Development I Flashcards
development
all changes that ocur during entire life cycle of ind; model orgs - spp chosen for research bc easy to study and maintain (ex: sea urchin, frog, chick, nematode)
fertilization
sperm (flagellum, small) + egg (larger, non motile); zygot is fert egg (single cell)
consequences of fert
restore diploid number (2n); determines sex; activates egg to stimulate rxns and begin development
egg
surrounded by plasma mem; one or more coverings depending on spp
egg covering
aid in sperm fert of some sp sperm; barrier to interspecific fert; ony same sp sperm gets into fert
steps of fert
(1) sperm dissolves protective layers around egg (need to get to PM) (2) molecules on sperm surface bind to receptors on egg surface = recognition (3) upon recog and fert surface of egg changes (4) prevents polyspermy
polyspermy
many sperm getting into one egg
sea urchine fert steps
(1) jellly coat of eggs releases chems into water (2) attracts sperm via chemotaxis (3) sperm + jelly coat = acrosomal rxn (4) sperm + egg recog causes PM fusion = plasmogamy (sperm nuc enters egg (5a) fast block to polyspermy (5b) slow block to polyspermy via cortical rxn
acrosomal rxn
head of sperm (acrosome) releases hydrolytic enx to partially digest jelly coat; acrosomal process forms lock and key mech; sperm head produces actin filament structure that penetrates coat; pserm protein moelcules bind to PM receptors to ensure intraspecific fert
sea urchine egg structure
intermost = plasma mem; vitelline layer (thin); outermost = jelly coat (thick layer to glycoproteins for recog)
advantages of observing sea urchine fert
readily available; easy to work w; lots of gametes; external fert so can view all steps
fast block to polyspermy (in sea urchines)
unfert egg = polarized and cytoplasm is neg charged; w/i secs egg PM ion channels open; NA+ ions rush in and cuase egg depolarization (1-3 sec after binding); prevents fusion w any other sperm bc of depolarized egg; transient bc only lasts approx 1 min
slow block to polyspermy (in sea urchines) via cortical rxn
sperm + egg starts diff signal transduction; Ca+ ions released from ER to cytoplasm; tiggers cotical granules formation; vessicles go to egg cortex beneath PM; release conents (enz, macromolecules); fills up (blacks) space btwn VL + PM of egg; cortical rxn; VL hardens, produces fert envelope, prevents sperm entry; cortical granules enz degrade all eg mem receptors; creates complete blcok, irreversible/permanent (takes about 1 min to set up)
mammal fert
egg structure: plasma mem, zona pellucida, follicle cells; internal fert; no fast block to polyspermy
mammal fert steps
(1) acrosomal rxn: spemr binds to ZP3 glycoprotein receptor on ZP (2) acrosome bursts, releases hydrolytic enz, digest through ZP (3) slow block to polyspermy via cortical rxn (4) Ca+ released into cytoplasm, creates granules (5) release contents at ZP (6) ZP changes - hardens, sperm receptors altered to prevent binding, no fert env formation
fert completetion
egg activation; fusion of sperm and egg nuclei (same time as egg act); end of fert = 1st zyote division
egg activation
series of metabolic rxns that start + speed up to begin embryonic dev; tiggered by Ca+ inc in cytoplasm: form cortical rxn, maternal enz + proteins activated, inc protein syn of maternal mRNA
fusion of sperm + egg nuclei (same time as egg act)
egg dev: sea urchine meiosis completed at time of release, human egg (secondary oocyte) at metaphase II finishes meiosis at meiosis and produces egg nuc and polar body; sperm nuc (n) guided to egg nuc (n) via microtubules, fusion = karyogamy, 20 mins after sperm entry to egg in sea urchins, serveral hrs after sperm entry to egg in humans
end of fert
1st zygote divisions; sea urch = about 90 mins after sperm bind egg; humans = about 12-36 hrs after sperm binds egg
cleavage
series of rapid mitotic divisions; clevage cell cycle; cleavage furrow; patterm of divison affected by yolk presence
clevage cell cycle
mainly S&M phases; syn and mitosis; no G1/G2 phases, no protein syn, no “growth” of cell size; inc cell number w smaller cell size afer each division, embryo size stays small; each new cell = blastomere
clevage furrow
indentation in cell surface after cytokinesis
clevage and yolk presence
yolk = proteins, fats, phospholipids; depends on spp + embryo needs
stages of cleavage
zygote (1 cell) undergos clevage to become embryo (2+ cells); humans = first cleavage 24 hrs after sperm binds, lots of division after to form blastula, at least 128 cells is blastomere, forms hollow ball inside is blastocoel (fluid filled cavity)
