MCB 100 1st Edition Lecture 22Outline of Last Lecture I. Protein synthesis by ribosomes- translationII. Fundamental properties of the genetic code III. Viral variations of the central dogma Outline of Current Lecture I. MutationsII. Genetic recombinationIII. Three ways for bacterial DNA to move from a donor strain to recipient strainIV. Three ways bacterial DNA can survive if it is an autonomous replicon V. Regulation of gene expression in bacteriaVI. Recombination of DNA technology (Chapter 8) Current LectureI. Mutations a. A mutation = stable change in the DNA of an organism that can be passed on to the offspring of that organismb. Mutations are permanent and rare c. A mutation produces a genotypic change d. Many mutations affect the phenotype of the organism, but not all of them e. Mutations result from errors in DNA base pairing during replication (enzyme that makes the new DNA strand, which is the DNA polymerase, is very faithful but not perfect) f. Three main characteristics of mutations:i. Rareii. Permanent iii. Inherited b. Mutations can occur spontaneously when DNA polymerase makes an error while synthesizing a new strand of DNA (each nucleotide gets added at 3' end; DNA polymerase can cut nucleotide away when it is not correct- editing function) c. A mutagenic agent causes damage to DNA that increases the likelihood of an error being made by DNA polymerased. Common mutagens are: x-rays, UV light, and many chemicals including coal tar derivatives, LSD and DNA base analogs such as 5-bromouracil) e. Three types of mutationsi. SubstitutionThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.1. One nucleotide is replaced by another2. can change a codon if within a gene ii. Deletion1. One or more nucleotides are left out2. Caused by ionized radiation ii. Insertion1. One or more extra nucleotides are added 2. Can cause a frame shift when ribosome is reading the gene--> from that point down, every codon is a mistake! 3. Can either destroy/modify/better the gene b. Three types of codon change: i. Missense mutations1. Encodes a different amino acid, this can inactivate the enzyme 2. Ex. Changing the GAG codon (glutamic acid) to GUG (valine) ii. Nonsense mutations1. Encode an early stop codon; usually eliminates the enzyme2. Ex. Changing CAA (glutamine) to UAA (STOP) ii. Neutral mutations1. Minor changes in DNA that have n effect on enzyme2. Ex. Changing a GUU codon to GUC has no effect (both codes for valine) II. Genetic recombinationa. Most of eukaryotic organisms, including most fungi, algae, and protozoa, have well developed sexual reproduction that includes the formation of diploid cells by the fusion of gametes (haploid sex cells such as sperm and ovum)--> sexual reproductionproduces an individual with a combination of 2 complete haploid genomes b. Genetic recombination in bacteria (integration of foreign DNA into the genome of arecipient cell): i. Bacteria don’t form diploid cells- they don’t form gametes/undergo meiosis--> DNA exchange in bacteria is limited to the one-way transfer of DNA from a donor cell to a recipient ii. Foreign DNA will be degraded unless it can be replicated and maintained in the recipient celliii. Transformation: genetic change produced in a bacterium that is caused by the uptake of naked foreign DNA which becomes a part of he recipient cell's genome 1. Was discovered by Griffith in 1928 in Streptococcus pneumonia 2. Note the role of homologous recombination in the insertion and integration of the foreign DNA into the chromosome of the recipient cell--> allows genotype of recipient cell to become permanently changed so the trait can be passed on to the offspring of the transformed cell3. Capsule = layer of polysaccharides that coats the outer surface of the cell.(in streptococcus pneumonia, the capsule protect the bacterium from thedefensive white blood cells of the host animal; capsule makes bacterium a much more virulent/dangerous/disease-causing pathogen)a. Encapsulated strains = smooth and shiny appearing colonies when grown on an agar mediumb. Unencapsulated strains = dry/rough colonies 2. In 1944- MacLeod and McCartya. Showed that the transforming substance from dead virulent strain was DNAa. Enzyme that breaks own DNA destroyed the transforming agent but some enzymes that break down proteins did not 2. Bacteria that can take up naked DNA = competent 3. Transformation is most efficient when the DNA size is relatively small, 1000-2000 base pairs--> just big enough to contain 1-3 genes4. Circular supercoiled plasmid DNA works better than linear DNA! Transformation by plasmids that are 4000-5000 base pairs long works well5. Electroporation- giving recipient cells a shock of electricity to cause them to be more likely to take up DNA i. Conjugation1. DNA is transferred from donor strain to recipient strain by direct cell to cell contact- DNA is transferred through a narrow cytoplasmic bridge2. Donor cell Is not killed by conjugation and doesn’t usually lose any DNA 3. Generally involves replication of DNA that is about to be transferred and donation of 1 copy to recipient cell 4. A sex pilus (F-pilus) = appendage that helps bacterial cells stick together so conjugation can occur--> genes for most sex pili are located on plasmids; genes that encode all of the proteins needed to make the F-pilus are found on the F-plasmid 5. Usually, DNA would be a plasmid when transferred by conjugation; some plasmids can mobilize the movement of chromosomal genes into recipient cell6. Plasmid is copied as it is transferred so the donor cell would not lose it! 7. F+ strain vs. HFR straina. F+ strain of E. coli has a copy of F plasmid in its cytoplasmi. Will transfer genes that are on the F-plasmidb. HFR strain has the F factor integrated into its chromosome i. Will transfer chromosomal genes that are near the insertion site of the F-factor ii. Occurs in linear order ii. Transduction1. DNA from donor cell gets incorporated into a defective virus particle called a transducing phage particle2. The defective virus attaches to a recipient cell and injects DNA from the donor strain3. Kills donor strain! 4. When DNA from donor strain gets into a recipient strain, it must be integrated into the genome of the recipient cell, or it will be degraded!5. A typical bacterial mating experiment needs specialized donor and recipient strains and some selective