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MUTATIONS

Section 5.6. MUTATIONS. What are mutations?. Errors made in the DNA sequence. These errors may have Deleterious Side Effects Or Positive Side Effects No Effect. EFFECTS OF MUTATONS. Deleterious side effects

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MUTATIONS

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  1. Section 5.6 MUTATIONS

  2. What are mutations? • Errors made in the DNA sequence. • These errors may have • Deleterious Side Effects • Or Positive Side Effects • No Effect

  3. EFFECTS OF MUTATONS • Deleterious side effects • Mutations in the cystic fibrosis transmembrane regulator (CFTR) gene results in cystic fibrosis which can be passed on from parent to child. • No effects • Positive Side Effects • Large size of the human brain arose from a series of mutations.

  4. HAPLOID VS. DIPLOID • A fundamental genetic difference between organisms is whether their cells carry a single set of chromosomes or two copies of each chromosome. • HAPLOID = a single set of chromosomes • DIPLOID = two copies of each chromosome • Many simple unicellular organisms are haploid, whereas complex multicellular organisms (e.g., fruit flies, mice, humans) are diploid.

  5. Types of Mutations • Silent Mutations • Missense Mutations • Nonsense Mutations • Frameshift Mutations • Point Mutations: • Deletions • Insertions/Addition • Substitutions • Chromosomal • Translocation • Inversion

  6. SILENT MUTATIONS • A mutation that does not result in a change in the amino acid coded for and. • Does not cause any phenotypic change.

  7. SILENT MUTATIONS: How do they occur? • Usually silent mutations occur in the non coding regions (introns) of DNA. • If introns are cut out of the primary mRNA transcript during the process of transcription, the mutation never surfaces. • Redundancy nature of the genetic code. • For example, if the amino acid phenylalanine is coded for the base sequences on UUU and UUC on mRNA. If there was a mistake made during transcription or the mutation occurs in the DNA so that the third base is now a G instead of an A (complementary base C instead of U of mRNA), phenylalanine will still be the amino acid that is translated. • The effect goes unnoticed.

  8. MISSENSE MUTATIONS • A missense mutation arises when a change in the base sequence of DNA alters a codon, leading to a different amino acid being placed in the protein sequence. • Sickle Cell Anemia results from a missense mutation.

  9. SICKLE CELL ANEMIA Normal hemoglobin (left) and hemoglobin in sickled red blood cells (right) look different; the mutation in the DNA changes the shape of the hemoglobin molecule, allowing it to clump together.

  10. NONSENSE MUTATION • A nonsense mutation occurs when a change in the DNA causes a stop codon to replace a codon specifying an amino acid. • During translation, only the part of the protein that comes before the stop codon is produced, and the fragment may be digested by cell proteases. • Nonsense mutations are often lethal!

  11. SUBSITUTIONS • The replacement of one base in a DNA sequence by another base. • Substitutions often cause… • missense • nonsense mutations.

  12. DELETIONS • A deletion occurs when one or more nucleotides are removed from the DNA sequence. • For example, if the 3rd base is removed in the sequence • AUGGGA UUC AAC GGA AUA • MET-GLY-PHE-ASP-GLY-ISO • AUG GAU UCA ACG GAA UA. • MET-ASP-LEU-THR-GLU The protein structure has been drastically altered  defective protein. Shifts in the reading frame usually result in drastic errors

  13. INSERTIONS • Insertion is the placement of an extra nucleotide in a DNA sequence. • Results in a shift of reading frame. • Since the DNA sequence is read in triplets of nucleotides, inserting an extra nucleotide will cause different amino acids to be translated.

  14. FRAMESHIFT MUTATIONS • When a mutation changes the reading frame, it is called a frameshift mutation. • Usually frameshift mutations result in different amino acids being incorporated into the polypeptide. • Insertions and deletions can both cause frameshift mutations.

  15. FRAME SHIFT MUTATIONS… • A deletion or insertion of ONE nucleotide will cause a frame shift mutation. • 1) Will a deletion or insertion of TWO nucleotides also cause a frame shift mutation? • 2) How about a deletion or insertion of THREE nucleotides?

  16. Answer… • The insertion or deletion of three nucleotides results in the addition or removal of one amino acid. The presence or absence of the amino will cause a change in the protein conformation but it may not have as serious an impact as would not building the appropriate protein at all.

  17. EXAMPLES

  18. POINT MUTATIONS • A point mutation is a mutations that occurs at a specific base pair in the genome.

  19. POINT MUTATIONS • Changes in a single base pair may produce one of three types of mutation: • Missense mutation • which results in a protein in which one amino acid is substituted for another • Nonsense mutation • in which a stop codon replaces an amino acid codon, leading to premature termination of translation • Frameshift mutation • which causes a change in the reading frame, leading to introduction of unrelated amino acids into the protein, generally followed by a stop codon

  20. TRANSLOCATION • A type of mutation that involves large segments of DNA. • Apparent at the chromosomal level. • Translocation is characterized by the relocation of groups of base pairs from one part of the genome to another.

  21. TRANSLOCATION • Usually translocations occur between two non-homologous chromosomes. • A segment of one chromosome breaks and releases a fragment, while the same thing happens to another chromosome. • The two fragments exchange places, sometimes disrupting the normal structure of genes.

  22. TRANSPOSABLE ELEMENTS • Some fragments of DNA are consistently on the move – they move from one location to another on the genome. • “Jumping Genes” • “Transposable Elements. “ • If they happen to fall within a coding region of a gene, they will disrupt the correct transcription of the gene, leaving it inactive.

  23. INVERSION • Inversion is a chromosomal segment that has reversed its orientation in the chromosome. • There is no loss or gain of genetic material, but depending on where the break occurs, a gene may be disrupted or come under other transcriptional control.

  24. Causes of Genetic Mutations

  25. SPONTANEOUS MUTATIONS • Some mutations are simply caused by errors of the genetic machinery. • DNA polymerase 1 reread the duplicated DNA to check for errors, yet on occasion, it misses a base or two, which results in a point mutation.

  26. INDUCED MUTATIONS • Mutations caused by a chemical agent or radiation. • Mutagenic Agents – agents that can cause a mutation. • Examples: Ultraviolet (UV) radiation, cosmic rays, X rays, certain chemicals.

  27. X-RAYS • x-rays and gamma rays. • cause breaks in phosphodiester bonds • result chromosome mutations like inversions, translocation, duplications.

  28. CANCER • Cancer is considered a genetic disease because it is always a result of a mutation in the genetic sequence. • Mutations  Oncogenes. • Oncogenes are mutant versions of genes that control cell growth and division.

  29. AIDS THERAPY • Chemicals that resemble DNA can also cause mutations. • Used in AIDS therapy. • Some of the chemical sin AIDS drugs resemble the nitrogenous bases in DNA and insert themselves into the virus’s DNA. When the viral DNA is to be duplicated, the DNA polymerase stops because it does not recognize the substituted chemical as a base. • Progression of the disease is slowed.

  30. Ethidium Bromide • A chemical commonly used in biotechnology to visualize DNA. • If UV light is shone on a fragment of DNA containing ethidium bromide, the DNA will phosphoresce. • Ethidium Bromide can bind to DNA and lead to mutations! • Be cautious!!

  31. Thalidomide • Thalidomide first appeared in Germany on 1st October 1957. It was marketed as a sedative with apparently remarkably few side effects. The Drug Company who developed it believed it was so safe it was suitable for prescribing to pregnant women to help combat morning sickness. • It was quickly being prescribed to thousands of women and spread to most corners of the globe. Nobody had any idea of what was to follow. Drug testing procedures were far more relaxed at this time, and although tests had taken place on thalidomide, they didn't reveal any of its tetragenic (roughly meaning causing malformations) properties. In most countries, drug companies were not required to submit testing results to the appropriate government agencies. The tests on thalidomide were conducted on rodents which metabolise the drug in a different way to humans. Later tests on rabbits and monkeys produced the same horrific side effects as in humans. • Towards the end of the fifties, children began to be born with shocking disabilities. It was not immediately obvious what the cause of this was. Probably the most renowned is Pharcomelia, the name given to the flipper-like limbs which appeared on the children of women who took thalidomide. Babies effected by this tragedy were given the name 'Thalidomide Babies'.

  32. Thalidomide

  33. HOMEWORK: Page References: Section 5.6 - Mutations (Pages 259-263) Homework: Page 258 # 1, 2, 3, 4, 5, 6, 7

  34. DON’T UNDERSTAND EVERYTHING? Check This Out!

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