Download MILITA ROY BEJOY NARAYAN MAHAVIDYALAYA

MILITA ROY
BEJOY NARAYAN MAHAVIDYALAYA
SPERM FORMATION
Maturation 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 by
discarding 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
Egg
Egg attain the large size due to accumulation of
the following necessary materials
 yolk proteins
 ribosomes
 t-RNA
 m-RNA
 morphogenic factors
 protective chemicals
Some of the structural components of the
amphibian egg
Jelly coat
Vitelline envelope
Cortical granule
Mitochondria
Yolk
Sperm enters at various stages of meiotics division of the
egg of different animals
Sperm Attraction
Chemotaxis
 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
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Sperm Attraction
 What is a sperm-activating peptide?
 RESACT- the 14 peptide amino acid is responsible for
chemotaxis. Causes increases in sperm respiration
and motility via a signal transduction mechanism.
Sperm – Egg Interaction
The acrosomal reaction in sea urchins: Acrosomal
membrane is fused with the sperm plasma
membrane , enzymes are released.
 Components of egg jelly bind to receptors on sperm
cell membrane
 Calcium channels opened, calcium enters sperm head
and induces fusion of acrosomal vesicle with
membrane leading to exocytosis of enzymes
 Acrosomal process forms from polymerization of
actin also facilitated by calcium
Sperm – Egg Interaction
The bindin protein
(present on the inner
membrane of
acrosome) are now at
the tip of the sperm
and plays an important
role in species specific
recognition.
Sperm – Egg Interaction
 Polymerization of egg actin leads to formation of
fertilization cone, helps for fusion.
Sperm – Egg Interaction
in mammals contact
occurs on side of
sperm head; CD9
associated integrin
protein in egg
needed for fusion
along with fertilin in
sperm
Preventing Polyspermy
 Why is polyspermy a problem?
Preventing Polyspermy
Preventing Polyspermy
Fertilization membrane is formed from the fusion
of Cortical granules with the plasma membrane of
egg. The
internal enzymes ( such as
Hyaleuronidase, Peroxidase) and hyalin are
released which form the membrane. The
membrane is a permanent structure and a
permanent 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
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 envelop
and two sperm histones can fuse with egg pronucleus.
 lengthy process – sperm DNA bound to protamines in
compacted form – glutathione breaks dissulfide bonds
to de-compact DNA; when sperm enters egg hasn’t
complete meiosis; DNA synthesis occurs separately in
each pronucleus; true diploid nucleus doesn’t form
untill 2-cell stage
Rearrangement of Egg Cytoplasm
 Cytoplamic rearrangement occurs as a result of
fertilization : Parallel microtubles between cortical
and inner cytoplasm appear responsible for
movement