acrosome reaction

slide share Arosome reaction

1. Topic
Prepared by
Rajamoni saikia
M.Sc1
st
semester
zoology

2. Itisonlywithinthepast135yearthatthespermsrollinfertilizationhas
beenknown.
Antonvanleeuwenhoek,thedutchmicroscopistwhoco-discoveredsperm
inthe1670s,
Eachspermcellconsistofahaploidnucleolus.
Infrontofthiscompressedhaploidnucleusliestheacrosomalvesicle,or
acrosome.
TheacrosomeisderivefromthecellsGolgiapparatusandcontainenzymes
thatdigestproteinsandcomplexsugars.
Acrosome+nucleus=spermhead.

3. Asecondinteractionbetweenspermandeggjellyresultintheacrosomereaction.
Inaacrosomereactionininitiatedbycontactofthespermwiththeeggjelly.
Exocytosisoccurinacrosomalvesicle.
Proteolyticenzymeandproteasomesthatdigestapaththroughthejellycoatto
theeggsurface.
Sulphatecontainingpolysaccharidebindtothespecificreceptorlocatedonthe
spermcellmembranedirectlyabovetheacrosomalvesicle.
Thusacrosomereactionconstituteabarriertointerspecificfertilisation.

4. Figure 47.3-1
Basal body
(centriole)
Sperm
head
Acrosome
Jelly coat
Sperm-binding
receptors
Vitelline layer
Egg plasma membrane

5. Figure 47.3-2
Basal body
(centriole)
Sperm
head
Acrosome
Jelly coat
Sperm-binding
receptors
Hydrolytic enzymes
Vitelline layer
Egg plasma membrane

6. Figure 47.3-3
Basal body
(centriole)
Sperm
nucleus
Sperm
head
Acrosome
Jelly coat
Sperm-binding
receptors
Hydrolytic enzymes
Vitelline layer
Egg plasma membrane
Actin
filament
Acrosomal
process

7. Figure 47.3-4
Basal body
(centriole)
Sperm
plasma
membrane
Sperm
nucleus
Sperm
head
Acrosome
Jelly coat
Sperm-binding
receptors
Fused
plasma
membranes
Hydrolytic enzymes
Vitelline layer
Egg plasma membrane
Actin
filament
Acrosomal
process

8. Figure 47.3-5
Basal body
(centriole)
Sperm
plasma
membrane
Sperm
nucleus
Sperm
head
Acrosome
Jelly coat
Sperm-binding
receptors
Fertilization
envelope
Cortical
granule
Fused
plasma
membranes
Hydrolytic enzymes
Vitelline layer
Egg plasma membrane
Perivitelline
space
EGG CYTOPLASM
Actin
filament
Acrosomal
process

9. Acrosome reaction
Acrosomereactionisinitiatedbyrepeatingpolymeroffucosesulphate.
Whenthissulphatebindstoitsreceptoronthespermthereceptoractivates
threespermproteins.
1)Acalciumtransportchannelthatallowsca2+toenterthespermheat.
2)AsodiumNa/Hexchangerthatpumpssodiumionintothespermasitpumps
hydrogenionout.
3)Aphpospholipaseenzymethatmakesanothersecondmessengerthephospholipid
inositoltrisphosphate(ip3).
Ip3abletoreleasecalciumfrominsidethesperm.
Theelevatedcalciumlevelinarelativelybasiccytoplasmtriggersthefusionof
acrosomalmembranewiththeadjacentspermcellmembrane.
Releasingenzymethatcanlyseapaththroughtheeggjellytothevitelline
envelop.

10. Itextendoftheacrosomalprocess.
Thisprotrusionarisesthroughthepolymerizationofglobularactin
moleculesintoactinfilament.
TheinfluxofcalciumisthoughttoinactivatetheproteinRhoBinthe
acrosomalregionandmidpieceofseauracinsperm.
ThisGTPbindingproteinhelpstoactiveinpolymrisingactintomakethe
acrosomalprocesses.

11. Theacrosomereactionallowthespermbyexocytosisreleaseofacrosomal
enzymetopenetratethezonapellucidaoftheegg.
Thespeciesspecificzonapellucidaproteinthatserveasaspermreceptor
alsostimulatesaseri9esofeventthatleadtofusionbetweentheplasma
membraneandoutréacrosomalmembrane.