Week 10: DNA Replication and Meiosis
Week 10: DNA Replication and Meiosis Bio 107
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This 5 page Class Notes was uploaded by Rachel Johnson on Friday October 30, 2015. The Class Notes belongs to Bio 107 at Washington State University taught by William Davis in Summer 2015. Since its upload, it has received 25 views. For similar materials see Biology in Biology at Washington State University.
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Date Created: 10/30/15
DNA Replication II Elongation 339 DNA polymerase synthesizes new strands Elongates primer Adds a nucleotide to a 3 OH group 339 Antiparallel strand synthesis problem Lagging strand runs 5 gt3 but needs to be read 3 gt5 DNA polymerase can t synthesize it easily 339 Leading strand synthesis Occurs in the 5 gt3 direction Towards the replication fork Continuous only requires one primer 339 Lagging strand synthesis Occurs in the 5 gt3 direction Away from the replication fork Discontinuous requires several primers Forms Okazaki fragments Short segments of DNA that range from hundreds to thousands of nucleotides in length Synthesizes until the primer from the previous segment is reached and then the DNA pol III jumps ahead again Termination 339 RNA replacement and ligation DNA pol I replaces RNA primers with DNA Binds to the sites of primers Ligase seals the DNA segments together DNA Replication III Error Control 339 DNA polymerase can proofread by back tracking to the error Uses its 3 to 5 exonuclease activity Cuts off the wrong bases and restarts synthesis End of Replication Problem 0 v Occurs in eukaryotes because of their linear chromosomes 0 v DNA polymerase can only add to a 3 OH group 5 primer cannot be replaced with DNA Becomes shorter and shorter with each replication Can lead to gene loss 339 Preventive measure telomeres Repetitive sequences at the ends of linear chromosomes Protects the gene from erosion Similar to shoelace caps Added by telomerase Doesn t need a primer Usually adds siX bases at a time Active in germ cells and some cancer cells Meiosis I Chromosome Terminology 339 Humans have 46 chromosomes 44 autosomes and 2 sex chromosomes 339 Homologous chromosomes homologues the two chromosomes in each pair Have genes controlling the same heritable traits 339 Haploid vs diploid Haploids contain half the number of chromosomes sex cells Haploids n Diploids contain all of the chromosomes Diploids 2n 0 v Nonsister chromatids the DNA strands from the male and female in a homologous pair Meiosis 339 Takes a single diploid cell with replicated chromosomes to four haploid cells with one copy of each chromosome in each 339 Stage 1 Meiosis I Creates two daughter cells with one sister pair in each 339 Stage 2 Meiosis II Creates four daughter cells with one copy of each chromosome Crossing Over 0 v Nonsister chromatids exchange DNA that codes for the same trait 0 v Occurs in Prophase I Begins with synapsis Crossing over occurs Chiasma appear 0 v Results in new combinations of genes
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