BSCI410: Mutation and Its Effects - Lecture 2 - Prof. Zhongchi Liu, Study notes of Molecular biology

Download BSCI410: Mutation and Its Effects - Lecture 2 - Prof. Zhongchi Liu and more Study notes Molecular biology in PDF only on Docsity! Instructor: Dr. Zhongchi Liu 3236 H.J. Pattersom Hall Phone: 5-1586 Zhongchil@gmail.com www.life.umd.edu/CBMG/faculty/liu/liu.html TA: Jennifer Baxter 2114 (Lab) or 2114 (Office) Microbiology Building Phone: 5-1758 Sugarpucker@gmail.com About the course: www.life.umd.edu/classroom/BSCI410-Liu/BSCI410/ Lecture 2: Mutation and its effect Read: Ch 7 p192-193; 196-198; 200-205 Figs: 7.2; 7.6; 7.7; 7.8; 7.12; 7.21; 7.22; 8.15; 8.16; -Mutation type -Mutational effect -Spontaneous Mutation -Mutagens i : : i z-o-F a3 c— COOH | NH H | ¢— COOH | AM ¢—cooH | NH =— z— £ : : 5 : 2 5 Mutations 1. Substitution-1 base --> one of the three other bases Transition: purine --> purine or pyrimidine --> pyrimidine A--> G or G--> A T--> C or C--> T Transvertion: purine --> pyrimidine or vice versa A--> T, C; G -->T,C; T-->A, G; C-->A,G 2. Deletion or insertion-often causes frameshift mutation causes missense, nonsense, silent, neutral or splicing mutational effects 3. Chromosomal rearrangement inversion or translocation can change multiple genes Effects of point mutations tyrosine TAT, TAC TAT -> CAT tyr -> his missense TAT -> TAA tyr -> stop nonsense TAT -> TTT tyr -> phe neutral in many cases TAT -> TAC tyr-> tyr silent Fig. 8.16 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (a) Short sequences dictate where splicing occurs. ~30 nucleotides Exon 1 Intron | Exon 2 “ 5' ! L 1 Jo. J L : J Splice donor Branch site Splice acceptor (b) Two sequential cuts remove the intron. 5' site 3' site 5' = GU CACUGAC AG “Lariat” % 5' 3 7 3 CACUGAC AG Qs | <3 nS 5! 3 Q 5 3 Nn Mature mRNA Intron is degraded The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Frameshift mutations (a) The mutagen proflavin can insert between two base pairs Molecule of proflavin eos , inserted between oe a ee stacked base pairs (b.1) Consequences of exposure to proflavin riB Wildtype Expose to proflavin 0 ri Exposure to proflavin We rtant CO FC?_ oe Original Second mutation mutation (b.2) Crossing IB’ revertant with wildtype yields riB- recombinants FCO FC7_ rie_FCO nie FC? (c) Different sets of mutations generate either a mutant or a normal phenotype CO aeaiee Te yaeison [Phenotype —or+ Mutant --oOrtt Mutant --7- 7 or----— Mutant -+ Wildtype pies Wildtype Orde torte tee et (d) Three single base deletions (-——-—) Fe as t Three single base insertions ( + + +) sa Sg (ATG, AAG AAT GCG CCG GAG GAA GCG GAC + GiiekioeA RRR aia (e) Single base deletion (-) # & correct triplet . incorrect triplet Fig. 7.2 Copyright © The McGraw-Hill Companies, inc. Permission required for reproduction or display. Starting sequence _TEREEERREEREEEN Type of mutation and effect on base sequence (a) Substitution Transition: Purine for purine, pyrimidine for pyrimidine _KEREEERRRERR EER Transversion: Purine for pyrimidine, pyrimidine for purine (b) Deletion EEE Er (c) Insertion tT, (d) Inversion Site of inversion 5 eT | 3 »—_RENGESEESERE B (@) Reciprocal translocation Chromosome 1  (b) Deamination Amina a ee Se Cytosine Uracil EE aay A Replication (c) X rays break the DNA backbone Tht — En Daletion He & (d) UV light produces thymine dimers: UV light Thymnine diver 4 eds Sugar-phosphate backbone CHy H H Thymine dimer Mutagen treatment greatly increases the mutation rate Exposure to X-ray, UV light Chemical treatment: base analogs 5’-bromouracil (=T or rarely C) hydroxylating agent (add OH-group to C) alkylating agent such as E!MS (ethylmethane sulfonate) deaminating agent such as nitrous acid intercalating agent such as Acridine Orange Transposons that insert into a gene and disrupt the normal reading frame Mutagens Fig. 7.12al Chemical Mutagens Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Type of mutagen Chemical action of mutagen (a) Replace a base: Base analogs have a chemical structure almost identical to that of a DNA base. Qe H-n-4 oO oO Qe H 5-Bromouraci!-normal Adenine 5-Bromouracil-rare state, Guanine state, behaves like thymine behaves like cytosine 5-Bromouracil: almost identical to thymine, Normally pairs with A; in transient state, pairs with G. Fig. 7.12a2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. How mutagens induce mutations Replication Replication ee Tt T:A — C:G substitution Base analog (5B.u.) ~ incorporated during Wild type DNA replication or repair Fig. 7.12c1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Type of mutagen Chemical action of mutagen (c) Insert between bases: Intercalating agents HN Proflavin Intercalated proflavin molecules Proflavin intercalates into the double helix. This disrupts DNA metabolism, eventually resulting in deletion or addition of a base pair. Fig. 7.12c2 Copyright © The McGraw-Hill Companies, inc. Permission required for reproduction or display. Insertion of a intercalated random base pair proflavin — Ti Disruption of DNA replication, repair, or recombination Deletion of a base pair Template DNA