Ovum General Structure:
The mature ovum is typically spherical and large sized. It is
like any other Eukaryotic animal cell. So it has a plasma membrane inside a PM,
Cytoplasm, nucleus, yolk and other organelles and inclusion.
Plasma membrane is composed of outer and
inner layer of protein both layer are 50A thick. And lipid layer is about 60A
thick. In most type of egg. The egg cytoplasm is also called ‘’Ooplasm.’’ It
also differentiated into Ectoplast or egg Cortex and inner Endoplast.
Ectoplast is just bellow the plasma
membrane. It is a transparent Viscous layer. It contain the presence of some
Cytoskeleton element like microtubule and microfilaments and also contain
numerous small vesical/ granules, called ‘’Cortical granules’’ which contain
Muccopolysaccarides.
The endoplasm occur inside the
ectoplasm. It contain many Mitochondria, GC, ER, Ribosome’s but centriole are
absent. It is also contain variety of molecule like translating M-RNAs,
Histone, Tubuline, Actin and Enzymes. They are also contain rich and various
type of inclusion like yolk, glycogen granules and fat droplets are the main
reserve food for developing embryo.
The nucleus of Ovum is greatly enlarge. It having large amount of nucleoplast and prominent nucleus and egg has 2-poles, Animal pole and Vegital pole. The part of cytoplast which is clear without yolk is called germinal vesicle/ Active cytoplasm (animal pole).
*Egg
Membrane:
The mature
egg in all organism is covered by Plasma Membrane. Which is unique membrane,
made up of Protein and Lipid Belayed.
The thickness is about 50A. In addition to this membrane most of animal egg
show extra or Accessory protective layer of egg.
a. Vitelline membrane
It is a thin transparent around the plasma membrane and in parent in the insect, mollusk, Amphibians and Birds egg.
b.
Zona radiate
It is striated appearance next to the plasma membrane. It
found in egg of sharks some bony fishes and some amphibians and reptile.
c.
Zonapellucida
It is modified layer of zone radiate occur in
Mammalian egg.