. Bacteria, with no nucleus or sexual cycle, reproduce clonally and divide by binary fission

. Bacteria’s circular chromosome starts replication at origin, proceeds bidirectionally to end

. Bacteria’s new chromosomes move to opposite ends and FtsZ protein creates middle septum

. FtsZ protein, similar to eukaryotic tubulin, forms a ring and contracts radially to pinch cell in 2

. Eukaryotic: 10-50 chromosomes in their body (somatic) cells. Humans have 46 (23 homologue pairs)

. The particular array of chromosomes (size, staining, etc.) in an individual is his karyotype

.  Humans are diploid (2n): 2 sets = 46 total chromosomes. One set of chromosomes is haploid (n) = 23

.  Chromosomes composed of chromatin = 40% DNA + 60% protein. RNA is present too in RNA synthesis

. DNA: single chromosome, 140 million nucleotides, made of DNA (- charge) & histone proteins (+charge)

. 4 primary histones (H2A, H2B, H3, H4), 147 bp DNA coiled 1.7 turns around 8 histones & 20-80 bp linker

. Eukaryotic organization: DNA->Nucleosome->beads on string->TADs->compartments->territories

. Topological Associated Domains (TADs): loops of DNA (nucleosomes) held by CTCF & cohesin proteins

. Organization of DNA-binding proteins CTCF & cohesin affect gene expression (activation or repression)

. Domains with different set-up of compartments & TADs are hetero- (silent) & eu-chromatin (active)

. Through cell cycle, x-shaped chromosomes compact on protein scaffold: TADs disappear in prophase

. SMC proteins (Structural Maintenance of Chromosome) interact with DNA, condensins replaces cohesion

. ATP needed for DNA loops in nucleosomes. Interactions of histones and nucleosomes makes “liquid DNA”

. Replication makes 2 DNAs (sister chromatids) held by cohesins around the kinetochore protein

 . Eukaryotic cell cycle has Interphase [G1(growth), S (DNA replication), G2 (organelles replicate)], M & C

. Centromere (one per chromatid) is point of constriction, kinetochore is site of microtubule attachment

. Mitosis (M) has prophase, prometaphase, metaphase, anaphase and telophase

. Prophase: chromosomes visible, centrioles move to poles and form spindle, nuclear envelope breaks

. Prometaphase: chromosomes attach to microtubules at kinetochores and move to equator of cell

. Metaphase: chromosomes align at metaphase plate (future axis of cell division), centrioles have Aster

. Anaphase: centromeres split, cohesins are removed and sister chromatids are pulled to opposite poles

. Telophase: spindle disassembles, nuclear envelope forms on both chromatids, nucleolus reappears

. Cytokinesis (C): constriction of actin creates cleavage furrow (animals), plate forms in plants

. Two irreversible steps in cell cycle: replication of DNA and separation of sister chromatids

. Cell cycle can be stop at checkpoints, check for accuracy and halted if there are errors

. 3 checkpoints: G1/S (decision to divide), G2M (mitosis), late metaphase (spindle proper attachment)

. Control Factors: MPF (maturation-promoting factor) induces division through phosphorylation

. MPF is cyclin plus a cyclin dependent kinase (cdk). Cdks are drivers of the cell cycle via phosphorylation

. Anaphase promoting factor (APC/C or cyclosome triggers anaphase itself

. Multiple Cdks control the cycle in eukaryotes as opposed to one in yeast

. Growth factors can override cellular controls that otherwise inhibit cell division

. Platelet-derived growth factor (PDGF) is an RTK that initiates a MAP cascade to stimulate cell division

. Cancer, uncontrolled growth of cells caused by mutation of tumor-suppressor genes & proto-oncogenes

. Proto-oncogenes are genes that become oncogenes when mutated. Only one is needed to cause cancer

. p53 are tumor suppressor genes that must lose function for the cancerous phenotype to develop

. p53 monitors integrity of DNA, if DNA is damaged division is halted, if major, p53 directs cell to kill itself

. Sexual life cycle: composed of meiosis and fertilization. Somatic cells are diploid, gametes are haploid

. Diploid cells carry chromosomes from 2 parents. Fertilization produces a diploid zygote

. Sexual reproduction involves meiosis (diploid ->haploid, >>in animals) and fertilization (haploid -> diploid

. Single -cell diploid zygote undergoes mitosis to produce diploid somatic cells

. Some diploid cells undergo meiosis to produce haploid gametes also called germ-line cells

. Meiosis has 2 rounds of division I and II, each with prophase, metaphase, anaphase and telophase

Division I (reduction division) gives daughter cells with one homolog. Division II separates sister chromatids

. Association of homologous chromosome (Synapsis) in prophase I forms synaptonemal complex (SC)

. SC= chromatin-attached-lateral elements (LE) bound to central elements (CE) by transverse filaments (TF)

. Meiotic cells have interphase (G1, S, & G2) followed by meiosis I and meiosis II

. Prophase I: nuclear envelope gone, chromosomes (2 sister chromatids) visible, sites of crossing over form

. Genetic recombination between no-sister chromatids takes place at sites called chiasmata

. Metaphase I: locked homologues separately attach microtubules to opposite poles at metaphase plate

. Anaphase I: microtubules shorten, chiasmata break, homologues (haploids) move to opposite poles

. Telophase I: nuclear envelops reform, non-identical chromosomes separate, cytokinesis may or not occur

. Meiosis II: resembles a mitotic division

. Prophase II: shorter than prophase I, spindle forms in each cell, nuclear envelope breaks down

. Metaphase II: chromosomes align at metaphase plate, kinetochore microtubules attach to poles

. Anaphase II: kinetochore microtubules shorten, non-homologous sister chromatids pulled to poles

. Telophase II: nuclear membrane reform. After cytokinesis, four haploid cells result

. In animals the four cells develop into gametes. In plants, fungi they divide mitotically then ++gametes

.  Meiosis errors: Nondisjunction failure to move to opposite poles. Aneuploid gametes + chromosomes

. Meiosis: cross over, no DNA synthesis, chromatids joined at centromere, kinetochores attach same pole

. Mitosis: homologues do not pair, kinetochores remain separate and microtubules attach to both

. Homologous pairing is specific to meiosis and centromeres of sister chromatids remain connected

. Sister kinetochores attach to the same pole during meiosis I in contrast to mitosis and meiosis II

. Cyclin B is lost between mitotic divisions, but not between meiotic divisions

.  Meiosis produces cells that are not identical, essential for evolution

. Sexually reproducing populations have greater genetic variation than asexually reproducing ones