amino acid is added or one is missing from the mutant protein. DNA: GTG GTC CGA AAC ACC GTG GTC TGC CGA AAC ACC mRNA: GUG GUC CGA AAC ACC GUG GUC UGC CGA AAC ACC Val-Val-Pro-Ans-Thr Val-Val-Cys-Pro-Asn-Thr 5. Frame Shift — When a deletion or insertion results in a different base pair being the beginning of the next codon, shifting it over, changing the whole sequence of amino acids. Meaning the reading “frame” changes, changing the amino acid sequence. DNA: GTG GTC CGA AAC ACC mRNA: GUG GUC CGA AAC ACC Val-Val-Pro-Ans-Thr GTG GTC GAA ACA CCT GUG GUC GAA ACA CCT Val-Val-Glu-Thr-Pro Name: Page 2 DNA Mutations Worksheet Period: Date: DNA Mutations Practice Directions: Transcribe and translate the original DNA sequence. Then, do the same for each mutated DNA sequence. Then, determine the consequence, if any, for each mutation, by circling your choice for each question. You will need a Genetic Code Chart. Original DNA sequence: TAC ACC AUG UGG met Trp Mutated DNA Sequence #1: TAC ATC mRNA transcript: (Circle any changes) AUG mRNA transcript: amino acids: Type of mutation (Circle one.) Point ð How did the mutation affect the amino acid sequence (protein)? (Circle one.) No change TTG TAC mRNA transcript: (Circle any changes) AUG amino acids: met Type of mutation (Circle one.) Point ð How did the mutation affect the amino acid sequence (protein)? (Circle one.) No change GAC CUG leu Cys CTT Arg ACT UGA Cys Stop Insertion or Deletion All the amino acids changed after the point of mutation 1 amino acid added/ deleted GGC GAC GAC T GAA CCG CUG Glu Pro Leu Premature stop signal Stop UGC CGC No stop signal UGA ACG Frameshift ð Substitution 1 amino acid changed Arg Asn Premature stop signal ACT UGC GCG AAC Substitution Mutated DNA Sequence #2: ACG CGC Asn Stop 1 amino acid changed GCG AAC UAG met amino acids: TTG Frameshift ð Insertion No stop signal 1 amino acid added/ deleted CUG A Leu or Deletion All the amino acids changed after the point of mutation Name: Page 3 DNA Mutations Worksheet Mutated DNA TAC ACC Sequence #3: mRNA transcript: (Circle any changes) amino acids: How did the mutation affect the amino acid sequence (protein)? (Circle one.) No change Mutated DNA sequence #4: TAC mRNA transcript: (Circle any changes) amino acids: Type of mutation (Circle one.) Point ð How did the mutation affect the amino acid sequence (protein)? (Circle one.) No change Premature stop signal ACC TTG AUG UGG AAC met Trp Asn 1 amino acid changed Mutated DNA sequence #5: TAC mRNA transcript: (Circle any changes) AUG amino acids: Type of mutation (Circle one.) Point ð How did the mutation affect the amino acid sequence (protein)? (Circle one.) No change Premature stop signal ACC Trp Premature stop signal or Deletion ACT UGA Stop Insertion GGA Deletion All the amino acids changed after the point of mutation CGA CT AAC CCU GCU Asn pro Ala No stop signal Insertion 1 amino acid added/ deleted UGA Stop or 1 amino acid added/ deleted No stop signal Stop ACT CGC Frameshift ð Substitution 1 amino acid changed GCG UGA All the amino acids changed after the point of mutation Arg TTG UGG met Insertion Frameshift ð Substitution Cys 1 amino acid added/ deleted No stop signal ACT UGC Arg Frameshift ð 1 amino acid changed ACG CGC Asn Substitution Date: GCG AAU Trp met Point ð TTA UGG AUG Type of mutation (Circle one.) Period: or GA Deletion All the amino acids changed after the point of mutation Name: Page 4 DNA Mutations Worksheet Period: Date: Conclusions 1. Which type of mutation is responsible for new variations (alleles) of a trait? Point mutation/substitution 2. Which type of mutation results in abnormal amino acid sequence? frameshift 3. Which type of mutation stops the translation of the mRNA? premature stop 2. A geneticist found that a particular mutation had no effect on the protein coded by a gene. What do you think is the most likely type of mutation in this gene? Why? Silent mutation because some amino acid can go after the mutation 4. Examine your genetic code chart. Name one amino acid that has more than one codon. Name an amino acid that has only one codon. Trp and met 5. Look at the following sequence: THE FAT CAT ATE THE RAT. Delete the first H and regroup the letters in groups of three- write out the new groups of three. Does the sentence still make sense? What type of mutation is this an example of? TEF ATC ATA TET HER AT This is a frameshift 6. Given the following three mRNA sequences, determine which two code for the same protein. Circle them. mRNA #1 Transcript Translate mRNA #2 AGU UUA GCA ACG AGA UCA Ser-Leu-Ala-Thr-Arg-Ser mRNA #3 UCG CUA GCG ACC AGU UCA Ser-Leu-Ala-Thr-Ser-Ser Ser-Leu-Ala-Thr-Arg-Ser Bonus: You have a DNA sequence that codes for a protein and is 105 nucleotides long. A frameshift mutation occurs at the 85th base - how many amino acids will be correct in this protein? Show your work. 28 amino acids because 84/3 occurs on the 85th AGC CUC GCC ACU CGU