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Growth and Division of the Cell (Mitosis: karyokinesis; duplication…
Growth and Division of the Cell
Mitosis: karyokinesis; duplication division
Interphase
S Phase: DNA is replicated in nucleus, (one chromatid to one chromosome)
G2 Phase: spindle microtubules are assembled, nuclear envelope breaks down
G1 Phase: after division, synthesis of nucleotides, longest part of cell cycle
Prophase: chromosomes condense, spindle fibers attach at kinectochores
Preprophase band: microtubules and actin makes band around cell, interior to plasma membrane
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Marks where new cell wall will attach to existing cell wall
Does not always create two equal-sized cells
Metaphase: chromosomes move to center (metaphase plate), separase enzyme digests cohesin and chromatids separate
Phragmoplast: microtubules, forms where metaphase plate had been
Trap dictyosome vesicles = plate-like vesicle with 2 walls and a lamella
Grows outward to walls of original cell
Cell plate = phragmoplast, vesicle, walls
Cell plate and plasma membrane fuse with original wall and membrane to form daughter cell walls and membrane
Anaphase: spindle fibers pull chromatids to separate ends of the cell
Telophase: nuclear envelope reappears, nuclei form, each new cell contains a full set of chromosomes
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Meiosis: production of gametes and plant spores
Diploid: two complete sets of chromosomes (one from egg, one from sperm)
Referred to as a "zygote"
Meiosis I
Anaphase I: homologous chromosomes (2 chromatids connected by centromere) move to opposite sides
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Telophase I: possible uncoiling of chromosome, but usually skipped step
Metaphase I: tetrads move to metaphase plate
Prophase I:
3: Pachytene and Crossing-Over: chromosomes shorten and thicken, paternal and maternal homologs recombinate genes allowing for genetic diversity in offspring
Diplotene: paired chromosomes begin to separate from each other, except at places called "chiasmata" where they are tangled, chromatids (4) called "tetrads"
Zygotene: homologous chromosomes pair up (2 chromosomes, 4 chromatids, 4 genes), align, form the synaptonemal complex, and is then called "bivalent"
Diakinesis: continued separation, chiasmata move to ends of chromosomes, only connected by centromeres
Leptotene: chromosomes condense and become distinguishable
Meiosis II
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Metaphase II: chromosome lines up at metaphase plate, centromeres divide, chromosome separate into two chromasomes
Anaphase II: separation of each new chromosome to opposite ends
Prophase II: no stages, prepare nucleus for division if Telophase I occured
Telophase II: new nuclei form. Nucleus contains one set of chromosomes with a single chromatid each. Results in 4 new haploid cells!
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Haploid: one set of chromosomes (sperm and egg cells)
Division of Algae
Nuclei
Nuclear envelope or nucleolus don't break down or do so later in mitosis
Gaps in nuclear envelope allow bundles of microtubules to pass through completely
Nuclei of dinoflagellates do not have histones, chromosomes always condensed
Cytokinesis
unicellular algae, have no cell wall, membrane pulled inward as cleavage furrow
Algae with cell walls, similar to plants with phragmoplast, dictyosome, and cell plate
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Plants arose from this type of cell wall division
Some green algae use different set of microtublues called "phycoplast" for cell division
Can be by cleavage furrow or by cell plate formation
Representative of evolutionary lines of eukaryotes
Division of Prokaryotes
Not mitosis/ meiosis
Bacteria, cyanobacteria, and archaea
DNA is circular without histones
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DNA is attached to cell's plasma membrane, replication causes daughter loop to be attached to membrane too
Cytokinesis is caused by infurrowing, pinching in two
Cytokinesis: division of protoplast
