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BIOL 1090 Midterm: Midterm review

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University of Guelph
BIOL 1090
Van Raayand Maathurs

Midterm review First level of condensation - DNA packaged into nucleosomes (11nm) - Nucleosome core  Made up of octamer of histones  146 nucleotide pairs around nucleosome  2H2a + 2H2b + 2H3 + 2H4 - Complete nucleosome  Made up of octamer of histones and H1 histone  166 nucleotide pairs around each nucleosome  H1 + 2H2a + 2H2b + 2H3 + 2H4 - Linker region susceptible to digestion by endonuclease - Linker region between 8 and 114 nucleotides Second level of condensation - Supercoiling of DNA from 11nm fibre into 30nm fibre - Driven by nucleosomal interactions - H1 involved - 30nm is basic structural unit of metaphase chromosomes (DNA in most condensed form) Third level of condensation - Attachment of the 30nm fibre at many positions to a non-histone protein scaffold - Cohesin and condensin make up the protein scaffold in the third level Cohesin - Ring shaped protein added to the 30nm DNA fibre at interphase - Cohesin holds sister chromatids together after DNA synthesis, before cells enter into mitosis - Most is degraded during mitosis as sister chromatids are pulled apart Condensin - V-shaped protein added to DNA at the beginning of mitosis - Functions to condense the 30nm fibre of DNA within one sister chromatid Centromeres of chromosomes - Holds sister chromatids together - Point of attachment for the spindle fibres Telomeres - Protect the ends of chromatids from DNase - Prevents fusion of choromosomal ends - Facilitate replication of the ends of DNA Mitosis - Occurs in somatic and stem cells - Nuclear choromosomes duplicated exactly and are divided equally and exactly into daughter cells - Mitochondria and chloroplasts are divided randomly between daughter cells - Endoplasmic reticulum and golgi are broken down and reformed in the daughter cells - Cellular organelles and cytoplasmic are divided more or less equally between daughter cells Cell Cycle  G1 phase – growth, cellular metabolism  S phase – DNA synthesis and chromosomal duplication  G2 phase – Preparation for mitosis  Mitosis – Prophase, Metaphase, Anaphase, Telophase  Cytokinesis Quiescent cells - Cells that are not actively cycling may leave after G1, entering a stage called G0 - Neurons are quiescent cells as they do not duplicate Interphase  Chromosomes duplicate to produce sister chromatids. (23 chromosomes would become 46)  Duplicated chromosomes are called sister chromatids  Held together by cohesin and condensin  Centrosome is duplicated Prophase  Duplicated chromosomes condense  Initiation of spindle formation  Fragmentation of Endoplasmic reticulum and golgi  Nucleolus disappears  Nuclear membrane starts to break down  Spindle microtubules invade the nuclear space Prometaphase  Chromosomal mictrotubules attach to kinetochores, which are on outer surface of centromeres  Chromosomes move towards the equator of the spindle Metaphase  Sister chromatids move towards the equator of the cell  Equatorial plane is called the metaphase plate  Nuclear membrane broken down Anaphase  Cohesin breaks down as sister chromatids are pulled apart  Centromeres split and chromatids separate  Sister chromosomes move towards opposite spindle poles  Spindle poles move further apart Telophase  Chromosomes cluster at opposite spindle pores  Chromosomes become dispersed and decondense  Condensin is degraded  Nuclear envelope assembles around chromosomes  Golgi and ER form  Daughter cells form by cytokinesis  New daughter cells are 2n:2c Meiosis Mitosis – sister chromosomes separate Meiosis – homologius chromosomes separate first, then sister chromatids separate Meiosis I - Prophase I o Leptonema o Zygonema o Pachynema o Diplonema
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