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Week 8 notes (including exam 2 review)

by: Emma Notetaker

Week 8 notes (including exam 2 review) CELL 2050

Marketplace > Tulane University > CELL > CELL 2050 > Week 8 notes including exam 2 review
Emma Notetaker
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About this Document

Review for exam 2
Dr. Meadows
Class Notes
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This 3 page Class Notes was uploaded by Emma Notetaker on Tuesday October 18, 2016. The Class Notes belongs to CELL 2050 at Tulane University taught by Dr. Meadows in Fall 2016. Since its upload, it has received 15 views. For similar materials see Genetics in CELL at Tulane University.


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Date Created: 10/18/16
Tuesday, October 18, 2016 Week 8 Ch 12 (cont.) • Holliday junction and single-strand break • homologous chromosomes align and single strand breaks occur in same place on both molecules • free end of each migrates to the other molecule • each invading strand joins to the broken end of the other DNA molecule —> Holliday junction • begins to displace original complementary strand • branch migration takes place as the strands exchange positions, creating 2 duplex molecules - mixture of both DNA (heteroduplex DNA) • ends of the 2 interconnected duplexes pulled away from each other and rotated to form cross-like structure cleavage in vertical plane makes crossover recombinants • • cleavage in horizontal plane makes non crossover recombinants • ALL PRODUCTS ARE heteroduplexes • double-strand break model of recombination - resembles double Holliday junction • 2 double stranded DNA molecules from homologous chromosomes align • double-strand break occurs in one molecule • nucleotides enzymatically removed, producing some single-stranded DNA on each side pruning of some genes • • free 3’ end invades and displaces a strand of unbroken DNA molecule • strand of unbroken strand loops out • 3’ end elongates (with complementary - blue becomes red), further displacing original strand • displaced strand forms a loop that base pairs with broken DNA (goes down farther) on other chromosome • DNA synthesis initiated and 3’ end of the bottom strand (displaced loop is used as template) • strands fuse —> produces 2 Holliday junctions, each can be separated by cleavage and reunion • 2 possibilities of cleavage and rejoining—> noncrossover recombinants • 2 possibilities of cleavage/rejoining —>crossover recombinants Exam 2 Review • Ch 8 types of chromosomal mutations/rearrangements • • aneuploidy • know types and how to figure them out • trisomy 21 (primary vs familial) • caused by nondisjunctions - depends on when this occurs • polyploidy: change in chromosome sets • auto: same species 1 Tuesday, October 18, 2016 • allo: 2 plants with different chromosomes, and are similar enough to form hybrid plant (almost homologs pair) • nondisjunction at early mitotic cell division —> complete set, so can form functional gametes • now gametes are allotetraploid (4n = 12) • via nondisjunctions • if in meiosis 1, will have double amount —> lead to autotriploid • may give example and ask if nonreciprocal translocation, reciprocal, or Roberstonian • Robertsonian translocation: be familiar with examples • ex: familial Down Syndrome • know worked problem about polyploidy • Ch 9 • genetic exchange in bacteria (known differences between the 3, how genes are mapped with each and the experiments associated with the 3) • conjugation (F factor, F+, F-, Hfr, F’) • transfer of bacterial genes from Hfr to F-: almost never gets full F factor • will cross over inside F- cell and bacterial genes transfer over • MAPPING BASED ON TIME • transformation • MAPPING BASED ON COTRANSFORMANTS • transduction via bacteriophages • MAPPING BASED ON COTRANSFORMANTS • RNA virus • retrovirus • how reverse transcriptase to integrate RNA into host DNA • CH 10 • know who did what in each experiment • ex: Avery, MacLeod and McCarty identified that transforming substance was DNA • structure of DNA and RNA • differences • RNA is single stranded • both held together by phosphodiester bonds • types of bases • bonds • polynucleotide chains • antiparallel • complimentary • 3’-OH, 5’-phosphate • secondary structures • Ch 11 • supercoiling • relaxed DNA is 10 bases/rotation • euchromatin vs heterochromatin (very tight) • chromatin organization • nucleosome: histone (+), 2 copies of each H2A, H2B, H3 and H4 (H1 outside - NOT part of nucleosome) • ~200 bp around each • chromosomal puffs: transcriptionally active regions - sensitive to DNase • sensitive to DNase because area is open so DNase can come in and chop it up 2 Tuesday, October 18, 2016 • telomere structure and function • mitochondria and chloroplasts • endosymbiotic theory • evidence • mitochondria similar in structure and DNA sequences to bacteria • have own genome/chromosomes • genes on nuclear chromosome encode proteins that make up the mitochondria • protists now hosts to endosymbiotic bacteria • replicative segregation • 2 different forms of mitochondria • through every cell division, random distribution of mitochondria • eventually, you may end up with homoplasmic (all mitochondria the same) or heteroplastic (2 types) • economic organization, aging • Ch 12 • replication theories • Messelson and Stahl • types: theta, rolling circle, linear • proteins/enzymes involved (and functions of initiation, unwinding, elongation) • nucleosome assembly on newly synthesized DNA • must remove histones, replicate, then make more histones and re-associate • elongation: gyrase loosens DNA • transcription bubble forms, SSBs bind to stabilize • helices sever H bonds between strands • primases make RNA primers • DNA polymerase III comes in and uses free 3’ OH groups to add on/synthesize DNA (elongation) • 5-3 activity and 3-5 exonuclease activity • DNA polymerase I removes and replaces primers • 5-3 nuclease and 3-5 exonuclease • **5-3 exonuclease activity - used to remove primers laid down by primase and replaces them with DNA in 5-3 direction • telomerase: end of linear chromosomes in replication • homologous recombination: Holliday junction 3


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