Section 1
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process of cleavage
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Last updated
6 years ago
Date created
Mar 14, 2020
Cards (59)
Section 1
(50 cards)
process of cleavage
: rapid mitotic division: cell cycle mainly synthesis and mitosis • No G1 or G2 PHASES→ little or no protein synthesis→ no growth
fast block
• 1st-gamete fusion depolarizes the egg cell membrane and sets up a ___ ____ to polyspermy o triggered by fusion of membranes o unfertilized egg: polarized cytoplasm, negatively charged relative to outside o in seconds after sperm fuses, ion channels in membrane open o Na+ ions diffuse across plasma membrane into egg o Egg depolarizes o Occurs in 1-3 sec after sperm binds to egg o Prevents fusion
2 ways to prevent polyspermy in echinoderms
fast block and slow block(cortical rxn)
zygote
is diploid and totipotent (potential to give rise to all types of cells and new individual)
Sea urchin ovum
-jelly coat -vitelline layer (thin) -plasma membrane
blastocoel
the fluid-filled cavity inside a blastula
Slow block to polyspermy
this block of polyspermy involves cortical reactions that require high concentration of Ca2+ ions(process takes about a minute and is IRREVERSIBLE)
acrosome
a tip of sperm that releases hydrolytic enzymes
holoblastic cleavage
• complete division of egg • little/moderate amts of yolk • echinoderms, frogs, most mammals
meroblastic cleavage
• incomplete division of egg • occurs in yolk-rich eggs • birds, other reptiles, many non-tetrapod fish
Ovum (Generalized)
• Plasma membrane • Protective coverings • Aid in fertilization by sperm of same species • Barrier to interspecific
Part I of Development
Fertilization • Egg attracts sperm • Sperm dissolves protective layers around egg • Sperm and egg recognize each other • Egg changes to prevent entry by more than 1 sperm • Egg activation: egg metabolic changes, fusion of nuclei
Model organisms
o Across a range of animal species, embryonic development involves common stage that occur in a set order o Easily studied in lab • Sea urchin (Echinodermata) • Frog (xenopus) • Chicken (gallus)
end of fertilization
when zygote begins to divide • Echinoderms: w.in 90 mins of sperm binding • Humans: 12-36 hrs after
jelly coat
thick glycoprotein layer; releases chemicals that attract sperm (via chemotaxis)
acrosomal reaction
triggered when sperm meets egg
Sperm
small mobile, flagellate
first step in fertilization for sea urchins
sperm dissolves protective layers (acrosomal reaction)
cleavage furrow
indentation in cell surface as cytokinesis divides in half
yolk
mixture of protein, phospholipids, fats: food for developing embryo
egg activation
egg metabolic changes, fusion of nuclei
Development
changes during life cycle of individual o Egg→embryo→juvenile→adult
Blastula
hollow ball of at least 128 blastomeres with fluid-filled cavity called blastocoel
egg/ovum
large, relatively immotile
cleavage pattern in frogs
cleavage is asymmetric due to distribution of yolk
zona pellucida
A thick, transpartent coating rich in glycoproteins that surrounds an oocyte.
Fertilization in mammals
is internal o Sperm must travel through a layer of follicle cells surrounding the egg, before it reaches the zona pellucida or extra cellular matrix of egg o Sperm binding triggers a cortical rxn o Overall, the process of fertilization is slow: first cell division occurs 12-26 hrs after fertilization
preventing polyspermy
no fast block identified in mammals, no fertilization envelope formed, cortical enzymes catalyze changes in zona pellucida, functions as slow block • Sperm binding triggers cortical reaction • Ca2+ released into cytoplasm • Cortical granules release enzymes to outside of cell • The rest happens inside egg cell
vegetal pole
has more yolk • first two cleavage furrows parallel to meridian (connects poles)
fusion of gametes in sea urchins
• Eggs have completed meiosis when released • occurs 20 mins after sperm nucleus enters egg
polyspermy
fertilization by more than one sperm
blastomeres
(what happens in cleavage) one large cell--> many smaller cells (____)
third step of fertilization in sea urchins
surface of egg changes to prevent polyspermy
fertilization
formation of diploid zygote from a haploid egg and sperm
embryo
zygote becomes ____ after 1st division
sea urchin (echinodermata
model organism for fertilization o Readily available o Easy to obtain a lot of gametes o Externally fertilized so relatively easy to see
Acrosomal rxn in mammals
sperm bind to ZP3 (specific glycoprotein) in zona pellucida • Binding triggers acrosome
cortex
rim of cytoplasm just beneath egg plasma membrane
cleavage
fertilization is followed by ____: rapid cell division without growth
Consequences of fertilization
• Restores diploid number • Determines sex in many organisms • Activates egg
Mammal ovum
follicle cells, zona pellucida, plasma membrane
cleavage pattern in echinoderms
• are deuterostomes: radial and indeterminate cleavage
generalized fertilization
• First: sperm dissolves protective layers • Second: molecules on sperm surface bind to receptors on eggs surface, membranes fuse • Third: surface of egg changes to prevent polyspermy • Polyspermy→ extra chromosome sets→ usually lethal • Fourth: sperm and egg nuclei fuse; egg activation
unfertilized egg
polarized cytoplasm, negatively charged relative to outside
Egg activation
rise in ca 2+ in cytosol increases rates of cellular respiration, protein synthesis • Egg (specifically, maternal enzymes ) are said to be activated • Proteins and mRNas needed for activation are already there
fusion of gametes in Humans
• Egg (secondary oocyte) stalled at metaphase II, fertilization triggers resumption of meiosis • → completion of meiosis→ female nucleus+ second polar body • occurs after several hrs
acrosomal process
• Structure compromised of actin filaments • Protrudes from sperm head and penetrates coat • Protein molecules at tip bind to specific receptors on plasma membranes
2nd step in fertilization for sea urchins
molecules on sperm bind to receptors on egg o Acrosomal process • "lock and key"; ensure conspecificity (important for external fertilizers) • same species? First? → if yes, move on! • Membranes fuse, no more sperm needed
cortical granules
vesicles in cortex • Releases enzymes into perivitelline space • Vitelline layer lifts away and hardens, forming fertilization envelope • Enzymes clip off and release external portions of any receptor proteins and any attached sperm
irreversible
slow block of polyspermy is ____
Section 2
(9 cards)