Presentation on theme: " The sequences of bases in DNA are like the letters of a coded message… what would happen if a few of those letters changed accidentally, altering the."— Presentation transcript:
The sequences of bases in DNA are like the letters of a coded message… what would happen if a few of those letters changed accidentally, altering the message?? Could the cell still understand its meaning? Mutation: a mistake or variation in the bases of DNA- mutations are heritable changes in genetic information.
Spontaneous Change in Hereditary Material caused by replication errors or environmental factors Genes or chromosomes
Some harmful; Some not DNA replicates during the S phase of interphase (prior to mitosis). If an error occurs during this process, DNA polymerase usually fixes the mistake. A mutation is the FAILURE of the DNA repair system to fix the error.
Point mutations: gene mutations that involve changes in one or a few nucleotides Substitution: 1 base is changed to a different base in the DNA sequence *think substitute teacher (switch) Frameshift (Insertion or Deletion): 1 base is inserted or removed from the DNA sequence *think adding another teacher to the room or removing the teacher completely (not going to happen! )
1) Single Point Mutations- 1 base gets replaced w/ another Ex: ACCTG AACTG Can lead to change in the codon change in amino acid change in protein change in trait EX: change in protein can cause normal red blood cells to have crescent (sickle shape)
Fig. 17-22 Wild-type hemoglobin DNA mRNA Mutant hemoglobin DNA mRNA 3 3 3 3 3 3 5 5 5 5 5 5 CCTT T T G G A A A A AA A GG U Normal hemoglobinSickle-cell hemoglobin Glu Val
Fig. 17-23a Wild type 3 DNA template strand 3 3 5 5 5 mRNA Protein Amino end Stop Carboxyl end A instead of G 3 3 3 U instead of C 5 5 5 Stop Silent (no effect on amino acid sequence)
Fig. 17-23b Wild type DNA template strand 3 5 mRNA Protein 5 Amino end Stop Carboxyl end 5 3 3 T instead of C A instead of G 3 3 3 5 5 5 Stop Missense
Fig. 17-23c Wild type DNA template strand 3 5 mRNA Protein 5 Amino end Stop Carboxyl end 5 3 3 A instead of T U instead of A 3 3 3 5 5 5 Stop Nonsense
2) Frame Shift- when a base is either deleted or added. This means the READING FRAME is changed and the bases “downstream” will be regrouped = disastrous results. EX: Deletion CCAGT CCGT Insertion CCAGT CCAAGT Again, can lead to a change in codon…trait!!!
Huntington’s Disease - The triplet CAG is repeated. This adds a string of glutamines to the protein called huntington. This abnormal protein increases the level of p53 protein in brain cells causes their death by apoptosis. This degeneration causes uncontrolled movements, loss of intellectual faculties and emotional disturbance. Muscular Dystrophy - CTC and CCTG repeats. This disease is characterized by the progressive weakness and degeneration of the skeletal muscles.
Insertion of 2 nucleotides (A & T) - 2566 Deletion of one C - 3659 Deletion of 3 nucleotides at 1654-1656 Generally results in abnormal amounts of salt which leads to a thick sticky mucus coating which coats cells - particularly the lungs.
Harmful Effects: Those that dramatically change protein structure or gene activity. *Example: Some cancers are the product of mutations that cause uncontrolled cell growth of cells. Beneficial Effects: Those that produce proteins with new or altered functions that may be useful to organisms in different/changing environments. *Example mutations have allowed for insects to resist chemical pesticides. Good for insects, bad for farmers & our food!
Mutagens are external agents that cause mutations. EX: Radiation from x-rays, UV light Viruses - human papilloma virus Environmental poisons- tobacc0 Carcinogens-cancer causing chemical(s)