milita roy bejoy narayan mahavidyalayabnmahavidyalaya.in/pdf/fertilization-pdf.pdfbejoy narayan...

MILITA ROYMILITA ROYBEJOY NARAYAN MAHAVIDYALAYABEJOY NARAYAN MAHAVIDYALAYA

SPERM FORMATIONMaturation of a sperm cell- 1. Nucleus is condensed

2. Acrosome is formed

3. Neck piece and tail piece is formed:formation of flagellum from centriole

Body elongated and become streamlined bydiscarding the excess cytoplasmic material

Ultrastructure of flagella:Flagella contribute to sperm motility

protofilaments consist of tublulin dimers histone H1 stabilizes flagellar microtubules dynein, attached to microtubules hydrolyzes ATP, ATP comes from mitocondria in

midpiece sliding of outer doublet

EggEgg attain the large size due to accumulation ofthe following necessary materials yolk proteins ribosomes t-RNA m-RNA morphogenic factors protective chemicals

Egg attain the large size due to accumulation ofthe following necessary materials yolk proteins ribosomes t-RNA m-RNA morphogenic factors protective chemicals

Some of the structural components of theamphibian eggJelly coatVitelline envelopeCortical granuleMitochondriaYolk

Some of the structural components of theamphibian eggJelly coatVitelline envelopeCortical granuleMitochondriaYolk

Sperm enters at various stages of meiotics division of theegg of different animals

Sperm AttractionChemotaxis

Movement toward a chemical, gradient is followed In Arbacia punctulata – the effects of adding resact to sperm suspension resact isolated from egg jelly is depicted in the picture

12 3 4

Sperm AttractionWhat is a sperm-activating peptide? RESACT- the 14 peptide amino acid is responsible for

chemotaxis. Causes increases in sperm respirationand motility via a signal transduction mechanism.

What is a sperm-activating peptide? RESACT- the 14 peptide amino acid is responsible for

chemotaxis. Causes increases in sperm respirationand motility via a signal transduction mechanism.

Sperm – Egg InteractionThe acrosomal reaction in sea urchins: Acrosomalmembrane is fused with the sperm plasmamembrane , enzymes are released.

Components of egg jelly bind to receptors on spermcell membrane Calcium channels opened, calcium enters sperm head

and induces fusion of acrosomal vesicle withmembrane leading to exocytosis of enzymes Acrosomal process forms from polymerization of

actin also facilitated by calcium

Components of egg jelly bind to receptors on spermcell membrane Calcium channels opened, calcium enters sperm head

and induces fusion of acrosomal vesicle withmembrane leading to exocytosis of enzymes Acrosomal process forms from polymerization of

actin also facilitated by calcium

Sperm – Egg InteractionThe bindin protein(present on the innermembrane ofacrosome) are now atthe tip of the spermand plays an importantrole in species specificrecognition.

The bindin protein(present on the innermembrane ofacrosome) are now atthe tip of the spermand plays an importantrole in species specificrecognition.

Sperm – Egg Interaction Polymerization of egg actin leads to formation of

fertilization cone, helps for fusion.

Sperm – Egg Interactionin mammals contactoccurs on side ofsperm head; CD9associated integrinprotein in eggneeded for fusionalong with fertilin insperm

in mammals contactoccurs on side ofsperm head; CD9associated integrinprotein in eggneeded for fusionalong with fertilin insperm

Preventing Polyspermy Why is polyspermy a problem?

Preventing Polyspermy

Preventing PolyspermyFertilization membrane is formed from the fusionof Cortical granules with the plasma membrane ofegg. The internal enzymes ( such asHyaleuronidase, Peroxidase) and hyalin arereleased which form the membrane. Themembrane is a permanent structure and apermanent solution to the problem of polyspermy.

Fertilization membrane is formed from the fusionof Cortical granules with the plasma membrane ofegg. The internal enzymes ( such asHyaleuronidase, Peroxidase) and hyalin arereleased which form the membrane. Themembrane is a permanent structure and apermanent solution to the problem of polyspermy.

Egg Activation increase in calcium levels trigger many reactions – can

block with EGTA can activate artificially using calcium ionophore most protein synthesis comes from stored mRNA by

removing an inhibitor

increase in calcium levels trigger many reactions – canblock with EGTA can activate artificially using calcium ionophore most protein synthesis comes from stored mRNA by

removing an inhibitor

Egg Activation signaling pathway releases intracellular calcium

ion concentration

Fusion of Genetic Material DNA & centriole forms initial spindle for division.

sperm nucleus decondensed to form pronucleus –involves phosphorylation of lamin protein in envelopand two sperm histones can fuse with egg pronucleus.

lengthy process – sperm DNA bound to protamines incompacted form – glutathione breaks dissulfide bondsto de-compact DNA; when sperm enters egg hasn’tcomplete meiosis; DNA synthesis occurs separately ineach pronucleus; true diploid nucleus doesn’t formuntill 2-cell stage

DNA & centriole forms initial spindle for division.

sperm nucleus decondensed to form pronucleus –involves phosphorylation of lamin protein in envelopand two sperm histones can fuse with egg pronucleus.

lengthy process – sperm DNA bound to protamines incompacted form – glutathione breaks dissulfide bondsto de-compact DNA; when sperm enters egg hasn’tcomplete meiosis; DNA synthesis occurs separately ineach pronucleus; true diploid nucleus doesn’t formuntill 2-cell stage

Rearrangement of Egg Cytoplasm Cytoplamic rearrangement occurs as a result of

fertilization : Parallel microtubles between corticaland inner cytoplasm appear responsible formovement

Cytoplamic rearrangement occurs as a result offertilization : Parallel microtubles between corticaland inner cytoplasm appear responsible formovement