BIOL 207 Entire Term Notes

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Biology (Biological Sciences)
Michael Harrington

Biology 207Lectures 1 7 Dylan Feist Mitosis Meiosis and Life CyclesCell Divisiony Makes new daughter cells y Everything in the original cell must be reproduced or evenly distributed Mitochondria for example are randomly distributed throughout a cell but chromosomes require special attentionEukaryotic Cell Cycle y The cell cycle is composed of the G1 S G2 and M phasesy DNA is replicated in the S phasey 2 identical pieces of DNA are called chromatids y Mitosis is the separation of chromosomes y Centromereproteins that hold sister chromatids together in cohesion rings The centromere has specific functions i Site where most cohesions are found ii Site where the microtubules attach to the chromosome y The breakdown of cohesion rings begins in Anaphase Quantifying DNA in Eukaryotes y Chromosome Setso Haploid cells have one chromosome set while diploid cells have two chromosome setso In humans gametes are haploid while from the embryo stage onward is diploidy Number of Chromosomes o The number of chromosomes in a haploid cellno There is no apparent relationship between chromosome number and complexity of an organismy Amount of DNA o The amount of DNA in a haploid cell is shown as a c valueo In a gamete the c value is 1 o In a cell in G1 the c value is 2 o In a cell in G2 the c value is 4 o Throughout mitosis the ploidy remains at 2n o The cvalue peaks in G2 at 4 from 2y Number of Genes o The number of genes in a haploid cell is the genomeo Humans have 25 000 nuclear genes 21 000 protein encoding and 4000 RNA encoding and 37 mitochondrial genesEukaryotic Life Cycle y Mitosiscell division of diploid cells y Mitosiscell division of haploid n cells y Fertilizationhaploiddiploid y Meiosisdiploidhaploid y In prophase I of meiosis homologous chromosomes pair with sister chromatids to produce a bivalent which consists of 4 pieces of DNA 4 chromatids and 2 chromosomesy In anaphase I homologous chromosomes are separatedy In anaphase II sister chromatids are separatedVariation in the Eukaryotic Life Cycle y Overview o Animals have a very short haploid stage o Plants have a short haploid stageo Fungi have a long haploid stage and a short diploid stagey Humans o Spermatogenesismeiosis produces spermatids which undergo differentiation which results in spermo Oogenesismeiosis produces four gametes However three of them are discarded as polar bodies in order to maximize volume in the final oocytey Differences between Animals Plants and FungiProperty Animals Plants Fungi Sexes MaleFemale MaleFemale on Mating types a one individual and aDo Haploid cells No Yes Yes dividereproduce N2n Single Double Cellular and fertilization event fertilization event Nuclear Fusion o Double fertilization is a major difference In double fertilization one sperm is used to fertilize the embryo and another is used to fertilize two polar nuclei to produce the endosperm o Budding yeast is an example of a fungal life cycle o In a fungal life cycle the four products of meiosis remain temporarily within an ascus which allows scientists to look at the cellso Unequal cell division is called budding Chromosomes During the Cell CycleNucleic Acid Rules y Made of triphosphate nucleotidescontain three phosphates bonded to a ribose sugar and a basey Made using a singlestranded DNA templatehas Ts not Usy Made 5 to 3nucleotides are attached to the 3 end y Pair antiparallel only fit together antiparallel DNARNA and RNARNA all pair this wayy Pair with complementary base pairingAT and CG Replication of circular pieces of DNA y Prokaryotic chromosomes prokaryotic plasmids and eukaryotic organelle chromosomes all replicate the same general way y At the ori two replication forks are made They travel in opposite directions When they meet they terminateReplication of Linear Pieces of DNA y In eukaryotic nuclear chromosomes there are more than one ori locations When the replication forks meet they annihilate each othery The end replication problem results when a DNA primer is placed on the lagging strand of DNA When the primers are removed DNA cannot be replaced where there is no 3 end As a result the molecule shortens every time replication takes place To fix this telomerase which carries its own template adds nucleotides to the parental stand DNA polymerase then completes the lagging strand Telomerase is an exception to the rule that nucleic acids are made with a ssDNA templatePackaging of Eukaryotic DNA y Interphase chromosomes o DNA must be accessible to DNA replication DNA repair and RNA synthesis machineryo In a group of DNA there will be a ball of histone proteins with DNA wrapped around The entire thing is called a nucleosome
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