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Mutations

Mutations. What Are Mutations?. Changes in the nucleotide sequence of DNA May occur in somatic cells (body cells) May occur in gametes (eggs & sperm) and be passed to offspring. Are Mutations Helpful or Harmful?. 1. Mutations happen all the time 2. Almost all mutations are neutral

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Mutations

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  1. Mutations

  2. What Are Mutations? • Changes in the nucleotide sequence of DNA • May occur in somatic cells(body cells) • May occur in gametes (eggs & sperm) and be passed to offspring

  3. Are Mutations Helpful or Harmful? 1. Mutations happen all the time 2. Almost all mutations are neutral 3. Chemicals & UV radiation cause mutations 4. Many mutations are repaired by enzymes(DNA polymerase)

  4. Consequence of Mutations Most mutations are minor Many are harmful Some are lethal A few may be helpful

  5. Significance of Mutations Most are neutral Eye color Birth marks Some are harmful Sickle Cell Anemia Down Syndrome Some are beneficial Sickle Cell Anemia to Malaria Immunity to HIV

  6. What Causes Mutations? There are two ways in which DNA can become mutated: Mutations can be inherited. Parent to child Mutations can be acquired. Environmental damage Mistakes when DNA is copied

  7. Are Mutations Helpful or Harmful? • Some type of skin cancers and leukemia result from somatic mutations • Some mutations may improve an organism’s survival (beneficial)

  8. TYPES OF MUTATIONS 1. Chromosome mutations Changes in chromosome structure Changes in chromosome number 2. Gene mutations Relatively small changes in DNA structure Occur within ONE particular gene 8

  9. Chromosome Mutations • May Involve: • Changing the structure of a chromosome • The loss or gain of part of a chromosome

  10. Chromosome Mutations • Five types exist: • Deletion • Inversion • Translocation • Nondisjunction • Duplication

  11. Deletion • Due to breakage • A piece of a chromosome is lost

  12. Inversion • Chromosome segment breaks off • Segment flips around backwards • Segment reattaches

  13. Duplication • Occurs when a gene sequence is repeated

  14. Translocation • Involves two chromosomes that aren’t homologous • Part of one chromosome is transferred to another chromosomes

  15. Translocation

  16. Nondisjunction • Failure of chromosomes to separate during meiosis • Causes gamete to have too many or too few chromosomes • Disorders: • DownSyndrome – three 21st chromosomes • Turner Syndrome – single X chromosome • Klinefelter’s Syndrome – XXY chromosomes

  17. Chromosome Mutation Animation

  18. Gene Mutations Changes in a single gene Takes place during DNA replication Can involve one or morenucleotides (bases) May be due to copying errors, chemicals, viruses, etc.

  19. Types of Gene Mutations 1. Point mutations A substitution one nitrogen base in a DNA sequence Effects of this change Missense Nonsense Silent

  20. Gene Mutations Point Mutations – changes in one or a few nucleotides Substitution THE FAT CAT ATE THE RAT THE FAT HAT ATE THE RAT

  21. Missense A type of point mutation that results in a change in a single mutation. Protein is changed EXAMPLE: sickle cell anemia

  22. Types of Gene Mutations 1. Point - Missense One base is replaced by a different one resulting in a change an amino acid of a protein which DOES change the protein!!!!!

  23. Normal DNA: TGA TCT ACT • mRNA: ACU AGA UGA amino acid: (arginine) Substitution= DNA: TGA TCC ACT • mRNA: ACU AGG UGAamino acid: (arginine)orSubstitution= DNA: TGA TTT ACT • mRNA: ACU AAA UGA amino acid: (lysine)

  24. Types of Gene Mutations Point mutation.Substitution Sickle Cell Anemia Normal- DNA: TAG CTT ATT mRNA: AUC GAA UAA Sickle Cell- DNA: TAG CAT ATT mRNA: AUC GUA UAA Change in one amino acid Glutamic acid is replaced by Valine

  25. Point Missense Mutation • Sickle Cell disease is the result of one nucleotide substitution • Occurs in the hemoglobin gene • One amino acid change causes the protein to not fold correctly.

  26. This is what happens in sickle cell anemia. The 17th nucleotide of the gene for the beta chain of hemoglobin is changed from an 'a' to a 't'. This changes the codon from 'gag' to 'gtg' resulting in the 6th amino acid of the chain being changed from glutamic acid to valine. This apparently trivial alteration to the beta globin gene alters the quaternary structure of hemoglobin, which has a profound influence on the physiology and wellbeing of the individual

  27. Nonsense mutations A type of Point mutations that create a premature stop codon. The protein is too short. Causes Cystic Fiberosis

  28. Nonsense mutations occur in between 15% to 30% of all inherited diseases including cystic fibrosis, hemophilia, retinitis pigmentosa and duchenne muscular dystrophy.

  29. Cystic fibrosis is a severe, genetically determined disease that involves both the lungs and the gastrointestinal tract. It occurs in about one in every two thousand births among white children and at a far lower rate in asian and black children. There are now more than 500 different mutations known to cause the disease. These mutations occur in a huge gene on chromosome 7 that encodes a protein of 1480 amino acids called the cystic fibrosis transmembrane conductance regulator (CFTR).

  30. The Cause of Cystic Fibrosis CFTR gene The most common allele that causes cystic fibrosis is missing 3 DNA bases. As a result, the amino acid phenylalanine is missing from the CFTR protein. Normal CFTR is a chloride ion channel in cell membranes. Abnormal CFTR cannot be transported to the cell membrane. The cells in the person’s airways are unable to transport chloride ions. As a result, the airways become clogged with a thick mucus.

  31. Silent Mutation • A type of point mutation that does not change the amino acid.

  32. 2. Frameshift Mutations Frameshifts occur when a base is inserted or deleted from the DNA sequence • Insertions • Deletions • This causes the frames being read to bond the incorrect amino acids

  33. Frameshift Mutation • Inserting or deleting one or more nucleotides • Changes the “reading frame” like changing a sentence • Proteins built incorrectly

  34. Gene Mutations Frameshift Mutations – shifts the reading frame of the genetic message so that the protein may not be able to perform its function. Insertion THE FAT CAT ATE THE RAT THE FAT HCA TAT ETH ERA T Deletion THE FAT CAT ATE THE RAT TEF ATC ATA TET GER AT H H

  35. Insertion • Insertion • One base is • addedto the DNA segment • Causes a frameshift

  36. Insertion mutations • Causes Fragile X chromosome • Males receive this X from their mom and causes mental retardation. • C and G repeat over and over. Examples – Huntington’s, some Parkinson’s, and Lou Gehrig’s disease

  37. In Huntingtons disease, the repeated trinucleotide is 'cag'. This adds a string of glutamines to the Huntington protein. The abnormal protein produced interferes with synaptic transmission in parts of the brain leading to involuntary movements and loss of motor control

  38. Fragile X syndrome is caused when a locus on the X chromosome contains a stretch of nucleotides in which the triplet 'cag' is repeated (as many as 400 times). This causes a constriction in the x chromosome making it quite fragile. Males who inherit this X chromosome are mentally retarded. Females are only mildly affected.

  39. Deletion One base is omittedfrom DNA segment Causes aframeshift Deletion

  40. Examples of insertion and deletions - FRAMESHIFTS • The sun was hot but the old man did not get his hat. • The unw ash otb utt tho ldm and idn otg eth ish at • By deleting the s in sun the whole protein is made wrong • The ssu nwa sho tbu tth eol dma ndid dno tge thi sha t • By inserting an extra s, the protein would be read incorrectly.

  41. Frameshift mutations may be beneficial, deleterious, or lethal. For example, induction of frameshift mutation has been used to make certain bacteria capable of producing nylonase, an enzyme that can degrade nylon. • Frameshift mutation has also been one of the possible causes of albinism. A shift in the reading frame can lead to formation of stop codon, hence, early terminating proteintranslation. An early termination of any of the enzymes necessary for the production of melanin can result in albinism.

  42. Tay Sachs disease is an example of a disease caused by frameshift mutation. The disease is caused by various mutations, including frameshift mutations, on chromosome 15 in the HEXA gene that codes for the alpha-subunit of the lysosomal enzyme beta-N-acetylhexosaminidase A.

  43. Frameshift Mutation • Original: • The fat cat ate the wee rat. • Frame Shift (“a” added): • The fat caa tet hew eer at.

  44. Gene Mutations Point Mutations – changes in one or a few nucleotides Substitution THE FAT CAT ATE THE RAT THE FAT HAT ATE THE RAT Insertion THE FAT CAT ATE THE RAT THE FAT CAT XLW ATE THE RAT Deletion THE FAT CAT ATE THE RAT THE FAT ATE THE RAT

  45. Types of Gene Mutations Frame shift mutations: Caused by the insertion or deletion of a nitrogen base in the DNA sequence Shifts the “reading frame” of the genetic message Affects every amino acid that follows the point of insertion or deletion Can alter a protein so that it cannot perform its normal function

  46. Amino Acid Sequence Changed

  47. Types of Gene Mutations Example of deletion mutations: Tay Sachs disease: A genetic abnormality caused by large amounts oflipids built up on neurons in the brain Leads to paralysis Cystic Fibrosis: Deletion- Three nucleotides or one codon omitted. Normal- DNA: TAG TAA AAA CCT CAC mRNA: AUC AUU UUU GGA GUGCystic DNA: TAG TAA CCT CAC Fibrosis- mRNA:AUC AUU GGA GUG

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